The application of toxicological parameters in emergency response and planning.

Effective emergency preparedness and response planning are needed to assist responders in making sound decisions under the stressful and confusing conditions accompanying a major accidental release of hazardous materials. One of the most important decisions to be made is the extent and duration of the evacuation of persons located nearby the accident site. If a decision must be made as to whether or not to evacuate nearby populations, an estimation of the areal extent (sometimes referred to as a 'toxic hazard corridor' or 'vulnerable zone') of the evacuation must be determined. This corridor, or zone, is based on estimates of the amount of material released, rate of release, vapor dispersion characteristics, and concentration limit or 'level of concern' that could cause some damage, irreversible health effects, or death. There is a strong dependency between the concentration limit chosen and the resulting evacuation area dimensions. It is therefore important for planners and emergency responders to have accurate estimates of concentration limits as well as guidance in the proper use and interpretation of these limits. This paper illustrates several cases where the selection of the concentration limit has played an important role.