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Vegetation fires

Charcoal found in Southern African caves indicate that humans have been 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.

Health impact

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 airborne particles (diameters smaller then 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 ultrafine 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 air pollutant.

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 severity.

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 particles.

  • 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 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, 60 000 ha of cocoa plantations were destroyed. In Mongolia, steppe and forest fires in 1996-97, killed 25 people and devastated 10.7 million ha of land.
  • In Kalimantan (Borneo), during the 1982-83 El Niño 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 hectares 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 hectares of land are burned annually and a 40-130 million ha annually in Australia.

Mitigation measures

During acute smoke emergencies, mitigating measures that can be taken include:

  • 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's response

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 micrometer 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 courses.

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 CD-ROM.


Sources: US Department of Health; The World Health Organization


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