For years hazardous materials responders have accessed exposure guidelines designed for industrial settings as their benchmarks for when to evacuate exposed people or for setting up hazard zones. Threshold Limit Values (TLV's), Permissible Exposure Limits (PEL's), and Immediately Dangerous to Life and Health (IDLH) values were adapted for first response work and based on air monitoring results were used for decision making. Also, the Department of Transportation (DOT) utilized evacuation distances in its Emergency Response Guidebook (ERG) that were based on acute exposures to the public. The problem with these industrial exposure levels is that they are inappropriate for emergency response. Not only are their values often too high they simply were not designed for the type of exposure that could be encountered at a hazmat release. The American Conference of Governmental Industrial Hygienists (ACGIH) even state in their TLV exposure publications that these values should not be used for any exposures other than at industrial settings. Additionally, IDLH is the level of exposure at which the elderly, respiratory impaired, and children would most likely experience severe health problems yet people in good health may not.
Over time it became obvious that an exposure level below the IDLH was needed that would provide better guidance to protect people before dangerous levels were reached. One such response from the Environmental Protection Agency (EPA), the Federal Emergency Response Administration (FEMA), and the DOT was to use 1/10 IDLH's as the new level of concern (LOC) in which to base evacuation decisions. Although the 1/10 IDLH LOC provided a safety factor by a magnitude of 10 in order to better protect hypersensitive individuals its exposure duration was designed for a mere 30 minutes. These levels also proved to be inappropriate for emergency response and consequently better guidelines have been, or are in the process of being, developed.
Emergency Response Exposure Guidelines
There are numerous exposure level guidelines to examine and possibly utilize in decision making at hazardous materials emergencies. They can be reviewed in more detail at http://response.restoration.noaa.gov/cameo/locs/expguide.html. Perhaps the two guidelines that governmental planners and emergency responders can best utilize for decision making are the Emergency Response Planning Guidelines (ERPG's) and the Acute Exposure Guideline Levels (AEGL's).
These guidelines have been developed by the ERPG committee of the American Industrial Hygiene Association International. There are currently guidelines developed for approximately 90 chemicals and more information on this document can be accessed at www.aiha.org.
ERPG's were developed to be used for planning purposes based on anticipated one-hour exposure health effects to humans. They are set-up in a three-tiered system based on severity of effects with Level 1 being the least severe and Level III being the most severe. While the guidelines are based mostly on animal studies and one-hour exposures the committee strongly advises against extrapolating ERPG values to longer duration exposures. ERPG's also do not have safety factors incorporated into them and they only estimate the effects that exposed people may develop. Consequently, ERPG's should only serve as planning tools. In the absence of better guidelines some governmental agencies, such as the Department of Energy, utilize ERPG's for planning purposes.
These guidelines, referred to as "eagles", are being developed by the National Research Council's Committee on Toxicology. As of June 2001 AEGL's have been developed for four chemicals (aniline, arsine, monomethylhydrazine, and dimethylhydrazine) with the objective to develop guidelines for 371 total chemicals. At least 30 chemicals per year should have AEGL's developed with 137 chemicals having a higher priority. The initial listing of 85 priority chemicals was first published in the Federal Register on May 21, 1997. Further information on these lists and AEGL development can be found at www.epa.gov and www.epa.gov/fedrgstr/. To examine the currently available AEGL's go to http://stills.nap.edu/books/0309072948/html/.
AEGL's are also defined using a three-tier system however; each level is developed with five exposure time periods; 10 minutes, 30 minutes, 1 hour, 4 hours, and 8 hours.
AEGL Level I
AEGL Level II is for airborne concentrations above which the general population could experience irreversible or other serious effects.
AEGL Level III is for airborne concentrations above which the general population could experience life-threatening health consequences or death.
(These definitions are paraphrased. For exact definition go to website above.)
TLV-TWA 2 ppm (average over 40 hours)
1/10 IDLH 10 ppm
IDLH 100 ppm
In contrast with the above industrial exposure levels the developed AEGL's may be the best exposure guidelines to use for determining the level of concern in concert with personal experience, judgment, training, and the results of air monitoring.
There is no one best guideline to determine hazmat exposure safety. ERPG's were developed for planning purposes and to date only provide guidance for approximately 90 chemicals. AEGL's show much promise to be used as tools by emergency responders to determine evacuations and/or hazard zones but to date have only developed guidelines for four chemicals. When all 371 of the identified chemicals from the extremely hazardous substances (EHS) list have developed AEGL's then responders will have a very comprehensive tool to aid in their decision making. When that day arrives AEGL's should prove to be much more appropriate for emergency response decision making than industrial exposure levels.