Page 39 - Occupational Health & Safety, October 2017

When the TLV for hydrogen sul- fide was 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—un- cover exposures of concern that were occurring at lower concentrations.
sent serious health hazards. Although TLV recommendations 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 in- stantaneous exposures and sensor readings exceeding the limit values.
Nuisance Alarms or True Warnings?
In many cases, setting action points and alarm set points on gas detectors based on instantaneous readings at low levels causes unwanted, nuisance alarms. Some- times these alarms are a true warning of a gas exposure. When the TLV for hydrogen sulfide was reduced from 10 parts per mil- lion to 1 part per million and recommen- dations on SO2 were reduced from 5 ppm to 0.25 ppm, that is exactly what they were designed to do—uncover exposures of con- cern that were occurring at lower concen- trations. 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 interfer- ing gas that is of no consequence.
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 cu- mulative 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 be- gin 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 is a concern, but is there really a need to monitor or be concerned with exposures to SO2, or chlo- rine, 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?
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?
Let the Sensors Do Their Job
Now it is time to take a realistic look at this situation. Decisions have been made to lower alarm set points to comply with ex- posure recommendations, partially in fear that someone will bring legal action based on exposures above the TLV. There is obvi- ously 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 for- get the TLV? What happens when a truly dangerous concentration of the gas does exist, one time in a thousand, and no sen- sor 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?
There is a 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
TLV 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 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.
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 monitor- ing 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 technolo- gies and equipment that enable our cus- tomers to comply with them. When we can do that, we have taken a giant step forward in fulfilling our mission.
Dave Wagner serves as Director, Applica- tions Engineering & Product Knowledge, at Industrial Scientific.
www.ohsonline.com
OCTOBER 2017 | Occupational Health & Safety 35