English Dutch French German Italian Portuguese Russian Spanish

Hydrogen Sulphide (H2S)

Exposure Effects
Existing Guidelines
Volcanic Examples and Incidents
Volcanic Gases and Aerosols Index


Hydrogen sulphide (H2S) is a colourless gas with a distinctive odour of rotten eggs. H2S odour perception is highly variable within the human population, ranging from 0.008-0.2 ppm (Amoore, 1983; Beauchamp 1984). It is flammable in air at concentrations between 4-46% by volume (Sax and Lewis, 1989) and burns with a pale blue flame. It is only moderately soluble in water (4.1 g L-1 at 20°C (Gangolli, 1999)) and has a density of 1.39 g L-1 at 25°C and 1 atm (Lide, 2003), 1.2 times that of ambient air. Typical concentration ranges of H2S in dilute volcanic plumes are 0.1-0.5 ppm, compared to the tropospheric background of 0.00005-0.024 ppm, and the gas has a residence time in the lower atmosphere of approximately 24 hours (Brimblecombe, 1996; Oppenheimer et al., 1998).

Exposure Effects

Hydrogen sulphide (H2S) is a toxic gas and the health hazard depends upon both the duration of exposure and the concentration. The gas is an irritant of the lungs and at low concentrations irritates the eyes and the respiratory tract. Exposure may result in headache, fatigue, dizziness, staggering gait, and diarrhoea, followed sometimes by bronchitis and bronchopneumonia (Sax and Lewis, 1989). There is some evidence of elevated presence of adverse health symptoms in communities exposed to long-term low levels of H2S in the environment (Bates et al., 2002; Legator, 2001), such as in geothermal areas, and the unpleasant smell of H2S can be a nuisance. Asthmatic subjects do not appear to respond as readily to low levels of H2S as they may do to SO2. Sense of smell to H2S is lost at concentrations below those of harm so people may have little warning of the presence of the gas at dangerous concentrations. Very large concentrations result in paralysis of the respiratory centre, causing breathing to stop and may potentially lead to death. If death does not occur during the exposure time, recovery generally occurs without later medical complications, although symptoms may occur for several months (Snyder et al., 1995). The concentration thresholds for health effects are outlined in the table.

Health effects of respiratory exposure to hydrogen sulphide 
(Amoore, 1983; Baxter, 2000; Faivre-Pierret and Le Guern, 1983 and references therein; NIOSH, 1981; Sax and Lewis, 1989; Snyder et al., 1995).

Exposure limits (ppm) Health Effects
Olfactory threshold -“rotten eggs” smell detectable
20 Sense of smell to gas lost
Concentrations tolerated for some hours without harm
20-50 Eye irritation
50 Prolonged exposure may cause pharyngitis and bronchitis
60 Prolonged exposure may cause conjunctivitis and eye pain
150+ Irritation of upper respiratory tract
Sense of smell lost
250 Pulmonary oedema with risk of death
500 Very dangerous, evacuation should occur well below this level
1000 Loss of consciousness occurs
1000-2000 Acute intoxication: symptoms include rapid breathing, distress, nausea and vomiting. May be rapidly followed by loss of consciousness, coma and cessation of breathing.
2000+ Immediate loss of consciousness and high probability of death

Existing Guidelines

Many countries/organizations do not have ambient air quality levels for H2S, as it is not perceived as a problem gas in most regions. Those that do are given in the tables below.

Ambient air quality guidelines for H2S

Country/ Institution Level (ppm) Level µg m-3 Averaging Period Guideline Type Date of Implemen- 
Relevant Law Notes Ref.
New Zealand   7 1 hour   May 2002   1 a
WHO   150 24 hours   1997 WHO 1997 2 b
State of Hawaii, USA 0.025 35 1 hour State standard       c
State of California, USA 0.03   1 hour 
State 1969; retained 1984    


  1. Measured at 0oC and 1 atm pressure. Based on odour nuisance and may be unsuitable in geothermal area
  2. Level for eye irritation
  1. http://www.mfe.govt.nz/publications/air/ambient-air-quality-may02/index.html
  2. WHO, 2000. Guidelines for Air Quality, World Health Organization, Geneva.
  3. State of Hawaii, 2002. 2001 Annual Summary Hawaii Air Quality Data, Department of Health Clean Air Branch, Honolulu, Hawaii.
  4. http://www.arb.ca.gov/research/aaqs/caaqs/h2s/h2s.htm

Occupational Guidelines for H2S

Country/ Institution Level (ppm) Level µg m-3 Averaging Period Guideline Type Date of Implemen- 
Relevant Law Notes Ref.
UK 10 14000 15 min MEL   New   a
5 7000 8 hour TWA MEL   New   a
USA 20   8 hour TWA Permissible Exposure accepted ceiling   OSHA Regulations (Standards - 29 CFR) 1 b
10 15000 10 min ceiling REL 2003 NIOSH   c
0.1   1 hour 
ERPG-1 2003 Emergency Response Planning Guideline   d
30   1 hour ERPG-2 2003 Emergency Response Planning Guideline   d
100   1 hour ERPG-3 2003 Emergency Response Planning Guideline   d
  1. ppm by volume at 25ºC and 760 torr. 50 ppm is acceptable for 10 mins once in an 8 hour period if no other exposure occurs.
  1. HSE, 2002. Occupational Exposure Limits 2002. HSE Books, Sudbury.
  2. OSHA Standards Website
  3. NIOSH Pocket Guide to Chemical Hazards (NPG).http://www.cdc.gov/niosh/npg/npg.html
  4. AIHA Emergency Response Planning Guidelines Committee, 2004. 2004 Emergency Response Planning Guidelines (ERPG) Update Set, American Industrial Hygiene Association, Fairfax.

Volcanic Examples and Incidents

Hydrogen sulphide (H2S) has been found in dangerous concentrations in the vicinity of fumaroles and the craters of volcanoes, as well as in geothermal and hot spring areas (Baxter, 2000). On volcanoes, workers may be totally unaware of H2S, because its smell may be undetectable, even at low levels, in mixtures of fumarolic gases:

  • Soufrière, Guadeloupe: During the phreatic eruption in 1976-1977 volcanologists working on the summit and residents in the town of St Claude, 3-4 km away, suffered from headaches. Consequent measurements of H2S showed that concentrations were ~74 ppm (100,000 µg m-3) on the summit and ~0.2 to ~0.37 ppm (300 to 500 µg m-3) in St Claude, well above occupational and ambient guidelines respectively (Le Guern et al., 1980).
  • Kilauea, Hawaii: In Hawaii Volcanoes National Park, surveys of near vent ambient air at Sulphur Bank yielded concentrations between 0.3 and 4.2 ppm in 1994 (Sutton et al., 1994) and 0.2-0.7 ppm on 23 July 2003 (C. Witham unpublished data). In both cases, the State's ambient standard was exceeded. Signs and barriers in the vicinity of the ground emissions warn tourists about the hazards in this area of the Park.
  • Alban Hills volcanic region, Italy: Measurements in a residential area revealed that occupational thresholds (10-15 ppm) were frequently exceeded and levels up to 40 ppm, a potentially harmful concentration, had occurred (Carapezza et al., 2003).
  • Rotorua, New Zealand: Rotorua sits on a geothermal field that is emitting H2S. About a quarter of the population has been regularly exposed to concentrations that exceed ~0.143 ppm (200 µg m-3), well above ambient guidelines, and maximum concentrations exceed ~1 ppm (1500 µg m-3). Chronic exposure to the gas has been associated with adverse health effects, including neurological, cardiovascular and respiratory effects, and several deaths have been associated with acute exposures to high concentrations that had accumulated in confined spaces (Bates et al., 2002). Maximum concentrations measured inside selected buildings in Rotorua reach >200 ppm in venting and enclosed areas, and ambient indoor levels of 0.3-20 ppm have been recorded (Durand and Scott, 2003).

Fatalities from volcanic and geothermal H2S poisoning have occurred in Rotorua and at volcanoes in Japan (see table), and in the last 100 years the gas was responsible for at least 46 deaths.

Mortality and morbidity incidents associated with volcanic H2S emissions in the Twentieth Century 
(after Hayakawa, 1999; Durand sourced in Collins, 2003).

geothermal area
Date Mortality/
Further detail
Nasu, Japan 6 Jul 1919 2 deaths  
Nasu, Japan 26 Nov 1921 1 death  
Rotorua, NZ 1946 1 death Spa pool
Rotorua, NZ 1948 1 death
1 person overcome
During sewer pipe maintenance
Hakone, Japan 5 Nov 1951 2 deaths Open-air bathing
Hakone, Japan 27 Mar 1952 1 death Indoor bathing
Rotorua, NZ Feb 1954 1 death 
4 persons overcome
Upon entering a septic tank
Rotorua, NZ Feb 1954 1 death Overcome in hot pool and drowned
Rotorua, NZ Jun 1954 1 death Digging sump hole
Tateyama, Japan 21 Jul 1954 1 death Open-air bathing
Daisetsu, Japan 21 Jul 1958 2 deaths  
Rotorua, NZ Feb 1962 2 deaths At night. Blamed on leaking pipe in groundwater-fed heating system
Rotorua, NZ May 1962 1 death In confined room
Tateyama, Japan 23 Apr 1967 1 death  
Tateyama, Japan 4 Nov 1967 2 deaths Campers
Narugo, Japan 26 Aug 1969 1 death Indoor bathing
Tateyama, Japan 30 Apr 1970 1 death In a cabin
Kusatsu-Shirane, Japan 27 Dec 1971 6 deaths Skiers
Hakone, Japan 2 Oct 1972 2 deaths  
Tateyama, Japan 25 Nov 1972 1 death Spa worker
Tateyama, Japan 12 Aug 1975 1 death  
Kusatsu-Shirane, Japan 3 Aug 1976 3 deaths Hikers
Tateyama, Japan 22 July 1985 1 death  
Akita Yakeyama, Japan 8 May 1986 1 death  
Rotorua, NZ Sep 1987 2 deaths At night. Faulty shower tray let gas into motel room.
Kirishima, Japan 26 Aug 1989 2 deaths Indoor bathing
Adatara, Japan 15 Sep 1997 4 deaths Hikers
Rotorua, NZ 19 Feb 2000 1 death Source of H2S unclear



American Industrial Hygiene Association, 1962. Hydrogen Sulfide. Hygienic Guide Series. Detroit, Michigan.

Amoore, J.E. and Hautala, E., 1983. Odor as an aid to chemical safety: odor thresholds compared with threshold limit values and volatilities for 214 industrial chemicals in air and water dilution. Journal of Applied Toxicology 3, 272-290.

Bates, M.N., Garrett, N. and Shoemack, P., 2002. Investigation of health effects of hydrogen sulfide from a geothermal source. Archives of Environmental Health, 57(5): 405-411.

Baxter, P.J., 2000. Gases. In: P.J. Baxter, P.H. Adams, T.-C. Aw, A. Cockcroft and J.M. Harrington (Editors), Hunter's Diseases of Occupations. Arnold, London, pp. 123-178.

Beauchamp, R.O.J., Bus, J.S., Popp, J.A., Boreiko, C.J. and Andjelkovich, D.A., 1984. A critical review of the literature on hydrogen sulfide toxicity. Critical Reviews in Toxicology 13: 25-97.

Brimblecombe, P., 1996. Air Composition and Chemistry. Cambridge University Press, Cambridge.

Carapezza, M.L., Badalamenti, B., Cavarra, L. and Scalzo, A., 2003. Gas hazard assessment in a densely inhabited area of Colli Albani Volcano (Cava dei Selci, Roma). Journal of Volcanology and Geothermal Research, 123: 81-94.

Collins, S., 2003, Sulphur City goes under scrutiny, The New Zealand Herald, 9 July 2003, Click for article.

Durand, M. and Scott, B.J., 2003. An investigation of geothermal soil gas emissions and indoor air pollution in selected Rotorua buildings, Institute of Geological & Nuclear Sciences Science Report 2003/28.

Faive-Pierret, R. and Le Guern, F., 1983. Health risks linked with inhalation of volcanic gases and aerosols. In: H. Tazieff and J.C. Sabroux (Editors), Forecasting Volcanic Events. Elsevier Science Publishers B.V., Amsterdam, pp. 69-81.

Gangolli, S. (Ed.), 1999. The Dictionary of Substances and their Effects, 2nd edn. The Royal Society of Chemistry. Cambridge.

Hayakawa, Y., 1999. Catalog of volcanic eruptions during the past 2000 years in Japan. Journal of Geography, 108(4): 472-488.

Legator, M.S., 2001. Health effects from chronic low-level exposure to hydrogen sulfide. Archives of Environmental Health, 56: 123-131.

Le Guern, F., Bernard, A. and Chevrier, R.M., 1980. Soufriere of Guadeloupe 1976-1977 eruption - mass and energy transfer and volcanic health hazards. Bulletin of Volcanology, 43(3): 577-593.

Lide, D.R. (Ed.), 2003. CRC Handbook of Chemistry and Physics, 84th edn. CRC Press. Boca Raton, Florida.

National Institute for Occupational Safety and Health (NIOSH), 1981. Occupational Health Guidelines for Chemical Hazards, DHHS (NIOSH) Publication No. 81-123. http://www.cdc.gov/niosh/81-123.html.

Oppenheimer, C., Francis, P., Burton, M., Maciejewski, A.J.H. and Boardman, L., 1998. Remote measurement of volcanic gases by Fourier transform infrared spectroscopy. Applied Physics B, 67: 505-515.

Sax, N.I. and Lewis, R.J., Sr., 1989. Dangerous Properties of Industrial Materials, 7th edn. Van Nostrand Reinhold. New York.

Snyder, J.W., Safir, E.F., Summerville, G.P. and Middleberg, R.A., 1995. Occupational fatality and persistent neurological sequelae after mass exposure to hydrogen sulfide. American Journal of Emergency Medicine, 13(2): 199-203.

Sutton, A.J., Elias, T., Navarrete, R., 1994, Volcanic gas emissions and their impact on ambient air character at Kilauea Volcano, Hawaii, U.S. Geological Survey Open-File Report 94-569, 34 p.