IV. Hydrogen Sulfide Exposure Limits: A Recommendation for Permitting and Regulations of Wells, Facilities, and Pipeline
July 22, 1997 | By Arlin Wasserman
and Dana Schindler
Great Lakes Bulletin News Service
Protection of health, safety and welfare is the Constitutional right of all citizens of our nation. The right to be safe and secure in the use and enjoyment of property extends to the protection of property values. In this regard, Michigan does not have a public exposure standard for one of the most dangerous chemical emissions prevalent in the state: hydrogen sulfide. (continued on next page)
Michigan's only current H2S standard is that established by OSHA. This standard of 10 ppm for a normal 8 hour work day applies to 160 pound healthy males. The state's 1977 Interagency Sour Gas Coordinating Committee in its Revised Guidelines for Sour Oil and Gas Wells and Associated Facilities notes that work place limits should never be extrapolated to the general public. Unfortunately, this is exactly the guideline being employed for public exposure.
The seriousness of recent evacuations and hospitalizations of the past 10 years in Michigan, at recorded levels of 8 to 10 ppm, have drawn attention to the seriousness of the problem. (Schindler, Preliminary Accident Survey) As serious as those actual events have been, they are over-shadowed by the potential danger for much greater credible accidents which can occur in wells, pipelines, and at processing plants. We wholeheartedly applaud the forthright scrutiny being taken by the DEQ and the MPSC in confronting this public health and safety issue.
The public exposure limit must be based on the Department of Community Health general recommendation for hazardous emissions, which takes 1/100 of the occupational limit as acceptable for a public exposure limit. This would be 0.1 ppm for hydrogen sulfide and takes into account the very young, individuals of average and poor health, the elderly, and the infirm. This general public "person exposure limit" would be a fixed concentration limit. Safety of the public will then be based on a "person exposure risk" which protects citizens, rather than the current use of blanket setbacks from buildings.
No surety or assurance of public protection exists with fixed building setbacks due to the potential for very dangerous variations in the dispersion of any release of gases containing dangerous levels of H2S. Until adequate regulations are in place, based on applicable modeling and expert research, the 0.1 ppm limit is an acceptable interim plan which protects the health, safety, welfare and property values of all citizens. The current policy of after-the-fact rulings, issued on an accident by accident basis will continue to place citizens in guinea pig jeopardy situations. The standards currently being applied are admittedly and recognizably ineffective in protecting the public from hazardous exposures.
The 0.1 ppm level of acceptable public exposure would, in fact, bring Michigan's H2S standard in line with, but still more lenient than other oil and gas producing states, such as Alberta at 0.01 ppm, California at 0.03 ppm, and Texas at 0.08 ppm one-hour averages.
The policy to accomplish this function requires that all wells, supporting facilities and pipelines be located so that the best of EPA-accepted gas dispersion models will yield no concentrations of H2S above the person exposure limit, 0.1 ppm, for any populated location -- homes, public buildings, businesses, parks, prisons, schools, churches, etc. -- under a maximum credible accident scenario.
Any such level selected cannot be taken to guarantee safety. Nor can it be argued that it is unnecessarily restrictive. It is a compromise that has a credible basis, drawing upon the best judgment of professionals in public health and in atmospheric dispersion modeling.
When sufficient data become available to make more accurate professional judgments, the maximum exposure level may be found to be greater or smaller. Or the use of a fixed level may itself be found to be inappropriate for some fraction of realistic accident scenarios.
Only when professionals in public health and in atmospheric dispersion modeling can provide assurance that the public safety will not be compromised by a change, should the 0.1 ppm acceptable maximum exposure limit for public health and safety and/or the modeling procedure be adjusted.
Determining Maximum Public Exposure Levels
Selection of the exposure limit is only part of the regulatory problem. It is essential to determine the maximum concentrations of H2S to which the public could be exposed in credible accident situations.
In May, 1994, for instance, a valve failure caused the release of H2S from the Victory 32 compressor station in Mason County. Hydrogen sulfide, trapped in atmospheric mists, was carried by the wind, settled into the low lying river valley, and followed it for six miles from the release site to cause emergency hospitalizations of those crossing the Jebavy Road bridge. (Schindler, Preliminary Accident Survey)
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