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?

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.

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.