|
|
IV. Hydrogen Sulfide Exposure Limits:
ARecommendation for Permitting and
Regulation of Wells, Facilities, and Pipelines
by Dana Schindler,
Human Health and Safety Committee
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.
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 whole-
heartedly applaud the forthright scrutiny being taken by the DEQ and the MPSC in confronting this public
health and safety issue.
Recommendation:
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.
Recommendation:
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 anypopulated 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.
Recommendation:
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)
(continued on next page)
|
|
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 