Demystifying Hazmat Chemistry

STUDENT HANDOUT
DEMYSTIFYING HAZMAT CHEMISTRY
Comparing the Three Threats
Oxygen deficiency, toxicity, and flammability can be plotted on parallel ladders. We already know
that cutoff for oxygen deficiency is 19.5%. Anything below 19.5% is considered to be within the
threat zone. Therefore, we can easily plot that on a hazard ladder.
We generally use IDLH when looking at the toxicity threat. Therefore, you can write in the IDLH
value at the left side of that ladder, then plot the concentration by percentage or parts per million.
A concentration of 1% is equal to 10,000 ppm, so regardless of which measurement you
use, you can plot it accurately. Anything to the right of where you draw your line is considered
to be within the threat zone.
You can do the same with flammability. Although you will plot only LEL, you should identify the flash
point and ignition temperature too because these temperatures will help you assess the risk.
Parallel Hazard Ladders
20.9%
19.5%
Oxygen
Deficiency
19.5% or below
20.7%
20.5% 20.3% 20.1% 19.9% 19.7% 19.3% 19.1%
0%
Toxicity
IDLH _______________
Flammability
LEL _________________
Flash Point _________
Ignition Temp _______
0%
1%
10,000
ppm
1%
10,000
ppm
2% 3% 4% 5% 6% 7% 8% 9%
20,000
ppm
30,000
ppm
40,000
ppm
50,000
ppm
60,000
ppm
70,000
ppm
80,000
ppm
90,000
ppm
2% 3% 4% 5% 6% 7% 8% 9%
20,000
ppm
30,000
ppm
40,000
ppm
50,000
ppm
60,000
ppm
70,000
ppm
80,000
ppm
90,000
ppm
If you have a reading of 19.5% oxygen—the minimum safe level per OSHA and NIOSH—you can
have slightly less than 6.7% (or 67,000 ppm) of a contaminant gas or vapor present in the atmosphere.
(Remember: Oxygen comprises 20.9% of the normal atmosphere. If you divide the
oxygen displacement—in this case, 1.4%—by .209, the result is 6.699.) If you look at the three
ladders on this page, you will see that they line up pretty closely.
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