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Heavy ash fall may result in the collapse of roofs under the weight of ash and high levels of respirable ash in the air (ash particles less than 10 microns in diameter). The collapse of roofs can be deadly for people within buildings, but falling ash is not yet known to result in serious injury or disease from inhalation. Ash and coarser particles inhaled from within a hot, dense pyroclastic flow or surge, however, almost always results in death from burns or asphyxiation. People exposed to ash fall and subsequent ash-filled air commonly experience various eye, nose, and throat symptoms. Based on historical eruptions, short-term exposures to ash, however, are not known to pose a significant health hazard. Long-term health effects of volcanic ash have not yet been demonstrated.

People should avoid unnecessary exposure to ash and wear an effective face mask when outside to reduce inhalation of ash particles. Patients with chronic bronchitis, emphysema, and asthma should take special precaution to avoid exposure to ash particles and be aware that the use of any respirator other than single-use (disposable) respirator may cause additional cardio-pulmonary stress.

Medical services can expect an increase number of patients with respiratory and eye symptoms during and after ash fall. People will generally be very concerned about the effects of ash, and questions usually arise about the content of the ash, particularly regarding the minerals quartz, cristobalite, or tridymite. These are free crystalline silica known to cause silicosis, a disabling and potential fatal lung disease typically found in miners and quarry workers exposed to high concentrations of siliceous dust over long periods of time. Exposure to respirable-sized free crystalline silica from most ash falls are typically of short duration (days to weeks), and data suggests that the recommended respirable exposure limit of 50 micrograms/m3 of air can be exceeded for short periods of times for the general population. See chronic medical aspects below.

Refer also to 'Health Hazards of Volcanic Ash - A Guide for the Public' on the International Volcanic Health Hazard Network (IVHHN) website. IVHHN was created in February 2003 with the goal to determine the health effects of volcanic emissions, including ash. IVHHN consists of experts and correspondents working in diverse scientific disciplines, such as volcanology, epideminology, toxicology, public health and physical chemistry. A major goal of IVHHN is to produce guidelines and protocols on volcanic health hazard management, which will be ratified by the International Association of Volcanology and Chemistry of the Earth's Interior (IAVCEI) and disseminated through volcano observatories to the public, scientists, local health practitioners and emergency managers. According to the IVHHN Web site, recommended safety guidelines for dealing with volcanic ash are being written.

Common respiratory symptoms

Potential respiratory symptoms from the inhalation of volcanic ash depend on a number of factors, including airborne concentration of total suspended particles, proportion of respirable particles in the ash (less than 10 microns in diameter), frequency and duration of exposure, presence of free crystalline silica and volcanic gases or aerosols mixed with the ash, meteorological conditions, and host factors (existing health conditions and the propensity of those exposed to incur respiratory problems), and the use of respiratory protective equipment.

Acute respiratory symptoms commonly reported by people during and after ash falls (Blong, 1984, p. 83-91):

These short-term effects are not considered harmful for people without existing respiratory conditions. People should take steps to minimize their exposure to breathing ash (see mitigation measures).

Eye symptoms 

Because volcanic ash is abrasive, people typically experience eye discomfort or irritation during and after ash fall, especially among those that use contact lenses. Commonly reported symptoms of ash include:

Individuals with Dry Eye Syndrome may also experience ailments due to the presence of ash. No chronic effects of ash on eyes have been noted. Following the 18 May 1980 eruption of Mount St. Helens, a "telephone survey conducted in several ash-affected communities suggested that 4-8 percent of the population experienced eye irritation but that only one in ten of these sought medical advice" (Blong, 1984, p. 90).

Skin irritation

Minor skin irritations are sometimes reported following ashfall. Following the 18 May 1980 eruption of Mount St. Helens, however, physicians interviewed in Yakima, Washington, located 120 km east of the volcano, reported no increase in chronic skin irritations.

Mechanical effects || Roof collapse || Automobile accidents ||

Roof collapses

The weight of volcanic ash on roofs can lead to their collapse, especially if the ash is wet and the building is not designed to support a heavy load. When a roof collapses under the strain of ash, people suffer direct injury or be killed. See effects of ash on roofs.

Automobile accidents

Driving in ashy conditions may be difficult or impossible due to slippery road conditions or poor visibility, resulting in automobile accidents that cause injuries. See Roads and Highways for driving conditions and safety strategies during and after an ashfall.

Chronic medical aspects || Crystalline silica || Free silica in ash || More information ||

Free crystalline silica in volcanic ash

Volcanic ash may contain varying proportions of free crystalline silica (silicon dioxide, SiO2) in the form of quartz, cristobalite, or tridymite minerals. The minerals are described as "free" silica because the silicon dioxide compound is not attached to another element to create a new mineral; for example, magnesium to form the mineral olivine. Exposure to respirable particles of free crystalline silica can lead to silicosis, a disease resulting in scarring of the lungs and impairment of their function.

Although there have been no documented cases of silicosis attributed to free crystalline silica in volcanic ash from eruptions in the past few decades, detailed studies for lengthy periods of time necessary to determine the potential long-term effects of ash are notably lacking.

The U.S. National Institute for Occupational Safety and Health (NIOSH) recommended in 1974 the exposure to respirable free silica be limited to 50 micrograms/m3 of air for workers up to a 10-hour work day, 40-hour work week over a lifetime. Historical data suggests that this exposure has been exceeded for brief periods of time (hours to days) in certain locations, but not over the working lifetime of people (2-3 decades).

Proportion of free crystalline silica in volcanic ash

Mount St. Helens, USA
Eruption column rises from Mount St. Helens, USAVolcanic ash from the 9-hour explosive eruption on 18 May 1980 that fell across eastern Washington consisted of 3 to 7 percent free silica (cristobalite and quartz) in the sub-10 micron size fraction.

At this proportion of free silica, the NIOSH-recommended standard would be exceeded if exposure to respirable ash was regularly greater than 0.8 to 1.0 milligram/m3 of air (Baxter and others., 1981).

Exposures to the ash and free silica by the general population in the affected communities of eastern Washington were of limited duration, and silicosis was not considered a potential threat to the general population. People who worked in areas of high concentrations of respirable ash, for example loggers removing timber near the volcano or agricultural workers in central Washington, were advised to take protective action. (See Bulletin #13, Research into the free crystalline silica content of Mount St. Helens ash, issued by the Mount St. Helens Technical Information Network.)

Media caution: Within days of the 1980 eruption, there were reports in the media that the volcanic ash from Mount St. Helens contained 60 percent or more free crystalline silica—far greater than the actual 3 to 7 percent of the respirable size fraction. This misinformation may have occurred because chemical analysis of ash and lava is commonly reported in terms of the percentage of total silica content, ranging from about 45 to 77 percent; the analysis includes that which is chemically combined with other elements, not free silica.

Soufriere Hills Volcano, Montserrat
Ash billows from Soufriere Hills lava dome, MontserratThe extended eruption of a lava dome at Soufriere Hills Volcano that began in 1995 generated large amounts of fine ash by (1) explosive events from the dome; and (2) frequent collapse of unstable parts of the growing dome that generated pyroclastic flows and associated plumes of ash. A detailed study of ash from both types of events determined that the sub-10 micron fraction of ash from the pyroclastic flows consisted of 10-24 percent crystalline silica, the highest yet documented for a historical eruption (Baxter and others, 1999). In contrast, the sub-10 micron fraction of ash from the explosive events consisted of 3-6 percent crystalline silica. The free silica minerals are produced within the lava dome over a period of many days or weeks.

Monitoring of the concentration of airborne respirable dust and ash around the volcano beginning in August 1997 showed that concentrations of ash have regularly exceeded 50 micrograms/m3 per 24-hour rolling average in areas subject to frequent ash fall. The exposures to cristobalite sometimes reached the 0.05 mg/m3 averaged over an 8-hour workday. Also, the monitoring consistently showed increased concentrations of airborne dust whenever there was human activity.

This study raises concern that exposure to long-lived eruptions of lava domes that produce persistent ash fall over many years may result in adverse health effects in affected communities.

More information

Crystalline silica health and safety topic, U.S. Department of Labor, Occupational Safety & Health Administration.

A Guide to working safely with silica, U.S. Department of Labor, Occupational Safety & Health Administration.

Historical eruptions: examples of effects of ash on human health

Principal health effects caused by ash fall from selected historical eruptions

Volcano; Nation; eruption year Deaths Injury Eyes Respiratory Nasal
Mount St. Helens; 1980 yes yes  yes
El Chichon; Mexico; 1982 yes, by roof collapse yes yes  
Mount Pinatubo; Philippines 1991 yes, by roof collapse
Rabaul; Papua New Guinea; 1994 yes, by asphyxiation
Usu Volcano; Japan; 1994 yes, by asphyxiation
Fogo; Cape Verde Islands; 1995 yes
Cerro Negro; Nicaragua; 199? yes
Etna; Italy; 1999 yes
Mt. Cameroon; Cameroon; 1999 yes yes
Pacaya; Guatemala; 1998 yes yes
Telica; Nicaragua; 1999 yes yes yes

Ruapehu, New Zealand—Respiratory effects

The 1995-96 eruption of Mount Ruapehu in New Zealand resulted in several ash falls on many communities, but none received more than a few millimeters of ash. It was estimated that 20 percent by weight was less than 30 microns in diameter. An increase of bronchitis was detected even with such a small amount of ash and the relatively low respirable portion. No other respiratory diseases were detected in the affected areas, and researchers found no evidence for exacerbation of asthma in children living in the ash fall areas (Johnston and Becker, 2001).

Mitigation measures || General public || Children || Overview table ||

People everywhere quickly develop simple methods for protecting themselves from ash fall and the billowing ash stirred up by wind and human activities. The basic strategy is to avoid unnecessary exposure to airborne ash and wear an appropriate and safe facemask when exposed to ash, especially during clean-up operations.

People are rarely evacuated from an area because ash is endangering human health. People with respiratory disease or symptoms, however, may elect on their own to leave an area of high exposure or heavy ash fall. If concentrations of respirable free crystalline silica in the ash exceed the NIOSH-recommended limit of 50 micrograms/m3 for an extended period of time (for example, months to years), the risk of silicosis should not be ignored.

Precautions for general public and public-service workers

  • Wear protective clothing and high-efficiency dust masks (the U.S. National Institute of Occupational Safety and Health has approved certain brands of masks). These masks and clothing should be available and easily accessible in preparation for and during volcano-related emergencies.
  • If no approved mask is available, a fabric mask improvised from handkerchiefs, cloth, or clothing will filter out the larger ash particles which may contribute to throat and eye irritation. Dampening the fabric with water will improve its effectiveness.
  • Patients with chronic bronchitis, emphysema, and asthma are advised to stay inside and avoid unnecessary exposure to ash.
  • Handle the ash in open, well-ventilated areas, and wet the dust whenever possible to prevent its movement.
  • In fine-ash environments, wear goggles or corrective eyeglasses instead of contact lenses to protect eyes from irritation.
  • Keep all doors closed when there is a heavy accumulation of ash.
  • Personnel not essential to the emergency should be kept inside and made to strictly observe all safety precautions during cleanup.
  • Remember that vehicular and industrial accidents are more likely to occur because of reduced visibility. Keep a proper distance between vehicles when driving.

Modified from, FEMA, 1984


Precautions for children

Children face the same hazards from the suspension of ash as other age groups, but their exposure may be increased because they are physically smaller and are less likely to adopt reasonable, prudent, preventive measures to avoid unnecessary exposure to ash. After the ash fall from the 1980 eruption of Mount St. Helens, the following recommendations were offered to the public by the Mount St. Helens Technical Information Network:

  • Keep children indoors when ash is visible indoors.
  • Children should be advised against strenuous play or running when as is in the air, since exertion leads to heavier breathing, drawing small particles more deeply into the lungs.
  • Communities in heavy ash fall areas may wish to organize day-care programs to reduce the economic burden of working parents.
  • If children must be outdoors when ash is present in the air, they should wear a mask, preferably one approved by NIOSH. Many masks, however, are designed to fit adults rather than children.
  • Small children may at times swallow ash, and evidence suggests that ingestion of ash is not a hazard to the health of children and adults.
  • Children should be prevented from playing in areas where ash is deep on the ground or piled up, especially if they are likely to roll in the ash.
  • More frequent cleaning of home interior areas where children play will minimize the amount of indoor ash exposure in areas of heavy past or future ash falls.

Modified from, Mount St. Helens Technical Information Network (Bulletin 14), 1980

Principal health effects of ash and main preventive measures (adapted from Baxter and others, 1986)

Consequence Health effect Monitoring Preventive measure
Inhalation of ash less than 10 microns in diameter Exacerbation of pre-existing lung disease Monitor total suspended particulate (TSP)

Monitor ash particles <10 micron in diameter

Wear high-efficiency masks

Protect home and offices from ash infiltration

Inhalation of free silica in volcanic ash Silicosis—chronic silicosis is a fibrous (scarring) reaction of the lungs caused by inhalation of crystalline silica Determine free silica content of respirable ash

Monitor exposure in high exposure individuals and jobs

Respiratory protective equipment
Ocular (eyes)
Foreign bodies in eyes Conjunctivitis, corneal abrasions Monitor wind direction and ash production for early warning to people downwind Goggles for heavy exposure
Roof collapse and ashfalls from roofs Trauma, including death Prevent excessive accumulation of ash on roofs
Automobile accidents from slippery roads and poor visibility Trauma, including death Monitor areas that will receive ash fall and issue public announcements regarding expected conditions and road closures Traffic control

Pre-eruption notification of what to do during an ash fall


Baxter, P.J., 1999, Impacts of eruptions on human health: In H. Siggurdson (ed.), Encyclopaedia of Volcanoes, Academic Press, New York, p.1035-1043.

Baxter, P.J., Ing, R., Falk, H., French, J., Stein, G.F., Bernstein, R.S., Merchant, J.A., and Allard, J., 1981, Mount St. Helens Eruptions, May 18 to June 12, 1980: an overview of the acute health impact: Journal of the American Medical Association, v. 246, n. 22, p. 2585-2589.

Baxter, P.J., Bernstein, R.S., and Buist, A.S., 1986, Health effects of volcanoes: an approach to evaluating the health effects of an environmental hazard: American Journal of Public Health, 1986, 76 (Supplement), p. 84-90.

Baxter, P.J., Bonadonna, C., Dupree, R., Hards, V.L., Kohn, S.C., Murphy, M.D., Nichols, A., Nicholson, R.A., Norton, G., Searl, A., Sparks, A.J., and Vickers, B.P., 1999, Cristobalite in volcanic ash of the Soufriere Hills Volcano, Montserrat, British West Indies: Science, v. 283, p. 1142-1145.

Blong, R.J., 1984, Volcanic hazards: a sourcebook on the effects of eruptions: Academic Press, Australia, 424 p.

Bradshaw, L., Fishwick, D., Kemp, T., Lewis, S., Rains, N., Slater, T., Pearce, N., and Crane, J., 1997, Under the volcano: fire, ash and asthma: New Zealand Medical Journal, v. 110, p. 90-91.

Hickling, J., Weinstein, P., and Woodward, A., 1999, Acute health effects of the Mount Ruapheu (New Zealand) volcanic eruption of June 1996: International Journal of Environmental Health Research, v. 9, p. 97-107.

Johnston, D. and Becker, J., 2001, Volcanic ash review—Part 1: Impacts on lifelines services and collection/disposal issues: Auckland Regional Council Technical Publication No. 44, 50 p. (see online reference).

Ronan, K.R., 1997, The effects of a "benign" disaster: symptoms of post-traumatic stress in children following a series of volcanic eruptions: Australasian Journal of Disaster and Trauma Studies. (http://www.massey.ac.nz/~trauma/issues/1997-1/ronan1.htm).

Yano, E., Higashi, H., Nishii, S., Maeda, K., and Koizumi, A., 1990, Health Effects of Volcanic Ash: A repeat Study: Archives of Environmental Health, v. 45, n. 6, p. 367-373.