The main question the public asks about planning for chemical emergencies is whether they, their home, and their loved ones, are at risk from a large chemical spill. Firefighters need to know this information so that they can make decisions about shelter-in-place or evacuation measures, and so they can determine what equipment and methods would be needed to handle the chemical spill. Firefighters might need special training to prepare to handle a chemical incident. Emergency planners need to "model" where a cloud or plume of chemical vapors will travel so they can help to appropriately "plan" the proper response and responder training, and to find ways to help prevent such an occurrence or minimize the impacts of a chemical spill. The term "plume" comes from the tendency of a vapor trail to look like a bird's tail feather starting out narrow and widening out along its length.

Emergency planning efforts include preparing for spills of the chemicals transported through the community. The area that could be affected is on either side of the road, to the maximum distance the vapors from a tanker load of spilled chemicals could travel. The plume of chemical vapors emanating from a large tanker of chlorine that has burst, for example, could travel many miles from the road. A prepared community has to conduct emergency planning for transportation accidents involving chemical spills, even though three out of four chemical spill incidents occur at facilities, and only one out of four involves a transportation accident.

Airborne chemical vapors pose their own extra risk to human health. The body is prepared to protect itself against poisons taken by mouth. The liver begins to produce enzymes that try to break down fat-soluble chemicals that were swallowed. However, if the poison enters through the lungs or the skin, the body does not offer the same kind of defenses. Furthermore, the body's ability to put up defenses may be compromised by taking certain medications, or by receiving "pulses" of toxins rather than a steady dose. A chemical spill incident provides the chance of a "pulse" of toxins.

90% of HazMat (hazardous materials) injuries are due to inhalation.