Protective Action Decision Factors to Consider

The choice of protective actions for a given situation depends on a number of factors. For some cases, evacuation may be the best option; in others, sheltering in-place may be the best course. Sometimes, these two actions may be used in combination. In any emergency, officials need to quickly give the public instructions. The public will need continuing information and instructions while being evacuated or sheltered in-place.

Proper evaluation of the factors listed below will determine the effectiveness of evacuation or in-place protection. The importance of these factors can vary with emergency conditions. In specific emergencies, other factors may need to be identified and considered as well. This list indicates what kind of information may be needed to make the initial decision.

The Dangerous Goods

• Degree of health hazard
• Chemical and physical properties
• Amount involved
• Containment/control of release
• Rate of vapor movement

The Population Threatened

• Location
• Number of people
• Time available to evacuate or shelter in-place
• Ability to control evacuation or shelter in-place
• Building types and availability
• Special institutions or populations, e.g., nursing homes, hospitals, prisons

Weather Conditions

• Effect on vapor and cloud movement
• Potential for change
• Effect on evacuation or protection in-place

NOTE: Every hazardous materials/dangerous goods incident is different. Each will have special problems and concerns. Actions to protect the public must be carefully selected. This section can help with initial decisions on how to protect the public. Officials must continue to gather information and monitor the situation until the threat is removed.

The following table can help to decide if evacuation or sheltering-in-place is the best option:

Consider Evacuation:	Consider Sheltering-in-place:
Vapors are flammable.	Vapors are toxic, and people are likely to be exposed by evacuating.
Buildings cannot be closed tightly.	Buildings can be quickly sealed by closing all windows and ventilation systems, if applicable.
The vapors are continuously generated and will hug the ground, or it will take a long time for the vapors to clear the area.	The vapors will quickly rise in the air column or rapidly dissipate.
For anyone outdoors.	For anyone already indoors.
There are few people to evacuate.	There are too many people to evacuate for current available resources.
The threat seems stable but long-lasting.	Circumstances are changing too quickly to evacuate safely.