Demystifying Hazmat Chemistry

STUDENT HANDOUT
DEMYSTIFYING HAZMAT CHEMISTRY
A simple hazard ladder such as the one below provides a visual representation of where you are
relative to the threat zone for oxygen deficiency (depicted by the shaded section).
An Oxygen Deficiency Hazard Ladder
20.9% (Normal)
19.5%
Oxygen
Deficiency
19.5% or below
20.7%
20.5% 20.3% 20.1% 19.9% 19.7% 19.3% 19.1%
Keep in mind that a concentration of 19.5% oxygen is not an immediate threat to life. It provides
a considerable safety margin. The following chart shows the effects of oxygen deficiency on one’s
mental and physical abilities.
The Effects of Oxygen Deficiency
However, any displacement in the oxygen concentration is a warning signal that there may be
a contaminant present in the atmosphere, assuming your meter is working properly. Further
monitoring is required.
Since oxygen comprises roughly one-fifth (1/5) of the normal atmosphere, a 1% oxygen displacement
means there is roughly a 5% concentration (50,000 ppm) of a contaminant gas or vapor. In other
words, although your meter is showing a 1% displacement, that contaminant gas or vapor is really
displacing one part oxygen and four parts everything else. (The illustration on the right shows the
relation between percent by volume, parts per million [ppm], and parts per billion [ppb].)
Atmospheric Displacement
(One Part Oxygen and Four Parts Everything Else)
The Relation Between
Percent by Volume
and Parts per Million/Billion
Oxygen (20.9%)
Nitrogen
and Other Gases
(79.1%)
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