Tuesday, December 4, 2012

Patient Health and Employee Safety Go Hand In Hand in Healthcare

The Joint Commission, the organization which accredits over 19,000 healthcare facilities in the US has published a report describing the need for synergy between patient health and employee health. The Joint Commission worked with both the National Institute of Occupational Safety and Health (NIOSH) and the National Occupational Research Agenda (NORA) and the Social Assistance Sector Council in producing this volume.

This report can be considered a sequel to the 2009 NORA report “State of the Sector Healthcare and Social Assistance," with input from many of the same individuals. The NORA report documents and criticizes the health industry for its disproportionate number of accidents compared to other industries and in the executive summary has the following statement:

The [Healthcare and Social Assistance] HCSA sector is burdened by the historical and entrenched belief that patient care issues supersede the personal safety and health of workers and that it is acceptable for HCSA workers to have less than optimal protections against the risks of hazardous exposures or injuries. Because patients and providers share the healthcare environment, efforts to protect patients and providers can be complimentary, even synergistic, when pursued through a comprehensive , integrated approach.

The Joint Commission report again highlights the problem and emphasizes the importance of considering safety as a whole and not separated between patient safety and worker safety. The goal of the report is described as follows:

This monograph is intended to stimulate greater awareness of the potential synergies between patient and worker health and safety activities. Using actual case studies, it describes a range of topic areas and settings in which opportunities exist to improve patient safety and worker health and safety activities. This monograph is designed to bridge safety-related concepts and topics that are often siloed within the specific disciplines of patient .

The report details methods to improve safety from a high level systems perspective down to guidance and links to resources showing where information needed to implement these changes may be found. The report also contains a number of case studies where improvements in safety were made; though the number of case studies is perhaps a little limited.

Overall, this report is a valuable contribution to improving both patient and worker safety and this blog encourages everyone who is involved in worker safety in health care to read it. We all look forward to reading the future report that describes how all the occupational safety problems have been solved and healthcare facilities across the country have a safety culture that embraces both patient and employee safety. While this Joint Commission report is definitely a step in the right direction, it may be a while before this final volume is written.

Wednesday, November 28, 2012

The EPA is responsible for the impact of commercial chemicals released into the environment. One major concern is the impact some chemicals have on the endocrine system within humans and other animals. The EPA has recently released a list of chemicals that it intends to screen over the next five years for endocrine activity as part of the Endocrine Disruptor Screening Program (EDSP). A more detailed explanation of the EDSP is available. The list of chemicals is also available.

Included on this list are several chemicals well known to people in healthcare sterile processing and food preparation and processing. These include:

Ethylene oxide

Hydrogen peroxide

Peracetic acid



Sodium hypochlorite

Ethanol and


It should be stressed that these chemicals are on the list of 10,000 chemicals awaiting assessment; they have not yet been assessed; and with 10,000 chemicals under consideration, it would probably be hard to identify any chemical with widespread use that is not on the list. Watch this blog for more information as it becomes available.

Tuesday, November 27, 2012

Why Don't More Companies offer a Hydrogen Peroxide Monitor?

Hydrogen peroxide is a widely used chemical, finding application in healthcare for sterilization, metal fabrication mills for pickling and pulp & paper as a bleaching agent. According to Wikipedia, in 1994, world production of H2O2 was around 1.9 million tonnes and grew to 2.2 million in 2006. The hazards of exposure to hydrogen peroxide vapor are well known, the OSHA permissible exposure limit (PEL) for hydrogen peroxide is 1 ppm, calculated as an eight hour time weighted average (TWA) [29 CFR1910.1000 Tbl Z-1], which can be compared to the PELs for some other familiar hazardous gases and vapors: carbon monoxide (50 ppm), Hydrogen cyanide (10 ppm), chlorine (1 ppm ceiling). Hydrogen peroxide is electrochemically active and so it can be detected relatively easily by an appropriate electrochemical sensor.

Hydrogen peroxide is widely used, its vapors are known to be very hazardous, it is relativley easy to detect, but of the many gas detection companies operating the United States (estimated at over 80 at one point), why do so few offer monitors for hydrogen peroxide? We are aware of only three or four including ChemDAQ. The answer is calibration!

There are over twenty gases that monitors are readily available from the gas detection companies including Cl2, CO, H2, HCN. HCl, H2S, NH3, NO, N2O, NO2, SO2, O3 and combustible gases. The common feature that all these gases have in common is that the certified gas mixtures are available from specialty gas companies that can be used to calibrate the respective gas monitors. The availability of a test gas makes the design a monitor much easier. The new monitor will look like an old monitor with new sensor, tweaked circuitry and software and a new label. The sensor is calibrated with a new test and off it goes to a life of productive service. Of course, this is a gross simplification of the work that must be done to release a new product but it illustrates the point.

However, if the calibration gas does not exist, then the gas monitor manufacturer has two choices – find a surrogate gas or generate their own test gas. Many sensors respond to more than one gas and so if the ratio of the responses is constant (cross sensitivity), then calibrating with a gas that comes in cylinder from a specialty gas company, multiplied the cross sensitivity ratio should give a calibration to the new target gas.

The operative word there is ‘should’ because sometimes cross calibration is unreliable. Many hydrogen peroxide sensors give a strong response to sulfur dioxide, but the cross sensitivity can be affected by the environment. We once tested a hydrogen peroxide sensor with both hydrogen peroxide and sulfur dioxide and found that the sensor responded well to sulfur dioxide but gave almost no response to hydrogen peroxide. One of the components in the gas path was removing the hydrogen peroxide. Hydrogen peroxide is much more reactive than sulfur dioxide (stronger oxidizing agent, spontaneously decomposes over time); so the fact that there are contaminants that will react more with hydrogen peroxide than sulfur dioxide should not be very surprising.

Clearly, if this test had been an attempt to cross-calibrate the hydrogen peroxide sensor with sulfur dioxide, the sensor would have tested as normal, even though it barely registered hydrogen peroxide; creating a potentially dangerous situation. Even if the sensor module leaves the factor correctly calibrated, the same problem can potentially occur if the customer then attempts to field calibrate the sensor with a sulfur dioxide or other surrogate gas. After all, how many users have hydrogen peroxide test gas of known concentration readily at hand. Field calibration of reactive gas sensors with less reactive surrogates runs the risk of the sensor appearing to be functioning normally, but not actually detect the target gas.

The role of calibration in any gas monitor is two fold. The first function is a basic check that the monitor is working properly, that it responds to gas when the gas is applied. The second function is to ensure that the sensor reading is accurate. Obviously these two functions are closely related and overlap to some extent.

Since hydrogen peroxide test gas is not readily available, it must be produced by the sensor manufacturer. Hydrogen peroxide can be produced by evaporating hydrogen peroxide solution. There is no great mystery here, the chemical literature describes several way of achieving this goal, but the problem for the manufacturer is to produce a consistent concentration of hydrogen peroxide over time, and to be able to determine what that concentration is.

It may sound simple, and in principle it is, but the folks at ChemDAQ have spent a lot of time and effort engineering this process in order to produce a reliable and accurate calibration method. ChemDAQ generates hydrogen peroxide test vapor from hydrogen peroxide solution and we have our generators run continuously in order to ensure that the system is at steady state. We also regularly titrate the gas stream to measure the hydrogen peroxide concentration so that we know what hydrogen peroxide concentration used it. This hydrogen peroxide test gas is then used to calibrate the hydrogen peroxide sensors.

All of ChemDAQ’s hydrogen peroxide calibrations are performed with hydrogen peroxide test gas. Similarly, all of ChemDAQ’s peracetic acid sensor calibrations are performed with peracetic acid test gas. This approach means that users of our equipment can be assured that their hydrogen peroxide sensors will respond to hydrogen peroxide vapor and the that the readings will be accurate.

If you use hydrogen peroxide and your hydrogen peroxide vapor monitors are not calibrated with hydrogen peroxide test gas, but with another gas such as sulfur dioxide then you may want to question how reliable that calibration is.

Thursday, November 15, 2012

We Don’t Use Hydrogen Peroxide, We Have a Sterrad® Plasma Sterilizer

We often hear refrains similar to that of the title when we discuss hydrogen peroxide monitoring with customers. Thirty years ago, most hospitals used ethylene oxide for their low temperature gas sterilization. In the 1990s, Advanced Sterilization Products (ASP), a J&J company, launched the Sterrad line of sterilizers. This product has been remarkably successful and is now the dominant low temperature sterilizer in the US, and many other countries around the world.

A sterilized product is one that is free of all microbial life, including the highly resilient sporoidal bacteria. Obviously, any chemical gas or vapor that can achieve sterilization poses a risk to anyone exposed to it. Hydrogen peroxide for example has an OSHA permissible exposure limit (PEL) of 1 ppm (8 hr time weighted average), the same as ethylene oxide. The Sterrad line of sterilizers generally has a good safety record, but as with any complex equipment malfunctions can occur, engineering controls can fail and user error can result in potential exposures. Therefore, ChemDAQ recommends gas monitoring for all gas and vapor sterilant chemicals.

The Sterrad sterilizers function by reducing the pressure, introducing hydrogen peroxide vapor (made by evaporating liquid hydrogen peroxide solution) which performs the primary sterilization step, and then the sterilizers activates its radio frequency coils to convert the hydrogen peroxide vapor into a plasma which eliminates residual hydrogen peroxide. The total cycle time for the 100S is about 55 minutes. [100 S data sheet].

As the old saying goes, ‘Time is Money’ and so there is a need for shorter cycle times. Chemical sterilization is achieved by exposing the articles to be sterilized to high concentrations of reactive gases or vapors. Shorter exposure times require higher concentrations of these gases. The NX series of sterilizers takes the 59% solution of hydrogen peroxide used in the 100S and internally concentrates it about 90%. Sterilizing with this solution allows cycle times of only about 28 minutes.

Most matter (solid, liquid, gas) is electrically neutral, but plasma, sometimes described as the fourth sate of matter, is different. Plasmas are found in stars and flames and even fluorescent lights etc., and consist of atoms with at least some of their electrons stripped off forming an ionic gas with lots of high energy, very reactive radicals. While the plasma contributes to sterilization the surfaces of an object, the radicals are so reactive that they would have very limited penetrating power into crevices etc. since they would react with the first surfaces they reach. Therefore the main sterilizing agent in the Sterrad sterilizers is the hydrogen peroxide vapor.

The other main hydrogen peroxide sterilizer used in US hospitals is the V-PRO from Steris Corporation. The Amsco® V-PRO sterilizer forms hydrogen peroxide vapor from a solution of 59% hydrogen peroxide, and also offers a 28 minutes cycle time. The V-PRO generally functions similarly to the Sterrads, though both manufacturers may take exception to this description; but it does not use a plasma to remove the left over hydrogen peroxide at the end of the sterilization cycle. Instead, the hydrogen peroxide is destroyed by passing it through a catalyst that converts it to oxygen and water. The Sterrads have a similar catalyst on their exhaust to remove any hydrogen peroxide vapor surviving the plasma treatment

In 1990 Amsco (a forebear of today’s Steris Corporation) sued Surgikos Inc (ASP was founded as a division of Surgikos) for patent infringement claiming that the Sterrad plasma process was merely icing on the cake and therefore Surgikos were infringing the Steris patent claiming hydrogen peroxide sterilization. [US patent 4,169,123]. Surgikos argued that the plasma process was an essential part of their process, as describe in their own patent [US patent 4,643,876]; and managed to convince the court that they were right. The cynic might claim that this success was more attributable to the skill of Surgikos’s attorneys that hard science; but patent was not infringed as the rest is Sterrad history.

While the technologists may argue whether the plasma phase really increases sterility, one fact is sure, having a plasma phase greatly helps marketing. What a ‘cool’ name: a Plasma Sterilizer!

In summary, both the Sterrad sterilizers and the V-Pro sterilizers use hydrogen peroxide as the sterilant chemical. The plasma phase may contribute to the sterilization, but even ASP say it is primarily there to remove residual hydrogen peroxide vapor. By their very nature, all chemical sterilants are potentially harmful to anyone exposed to them. Even though both Sterrad and V-Pro sterilizers and designed and built to the highest standards, leaks can occur and therefore all chemical sterilizers should be monitored for leaks. Like a fire alarm, major leaks rarely happen, but if they do, you will be glad you had a ChemDAQ monitor there. Amsco® is a registered trademark of Steris Corporation; Sterrad® is a registered trademark of Advanced Sterilization Products.

Friday, October 26, 2012

Occupational Health: Protecting workers Against Chemical Exposures

Infection Control Today recently ran an article written by Kelly Pyrek, with the above title that highlights the risks of chemical exposure to healthcare workers.

The author noted that "Occupational exposure to chemicals is common and frequent in hospitals" and went on to say that self reported exposures tend to be significantly under reported. The article looked at both respiratory and dermal exposures. Respiratory exposures arose in particular from sprayed cleaning chemicals and not only resulted in irritation but twice the rate occupational asthma compared to the general work environment. Occupational Asthma was especially prevalent among healthcare workers involved in medical instrument cleaning and exposed to general cleaning products and disinfectants. Dermal exposures mainly arose via contact with the hands due to inadequate protection.

The importance of using personal protective equipment (PPE), and receiving proper training on how to use it was emphasized including gloves, goggles and masks. Some discussion was also given to the use of alternative "Environmental Cleaning Chemicals" but efficacy concerns limit what can be used. The article summarized that there are many actions that can be taken involving different chemicals, modified work practices and better training that can have a major impact.

ChemDAQ has often stressed the importance of workers being aware of the risks of exposure to sterilant chemicals and this article shows that even common cleaning chemicals present a health risk to workers. Patient Safety is of paramount concern in healthcare, and the prevalence of hospital acquired infections has resulted in greater emphasis on disinfection and cleaning. Unfortunately, it is all too easy for hospital administrators to focus so much on patient safety that the safety of their employee gets over looked.

As the NIOSH NORA report stated "The HCSA sector is burdened by the historical and entrenched belief that patient care issues supersede the personal safety and health of workers and that it is acceptable for HCSA workers to have less than optimal protections against the risks of hazardous exposures or injuries." However, there are signs that the old ways are changing. Recent articles have discussed this issue, and more enlightened institutions know that patient safety and employee safety go hand in hand.

It almost goes without saying that any chemical used to kill a broad spectrum of microbial life is likely to have adverse effects on people exposed to it. Some of the effects will be immediate, others may take longer to become apparent. This article in Infection Control Today is valuable in informing people that occupational exposure to even every-day cleaning agents can have adverse effects. Disinfectant and cleaning chemicals provide life saving functions in healthcare, but whenever these chemicals are employed it is important to assess the risks, develop work practices to minimize exposure, provide adequate PPE, and train workers how to use these chemicals safely.

Tuesday, October 2, 2012

The ECHA is a Valuable Source of Chemical Safety Information

Often users, managers and industrial hygienists want to know the hazards associated with the chemicals that they use. There are many resources available for information on chemical hazards, including governmental and private sources. One of the more comprehensive sources is the European Chemical Agency (ECHA). The ECHA provides a lot of information in a relatively simple to use format; but this database is not widely known on this side of the Atlantic.

The ECHA has the goal to be the preeminent source for chemical safety information in the world. This agency was created under the European Union’s REACH program. REACH stands for the Registration, Evaluation, Authorization and Restriction of Chemical substances and went into law June 2007. Manufacturers and importers are required to gather information, including safety information, on the chemicals they manufacture, and to provide it to the ECHA which in turn provides public access to this information via an on-line searchable database. This database is a great resource for anyone looking to find safety information about chemicals commonly used in the workplace. Using peracetic acid (PAA) as an example, the ECHA search engine for hazardous chemicals is available at http://echa.europa.eu/web/guest/information-on-chemicals/registered-substances. Simple enter “peracetic” into the search line and click on the disclaimer box brings up a link to the dossier for PAA. Click on view to access the information. The information is divided into nine general categories:

    General Information

    Classification and Labelling

    Manufacture, Use & Exposure

    Physical and chemical properties

    Environmental fate and pathways

    Ecotoxicological Information

    Toxicological information

    Guidance on safe use

    Reference substances

For those people who want more general information, the Guidance on Safe Use Section provides general advice on using PAA, first aid measures, labels, exposure levels (for acetic acid and hydrogen peroxide) etc.

For those people who want more detail, for example information on research conducted on the chemical safety aspects of a particular compound, this level of information, chemical compatibility, is also available. Clicking on Toxicological Information generates the following submenu:

    Toxicological information.001

    Toxicokinetics, metabolism and distribution

    Acute Toxicity

    Irritation / corrosion


    Repeated dose toxicity

    Genetic toxicity


    Toxicity to reproduction

Selecting Acute Toxicity

    Acute toxicity: oral

    Acute toxicity: inhalation

    Acute toxicity: dermal

    Acute toxicity: other routes

The Acute Toxicity Inhalation section gives a list of 14 summaries of research studies on the acute inhalation toxicity of PAA. The long menu structures above are included in order to give an idea of how much information is available at this website.

This website offers a lot of safety information in summary form that is easy to use for the individual who just needs general guidance, but the website also has a lot of other information for those people who need more detail.

Friday, September 21, 2012

LEL and Other Combustible Gas Concentration Units

We are all used to converting units from metric to standard and from US standard to UK standard (a UK gallon = 1.20 US Gallons) but gas concentrations take it to a new level of complexity. We have absolute concentrations: mg/m3, relative concentrations: % ppm, ppb, and flammable concentrations: % LEL and probably some others I have not thought of. This article will try to explain the differences between these units and why people use one over another.

A true concentration is the amount of gas present per unit volume. For this reason, many gas concentrations are given in units of mg/m3. While this unit is correct, and is widely used in government regulations and industrial hygiene, it is more common to use relative units such as parts per million (ppm) or parts per billion (ppb). Relative units such as ppm and percent have the advantage that they do not change with pressure.

Oxygen in the air is about 20.9 % by volume (for any volume of air, 20.9 % of it is oxygen). Room air is 20.9% and so is compressed air in a scuba diver’s tank at ~ 2,000 psi. Similarly if I want to calibrate a gas monitor with 10 ppm of for example carbon monoxide, I can purchase a cylinder of 10 ppm carbon monoxide at 2,000 psi and deliver it to my gas monitor at close to atmospheric pressure and it is still 10 ppm. If one were working in mg/m3, the concentration at 2000 psi would be about 135 times as high as at ambient pressure because for every unit of volume there is 135 times more gas present. Since these relative concentrations are by volume of gas, they are sometimes written as ppmv, ppbv or % v/v in order to distinguish other relative measures such as ppm in liquids which are normally by weight.

One difficulty that arises is that many toxic gas sensors respond to the concentration of gas rather than the relative concentration. Thus if a gas sensor is calibrated at sea level and then shipped to Denver, (5,280 ft), the pressure is about 80% of sea level and so the absolute concentration will of any gas component will be lower than at sea level for the same ppm or % volume. Users of ChemDAQ products will be pleased to know that altitude is not an issue for their equipment since there is an automatic compensation parameter set in the monitor at the time of installation to correct for differences in altitude between ChemDAQ (where the sensor modules are calibrated) and the end user. LEL sensors also respond to the concentration and depending on how the sensor is constructed, some oxygen sensors respond to the absolute concentration, and others to the relative concentration.

Most of us however, happily live our lives at relatively constant atmospheric pressure and so the two units are readily interconvertible (see free ChemDAQ ppm to mg/m3 converter on the ChemDAQ website [bottom of page]) and we can use relative units without problem.

Another reason for using relative units occurs with flammable gases where percent LEL is widely used. Most flammable gases have a concentration range over which mixtures with air will burn. If there is too little fuel then there is insufficient heat produce for the flame to propagate and similarly if there is too little oxygen, again there is too little heat for the flame to propagate. A typical gas such as propane has flammability/explosive limits in air of 2.2 to 9.5 % by volume. [Matheson Gas Data Book, 6th Ed.], so any propane/air mixture in this range is flammable and so is potentially explosive. The lower limit of flammability is called the Lower Explosive Limit (LEL) and the other limit is the Upper Explosive Limit (UEL). The LEL and UEL values vary from gas to gas.

If one working in an environment where there is a risk of an explosive gas mixture forming, then no-one really cares if the concentration is 2.1% volume, they want to know whether the atmosphere is explosive or not and whether they should get out. Flammable gas monitors for workplace safety are therefore calibrated in % LEL which provides an immediate measure of the risk of forming an explosive atmosphere. The gas monitors typically have a range of 0 to 100% LEL. If the concentration reaches 100% LEL, then there is a potentially explosive atmosphere and so the alarms are set lower, typically 10% and 20% LEL.

To convert from % LEL to ppm, it is necessary to know the Lower Explosive Limit. Using ethylene oxide (EtO) as an example, the LEL is 3% by volume, which is equal to 30,000 ppm. It is common therefore in facilities that use large amounts of EtO to have two different types of monitor. One set of monitors measures EtO at parts per million concentrations to warn about potentially toxic exposures (OSHA Permissible exposure limit for EtO is 1 ppm calculated as an 8 hr Time weighted average) the other set of monitors is to detect potentially flammable gas mixtures that threaten not only people but also the building. Hopefully before the LEL monitors go into alarm the ppm levels alarms will have warned everyone to clear the air, but the LEL monitors are used to increase ventilation or turn on the sprinkler system.

There are even more units of gas concentration out there which are less common, but if anyone wants more explanation of these, please leave a comment.

Friday, September 14, 2012

Using Hydrogen Peroxide Monitors to Measure Peracetic Acid Vapor

Peracetic acid (PAA) also known as peroxyacetic acid has become widely used as a disinfectant and sterilant in healthcare, food processing, meat and vegetable production, water treatment and many other industries. PAA is a strong oxidizer and a primary irritant and the health effects of over exposure, especially to the vapor are well known.

As a result of these risks the US-EPA has issued Acute Exposure Guidelines for PAA and there are three AEGL levels: “AEGL-1 is the airborne concentration, expressed as parts per million or milligrams per cubic meter (ppm or mg/m3) of a substance above which it is predicted that the general population, including susceptible individuals, could experience notable discomfort, irritation, or certain asymptomatic nonsensory effects. However, the effects are not disabling and are transient and reversible upon cessation of exposure.” AEGL 2 is the level where those exposed may experience “irreversible or other serious, long-lasting adverse health effects or an impaired ability to escape.” And AEGL 3 is the level where those exposed may experience “life-threatening health effects or death.

PAA is normally found as an equilibrium mixture with acetic acid and hydrogen peroxide:


Therefore, whenever PAA solution is used, in addition to PAA vapor there is also hydrogen peroxide vapor and acetic acid vapor, both of which have OSHA permissible exposure limits (PELs) of 1 ppm and 10 ppm respectively calculated as an eight hour time weighted average, both significantly higher than the AEGL 1 for PAA of 0.17 ppm. Currently there is no OSHA PEL for PAA or ACGIH TLV, though the ACGIH has proposed a 15 minute short term exposure limit (STEL) for PAA of 0.2 ppm. The analysis below will use the AEGL 1 but it is simple to adjust the numbers if the new ACGIH STEL is adopted.

ChemDAQ recently launched a PAA monitor as part of its Steri-Trac® gas monitoring system that also includes monitors for hydrogen peroxide. Prior to the launch of this product, there were no monitors for PAA and very few analytical methods available, despite the widespread use of PAA. Employers seeking to protect their workers would often rely on detecting only the hydrogen peroxide and acetic acid components, but this approach is flawed in that PAA vapor is more hazardous that either of the other two vapors and in mixtures with a high PAA content, it is the dominant vapor present.

The best strategy to designing a gas detection system is to assess which vapor presents the greater hazard and detect that one. As discussed above, PAA is usually used as an equilibrium mixture with hydrogen peroxide and acetic acid and it is supplied in a variety of blends, some with a high PAA/H2O2 ratio and some with a low PAA/H2O2 ratio. Ratios in commercial blends typically vary from 10:1 to 1:5 PAA:H2O2.

The last piece to the puzzle is the vapor pressures of hydrogen peroxide and PAA solutions. At room temperature the vapor pressures of PAA and hydrogen peroxide are 1.93 and 0.26 kPa respectively at 25 oC [CRC Handbook of Chemistry & Physics 76th Ed, Lange’s Handbook of Chemistry, 12th Ed). Combining the vapor pressure and the PEL/AEGL 1 for the two compounds gives the relative hazard (43:1 PAA/H2O2). Multiply this number by the ratio of PAA/H2O2 in the composition gives the risk factor for that PAA blend.

If we assume that the risk of a minority vapor can be ignored if the risk is less than 20 % for the combination of both PAA and hydrogen peroxide, then if the risk factor is less than 0.2, the predominant risk is hydrogen peroxide and a hydrogen peroxide monitor will suffice. If the risk factor is greater than 5, then the predominant risk is PAA and a PAA monitor only is sufficient. If the risk factor is between 0.2 and 5, then both PAA and hydrogen peroxide vapors pose a risk and both types of monitor should be employed.

The risk factors for several common blends are shown below. The risk factors for other blends may be readily calculated as described above.

PAA (wt %) H2O2(wt %) Risk Factor Monitor
0.23 7 1.4 H2O2 and PAA
2 22 4 H2O and PAA
5 25 8.8 PAA
10 20 22 PAA
15 10 66 PAA
32 6 234 PAA

In Conclusion, for all of the brands and blends that we currently have data on (~ 70), none of them would be adequately monitored using a hydrogen peroxide monitor alone and those facilities using only a hydrogen peroxide monitor maybe seriously underestimating the exposure risk of their employees. The majority of PAA blends would require PAA monitors only and a few blends, with low PAA/H2O2 ratios, need both hydrogen peroxide and PAA monitors in order to adequately monitor the vapor.

Tuesday, September 11, 2012

Requirement to Monitor for Hydrogen Peroxide

One of the topics that we often receive questions on concerns whether there is a legal requirement to monitor for hydrogen peroxide. The short answer is that there is no regulation from OSHA explicitly saying that hydrogen peroxide must be monitored, just as there is no explicit order requirement to monitor for carbon monoxide in a steel mill or hydrogen sulfide in a petroleum plant.

The reason why there is no statement requiring monitoring, is because OSHA along with most other government agencies intentionally write their regulations to set goals not prescribe means to create a safe workplace. i.e. performance based versus prescription based regulation. the goal is a safe work environment, gas detection is a means to achieving it. There are two reasons for this performance based approach. The first is that developing regulations is a slow process and if OSHA were to specify a particular method, it would probably be obsolete even before the final rule was published in the Federal Register. The second reason is that the circumstances at every employer are different and so the means to solve an exposure problem at one facility may be inapplicable to another facility. For example, the same regulations governing workplace exposure to hydrogen peroxide apply to a hospital sterilizing medical equipment, a titanium plant using hydrogen peroxide to pickle titanium ingots to remove mill scale and a sewage treatment plant using hydrogen peroxide to reduce odor emissions.

The Occupational Safety and Health Act (1970), imposes a legal duty on employers to “furnish to each of his employees employment and a place of employment which are free from recognized hazards that are causing or are likely to cause death or serious physical harm to his employees.

[Sec. 5] The hazards of exposure to hydrogen peroxide vapor are well known and have been for decades, and OSHA sets the legal standard for when exposures to hydrogen peroxide are considered free from recognized hazards etc. in its Permissible Exposure Limits (PELs) “An employee's exposure to any substance in Table Z-1, the exposure limit of which is not preceded by a "C", shall not exceed the 8-hour Time Weighted Average given for that substance any 8-hour work shift of a 40-hour work week.” The permissible exposure limit for hydrogen peroxide is 1 ppm calculated as an 8 hr time weighted average and the employer has an affirmative legal duty to ensure that the PEL is not exceeded.

Many people believe that hydrogen peroxide is completely safe, after all it is sold in super markets for treatment of minor cuts. However, gas or vapor sterilization is achieved by exposing the articles to be sterilized to high enough concentrations of reactive gases or vapors to ensure that all microbial life is destroyed (probability survival < 1 in a million). If the concentration of hydrogen peroxide in the sterilizer is high enough to kill even bacterial in the sporoidal form, then in the event of a leak, the concentration is high enough to pose a risk to nearby workers.

Some people may have received assurances from the folks who sold them a hydrogen peroxide sterilizer that their equipment could never leak. People in sales are often very enthusiastic about their products and often portray them in their best light. Modern sterilizers available today are indeed designed and manufactured to the highest engineering standards, and most are tested for leaks as part of the design process. However, as with any complex piece of equipment components can fail, user error happens and of course wear and tear takes its toll. Even though the sterilizers contain many safety features and are designed not to leak, the manufacturers will usually acknowledge that leaks can sometimes occur. If you are assured that it cannot leak, just request a statement to that effect in writing.

ChemDAQ has many customers with monitors monitoring their hydrogen peroxide sterilizers. In case further evidence were needed that sterilizers can sometimes leak, last year, one of our hospital customers installed ChemDAQ’s gas monitoring system for their four new hydrogen peroxide sterilizers (no names here!). All four sterilizers emitted a cloud of around 20 to 40 ppm hydrogen peroxide each time the door was opened at the completion of the cycle, which would have been particularly harmful if people are reaching in to retrieve the load, especially since the NIOSH immediately dangerous to life and health level for hydrogen peroxide is only 75 ppm. The FDA’s MAUDE data base also provides other examples of sterilizer malfunction including exposure of workers to hydrogen peroxide vapor.

Employers must ensure that their employees are not exposed to hydrogen peroxide levels greater than the PEL, but hydrogen peroxide has almost no odor and so odor cannot be used to detect the presence of a hydrogen peroxide leak. Therefore absent some kind of monitor, it would be very difficult to measure the hydrogen peroxide concentration.

Some facilities use badges for hydrogen peroxide, but badges suffer from two major defects. A typical badge is worn for a shift and then sent to a lab to be analyzed (typically 1 - 2 weeks). Thus badges provide no warning of current exposure; they merely document exposures that have already happened. The second drawback is that leaks, like other faults usually occur at unexpected times and so if, for example badgering, is performed every month, then there will be between one to 31 days (plus badge analysis time) before any leak is discovered.

A continuous monitor offers greatly superior performance by providing the instantaneous hydrogen peroxide concentration, and alarms if the concentration goes too high thus providing real-time protection of employees. Most systems also include the capability to log data, calculate time weighted average exposures and warn if the OSHA PEL will be/has been exceeded and provide record keeping, reports etc. that enable an employer to demonstrate that their employees have not been exposed above the OSHA PEL.

In summary, installing a gas monitor for hydrogen peroxide is NOT mandated by OSHA, but OSHA does require that employers ensure that employees are not exposed to hydrogen peroxide over the PEL. Hydrogen is odorless and generally imperceptible until present at concentrations greater than the PEL and so some kind of analysis method is required to detect it. While the employer is free to employ any effective method to ensure that its employees are not overly exposed to hydrogen peroxide, continuous monitoring is the most effective method for employers to meet the OSHA requirement. Since hydrogen peroxide vapor is imperceptible until above safe levels, if there is a leak, Are You Safe? How do you Know?

Friday, September 7, 2012

Gas Stratification is Not Relevant to Gas Monitor Placement

We all know that objects more dense that water sink and those less dense than water float; and that light gases such as hydrogen rise and heavy vapors sink. In meteorology we see warm air rising over colder air masses and in science experiments we see denser gases like carbon dioxide being poured like liquids. If any more confirmation were needed, the disappearance of a helium filled balloon from a child's birthday party into the heavens should put all doubts to rest that lighter gases rise and heavier gases sink.

It therefore makes intuitive sense that a heavy gas will accumulate in low lying areas and lighter gases will collect in high areas. We often see published advice from gas detection vendors for example that sensors for ammonia (mol. wt. = 17 g/mol) which is lighter than air (av. mol. wt ~ 29 g/mol) should be placed up near the ceiling and monitors for heavier gases such as carbon dioxide (mol. wt. 44 g/mol) should be placed near floor level. Even though it makes intuitive sense, does gas stratification occur in practice?

Stratification is the extent to which the heavier gases tend to settle to the bottom and the lighter gases rise to the top of an initially uniform air mixture, in the absence of bulk air movement. In well ventilated areas, gas stratification is irrelevant. The air movement from the ventilation will mix up the room air sufficiently that the gas and vapor concentrations will be uniform with height above the ground. Therefore, in well ventilated work environments, such as a hospital sterile process department with a high air turnover (typically at least 10 air exchanges per hour), we recommend placing gas monitors for toxic gases about five feet of the ground so that they correspond to the breathing zone of individuals regardless of the identity or molecular mass of the gas or vapor being detected.

Stratification is widely believed by many to occur in locations where there is little air movement; however a 2009 paper by Badino, which discusses stratification of air in caves, provides a very good mathematical analysis which goes a long way to answering the stratification question. His analysis shows that stratification does occur, but it requires a column of static air several kilometers high to have a major impact; and so stratification will not be relevant to most occupational safety gas monitoring applications.

Caves full of deadly carbon dioxide do exist, as do other confined spaces such as sewers, storage vessels etc.; but Badino argues that these arise not because of stratification but because these gases and vapors form in the caves and diffuse out very slowly causing a local high concentration. He also points out that many of these situations are also dangerous because of the low oxygen concentration, which he argues is due to the oxygen being consumed in the reaction with organic matter rather than stratification. These confined spaces present a significant danger to anyone entering them, regardless of whether the mechanism is stratification, diffusion or another cause. Therefore, whenever entering a confined space, especially one with little air movement, it is important to follow the normal confined space entry procedures and regulations.

Theilacker and M. J. White conducted a study of gas diffusion and stratification after a helium leak at Fermi Lab. Since helium is such a light atom (mol. wt. = 4 g/mol) they had expected it to displace oxygen from ceiling, but they saw no difference in the readings of the oxygen monitors as a function of height above the floor. The conclusion of their studies with both helium and sulfur hexafluoride, a large heavy molecule (mol. wt. 146 g/mol) was that "modest gas velocities will fully mix the spilled gases with air. The gases remained fully mixed over long distances in tunnels, or for long times in enclosed spaces." In other words stratification is not a issue with gases under normal working conditions, even if your normal work environment is 25 feet underground in a four mile long particle accelerator tunnel.

While these two papers are not the end of the story, the take home message is the same as we have been saying for many years. In most work environments with good ventilation, stratification of gases is not going to occur to a significant extent. Thus if measuring the concentration of a lighter than air gas such as ammonia or a heavier than air gas such as ethylene oxide, for workplace safety applications, in both cases the monitors should be placed at head height or about 5' off the ground. However, confined spaces, especially those with little air movement, present real dangers, even if the cause is not gas stratification, and so normal confined space entry procedures and regulations should be followed.

Thursday, August 16, 2012

Response to Low ppm Readings on a Hydrogen Peroxide Monitor

Many users are concerned about exposure to hydrogen peroxide vapor from their sterilizers and so have invested in continuous monitors for hydrogen peroxide. These monitors provide a real time reading of the hydrogen peroxide concentration in ppm but now the user needs to interpret these numbers and respond appropriately.

If there is a large leak of hydrogen peroxide vapor and the hydrogen peroxide monitor is in high alarm, the response is simple – clear everyone out of the immediate area until the ventilation reduces the concentration to safe levels (as determined by the monitor). Fortunately massive leaks rarely occur, but it is not uncommon for people to see low ppm readings on their hydrogen peroxide monitors. The question then arises as to what constitutes over exposure to hydrogen peroxide vapor and what actions should be taken.

Some people rely only on the OSHA permissible exposure limit (1 ppm, calculated as a time weighted average (TWA) over 8 hours). The argument goes that so long as the OSHA PEL is not exceeded all is good in the world of hydrogen peroxide exposure. Sometimes this calculation is tempered by saying that the hydrogen peroxide exposure should not go over the NIOSH IDLH (75 ppm for hydrogen peroxide).

Following this logic, it would be OK for someone to be exposed to 50 ppm hydrogen peroxide continuously so long as it does not exceed the PEL, i.e. < 480 minutes/50 ppm = < 9.6 minutes, and 25 ppm for < 19.2 minutes etc. are OK. I would not want to be the person exposed and certainly not on a regular basis. These numbers may seem high but we have seen hydrogen peroxide vapor in the 30 to 40 ppm range being emitted from one model of hydrogen peroxide sterilizer whenever the door was opened after completion of a cycle. Hydrogen peroxide has essentially no odor and so apart from some a monitor or other method to detect hydrogen peroxide there is no way to know if hydrogen peroxide vapor is present.

Probably the most respected industrial hygiene organization in the world is the ACGIH and the ACGIH has issued a threshold limit value for hydrogen peroxide of 1 ppm calculated as an 8 hour TWA. The similarity with the OSHA PEL is not coincidental since the OSHA PELs were initially derived from the ACGIH TLVs in 1972 and neither the ACGIH TLV nor OSHA PEL have revised the exposure limit for hydrogen peroxide since then.

For compounds with no short term exposure limits the ACGIH recommends the following: Excursions in worker exposure levels may exceed 3 times the TLV-TWA for no more than a total of 30 minutes during a work day, and under no circumstances should they exceed 5 times the TLV-TWA, provided the TLV-TWA is not exceeded. [2008 TLVs and BEIs based on the Documentation of the threshold Limit Values for Chemical Substances and Physical Agents and Biological Exposure Indices, p 5.]

Applying this guidance to hydrogen peroxide, worker exposure may exceed 3 ppm for no more than 30 minutes during the work day and under no circumstances should they exceed 5 ppm. These levels are thus similar to a short term exposure limit (STEL) and ceiling limit respectively and are consistent with the STELs for hydrogen peroxide promulgated by several governmental occupational safety agencies. Washington state for example has a STEL of 3 ppm (15 min TWA) and the United Kingdom and some other European countries have a 2 ppm STEL. [Ref EH40, 2005]. While there is no OSHA STEL for hydrogen peroxide, this ACGIH guidance represents best practice when using hydrogen peroxide.

If the monitor always reads less than 1 ppm then the user need have no immediate concerns about exposure to hydrogen peroxide, the 8 hour TWA will be less than the OSHA PEL. However, we have found on many occasions that the readings often start our small but over time they increase. Thus if the readings increase over successive cycles of the sterilizer and become significantly higher than previously seen, even if still within safe limits, then these numbers can serve as an indicator that the sterilizer should be serviced soon.

If the readings occasionally rise between 1 to 5 ppm, as may some times occur when the sterilizer door is opened, then the user should step away from sterilizer and return once the readings have fallen to safe levels (< 1 ppm). If this ‘puff’ of hydrogen peroxide is new to the operation of the sterilizer, then again, it is time for maintenance.

If the hydrogen peroxide monitor goes above 5 ppm, then this concentration poses a potential hazard to employees and the problem should be rectified and the sterilizer manufacturer should be asked to correct the problem. If the manufacturer says that the sterilizer or other equipment is operating normally, then other measures such as engineering controls, modified work practices etc. should be employed to ensure workers are not exposed to hydrogen peroxide above 5 ppm.

Friday, July 6, 2012

Exposure Badges Do Not Provide Adequate Protection Against Toxic Gases

Toxic gases are found in many workplaces across many industries ranging from carbon monoxide in coal mines, hydrogen sulfide in waste water treatment and chlorine in paper mills. Typically, the workplace is designed to minimize worker exposure to these gases through work practices, process design, PPE & engineering controls etc. However, it is widely recognized that despite the best efforts of the design engineers, exposures to toxic gases can still occur and so most facilities using toxic gases employ fixed and/or portable instruments that continuously monitor the atmosphere and provide a warning to people working there in the event of a leak.

Employers provide continuous monitors because in part because they want to protect their workers and in part because they are required to provide a safe work environment. The Occupation Health and Safety Act of 1970 requires an employer to "furnish to each of his employees employment and a place of employment which are free from recognized hazards that are causing or are likely to cause death or serious physical harm to his employees". This statute provides a general legal duty, and OSHA's standards, which provide more specific legal requirements, such as maximum permissible exposure limits (PELs) for toxic gases. However, OSHA recognizes that each workplace is different and so OSHA leaves determining the best means to achieve these levels to the employer.

Prior to the development of continuous monitors, several chemical methods were developed for determining workplace exposures of toxic gases. Three common methods are:

1) Drawing a known volume of air through an impinger (bubbler) containing a reagent that reacts with the target gas, and the resulting product is then analyzed by laboratory.

(2) Gas exposure badges, in which the target gas reacts with a reagent impregnated on the surface of the badge and the product is again analyzed by a laboratory and

(3) Gas detection tubes in which the target reacts reacts with a reagent on a solid support giving a color change such that the extent of the color change along a graduated scale provides an indication of the gas concentration.

For routine monitoring, these methods have largely been replaced by continuous monitors. Impingers are still used today since many standard test methods call for them, and impingers and badges have some value for those 'exotic gases' for which continuous monitors are not available. The primary drawback of impingers and badges is that they do not provide any warning of what the worker is currently being exposed to, but only report what he or she has already been exposed to. For someone inhaling a toxic gas, now is important, two weeks time, or however long it takes for the lab reports to come back is not adequate. If a person protected by a continuous monitor is exposed to a high concentration of the toxic gas or vapor, a continuous monitor will alarm before the gas concentration reaches dangerous levels and so prevent that person from being exposed. Prevention is always better than an apology!

For this reason, one almost never sees exposure badges being used in general industry. They don't use exposure badges in water treatment plants, or chemical plants or other industries for gases for which continuous monitors are available. There is however one exception, the health care industry. The health care industry uses many toxic chemicals such as drugs for angioplasty, anesthetic gases and sterilization/high level disinfection. The high level disinfectants in particular included gases and vapors such as ethylene oxide (OSHA PEL 1 ppm, NIOSH IDLH 800 ppm) and hydrogen peroxide (OSHA PEL 1 ppm, NIOSH IDLH 75 ppm) are well known to be toxic (otherwise they would not work as disinfectants and sterilants).

The argument has been made that these compounds are normally completely contained within the sterilizers, devices designed to retain these gases/vapors and so leaks are unlikely; but it is unclear how this situation is different from a cold food storage facility using ammonia based refrigeration (OSHA PEL = 50 ppm, NIOSH IDLH = 300 ppm). In both cases, the equipment is designed to keep the the gas inside, but the sterilizer door must be opened on a regular basis to load and unload the items being sterilized. I have never seen a food storage facility or similar establishment using ammonia exposure badges to protect its employees, but it is not unusual to find hospitals that monitor their employees exposure to ethylene oxide or hydrogen peroxide with exposure badges. Continuous monitors are commercially available for ethylene oxide, hydrogen peroxide, ozone, peracetic acid etc, in many cases from several suppliers. The question therefore is why do many hospitals insist on using badges to monitor worker exposure instead of continuous gas monitors.

The National Occupation Research Agenda's (NORA's) Report on workplace safety in healthcare offers an answer: "a key barrier to addressing them [chemical hazards] is the misconception that HCSA [Heathcare sector] work is safer than other work involving exposure to chemical and physical hazards." However a recent Bureau of Labor Statistics report however refutes this assumption.

The same NORA report later comments that "For instance, several authors have pointed out that for many healthcare personnel (HCPs), patient-care issues (i.e., patient health, well-being, and safety) take precedence over personal safety [DeJoy et al. 1995]. There is also a concern that, at least in some settings, a culture and climate of risk acceptance may be the norm; some workers may come to expect that the risk of exposure or injury is simply part of the job."

We often see two versions of this story. The first is an unwillingness to accept the risks posed by the use of the disinfectant and sterilant chemicals in healthcare. This version is easier to understand. The overall risk is a function of the hazard presented by exposure (these are sterilant and disinfectant chemicals after all) and the probability of exposure. If the employer believes, after reasonable investigation, that the risk of exposure is negligible, then the employer can at least argue for not monitoring.

If however, the employer acknowledges that there is risk of exposure, that equipment and engineering controls can sometimes fail and that therefore some kind of monitoring of these gases and vapors is needed then why use an exposure badge, a technology that become obsolete in the 1980s? If an organization uses hazardous chemicals that present a significant risk of exposure, that risk is recognized, and continuous monitors are readily available, then is resorting to badges really meeting the expected standard of care for workplace safety for those employees using these chemicals?

Legal issues aside, the main question for managers who need to decide what type of protection from toxic gases is whether to use continuous monitors, equipment that is widely accepted across many industries to provide good protection for their people or to use exposure badges that have since fallen from main stream use because they don't provide the level of protection needed to keep their workforce safe.

It is dangerous and unfair to paint an industry with too broad a brush and many hospitals have excellent safety records and ensure that their staff are well trained and have modern safety equipment. These facilities should be applauded for setting the standard in healthcare that others would do well to follow.

Monday, June 25, 2012


The goal of this blog is provide useful information about gas detection and safety, relevant regulations, ChemDAQ's news, industry topics and to be a resource for those who work in these areas. If you have any questions or would like more information about any related topic, please submit a comment below.

Thursday, June 14, 2012

The Role of Calibration in Gas Detection

Everyone who uses gas monitors is aware of the need to calibrate them, but we are often asked why this is.

The first reason is that calibration performs a basic function check to ensure that the equipment is working properly. ChemDAQ sensors are generally very reliable and probably could be used for a long time without significant reduction in sensitivity. However, as with any device, there is always a risk of failure. Periodic calibration provides a basic function check to make sure that the sensors respond to gas correctly.

The second reason for calibration is ensure that the gas monitor reads the correct value when exposed to the target gas or vapor. Using electrochemical sensors as an example, the output current from the sensors is proportional to the gas concentration and calibration provides that proportionality constant. In principle it is possible to derive this calibration parameter from the diffusion properties of the sensor components, such as the membranes and spaces etc. of a sensor and calculate the steady state response by applying the relevant laws of electrochemistry and diffusion; however this method is neither practical on a regular basis nor particularly accurate.

Instead, a more practical approach is to exposure the sensor to clean air (zero air) and set the baseline to zero, and then apply the span gas and adjust the output of the sensor module so that the reading on the monitor matches the concentration of the gas applied.

Reactive gases cause difficulties in calibration for several inter-related problems. The first is that reactive gases are more hazardous and so must be detected at lower concentration than less hazardous gases, for example the OSHA PEL for ethylene oxide and hydrogen peroxide are both 1 ppm, whereas the PEL for the less toxic carbon monoxide is 50 ppm.

Secondly, the lower the concentration, the more severe adsorption effects will be. Materials compatibility is also critical. Pass 50 ppm carbon monoxide down a well used vinyl tubing and 50 ppm will come out the other side. Pass 1 ppm hydrogen peroxide down a used or pristine vinyl tubing and only air will come out. Even tubing that is chemically compatible with hydrogen peroxide or other reactive gases may still remove the test gas if the tubing is contaminated or damp. The more reactive the gas, the more difficult it is to ensure the calibration process is not flawed. For the manufacturers of monitors for these reactive gases, a large percentage of the technical support issues concern calibration problems.

For many gases, such as ethylene oxide, the gas is delivered in cylinders along with a certificate certifying what the gas concentration is. For other gases and vapors, such as hydrogen peroxide, we have to generate the hydrogen peroxide in-house and then calibrate the hydrogen peroxide test gas against a known standard before we can use it to calibrate the sensor modules.

It is primarily for these reasons that ChemDAQ provides factory calibration for all its customers. Factory calibration ensures that the calibration is performed correctly and accurately. In addition, factory calibration is much more convenient to the end user since they can simply swap out a precalibrated sensor instead of havin to work with compressed gas cylinders or other gas sources. ChemDAQ's monitors mainly detects sterilant gases, highly reactive gases and vapors used to sterilize medical and food equipment and supplies. While some of these gases are available in calibration cylinders, many of the others are not. ChemDAQ equipment is therefore designed to be factory calibrated to avoid problems with calibration using very reactive gases.

ChemDAQ's SXP® calibration service offers other benefits as well. Tracking is one major advantage. Some facilities are very good in tracking when their gas monitors are due to be calibrated, but many others are not so diligent and uncalibrated sensors are a regular cause of error in gas detection systems. ChemDAQ's SXP service includes tracking the calibration status of the sensors, and ChemDAQ will contact each customer when their sensors are due for exchange.

One of the more widely used methods to improve the sensitivity of gas sensors is to use a chemical filter. A chemical filter in front of the sensor reacts with the gas or vapor one does not want to detect so that only the target gas reaches the sensor. Chemical filters have a capacity beyond which they no longer react with the interfering gas or vapor. Depending on the chemistry, the capacity of some filters is large and the filter rarely needs to be changed, for others the capacity is more limited and the filter needs to be changed more frequently.

One of ChemDAQ's claims to fame is our specific filter for the EtO sensor. This patented filter reacts with alcohols, many VOCs and even carbon monoxide (there are not too many compounds that react with carbon monoxide at room temperature); but it still allows EtO to pass through unhindered. This filter works remarkably well, but it does have a limited capacity. Therefore this filter is replaced every calibration cycle.

In summary, calibration is an essential part of gas detection as a basic function check and to ensure that the gas monitor reads the correct value. Some manufacturers have their customers calibrate on-site, which is OK for stable gases but becomes increasingly problematic for reactive gases. ChemDAQ's solution to this problem is to factory calibrate all monitors which ensures that the calibration is performed correctly and by tracking each customer, ensure that the calibration is performed when due. Factory calibration offers other benefits as well such as ease of operation for the end user and automatic replacement of consumables such as chemical filters.

Tuesday, June 5, 2012

The Correct Placement of Gas Monitors

We are often asked about the correct placement of area gas monitors. Area monitors monitor an area and tell workers whether it is safe to be in that area.

Area monitors should be placed close to potential sources of the gas or vapor being monitored, so for example if the gas is ethylene oxide used for hospital sterilization, then the monitors should be placed close the sterilizer, the abator (if used) and locations where the ethylene oxide is stored. An area monitor should detect the gas before it reaches the people working in the area and so can give more advanced warning than a personal monitor.

The monitors should be placed at a height similar to breathing zone for most people, typically about five feet (1.5 m) off the floor. The sensor or sampling point should be open to air and not covered or blocked.

A common question is how far can a gas monitor detect gas, and the accurate answer for diffusion type sensors is that the sensors detect only the gas that reaches them. It is possible to model the gas diffusion in static air, but the results are of little use because this model does not apply to real life. In a typical hospital sterilization department, aseptic food processing or commercial sterilization environment with large air turn overs (e.g. > ~10 turnovers/hr) it is difficult to predict how far the gas will travel because of the rapid turbulence of the air. We typically use a rule of thumb that gas monitors have a maximum radius of detection of about 5 feet and so two gas monitors should be no more than 10 feet apart (~3m). However, the optimum design of the gas monitoring system must take into account the place of the gas sources, e.g. (sterilizers), abators and ventilation.

We are often asked about the best placement of a monitor on or near a sterilizer (typically small dishwasher sized sterilizers, not the large commercial ones). If the sterilizer is wall mounted, then we recommend placing a monitor on the wall close to the front of the sterilizer. Sterilizers can potentially leak from the door when it is opened and so we need a monitor close by to provide suitable warning. This is particularly true in situations where users regularly open the sterilizer door and reach in to remove the load.

If the sterilizer is a free standing unit, the sensor should be placed above the door (ChemDAQ's remote sensor) and have a monitor on a nearby wall. If above the door is not possible, then as close to the front of the sterilizer as possible. Sterilizers can sometimes emit gas or vapor when the door is first opened after a cycle. We have seen 30 to 40 ppm hydrogen peroxide be emitted by some sterilizers each time the door was opened, significantly higher than the OSHA PEL of 1 ppm (8 hr TWA) and similar magnitude to the NIOSH Immediately Dangerous to Life and Health value (75 ppm).

Even though the OSHA PEL is not reached, other authorities that have updated their occupation exposure levels more recently than OSHA have introduced a STEL for hydrogen peroxide, for example 3 ppm in the State of Washington and 2 ppm in the United Kingdom While these limits are not enforceable outside Washington State and the UK respectively, they do indicate that exposure to high concentrations of vapors like hydrogen peroxide is best avoided.

Where there are several free standing sterilizers in a row, the best configuration is to have a sensor over every door to provide protection as described above. In some cases, cost demands that a monitor is placed between each pair of sterilizers. This configuration is will detect major leaks of gas or vapor but will not provide warning against small releases of gas or vapor when the sterilizer is opened.

Since hydrogen peroxide has almost no odor, workers would be exposed to this vapor cloud if they were not protected by a monitor. If the remote sensor is placed above the door, then workers can step away from the sterilizer after opening the door and return once the monitor says it is safe to do so. It is important that the remote sensor be placed above the door and not be pushed back since the plume of gas coming from the sterilizer is likely to completely pass by a sensor that has been pushed away, but the person leaning in to unload the sterilizer may not be so fortunate.

Another potential sources of leakage is at the rear of the sterilizer, from leaks in the plumbing or exhaust. If the sterilizer exhaust goes to a separate abator (EtO only), then the abator should be monitored too. There have been several cases of ethylene oxide leakage from holes in the duct between the sterilizer and abator, or failure of fans to exhaust the gas.

Another common question is whether a monitor for heavier gases and vapors should be placed low because the gas sinks in air. Those who did Chemistry may remember the experiments with heavy gases and vapors like nitrogen dioxide and bromine that form brown clouds that sink to the floor. In some applications where the air is static (man-holes, grain silos and other confined space entry) stratification of gases by mass is an important issue. People who go down manholes sometimes put their monitors at ankle height while descending, so that they will hear an alarm before their head reaches that level. For most common applications with high air turnover, the air turbulence is so great that stratification is not significant. The monitors should therefore be placed at breathing height.

In conclusion, area gas monitors should be placed near the sources of gas so that they can inform people whether it is safe to be in the area and when it is safe to return to an area after a release of gas or vapor. The monitors should be placed at breathing height, ~ 5 feet, and where there are multiple sources close together, the monitors should be no more than 10 feet apart. Every facility is different and so your ChemDAQ rep. will work with you to design a system that meets your needs.

Wednesday, May 23, 2012

OSHA: It’s Not As Easy Making Standards As You Might Think!

Many people have commented about how slow OSHA is to issue new standards or to update the old ones. As has been discussed on this blog before, most of the current OSHA PELs were adopted under the 1970 Occupational Safety and Health Act (OSH Act) from the 1968 ACGIH TLV values. With a few exceptions, the majority of the PELs today are unchanged since they were first adopted even though a considerable amount of chemical safety data has been collected since then and the ACGIH TLVs have been regularly updated.

• Recently the Government Accountability Office (GAO) issued a report “Workplace Safety and Health – Multiple Challenges Lengthen OSHA’s Standard Setting, April 2012” asking why. The GOA found that it took OSHA from 15 months to 19 years, average 7 years to pass a standard over the period from 1981 to 2010. OSHA as with other government agencies has a fairly long procedure to issue standards requiring giving notice and opportunity for interested parties to comment before issuing a standard as required under the Administrative Procedure Act. However the GAO found that there were several reason why OSHA took so much longer than other agencies.

• Courts generally defer to the expertise of government agencies and will only overturn a regulation if it is found to be ‘arbitrary and capricious,’ an easy standard to defend against anyone trying to get a regulation overturned. OSHA in contrast is held to a much more difficult standard, the “substantial evidence in the record considered as a whole.” OSHA has had several major standards overturned in the courts (Benzene standard US Supreme Court, 1980) and the PEL update (11th Cir. 1992) and has since been rather reluctant to issue any new PELs absent overwhelming support.

• OSHA is required by the US Supreme Court and Executive Order to understand how any new standard would operate in any workplace that it applies to. OSHA’s mandate of every workplace in the US is very broad; and so OSHA, or more often OSHA’s contractors typically spend a lot time assessing both technological and economic feasibility before issuing new standards.

• OSHA has not worked as closely with NIOSH, and other agencies as it could have done. NIOSH’s role is to perform occupational safety research and for a while OSHA was duplicating this effort.

• Unlike some other agencies such as the EPA and section 112 of the Clean Air Act, OSHA is not required to periodically update its standards; and so they languish steadily graying. The report also said that OSHA officials consider that it reflects poorly on the agency when OSHA issuing citations to employers that are following current industry consensus standards, but are being cited because the OSHA standard is obsolete.

OSHA also has the authority under the OSH Act (sec. 6) to issue emergency standards for 6 months, but has declined to do so since 1983 because of the evidence needed to meet the statutory requirements.

The GAO recommends that OSHA work more closely with other government agencies, especially NIOSH, and OSHA is working more closely with them than before. Another suggestion is the change the evidential standard that OSHA must reach to issue a standard, but there is a concomitant concern to lower quality regulation. This blog supports the idea of changing the evidential standard or using consensus standards such as ACGIH, but also requiring periodic review of the standards as assurance of regulation quality. Such a change would require modification of the OSH Act and thus Congressional action.

Thursday, May 17, 2012

Federal Governments Looks to ACGIH for Occupational Exposure Levels

There is a little known group called the Federal Advisory Council on Occupational Safety and Health (FACOSH) whose function is to advise the Secretary of Labor on matters relating to the occupational safety and health of federal employees. FACOSH's objective is to minimize the number and severity of workplace injuries and illnesses in the Federal Government.

One of the topics discussed at the May 3rd meeting was the use of occupational exposure limits (OELs) by the federal government other than the OSHA permissible exposure limits (PELs). In particular, several federal government agencies also use the NIOSH recommended exposure limits (RELs) and ACGIH Threshold Limit values (TLVs). The Executive Summary of the FACOSH report explains their position.

Executive Summary Because the Occupational Safety and Health Administration’s (OSHA’s) Permissible Exposure Limits (PELs) have remained unchanged since their adoption on May 29, 1971, and do not account for 40 years of advances in technology or the latest peer-reviewed published toxicological information, the Federal Advisory Council on Occupational Safety and Health (FACOSH) asked its Emerging Issues Subcommittee to analyze Federal agencies’ use of PELs. The Subcommittee examined how Federal Executive Branch agencies use occupational exposure limits (OELs) published by other agencies, professional organizations, and other foreign or domestic entities.
The Subcommittee considered all aspects of controlling a potential hazardous chemical in the workplace including risk assessment approaches and the hierarchy of controls. The Subcommittee concluded that FACOSH should recommend that Executive Branch departments and agencies use the most protective and feasible OELs in Federal workplaces, notwithstanding the existence of a PEL for a given substance of concern; require contractors, subcontractors, recipients, and subrecipients to use the most protective and feasible OEL while working on behalf of the Federal government; and designate a person deemed to be competent by virtue of training and experience to make recommendations regarding acceptable chemical exposure risks, appropriate OELs, and employee exposure controls.

The committee recognizes that the OSHA PELs are dated and that many of the exposure limits are well above the values consistent with current understanding of occupational safety. It also concluded that because of the evidential and procedural requirements OSHA must meet, it is unlikely that OSHA will issue many new PELs. Therefore several federal agencies already use the more restrictive of the ACGIH and the OSHA PEL.

• The Department of State uses the more restrictive of the OSHA PELs or the ACGIH TLV, and if neither exists, then it uses the NIOSH PEL.
• The Department of Energy uses the more restrictive of the OSHA PELs or the ACGIH TLV, together with OELs from several other sources.
• The Department of Defense (Army) uses the more restrictive of the OSHA PELs or the ACGIH TLV and the Navy, Airforce and Marine Corps use a combination of OSHA, ACHIH and other standards.

The committee is recommending that this policy be adopted across the federal government. The full report is titled “Recommendations for Consideration by the U.S. Secretary of Labor on the Adoption and Use of Occupational Exposure Limits by Federal Agencies Prepared by the Federal Advisory Council on Occupational Safety and Health (FACOSH)]”, available from regulations.com.

It is a sad reflection of the state of the current OSHA PELs that even the federal government needs to look elsewhere for modern standards. Almost everyone recognizes that the current procedure is so slow that OSHA is effectively unable to function in developing new and revised standards. OSHA plans to update the PELs, but the problem is that OSHA’s hands are tied by the procedures and evidential standards it must meet. This blog supports reform of the Occupational Safety and Health Act of 1970, sec 6 that sets the procedures that OSHA must follow to issued new or updated standards.

Organizations outside the federal government should also follow the recommendations of this committee and use the more restrictive standards of the OSHA PELs, ACGIH TLV and other recognized standards to promote workplace safety.

Tuesday, May 15, 2012

Safe Use of Chemicals for Sterilization in Healthcare

ChemDAQ’s Richard Warburton has an article in the latest issue of The Association for Advances in Medical Instrumentation’s (AAMI) peer reviewed journal Biomedical Instrumentation and Technology. The Spring 2012 edition focuses on sterilization; and the article is titled “Safe Use of Chemicals for Sterilization in Healthcare” The article reviews the various types of low temperature chemical sterilization used today. Sterilization is achieved by exposing the items to be sterilized to high concentrations of reactive chemicals and sterilant chemicals, therefore these chemicals are by their nature hazardous, otherwise they would not function well in this role. Sterilant chemicals fall into two broad chemical groups, the alkylating agents (ethylene oxide, aldehydes) and the oxidizing agents (hydrogen peroxide, peracetic acid, ozone). The article discusses the hazards associated with their use, the evolving occupational exposure limits associated with them (especially PAA) and offers advice to employers how to assess and mitigate the risk of using these chemicals and meet the requirements of the workplace safety laws. Article Citation: P. Richard Warburton (2012) Safe Use of Chemicals for Sterilization in Healthcare. Biomedical Instrumentation & Technology: Reprocessing, Vol. sp12, No. 1, pp. 37-43. The journal requires AAMI membership or payment to gain access.

Flammable Cabinets for Ethylene Oxide Must be Vented.

Many hospitals use ethylene oxide (EtO) for low temperature sterilization despite the faster cycle times of competing technologies using hydrogen peroxide or ozone because of its great efficacy, broad application (lumens, cellulose products can all be sterilized) and much less damage to certain medical devices than the oxidative sterilants. EtO sterilization used to be supplied in tanks, blended with non-flammable balance gases, but the modern trend is to use single use cartridges with about 100 to 170 g of 100% EtO in them. These single use cartridges greatly improve safety compared to the older tanks because if there is a leak the amount of EtO involved is much smaller and cylinders no longer have to be changed. As with all the sterilant gases, EtO poses health risks for anyone exposed to it. It has the same OSHA permissible exposure limit (PEL) and hydrogen peroxide, (1 ppm calculated as an 8 hr time weighted average (EtO 29 CFR 1910.1047, H2O2 29 CFR 1910.1000 Tbl Z-1 because of EtO’s toxicity and carcinogenicity. In addition, EtO is a flammable low boiling point liquid (BP = 12 oC) and so should be stored in an NFPA approved flammable cabinet (NFPA 30). Most hospitals that we visit do store their single use cartridges in flammable cabinets, but a surprising number do not vent the cabinets. These single use cartridges often seep small amounts of EtO. If the cartridges were in the open, the EtO seepage though not good would be dispersed into the air and with the high air turn over in most sterile processing departments, not pose a great threat. However, if the cartridges are in an unvented flammable cabinet, the EtO that seeps from the cartridges can accumulate within the cabinet to be released only when the door is opened. We have seen a surprisingly large number of unvented flammable cabinets being used to store EtO single use cartridges. Facilities are using flammable cabinets because of the flammability of EtO, but are ignoring the toxicity of EtO. Hospitals that use EtO are required to have a dedicated exhaust and so in most cases the cost of connecting the EtO flammable cabinet to the exhaust is minimal. If the EtO flammable cabinet in not vented then the cost in terms of employees health in the long term may be much larger. It is not just ChemDAQ that is raising this concern, 3M, one of the major suppliers of these single use cartridges also recommends the use of vented flammable cabinets. Most flammable cabinets have vents built into the side of them by the manufacturer, and so exhaust ducts can easily be connected to the flammable cabinets using standard plumbing fixtures. It is important that the cabinets be actively vented, i.e. the gas inside the cabinet is sucked out. Simply opening the vents on the side of the cabinet and relying on air diffusion does not suffice since air diffusion is relatively slow especially if there are flame arrestor grids in the vent holes. In summary, EtO cartridges should be stored in a flammable cabinet, but since EtO has such a low PEL, the cabinet should be actively vented to prevent exposure of workers using the EtO cartridges to EtO.

Friday, April 27, 2012

Workers Memorial Day

Tomorrow, April 28th is Workers Memorial Day, a day when we remember those people who died from injuries in the workplace. Secretary of Labor Hilda L. Solis issued a statement saying "Tomorrow, April 28, is Workers' Memorial Day, an occasion for reflection and remembrance of the thousands of workers who needlessly have suffered fatal injuries on the job every year. We also think of those workers who have been seriously injured or sickened as a result of preventable workplace hazards. "We are never prepared to say goodbye to the people we love, but we are even less so when we send our loved ones off for a day's work. It is our duty to ensure that all workers come home safely at the end of each workday, and we stand behind our firm conviction that workplace injuries and fatalities are entirely preventable. "On this day, I urge all Americans to raise their voices in support of workers' right to a safe and healthful workplace. In the 41 years since the Occupational Safety and Health Act was enacted, we have made tremendous progress, but our steadfast mission to make every job in America a safe job must continue. One workplace death is too many. Making a living shouldn't include dying.". And as the Secretary has said previously "With every one of these fatalities, the lives of a worker's family members were shattered and forever changed. We can't forget that fact." These statistics report tragic accidents that occur suddenly and with immediate impact, however many workplace injuries, such as those that result from chemical exposure may not produce symptoms for many years and so are not counted in the work place safety statistics. We know that many chemicals used in the workplace are carcinogenic and for a select few, OSHA has promulgated 27 legally binding standards covering nearly 40 carcinogens. However, there are hundreds of known human carcinogens according to International Agency for Research on Cancer and the National Toxicology Program. These organizations also name a much larger number of compounds that are suspected carcinogens. The American Cancer Society has them in a convenient list. This list is conservative and only includes those compounds shown to cause cancer or with incriminating evidence against them. The actual number of cancer causing compounds is certainly much higher. Cancer is one of the major causes of death in the US. In 2010, according to the CDC it was the second leading cause of death behind heart disease with 567,628 out of 2,437,163 deaths. and in 2012 the American Cancer Society estimates there will be 1,638,910 new cases of cancer. In pre-industrial cultures, while cancers did occasionally occur, they were very rare, indicating that cancers are largely caused by environmental factors; see for example Cancer As an Environmental Disease, By P. Nicolopoulou-Stamati, 2004 There are many different types of cancer and for those interested, the probability of a man or woman dying from a particular type of cancer has been tabulated. While exposure to cancer causing agents occurs in many aspects of life from smoking to exposure to benzene in gasoline, workplace exposures are considered to be at higher levels than for public exposures. We know that we are all exposed to many cancer causing agents, especially in the workplace, that many people will develop cancer from reasons unknown and that a large proportion of them will die of it. However, it is very rare that somebody with a cancer diagnose can be associated with exposure to a particular chemical. We don’t know what proportion of the over half million people who will die from cancer this year will do so because of workplace exposure, but it is likely that this number of hidden workplace fatalities far exceeds the 4,690 fatal workplace accidents (2010) that we are remembering tomorrow.

Thursday, April 19, 2012

Global harmonization Standards and the EPA

Recently OSHA provided a final rule for how it was going to change its hazard Communication standard 29 CFR 1910.1200 to reflect the global harmonization on chemical hazards (see earlier discussions of this topic in this blog).

The EPA operates under the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) and has its own regulations for describing chemical hazards on a safety data sheet. As a first step towards harmonization, on April 20th the EPA will publish a notice of the differences between its requirements for safety data sheets and OSHA's in the Federal Register.

We all know that regulations change at a glacial pace, and while this notice is not actually harmonization, hopefully this is the first small step in the right direction.

The ChemDAQ blog will continue to follow this story.

Thursday, April 12, 2012

Environmentally Friendly… to Whom?

ChemDAQ’s own Richard Warburton* recently had a paper published in Infection Control Today, the January 13th, 2012 edition. In this article, Richard points out that many people consider chemicals that are safe for the environment are obviously safe for general use. While this may be true for many compounds such as sugar which is generally benign except to our waistlines, Richard argues that an environmentally toxic chemical is one that is persistent in the environment (think DDT or mercury).

In contrast a chemical which is highly reactive is hazardous because of this reactivity but it is environmentally benign because it reacts so quickly that it disappears quickly. He gives the example of pouring either a solution of a cadmium salt or 30% hydrogen peroxide on to the ground. The hydrogen peroxide will fizz and froth and be gone in a few hours, but the cadmium may still be at detectable levels twenty years later in nearby water wells.

The take-home message is not to say that persistent chemicals cannot be harmful; some definitely are, but rather to illustrate that because a chemical product is labeled ‘green’ or ‘environmentally safe’ it doesn’t mean it is necessarily safe for those exposed to it.

* P. Richard Warburton, PhD, JD, is Chief Technology Officer and General Counsel at ChemDAQ Inc.

Wednesday, April 11, 2012

ChemDAQ Provides a Free Gas Concentration Converter

Gas concentrations are usually expressed in terms of parts per million, or mg/m3. Being able to convert from one unit to another is important since some regulations, industrial hygienists etc. prefer one format over the other. However, converting from one to other is not as simple as converting temperature from degrees Fahrenheit to degrees centigrade because ppm and mg/m3 are not strictly the same thing, mg/m3 is an actual concentration whereas ppm is a relative concentration.

If all this unit conversion sounds difficult, it need not be. ChemDAQ has produced a free unit conversion spreadsheet tool, available for download from the ChemDAQ website (at the bottom of the page). This tool allows simple conversion from ppm to mg/m3 and back again and even provides the molecular weights for many common gases and vapors found in healthcare. If we have missed any compounds that would be useful, please let us know and we will add them to the list.

A more detailed explanation of the difference between ppm and mg/m3 is provided below for those who are interested.

More Detailed Explanation
A concentration is defined as the amount of something per unit volume, so if the amount of a gas is expressed by its weight in mg, then the amount of gas per cubic meter (mg/m3) is the concentration. For a given gas concentration, the mass of gas per unit volume will be proportional to the molecular weight. Thus 1 liter of air has a mass (weighs) about 1.1 g, but 1 liter of 100% chlorine would weigh about 2.8g. The concentration unit of mg/m3 is the mass of the gas per cubic meter.

A part per million, as the name implies, is a relative concentration. If ethylene oxide - air mixture contains 1 ppm ethylene oxide, then for every million air molecules there is one ethylene oxide molecule. Parts per million are particularly useful when dealing with compressed gases, which may be why we use it in gas detection so much. A 2000 psi compressed gas cylinder of 10 ppm ethylene oxide has a much higher internal concentration in terms of mg/m3 than the test gas coming out of the regulator at 1 psi, but the relative concentration of EtO to air, i.e. 10 ppm is the same.

Therefore the relative amount of gas (in ppm) must be multiplied by the molecular weight, as well as changing the units to calculate the weight. In addition to adjusting the units, to convert from ppm to mg/m3, it is necessary to specify a temperature (usually 25 oC) and a pressure (usually 1 atm.).

If the conversion of gas concentrations from ppm to mg/m3 or vice versa sounds involved, use the ChemDAQ gas concentration conversion tool, . The tool is written as an Excel spreadsheet. Enter the concentration (as ppm or mg/m3) in the appropriate box, enter the molecular weight from the handy table shown on the right hand side and the result will be calculated. The converter uses 1 atmosphere pressure and 25oC as a default, but other values can be entered if needed.

Please let us know if you have any comments about the converter, good or bad. If there are any other gases or vapors you would like to see added to the table or other functionality added to the converter, please leave a comment to let us know.

Tuesday, April 10, 2012

Industry News: CSA Publishes New Standard on Chemical Sterilization

The Canadian Standards Association (CSA) has just published its new standard “Chemical Sterilization of Reusable Medical Devices in health Care Facilities” Z314.23-12, available from either CSA or the American National Standards Institute.

CSA Describe the new Standard as follows

This is the first edition of CSA Z314.23, Effective chemical sterilization in health care facilities. It is one of a series of CSA Standards dealing with the safe and effective sterilization of medical supplies and equipment. It supersedes CAN/CSA-Z314.2, Effective sterilization in health care facilities by the ethylene oxide process, published in 2009, 2001, 1991, 1984, and 1977.

This Standard specifies essential elements in implementing a program for using chemicals to sterilize medical devices in health care facilities. Such chemicals can be vapour, gaseous, or liquid and are delivered in validated concentrations and quantities in defined sterilizers.
The body of this Standard contains requirements that are common to all chemical sterilization processes, whereas requirements specific to a particular chemical sterilization technology are contained in Annexes A to E.
The following chemical sterilants are currently approved for use in sterilizers in Canada and are addressed in this Standard:
(a) gaseous and vapour chemicals:
(i) ethylene oxide;
(ii) hydrogen peroxide;
(iii) ozone; and
(iv) hydrogen peroxide-ozone; and
(b) liquid chemicals: peracetic acid.
Exposure to chemical sterilants can present risks to health care personnel and patients; this Standard includes measures to minimize the risk of such exposure as well as discharge to the environment of sterilizing chemicals and by-products.

Further details are available at CSA's website.