Carbon dioxide (CO2) is a colourless and odourless gas. It is non-flammable and chemically non-reactive (Sax and Lewis, 1989). CO2 is 1.5 times as heavy as air (its density is 1.80 g L-1 at 25°C and 1 atm (Lide, 2003)) and, if it is emitted slowly, flows down-slope and may accumulate at low elevations. Concentration ranges of CO2 in dilute volcanic plumes can range from 1 ppm to hundreds of ppm above the tropospheric background of ~360 ppm (T. Elias pers. comm.; Oppenheimer et al., 1998), and the gas has a residence times in the lower atmosphere of approximately 4 years (Brimblecombe, 1996).
Due to the high levels of CO2 required to cause harm, concentrations of CO2 are often expressed as a percentage of the gas in air by volume (1% = 10,000 ppmv). This is in contrast to other volcanic gases.
Carbon dioxide (CO2) is a toxic gas at high concentration, as well as an asphyxiant gas (due to reduction in oxygen). Irritation of the eyes, nose and throat occurs only at high concentrations. The concentration thresholds for health effects are outlined in the table.
Health effects of respiratory exposure to carbon dioxide
(Baxter, 2000; Faivre-Pierret and Le Guern, 1983 and refs therein; NIOSH, 1981).
|Exposure limits (% in air)||Health Effects|
|2-3||Unnoticed at rest, but on exertion there may be marked shortness of breath|
|3||Breathing becomes noticeably deeper and more frequent at rest|
|3-5||Breathing rhythm accelerates. Repeated exposure provokes headaches|
|5||Breathing becomes extremely laboured, headaches, sweating and bounding pulse|
|7.5||Rapid breathing, increased heart rate, headaches, sweating, dizziness, shortness of breath, muscular weakness, loss of mental abilities, drowsiness, and ringing in the ears|
|8-15||Headache, vertigo, vomiting, loss of consciousness and possibly death if the patient is not immediately given oxygen|
|10||Respiratory distress develops rapidly with loss of consciousness in 10-15 minutes|
|15||Lethal concentration, exposure to levels above this are intolerable|
Convulsions occur and rapid loss of consciousness ensues after a few breaths. Death will occur if level is maintained.
Gas masks may be of limited use in high CO2 concentrations due to the lack of oxygen. Hence it has been recommended that working or living areas should be immediately evacuated when concentrations exceed 1.5% by volume (the occupational short-term exposure limit value). Ambient guidelines for CO2 do not exist. Occupational guidelines for CO2 concentrations are given in the table.
Occupational guidelines for CO2
(Concentration of 1% = 10000 ppm)
|Country/ Institution||Level %||Level mg m-3||Averaging Period||Guideline Type||Date of Implemen-
|EU||0.5||9000||8 hour TWA||OEL||Commission Directive 91/322||a|
|0.5||9150||8 hour TWA||MEL||ILV||b|
|>0.5||9000||8 hour TWA||PEL||OSHA Regulations (Standards - 29 CFR)||1||d|
|0.5||9000||10 hour TWA||REL||2003||NIOSH||c|
- HSE, 2002. Occupational Exposure Limits 2002. HSE Books, Sudbury.
- NIOSH Pocket Guide to Chemical Hazards (NPG). http://www.cdc.gov/niosh/npg/npg.html
- OSHA Standards Website
Carbon dioxide (CO2) release during eruptions and from vents, the ground, and lava flows can pose a hazard where concentrations are very high and the gas is trapped near the surface. Emissions are most dangerous where they can build up in confined spaces such as natural topographic depressions, excavations and pits, or building basements and cupboards, and Le Guern et al., (1982) proposed that areas located down-slope from old fissures are of particularly high risk. Deaths from increased CO2 concentrations have been reported at Vestmannaeyjar on Heimaey (during the 1973 Eldfell eruption); Vulcano, Italy; Mammoth Mountain, USA and Nyiragongo, DR Congo amongst others (see table). The three events that dominate the CO2 casualty list are the gas-outbursts of Lake Nyos and Lake Manoun, Cameroon and the gas cloud emission at Dieng. Although the two lake outbursts are frequently quoted in volcanic literature, their initiation is thought to be unrelated to volcanic activity at the time. The phreatic eruption on the Dieng Plateau, Indonesia in 1979, was the worst CO2 related tragedy not associated with lake-overturn. This eruption released a cloud of CO2 that overwhelmed ~142 villagers trying to escape from the area and claimed more lives when people tried to rescue the bodies. Gases sampled at the active fissure shortly afterward contained CO2 concentrations of 98-99% (Le Guern et al., 1982). The 18 April 1906 eruption of Vesuvius, Italy is also implicated in a CO2 related death: Perret (1924) recorded that CO2 from the eruption rendered the air "almost irrespirable" and, along with fine ash, blames it for the death of a 19 year old who had a recent history of bronchitis. Gas following major gullies on the west flank of Concepción, Costa Rica during its eruptive activity in 1986 resulted in sore throats and drowsiness and was tentatively thought to be CO2 (Smithsonian Institution, 1986). In Indonesia, CO2 clouds have been reported to flow down the slopes of Tangkubanparahu volcano, sometimes killing children (Le Guern et al., 1982).
Ground emissions of CO2 are particularly hazardous, as there is often little warning of high concentrations:
- Nyiragongo, DR Congo: During the 2002 eruption, measured CO2 concentrations in some locations ranged from 20-30% up to 90%, well above the lethal concentration. These ground CO2 emanations were called mazuku or "evil winds" by the population and pockets of the gas were found to reach heights of up to 40 m. In the years prior to the eruption, ground emissions of CO2 in the Goma and Lake Kivu area were probably responsible for a number of fatalities (Baxter and Ancia, 2002).
- Vulcano, Italy: During the 1980s, CO2 emissions were responsible for occasional deaths of animals (rabbits, goats) and of two children (Baubron et al., 1990). In 1988, measurements of CO2 at Vulcano - an area densely inhabited during the summer - revealed that concentrations in the ground and in water wells around the volcano, were high enough to be a health hazard and in some locations emissions were nearly 100%. The maximum concentrations were found in a campsite and, following transmission of this data to local authorities, camping around the cone was stopped. Soil gas emissions of CO2 pose a hazard to workers and residents in volcanic and geothermal areas, due to their diffusion and accumulation in confined locations:
- Mammoth Mountain, USA: A number of cases of near asphyxia have been reported by people entering small snow-covered cabins in the Mammoth Mountain area (Farrar et al., 1995; Sorey et al., 1998) and the death of a cross-country skier in a snow well in 1998 is thought to have been caused by asphyxia (Hill, 2000). CO2 concentrations measured in the well two days after the body was discovered were 70%. Lethal concentrations were also found in a cabin and vault near Horseshoe Lake on the mountain, and a campground in the area was consequently closed for overnight use (Farrar et al., 1995).
- Kilauea Volcano, Hawaii: Measurements in summit lava tubes show CO2 concentrations up to 1%, well above the occupational TWA standard, and volcano speleologists have reported mental confusion and exhaustion whilst mapping these tubes. CO2 excursions measured in the entrance to a seismic vault located just below ground surface have been as high as 0.5% (USGS, Hawaiian Volcano Observatory, unpublished data).
- Furnas, Azores: In Furnas Caldera, levels of CO2 measured in the soil range from background (<1.5%) to 100%. About one-third of the houses in Furnas village, located in the caldera, were sited in areas of elevated CO2 soil degassing in 1993. Unventilated, confined spaces in some houses contained levels of CO2 that could cause asphyxiation and observations suggested that large and potential lethal surges of CO2 could occur without warning (Baxter et al., 1999).
- Rotorua, New Zealand: High levels of CO2 have been found in buildings in Rotorua, which is located on an active geothermal area. Here, indoor ambient concentrations can reach 2%, and closer to venting areas, 15% (Durand and Scott, 2003).
- Alban Hills Volcanic District, Italy: Elevated CO2 concentrations have been linked to the death of at least 10 people in the central Italian region of Lazio over the last 20 years (Beaubien et al., 2003). The CO2 asphyxiation of 29 cows in a heavily populated area near Rome in September 1999 prompted soil-gas studies to examine the distribution of the local health risk (Beaubien et al., 2003, Carapezza et al., 2003). The studies found that CO2 concentrations at 1.5 m height above the ground in a residential area on the northwestern flank of the Alban Hills episodically exceeded the occupational threshold of 0.5%. At 0.75 m height, 0.3-0.5% was frequently exceeded (Carapezza et al., 2003), suggesting an increased hazard to children.
Mortality and morbidity incidents associated with volcanic CO2 emissions
|Volcano||Date||Mortality/ Morbidity||Further Detail||Reference|
|Vesuvius||18 April 1906||1 death||Youth with recent history of bronchitis. Effect probably combined with that of ash.||Perret, 1924|
|Nyamuragira (Kituro)||1948?||1 injury||Volcanologist pulled unconscious out of 2 m deep crater||Le Guern et al. (1982)|
|Heimaey, Vestmannaeyjar, Iceland||23 Jan 1973||1 death||5200-5300 people evacuated due to lava and CO2 risk||Thorarinsson, 1979|
|Dieng, Indonesia||20 Feb 1979||~149 deaths
|People caught by a cloud of gas whilst on path||Cronin et al., 2002; SEAN 04:02|
|Lake Monoun, Cameroon||16 Aug 1984||37 deaths
|Lake release. Area residents evacuated||Sigurdsson et al., 1987|
|Lake Nyos, Cameroon||21 Aug 1986||1746 deaths
|Lake release. 4430 others escaped||Othman-Chande, 1987|
|Vulcano, Italy||1980’s||2 deaths||Both were children||Baubron et al., 1990|
|Mammoth Mountain, USA||March 1990||1 injury||Forest service ranger experienced severe symptoms of asphyxia from high CO2 concentrations from soil degassing||Sorey et al., 1998|
|Rabaul, Papua New Guinea||24 June 1990||6 deaths||(no eruption)||Itikarai and Stewart, 1993|
|Hakkoda, Japan||12 July 1997||3 deaths, some hospitalisations||Casualties were members of the Japanese army (no eruption)||Hayakawa, 1999|
|Mammoth Mountain, USA||24 May 1998||1 death||Cross-country skier in snow well||Hill, 2000|
|Alban Hills Volcanic District, Italy||December 2000||1 death||Elderly man died of CO2 asphyxiation after having fallen into an abandoned well||Beaubien et al., 2003; Carapezza et al., 2003|
|Nyiragongo, DR Congo||January 2002||2 injuries||Two women cleaning a church fainted due to CO2 build-up following the eruption||BGVN 27:04|
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