Demystifying Hazmat Chemistry

STUDENT HANDOUT
DEMYSTIFYING HAZMAT CHEMISTRY
By plotting all three threats on parallel ladders, you can easily identify which one you will encounter
first. For example, if you had a product with an IDLH of 2% (or 20,000 ppm) and an LEL of 8.5%
(or 85,000), it becomes clear that you will encounter a toxic atmosphere before you encounter an
oxygen-deficient atmosphere or a flammable atmosphere. (Of course, you could tell this just by
looking at the numbers. The illustration simply makes it easier to visualize.) However, let’s take
a look at another example, one where the numbers are closer and where numbers alone can be
misleading. The following illustration shows gasoline plotted on three parallel hazard ladders.
As you can plainly see, the IDLH of gasoline (estimated to be 9000 ppm) is lower than the LEL
(1.4% or 14,000 ppm).
Gasoline Plotted on Three Parallel Ladders
Oxygen
Deficiency
19.5% or below
20.9%
0%
20.7%
Gasoline
19.5%
20.5% 20.3% 20.1% 19.9% 19.7% 19.3% 19.1%
Toxicity
IDLH _______________
9000 ppm (est)
Flammability
LEL 1.4% _________________
(14,000 ppm)
Flash Point _________ -45 o F
Ignition Temp _______ 853 o F
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
Numbers do not always tell the whole story, however.
Going strictly by the numbers, one might think that you
will encounter a toxic atmosphere before you encounter
a flammable atmosphere. But you need to look at the
big picture to accurately assess this threat. You need to
look at the numbers in relation to your incident objectives
and operations. And you may find you need to look at
different exposure values based on those operations and
how much time they take.
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