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2150EX Area Velocity Flow Module
Appendix D General Safety Procedures
Whitney, oxygen is equal to 12.2%t. Many hikers go there,
and to higher peaks as well. After adequate acclimation,
they may climb to the top of Mt. Everest, where oxygen is
equal to only 6.7%.
"The lowest oxygen concentrations that I have observed in
a sewer atmosphere was 13 percent. It was in a sealed
chamber, near sea level, upstream from an inverted siphon
on a metropolitan trunk. A man would be foolish to enter
the chamber. Without ventilation, he might die, but not
from lack of oxygen.
"It seems unlikely that anyone has ever died in a sewer
from suffocation, that is, a lack of oxygen. Deaths have
often been attributed to 'asphyxiation.' This is a word
which, according to the dictionary, is used to mean death
from an atmosphere that does not support life. The word
has sometimes been misinterpreted as meaning suffoca-
tion, which is only one kind of asphyxiation.
"In nearly all cases of death in sewers, the real killer is
hydrogen sulfide. It is important that this fact be recog-
nized. Many cities diligently test for explosive gases, which
is very important, and they may measure the oxygen con-
centration which usually is unimportant, but they rarely
measure H
S. Death has occurred where it is unlikely that
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there was any measurable reduction in the oxygen concen-
tration. Waste water containing 2 mg per liter of dissolved
sulfide, and at a pH of 7.0, can produce, in a chamber with
high turbulence, a concentration of 300 PPM H
S, in the
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air. This is considered to be a lethal concentration. Many
people have died from H
S, not only in sewers and indus-
2
tries, but also from swamps and from hot springs. In one
resort area, at least five persons died from H
S poisoning
2
before the people were ready to admit that H
S is not a
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therapeutic agent. Hardly a year passes in the US. without
a sewer fatality from H
S as well as deaths elsewhere in
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the world.
"The presence of H
S in a sewer atmosphere is easily
2
determined. A bellows-and-ampoule type of tester is very
satisfactory for the purpose, even though it is only crudely
quantitative. When using a tester of this type, do not bring
the air to the ampoule by way of a tube, as this may change
the H
S concentration. Hang the ampoule in the air to be
2
tested, with a suction tube to the bulb or bellows.
"Lead acetate paper is very useful as a qualitative indica-
tor. It cannot be used to estimate the amount of sulfide, but
it will quickly turn black in an atmosphere containing only
a tenth of a lethal concentration.
"Electrodes or other similar electrical indicating devices for
H
S in air have been marketed. Some of them are known to
2
be unreliable, and we know of none that have proved
dependable. Do not use one unless you check it at frequent
intervals against air containing known H
S concentra-
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D-5
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