THE HEALTH HAZARDS OF VOLCANIC ASH
A guide for the public
This document has been prepared by the International Volcanic Health Hazard Network (IVHHN), Cities and Volcanoes Commission, GNS Science and the United States Geological Survey (USGS) to promote the safety of those who experience volcanic ashfall. This guide explains the potential health effects of volcanic ash and gives details on how to protect yourself and your family in the event of a volcanic ash fall.
What is volcanic ash?
Volcanic ash is composed of fine particles of fragmented volcanic
rock (less than 2 mm diameter). Volcanic ash is often hot very
close to the volcano but is cool when it falls at greater distances.
It is formed during volcanic explosions, from avalanches of hot
rock that flow down the side of volcanoes, or from red-hot liquid
lava spray. Ash varies in appearance depending upon the type of
volcano and the form of the eruption. Thus, it can range in color
from light grey to black and can vary in size from being like grit
to being as fine as talcum powder. Airborne ash blocks out
sunlight, reducing visibility and sometimes causes complete
darkness during day light.
Large ash deposits can incorporate into existing soils and become the future topsoil of a volcanic region. The fertility of the soils around many volcanoes is due to old ash deposits. This beneficial effect of volcanism outweighs, over time, the hazards.
Eruptions can also generate thunder and lightning from
friction between the fine, airborne particles which can be
localized above the volcano or accompany large ash plumes as
they move downwind from infrequent eruptions, so
fertile volcanic areas are often densely populated.
Freshly fallen ash particles can have acid coatings which may
cause irritation to the lungs and eyes. This acid coating is rapidly
removed by rain, which may then pollute local water supplies.
Acidic ash can also damage vegetation, leading to crop failure.
In most eruptions, volcanic ash causes relatively few health problems, but generates much anxiety. People can be more
fearful of the health hazards of volcanic ash and gases than of the risk of dying from more major hazards, such as pyroclastic
flows. However, ash falls can affect very wide areas around volcanoes and may cause major disruption to normal living.
Medical services can expect an increase in the number of patients
with respiratory and eye symptoms during and after an
ashfall event (see IVHHN guidelines on advice to the medical community).
What are the effects of ash on health?
Effects of ash on health may be divided into several categories:
Respiratory effects, eye symptoms, skin irritation and indirect
In some eruptions, ash particles can be so fine that they are
breathed deep into the lungs. With high exposure, even healthy
individuals will experience chest discomfort with increased
coughing and irritation.
Common acute (short-term) symptoms include:
- Nasal irritation and discharge (runny nose).
- Throat irritation and sore throat, sometimes accompanied by dry coughing.
- People with pre-existing chest complaints may develop severe bronchitic symptoms which last some days beyond
- exposure to ash (for example, hacking cough, production of sputum, wheezing, or shortness of breath).
- Airway irritation for people with asthma or bronchitis; common complaints of people with asthma include
- shortness of breath, wheezing and coughing.
- Breathing becomes uncomfortable.
In rare circumstances, long-term exposure to fine volcanic ash may lead to serious lung diseases. For these diseases to occur, the
ash must be very fine, contain crystalline silica (for the disease silicosis to occur) and the people must be exposed to the ash in
high concentrations over many years. Exposure to crystalline silica in volcanic ash is typically of short duration (days to weeks),
and studies suggest that the recommended exposure limits (similar in most countries) can be exceeded for short periods of
time for the general population.
People suffering from asthma or other lung problems such as bronchitis and emphysema, and severe heart problems are most at risk.
Why are people with chronic lung problems at special risk?
The fine ash particles irritate the airways and cause them to
contract, making breathing more difficult in people who already have
lung problems. The fine dust also causes the lining of the airways to
produce more secretions which can cause people to cough and breathe
more heavily. Asthma sufferers, especially children who may be
heavily exposed to the ash when they play, may suffer bouts of
coughing, tightness of the chest and wheezing. Some people who have never knowingly had asthma before, may experience asthma symptoms following an ash fall, especially if they go outdoors in the ash and over-exert themselves.
What factors affect respiratory symptoms?
The development of respiratory symptoms from the inhalation of volcanic ash depends on a number of factors. These include the
concentration of particles in the air, the proportion of fine particles in the ash, the frequency and duration of exposure, the
presence of crystalline silica and volcanic gases or aerosols mixed with the ash, and meteorological conditions. Existing
health conditions and the use of respiratory protective
equipment will also influence the symptoms experienced.