There are essentially two ways to protect the public from the effects of hazardous material discharges into the environment.
A. Evacuation: involves moving threatened persons to shelter in another area.Evacuation is clearly safer with respect to the hazards, but has certain limitations and may pose new problems. Evacuation takes time and may not be possible if large numbers of persons or a large volume of vapor is present. Evacuation through a toxic atmosphere may actually cause more harm than good in some cases.
B. Sheltering in place: involves giving instructions to people to remain where they are until the danger passes.
* Evacuation is best considered when:
A. There is an immediate danger of fire or explosion.* Large scale evacuation will be directed by the Police Dept. Incident Command and will require the coordinated efforts of several agencies.
B. The potential for discharge is great, it has not taken place, and there is time available to relocate the people.
C. The discharge has taken place but people are sufficiently protected to permit time for evacuation.
D. People not yet in the path of a release will be threatened by changing conditions.
* The decision to shelter in place is appropriate when the hazardous material will not affect the structure or its occupants or the hazard will pass a structure with little infiltration.
* Sheltering in place is the alternative when:
A. Pre-planning has identified options for problem areas such as hospitals, jails, nursing homes, public assemblies, etc.* The success of either option will depend on the preplans and effectiveness of communication resources, notification and public information.
B. Evacuation cannot be properly managed with the manpower, resources, and facilities presently available.
C. The hazardous material displays the following characteristics:1. Low to moderate toxicity;
2. Totally released and dissipating;
3. Small quantity solid or liquid leak;
4. A migrating vapor of low toxicity and quantity and people are safer indoors than outside; and
5. Release can be rapidly controlled at the source.