WILDLAND / VEGETATION FIRES
Fact sheet WHO/254
Charcoal found in Southern African caves indicate that humans were able
to use fire 1.5 million years ago. Since then, the fires managed to escape from the caves
and have regularly swept through vegetation all over the world. Wildfires can be started
both by people and by acts of nature. Whatever the origin, people and animals die, crops
and resources are destroyed, and smoke adversely affects the health of many more people
outside the immediate area of wildfire.
Gas and particle emissions produced as a result
of fires in forests and other vegetation impact the composition of the atmosphere. These
gases and particles interact with those generated by fossil-fuel combustion or other
technological processes, and are major causes of urban air pollution. They also create
ambient pollution in rural areas. When biomass fuel is burnt, the process of combustion is
not complete and pollutants released include particulate matter, carbon monoxide, oxides
of nitrogen, sulphur dioxide, and organic compounds. Once emitted, the pollutants may
undergo transformation processes with physico-chemical changes. Thus, vegetation fires are
major contributors of toxic gaseous and particle air pollutants into the atmosphere. These
fires are also sources of "greenhouse" and reactive gases. All these pollutants
are also emitted into the air when biomass fuels are used.
In developing countries, vegetation fires increase the risk of acute respiratory
infections, a major killer of young children. The health of women is also adversely
affected, as they are already exposed to high levels of air pollution in the home as a
result of spending many hours cooking over non-vented indoor stoves.
Biomass air pollution consists mostly of fine and ultra-fine particulate matter. Fine
air-borne particles (diameters smaller the 2.5 micrometers) have potentially detrimental
health effects because they can penetrate deep into the human lungs and may cause a whole
range of health problems. The WHO Air Quality Guidelines speak of a definite link between
exposure to fine and ultra-fine particles and hospital admissions, visits to emergency and
outpatient departments, and mortality due to respiratory and cardiovascular diseases.
Particulate pollution affects more people globally on a continuing basis than any other
In 1997-98, forest fires in South-east Asia affected some 200 million people in Brunei
Darussalam. Indonesia, Malaysia, the Philippines, Singapore, and Thailand. Massive
movements of population fleeing the fires and smoke added to the emergency, while the
increase in the number of emergency visits to hospitals during the crisis demonstrated its
The comparison of medical data reported during the 1997/1998 forest fire events in
South-east Asia with corresponding data in 1995/1996 revealed the following impact of
smoke on public health which is consistent with our knowledge of the effects of fine
- The number of cases of pneumonia increased 5-25 times in
South-east Kalimantan (Borneo) and 1.5-5 times in South Sumatra.
- The number of outpatient visits with respiratory diseases in
Malaysia increased 2- to 3-fold.
- In September 1997 in Jambi (Sumatra), the number of reported cases
of upper respiratory tract infections was 50% higher than in the previous month.
Health-related consequences of smoke from forest fires in the
Americas have also been documented:
- During the fires in 1997 in Alta Foresta, Brazil, outpatient
visits for respiratory disease increased 20-fold.
- During the 1993 California fires, a 40% increase in asthma and a
30% increase in emergency visits for chronic obstructive pulmonary diseases was recorded.
Causes and consequences
In remote regions, fires are often started by
lightning, but in more populated areas people are the main cause.
- Fires in tropical monsoon forests recur every 1 to 3 years.
- In North America and Eurasia, between 5 and 20 million hectares
(ha) of forest are consumed by uncontrolled fires every year.
- In tropical savannahs, it is estimated that over 300 million
metric tons of vegetative matter burn annually.
Even as recently as 1997-98, forest fires in
South-east Asia caused the evacuation of populations and had serious effects not only on
health but on national economies and security. Such was the emergency that Indonesia
officially requested assistance from the United Nations.
- In Australia's Ash Wednesday Fires of 1983, 75 people died, 2539
homes were destroyed, and 300,000 domestic animals perished. In Côte d'Ivoire during
forest and savannah fires in 1982-83, 100 people died and 12 million ha of land, 40,000 ha
of coffee plantations, and 60,000 ha of cocoa plantations were destroyed. In Mongolia,
steppe and forest fires in 199697, killed 25 people and devasted 10.7 million ha of land.
- In Kalimantan (Borneo), during the 1982-83 El Nifio drought, fires
destroyed more than 5 million ha of forest and agricultural land, while in 1997-98, also
in Indonesia, fires on the islands of Sumatra and Borneo consumed 9 million ha of
vegetation. During the drought in the former USSR in 1987, some 14.5 million ha of forest
were destroyed by fire.
- In the summer of 2000, due to unusually dry, hot weather,
wildfires have been raging all across the western United States, from Arizona up to the
Canadian border. The National Interagency Fire Center in Idaho, USA, reported that the 25
largest fires burning in Montana, USA, represented almost half of the 964,721 acres
burning across the West of the United States, in what has been described as the nation's
worst wildfire season in half a century.
- Forests everywhere have been and are being threatened by
uncontrolled degradation and conversion to other types of land uses, influenced mainly by
increasing agricultural expansion, and environmental mismanagement, including lack of
adequate fire control, excessive logging, and overgrazing.
- Every year, 1 to 2 billion metric tons of plant mass are burned in
the process of land clearing. It is estimated that between 800 and 1,200 million metric
tons of agricultural residuals are burned annually, making this practice a major source of
atmospheric pollution, mainly in the tropics.
- In prescribed fires for forest management in North America, 2
million ha of land are burned annually and 40-130 million ha annually in Australia.
The figure indicates the average area burned
annually in the various regions of the world
During acute smoke emergencies, mitigating measures that can be
- remaining indoors
- reducing physical activity and refraining from smoking
- using air cleaners
- using gas masks and respirators
- evacuating susceptible people to emergency shelters
Schools, childcare centres, retirement homes, nursing homes,
hospitals, and hospices should provide air-conditioned rooms for susceptible individuals.
Air-conditioned emergency shelters with adequate particle filtration should be located
inside large commercial buildings, educational facilities, or shopping malls.
WHO has issued comprehensive guidelines for
governments and responsible authorities on actions to be taken when their population is
exposed to smoke from fires. WHO's Health Guidelines for Vegetation Fire Events gives
information on vegetation fires at the global, regional, and national levels obtained by
remote sensing techniques, on the characteristics of the sources' extent and on the
pollutants being released.
The Guidelines examine acute and chronic health effects of air pollution due to biomass
burning, advice on effective public communications and mitigation measures, and guidance
for assessing the health impacts of vegetation fires. They also provide measures on how to
reduce the burden of mortality and preventable disability suffered particularly by the
poor, and on the development and implementation of an early warning air pollution system.
Early warning systems for fire and atmospheric pollution are essential components of fire
and smoke management, and are based on space, ground, and climate monitoring, as well as
modelling. The use of "fire-weather" forecasts and assessment of vegetation
dryness may also be included. Air quality monitoring should be conducted on a regular
basis in major cities and other populated areas likely to be affected by vegetation fires
and should include information for public health warnings. Monitoring stations in rural
areas should provide background information on particulate concentration, with the
concentration of particles having diameters below 2.5 micrometers measured by a
ground-based network of air samplers.
Accompanying the Guidelines are background papers and a teachers' guide. The
recommendations and texts were drafted at a meeting of experts convened by the United
Nations Environmental Programme, the World Meteorological Organization, and WHO held in
Lima, Peru, in October 1998.
The papers presented at this meeting were published separately as Health Guidelines for
Vegetation Fire Events - Background Papers. Another document - Health Guidelines for
Vegetation Fire Events - Teachers' Guide compiles educational material for use in training
These are the first WHO publications providing advice and guidance on the management of
vegetation fire events. All three publications form a set, which can be useful in handling
this important public health issue in a practical manner. They are also available on
N.B. - The Mediterranean Council for Burns and Fires
Disasters is the official WHO Collaborating Centre for Prevention and Treatment of Burns
and Fire Disasters. See also the Annals: 12: 236, 1999.