Demystifying Hazmat Chemistry

STUDENT HANDOUT
DEMYSTIFYING HAZMAT CHEMISTRY
Comparing Three Primary Threats
We generally evaluate hazmat incidents in
terms of three threats: oxygen deficiency, toxicity,
and flammability. These three threats
impact some of the decisions we have to make,
for example, what personal protective equipment
to wear or what community protective
actions to implement.
Toxicity
Oxygen Deficiency
Flammability
Oxygen Deficiency
The normal atmosphere is comprised of roughly 78% nitrogen, 20.9% oxygen, and 1.1% argon
and other gases. Although 20.9% oxygen is considered normal, we don’t hit the “threat zones”
until we drop below 19.5% or rise above 23.5%.
The Limits of an Acceptable Oxygen Concentration
If the oxygen level is above 23.5%, the atmosphere is considered to be potentially explosive. An
oxygen-enriched atmosphere will cause any flammable or combustible material to ignite more
readily and burn more fiercely.
For the purposes of this discussion, however, we want to focus on oxygen-deficient atmospheres.
An oxygen concentration of 19.5% is considered by OSHA and NIOSH to be the minimum safe
level. Below that, responders must wear self-contained breathing apparatus (SCBA) or supplied
air respirators (SAR). Air-purifying respirators (APR) are not acceptable under these conditions,
even if they are capable of filtering contaminants present in the atmosphere, because they do not
provide responders with a source of oxygen.
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