Teledyne 6712SR - Manual (Page 201)

6712SR Refrigerated Sampler
Appendix C General Safety Procedures
C-5
does not support life. The word has sometimes been misinter-
preted as meaning suffocation, which is only one kind of asphyxi-
ation.
“In nearly all cases of death in sewers, the real killer is hydrogen
sulfide. It is important that this fact be recognized. Many cities
diligently test for explosive gases, which is very important, and
they may measure the oxygen concentration which usually is
unimportant, but they rarely measure H2S. Death has occurred
where it is unlikely that there was any measurable reduction in
the oxygen concentration. 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 H2S, in the
air. This is considered to be a lethal concentration. Many people
have died from H2S, not only in sewers and industries, but also
from swamps and from hot springs. In one resort area, at least
five persons died from H2S poisoning before the people were
ready to admit that H2S is not a therapeutic agent. Hardly a
year passes in the US. without a sewer fatality from H2S as well
as deaths elsewhere in the world.
“The presence of H2S in a sewer atmosphere is easily deter-
mined. 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 H2S concen-
tration. Hang the ampoule in the air to be tested, with a suction
tube to the bulb or bellows.
“Lead acetate paper is very useful as a qualitative indicator. 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 H2S
in air have been marketed. Some of them are known to be unre-
liable, and we know of none that have proved dependable. Do not
use one unless you check it at frequent intervals against air con-
taining known H2S concentrations. A supposed safety device
that is unreliable is worse than none at all.
“Remember that the nose fails, too, when it comes to sensing
dangerous concentrations of H
2
S.
“Various other toxic gases have been mentioned in some publica-
tions. It is unlikely that any person has been asphyxiated in a
sewer by any of those other gases, except possibly chlorine. The
vapor of gasoline and other hydrocarbons is sometimes present in
amounts that could cause discomfort and illness, but under that
condition, the explosion hazard would be far more serious. The
explosimeter tests, as well as the sense of smell, would warn of
the danger. Pipelines in chemical plants might contain any
number of harmful vapors. They, too, are sensed by smell and
explosimeter tests if they get into the public sewer. Such occur-
rences are rare.
“The attempt to instill a sense of urgency about real hazards is
diluted if a man is told to give attention to a long list of things
that in fact are irrelevant.