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H2S Gas and its Sensor

Intro to Hydrogen Sulfide

Hydrogen sulfide is a chemical compound with the formula H2S. It is a colorless chalcogen-hydride gas, and is poisonous, corrosive, and flammable, with trace amounts in ambient atmosphere having a characteristic foul odor of rotten eggs. Hydrogen sulfide is one of the leading causes of workplace gas inhalation deaths in the United States. According to the Bureau of Labor Statistics (BLS), hydrogen sulfide caused 46 worker deaths between 2011 and 2017.

Gas Characteristics

  • Colorless
  • Strong odor (rotten eggs)
  • Extremely flammable
  • Highly toxic
  • Corrosive
  • Explosive
  • Heavier than air
  • Primarily accesses the body through inhalation
  • Other Names: “knock down gas,” “swamp gas,” “sewer gas,” “stink damp,” “manure gas,” etc.
  • CAS 7783-06-4
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Industrial H2S hazards and sources

  • Petrochemical facilities
  • Natural gas drilling and refining
  • Wastewater treatment industries
  • Agricultural farms
  • Oil and gas refining
  • Mining
  • Tanning
  • Rayon manufacturing
  • Food processing plants
  • Breweries
  • Landfills
  • Nuclear power plants
  • Hot asphalt paving
  • Textile manufacturing

On average, there are 6 worker fatalities per year in the U.S. due to exposure to hydrogen sulfide.

(Bureau of Labor Statistics)

High Risk Scenarios

  • Prominent in confined spaces
  • Windless or low-lying areas that increase the potential for pockets of hydrogen sulfide to form.
  • Marshy landscapes where bacteria break down organic matter to form hydrogen sulfide.
  • Hot weather that speeds up rotting of manure and other organic materials and increases the hydrogen sulfide vapor pressure.
  • Poor settling, excessive sludge production, and corrosion are all results of high concentrations of H2S. In wastewater treatment plants hydrogen sulfide can corrode the cement walls around the basin and guardrails.
  • Sanitation workers can be exposed when cleaning or maintaining municipal sewers and septic tanks.
  • Farm workers can be exposed when cleaning manure storage tanks or working in manure pits.

H2S Sensor Info

Type: Electrochemical
Range: 0-100ppm (0.1ppm resolution)
High Range: 0-500ppm (0.5ppm resolution)
Carbon monoxide and hydrogen sulfide (COSH): CO: 0-500 ppm (1 ppm resolution), H2S: 0-100 ppm (0.1 ppm resolution)

Alarm Levels

Low Alarm: 10 ppm
High Alarm: 15 ppm
STEL — 15 minute — Short Term Exposure Limit: 5 ppm
TWA  — 8 hour time weighted average: 1 ppm

Questions about the detection of H2S?

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Special Applications and Considerations

  • Always test a confined space for H2S before entering- should be done by a trained professional, using H2S detector tubes or a multi-gas meter.
  • If H2S is present, continually ventilate the area to clear out the gas.
  • If the gas can’t be removed from the area, the person entering the space MUST use proper respiration equipment and PPE, as well carry communication and rescue equipment.
  • Condensing humidity, high water concentrations (especially prominent in CSE’s) in Wastewater industry. This causes high concentrations of H2S.
  • Other common CSEs where H2S exposure is probable (and likely to build up to high levels):
    • Wells
    • Tunnels
    • Manholes
    • Sewers
    • Septic Tanks
  • As H2S is explosive and flammable, great care must be used to avoid triggering this in a confined space where avoiding the impact would be nearly impossible.
  • CONTINUOUSLY monitor gas levels in CSEs. Concentrations can change rapidly.

Health Risks and Handling of H2S

concentration
symptoms/effects
0.00011 — 0.00033
Typical background concentrations
0.01 — 1.5
Odor threshold (when rotten egg smell is first noticeable to some). Odor becomes more offensive at 3 — 5 ppm. Above 30 ppm, odor described as sweet or sickeningly sweet.
2 — 5
Prolonged exposure may cause nausea, tearing of the eyes, headaches or loss of sleep. Airway problems (bronchial constriction) in some asthma patients.
20
Possible fatigue, loss of appetite, headache, irritability, poor memory, dizziness.
50 — 100
Slight conjunctivitis ("gas eye") and respiratory tract irritation after 1 hour. May cause digestive upset and loss of appetite.
100
Immediately Dangerous to Life and Health (IDLH)
100
Coughing, eye irritation, loss of smell after 2 — 15 minutes (olfactory fatigue). Altered breathing, drowsiness after 15 — 30 minutes. Throat irritation after 1 hour. Gradual increase in severity of symptoms over several hours. Death may occur after 48 hours.
100 — 150
Loss of smell (olfactory fatigue or paralysis).
200 — 300
Marked conjunctivitis and respiratory tract irritation after 1 hour. Pulmonary edema may occur from prolonged exposure.
500 — 700
Staggering, collapse in 5 minutes. Serious damage to the eyes in 30 minutes. Death after 30 — 60 minutes.
700 — 1000
Rapid unconsciousness, "knockdown" or immediate collapse within 1 to 2 breaths, breathing stops, death within minutes.
1000 — 2000
Nearly instant death
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FIRST AID

IN ALMOST ALL CASES OF CONTACT WITH H2S, CALL POISON CONTROL AND GO TO THE HOSPITAL

  • If INHALED, move victim to fresh air, don’t allow them to move about unnecessarily, have them seated in a comfortable position, administer supplemental oxygen if necessary.
  • DO NOT make mouth to mouth contact, use face shields/guards.
  • If SKIN CONTACT is made, remove clothing that may restrict circulation, remove the source of contamination, DO NOT rewarm, or rub the affected are on site.
  • Loosely apply a sterile cover to affected area, NO smoking or drinking for victim.
  • If EYES are contacted, wash out eyes with lukewarm water IMMEDIATELY, 15 — 20mins. If liquefied gas was the source, rinse for briefer period of time, then cover eyes in a sterile dressing.
  • If a FIRE occurs, use carbon dioxide, dry chemical powder, water spray or fog to extinguish.
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IF ACCIDENTALLY RELEASED
  • In event of a spill or leak, immediately put on escape-type respirator and exit the area.
  • Evacuate the area immediately. Isolate the hazard area. Keep out unnecessary and unprotected personnel. Evacuate downwind locations.
  • Do not touch damaged containers or spilled product unless wearing appropriate protective equipment.
  • Ventilate area. Eliminate all ignition sources. Use grounded, explosion-proof equipment. Distant ignition and flashback are possible.
  • Liquid: stop or reduce leak if safe to do so. If not, allow liquid to vaporize.
  • Ventilate the area to prevent the gas from accumulating, especially in confined spaces. Gas: stop or reduce leak if safe to do so.
  • Ventilate the area to prevent the gas from accumulating, especially in confined spaces.

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