Parameters:
(1) initial isolation distance for the hazardous material in meters
(2) protection action zone (PAZ) distance for the hazardous material in meters
(3) wind direction
(4) occurrence during day or night
(5) size of the spill
(6) fire and/or explosive potential
Steps:
(1) Try to identify the hazardous material that has spilled.
(2) Anyone who is unprotected should immediately move away from the spill, moving upwind (against the wind).
(3) Designate the initial isolation zone by drawing a circle around the spill with a radius equal to the initial isolation distance specified for the hazardous material.
(4) Designate the protective action zone (PAZ) downwind from the the spill site that is a large rectangle with:
(4a) one side running through the spill at right angles to the wind, with the spill site bisecting it
(4b) the other side having a length equal to the protective action zone distance parallel to the wind direction
(5) Evacuate anyone downwind who is in the protective action zone.
where:
• The direction of the wind may shift about during the incident but the protective action zone should be large enough for most situations.
• The size of the protective action zone tends to be greater at night. A person who is asleep may be overcome without being able to escape.
• The size of the protective action zone may need to be increased under high wind conditions.
• A person who has been exposed to the hazardous material may need to undergo decontamination.
If the initial isolation distance is not known, then isolate based on the size of the spill.
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Size of Spill
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Default Initial Isolation Distance (Radius)
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small (< 200 liters)
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500 to 1,000 feet (150 to 300 meters)
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large (> 200 liters)
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1,000 to 1,500 feet (300 to 450 meters)
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tanker or rail car
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2,500 feet or more (760 meters)
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