Teledyne 6712FR manual

6712FR Refrigerated Sampler

Appendix C General Safety Procedures

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 metro- politan 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 suf- focation, 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 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 U.S. without a sewer fatality from H2S as well as deaths elsewhere in the world.

The presence of H2S in a sewer atmosphere is easily determined.

Abellows-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 concentration. 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 dan- gerous concentrations of H2S.

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

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