From the health perspective, there are a number of ways of classifying chemical emergencies, and none of them is comprehensive or excludes all others. Classification could be based on:
- the chemical(s) involved, the amount released, their physical form, and where and how the release occurred;
- the sources of the release;
- the extent of the contaminated area;
- the number of people exposed or at risk;
- the routes of exposure;
- the health or medical consequences of exposure.
The key channels for human exposure in the case of chemical accident are air or water dispersion of hazardous materials (such as flammable, explosive, corrosive, oxidising, asphyxiating, bio-hazardous, toxic, pathogenic or allergenic).