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For routine monitoring, these methods have largely been replaced by continuous monitors.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.

Questions

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.

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.