Over the last several years, organizations such as the American Conference of Governmental Industrial Hygienists (ACGIH) have lowered their Recommended Exposure Limits (RELs) on a number of common hazardous gases. For example, the ACGIH dramatically lowered the Threshold Limit Values (TLVs) for both hydrogen sulfide and sulfur dioxide. In similar fashion, the ACGIH has named in its 2017 Notice of Intended Changes list other common gases such as chlorine, chlorine dioxide and phosphine among its targets for adjustments to the exposure limits.
Let’s get this straight. This is not an editorial rant against the practices of the ACGIH. The plain and simple truth is that the ACGIH makes recommendations based on a thorough review of scientific evidence regarding what exposure levels constitute a threat to worker health and safety. Whether or not it is practical for systems to detect various compounds at the exposure limits does not fall within the scope of the ACGIH. This is a discussion on how equipment manufacturers and the industrial hygiene and safety community are addressing the need to detect and monitor toxic gases at ever-decreasing levels. It is the reaction of these stakeholders that I find the most puzzling and frustrating.
What do lower TLVs mean for manufacturers?
Manufacturers of portable gas monitors, the type of equipment used to detect toxic gases in industrial hygiene and safety applications are held hostage by technology. Although they would certainly argue this, over the last 30 years, the technology offered by gas sensor manufacturers has not changed much. The same basic electrochemical sensors used to detect toxic gases 30 years ago are still used today. Sure, the sensors have gotten much smaller, allowing manufacturers to build smaller instruments, but the chemistry is the same old, same old. One would think that over three decades sensor researchers and developers would be able to make improvements in technology that would result in products that provide detection of gases at much lower concentrations, with much greater stability and accuracy. But this is not the case. Why is there so much comfort in the status quo when the people who need the protection of these products require so much more? (By the way, I am one of the said instrument manufacturers; guilty as charged.)
What do lower TLVs mean for industrial companies?
Regardless of the fact that the ACGIH TLV recommendations do not represent regulatory standards, many companies are compelled to adopt these values into their safety and industrial hygiene programs. Industrial hygiene and safety professionals who are responsible for the health and welfare of employees know that controlling exposures or monitoring substances at these levels may not be practical. There is a realistic fear that a worker who becomes injured or ill, and believes that it is the result of an exposure to a hazardous substance, will retain a very litigious attorney who can present undeniable evidence that the ACGIH recognizes and publishes guidelines saying that exposures above the recommended levels represent serious health hazards. Although TLVs point to Time Weighted Average (TWA) or Short Term Exposure Limit (STEL) average exposure readings, IH and safety decision makers often lean toward setting action points based on instantaneous exposures and sensor readings exceeding the limit values.
In many cases, setting action points and alarm set points on gas detectors based on instantaneous readings at low levels causes unwanted, nuisance alarms. Sometimes these alarms are a true warning of a gas exposure. When the TLVs for hydrogen sulfide were reduced from 10 parts per million to 1 part per million and recommendations on SO2 were reduced from 5 PPM to 0.25 PPM, that is exactly what they were designed to do—uncover exposures of concern that were occurring at lower concentrations. Many times however, the alarms are the temporary reaction of the sensor to outside factors such as steep changes in temperature and relative humidity or the presence of some trace level cross interfering gas that is of no consequence.
How do lower TLVs affect how gas detectors are actually being used?
To a certain extent, the instrument manufacturers have stepped up. There is more emphasis put on providing true TWA and STEL reading and alarm features in the instruments that allow actions to be taken based on the average, continuous and cumulative exposure limits represented by the TLVs. The fear of the equipment providers is that workers who encounter numerous alarms at the lowered instantaneous levels will lose faith in their monitors and will begin to ignore all alarms or stop using the equipment based on the perceived “quality” or “reliability” of the device. The employers of those workers share that same fear. But what do they do about it?
Too often, there is a rationalization of whether or not a particular gas needs to be monitored in the first place. Yes, hydrogen sulfide or carbon monoxide are a concern, but is there really a need to monitor or be concerned with exposures to SO2, or chlorine, or whatever the particular gas may be? If the sensors are a nuisance to the workers, limit productivity, and cast a cloud of doubt on the equipment, why not just remove them from the instruments and make the problem go away?
Now it is time to take a realistic look at this situation. Decisions have been made to lower alarm set points to comply with exposure recommendations partially in fear that someone will bring legal action based on exposures above the TLVs. There is obviously concern that the gas in question may present a problem and enough work has been done to learn that limits at such low levels tend to cause too many unwanted alarms. So get rid of the sensors? So forget the TLVs? What happens when a truly dangerous concentration of the gas does exist, one time in a thousand, and no sensor is there to detect it? Where is the fear of consequences from that event? Where is the fear of litigation—knowing full well that such an exposure or event may occur? Puzzling, isn’t it?
What’s the solution?
As stated above, many gas monitoring instruments today do put more emphasis on the TWA and STEL exposure levels and provide those readings and alarms to accompany the response to instantaneous levels of gas detected. In the case of H2S, an instantaneous alarm set point at 2 PPM may eliminate 85 percent of the “nuisance” alarms occurring at 1 PPM and still provide five times more protection than when the alarms were set at the old TLVs of 10 PPM. At the same time, a TWA alarm can be set at 1 PPM or below and still provide the full protection as defined by the exposure recommendation. Why not just change the set points, keep the sensors, and allow them to do their job?
There is a desire to strive for perfection where perfection doesn’t exist. There is no doubt that the industry needs to advance the technology to get closer to that perfect level. At the same time, there is a need to use the technology available today to its fullest capability to provide the highest level of protection.
As a manufacturer of gas monitoring instruments with a vision to eliminate death and injury in the workplace due to accidental gas exposure, we are compelled to review the established guidelines and work to develop and provide the technologies and equipment that enable our customers to comply with them. When we can do that, we have taken a giant step forward in fulfilling our mission.