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).
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
|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|
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-
|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||
- Measured at 0oC and 1 atm pressure. Based on odour nuisance and may be unsuitable in geothermal area
- Level for eye irritation
- WHO, 2000. Guidelines for Air Quality, World Health Organization, Geneva.
- State of Hawaii, 2002. 2001 Annual Summary Hawaii Air Quality Data, Department of Health Clean Air Branch, Honolulu, Hawaii.
Occupational Guidelines for H2S
|Country/ Institution||Level (ppm)||Level µg m-3||Averaging Period||Guideline Type||Date of Implemen-
|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|
||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|
- 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.
- HSE, 2002. Occupational Exposure Limits 2002. HSE Books, Sudbury.
- OSHA Standards Website
- NIOSH Pocket Guide to Chemical Hazards (NPG).http://www.cdc.gov/niosh/npg/npg.html
- AIHA Emergency Response Planning Guidelines Committee, 2004. 2004 Emergency Response Planning Guidelines (ERPG) Update Set, American Industrial Hygiene Association, Fairfax.
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).
|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|
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