: Hi, I have had a sewer smell in my house on several floors and several different places. I was told it
: was methane (which we knew already). My question
: is just how harmful is the methane gas and how worried should I be about it? I have small children too who might be affected. Thanks
HYDROGEN SULFIDE HAZARDS IN
MUNICIPAL & INDUSTRIAL ACCOUNTS
Alken-Murray personnel working in areas where hydrogen sulfide is present are to diligently study this
section of the website.
Hydrogen sulfide has the characteristic odor of rotten eggs. However, it rapidly deadens the sense of
smell. Therefore, odor cannot be depended upon as a means of detection of this gas. After working for a
short time in an area with a small amount of hydrogen sulfide, a person can no longer detect this gas and
will not identify larger lethal concentrations.
Hydrogen sulfide is a highly toxic gas which, when inhaled in higher concentrations has no odor and can
rapidly cause death, perhaps in 2-3 minutes. It is also highly flammable and certain concentrations (4.3-
46%) in air can explode upon ignition.
Even at low concentrations, hydrogen sulfide acts as an irritant to the eyes and respiratory tract. Moderate
concentrations cause headaches, dizziness, nausea and vomiting in that order. The greatest danger,
however, is from its acute effects. Massive dosage, that is contact with high concentrations (1000 ppm or
more) can cause immediate loss of consciousness (in 1-2 seconds) which is rapidly followed by respiratory
failure and death (2-3 minutes).
(See toxicity chart in front of this article).
Most industrial and municipal waste water treatment plants have information concerning the amount of
hydrogen sulfide present in the gas produced on their properties. Always obtain this information before
visiting a plant. Your safety depends on your knowledge of the hazards, and the application of adequate
safety procedures including the intelligent use of appropriate personal protective equipment such as:
1.A respirator with canisters suitable for use with hydrogen sulfide up to 2% concentration (20,000
part per million).
2.A hydrogen sulfide detection unit for monitoring amounts of hydrogen sulfide present.
3.A self-contained air breathing apparatus.
This equipment should be available at the waste water treatment plant. OSHA regulations require that they
measure the amount of hydrogen sulfide in their plant and that they provide you with these data.
Regulation Section 1910.134 (e)(1) of the Occupational Safety & Health Act says "In areas where an
individual using a respirator could be overcome by a toxic or oxygen deficient atmosphere due to the failure
of the respirator, at least one additional man shall be present. Communication, (visual, voice, or signal line)
shall be maintained between both or all individuals present. Planning shall be such that one individual will
be unaffected by any likely incident and have the proper rescue equipment to be able to assist the other(s)
in case of emergency."
Alken-Murray Corporation insists that its representatives follow the above regulation. If the area is
contaminated by a hazardous or noxious gas (over 300 ppm hydrogen sulfide) and another individual is not
present, do not enter the area or do any work in the contaminated area.
Procedure to be used based on detection tests
If the concentration is equal to or less than 10 parts per million, a respirator (gas mask) is not
If the concentration is more than 10 ppm, but less than 50 ppm, exposure without a respirator is
permissible, but only ONCE and for less than 10 minutes. Beyond this time, a respirator is to be
When the concentration is higher than 50 parts per million, a respirator is to be used at all times.
One hour of exposure to concentrations of hydrogen sulfide between 50 and 100 ppm will cause
the average individual to exhibit sub-acute poisoning symptoms such as mild conjunctivitis and
respiratory tract irritations.
Concentrations between 200 and 500 ppm produce marked poisoning symptoms.
Hydrogen sulfide at a concentration of 600 ppm can be fatal in 30 minutes, and only 1,000 ppm,
that is 0.1% hydrogen sulfide, can be fatal in only 2 to 3 minutes. You cannot detect when
concentration increases from 100 to 1000 ppm by smell. There is no warning odor at higher