Date: Mon, 3 Oct 2011 13:38:21 -0400
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From: "Secretary, ACS Division of Chemical Health and Safety"

Subject: 7 RE: [DCHAS-L] H2S Antidotes
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Subject: RE: [DCHAS-L] H2S Antidotes
Date: October 3, 2011 11:52:35 AM EDT

The best reference is the ATSDR Profile on Hydrogen Sulfide.  It is
generally accepted that a single breath at 1000 ppm or higher causes cardiac
arrest.  A "few" breaths at about 500 ppm have been documented to cause a
rapid loss of consciousness and subsequent arrest.

The odor threshold is so low that most people self-evacuate from the
affected area before lethal levels are encountered.

Read the ATSDR Profile; it is long (229 pages) but useful.

==From: Mike Stolle 
Subject: RE: [DCHAS-L] H2S Antidotes
Date: October 3, 2011 11:51:18 AM EDT

Robert, remember that Hydrogen Sulfide is heavier than air and threshold
levels  for human exposure are generally 300 to 350ppm and many personal
detectors are set at 5- 10 ppm with high alarms set at 15ppm.  My feeling is
that a fatal exposure would totally depend on the strength of the
concentration and whether the exposed individual was breathing heavily or at
rest, breathing at a shallow rate.  UNFORTUNATELY, these are subjective
measures and depend on conditions at the time.  My experience in the oil
industry tells me to stay as far away from it as possible.
Take care and stay safe.

Mike Stolle CSP CHCM

From: toxicking 
Subject: Re: [DCHAS-L] H2S Antidotes
Date: October 3, 2011 11:49:49 AM EDT
Dear Dr. Weeks:

Thank you for your e-mail.  I am very familiar with hydrogen sulfide toxicity and the scientific literature on the substance.

Set forth below is data that I derived and quoted almost verbatim from the WHO publication, "Concise International Chemical Assessment Document 53 Hydrogen Sulfide: Human Health Aspects," 2003, so that you would have authoritative scientific information.

There have been numerous case reports of human deaths after single exposures to high concentrations (â≈¥700 mg/m3) of hydrogen sulfide gas (WHO 2003).  Most fatal cases associat ed with hydrogen sulfide exposure have occurred in relatively confined spaces; the victims lost consciousness quickly after inhalation of hydrogen sulfide, sometimes after only one or two breaths (the so-called slaughterhouse or sledgehammer effect)(WHO 2003).   Many of the case-studies on hydrogen sulfide poisonings and death involved assumed accidental poisonings for which the exposure concentrations and/or durations were not known (WHO 2003).  Death occurring after single exposures to high concentrations of hydrogen sulfide appears to be the result of respiratory failure or arrest, with most cases initially presenting with respiratory insufficiency, non-cardiogenic pulmonary edema, coma, and cyanosis (WHO 2003).

I hope that this information helps you.

Have a nice day.

Stephen King, Ph.D., M.P.H.
Toxicologist & Epidemiologist

WHO 2003 -  Concise International Chemical Assessment Document 53 Hydrogen Sulfide: Human Health Aspects.  World Health Organization, Geneva, Switzerland, 14, 2003.

From: "Wright, Mike" 
Subject: RE: [DCHAS-L] H2S Antidotes
Date: October 3, 2011 11:47:15 AM EDT

Our union members deal with this stuff in steel industry coke batteries
and oil refineries. It can also be produced from rotting vegetation;
even that source can be dangerous in confined spaces. The IDLH level for
H2S is 100 ppm. An atmosphere of 1000 ppm will produce immediate
unconsciousness. H2S paralyzes the respiratory center in the brain. It
also interferes with O2 transport in red blood cells and can cause
pulmonary edema by forming acid in the alveoli.

Most deaths are from respiratory paralysis. And yes, one breath at 1000
ppm or higher can do it.

H2S has very good warning properties; it's detectable by smell at less
than 1 ppm. But that's a trap, since the same mechanism that causes
respiratory shutdown also affects the sense of smell at lower
concentrations. If there is any chance of significant exposure you need
detectors, a rescue capability using SCBA, and good training.
Interestingly, H2S is a neurotransmitter or a neuromodulator in
conjunction with NO, which probably explains its profound effect on the
nervous system.

I don't believe there's any "antidote" in the traditional sense,
although induced methemoglobinemia in a hospital can scavenge H2S.
Emergency treatment is much more important; it consists mostly of O2 and
ventilatory support. If reached in time, victims can fully recover.

Michael J. Wright
Director of Health, Safety & Environment
United Steelworkers
5 Gateway Center
Pittsburgh, PA 15228
==From: Bob Weeks 
Subject: RE: [DCHAS-L] H2S Antidotes
Date: October 3, 2011 1:15:24 PM EDT

I teach a HAZCOM class and one of the trainees said that one breath at 700
ppm was fatal. Guess I forgot to put the 700 in my initial email. In one of
my HAZWOPER classes a student related an incident in the SE corner of NM
where oil well production is prominent. He said that a couple of guys were
driving through production areas examining the settling tanks and one said,
"What about that tank?  I'll check," he said. Got out of the pickup, went
over, unlocked the lid, got his flashlight, stuck his head in and never
pulled it out. Died instantly.

==From: Diane Doty 
Subject: Re: [DCHAS-L] H2S Antidotes
Date: October 3, 2011 1:19:21 PM EDT

From what I have read, H2S smells like rotten eggs.  When the concentration is high enough, a person exposed
to H2S can no longer smell the rotten egg odor.  And yes, at that level, it will cause death.
==From: Mary Beth Mulcahy 
Subject: Re: [DCHAS-L] H2S Antidotes
Date: October 3, 2011 12:58:04 PM EDT
To: DCHAS-L Discussion List 
I work for the Chemical Safety Board (CSB) and looked up accidents related to H2S. The CSB did a report on a H2S injury many years ago ( and cited the toxicology profile for from the Agency for Toxic Substances and Disease Registry (ASTDR) which discusses people losing consciousness after just one breath ( The ASTDR profile has many documented references contained within that can point you to more data.


Mary Beth Mulcahy

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