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Biomass fuels and health

Kirk R. Smith and Jamuna Ramakrishna



This paper examines the health effects of indoor smoke produced by the burning of biomass in the households of developing countries. Although there are no specific studies comparing the health status of a population before and after the removal of smoke, enough information is available to draw some conclusions. The smoke emissions produced by the burning of biomass are described. Studies of the health impact of the smoke and its pollutants are reviewed. Recommendations are made for improving health conditions, assuming that a majority of the world's households will continue to burn biomass.


Air pollution can be measured from

· Fuel use, which provides a general indicator because pollutant release is roughly proportional to fuel use,

· Emissions monitoring, which is more accurate than measuring fuel use,

· Exposure monitoring, which takes into account concentration and duration and is usually the best and most practical measure for populations of any size, and

· Pollutant dose, which is the best indication but is relatively expensive to measure.

Smoke emissions are affected by fuel quality and the degree of incomplete combustion. When all of the organic matter in biomass is burned, essentially only carbon dioxide and water are emitted. The pollutants are not in the fuel; they are created during combustion. In small, simple domestic stoves, it is very difficult to achieve complete combustion.

The pollutants of concern in biomass smoke are suspended particulates, carbon monoxide, and hydrocarbons. The total suspended particulates (TSP) include inorganic carbon and a range of several hundred hydrocarbons, many of which can affect health. These toxic hydrocarbons, which exist in both gaseous and particulate form, include Benzo[a]pyrene (BaP) (the most studied of carcinogenic chemicals), acenaphthylene, and formaldehyde. Particulates from biomass combustion have toxicities that are similar to those of the particulates in the smoke from coal or diesel fuel.

A comparison of the emissions of common pollutants from several fuels indicates that small-scale biomass combustion produces higher emissions than fossil fuels. However, this does not prove that biomass combustion produces unacceptable pollution levels. Indoor concentrations are affected by such factors as fuelling rate, emission factor, ventilation rate, and room volume. Estimates of exposure include temporal and spatial factors. When air samplers are worn by cooks, a wide variation in exposures to common pollutants and BaP is observed. This is due to local weather and ventilation conditions. Generally, studies are inconclusive about the health impacts of exposure to indoor smoke because of the lack of data, inconsistent research techniques, the vast number of toxic pollutants to be studied, and the lack of comparative analysis with other pollutant exposures (for example, cigarette smoke). What seems clear is that a majority of the world's population in rural areas receives exposures and doses of major pollutants that exceed the levels experienced by their urban neighbours.

Health Risks

Research on the health impact of the burning of biomass shows a link between domestic smoke and poor health. Risks can be divided into noncancerous (respiratory abnormalities and acute respiratory infections) and cancerous risks.

Research in India, Nepal, and Papua New Guinea indicate that there is a link between respiratory abnormalities and symptoms and biomass smoke. More than 6 million children die each year from acute respiratory infections (ARI), and air pollution is a risk factor in ARI morbidity. In South Africa, a majority of respiratory problems in infants can be related to daily exposure to smoke. In Nepal, there is a positive correlation between ARI episodes and the amount of time that children spent near the fireplace. However, the suspected relationship between exposure to biomass smoke and cancer has not been established despite the large quantities of suspected carcinogens in some biomass smoke.

Studies of Specific Pollutants -Exposure to fossil-fuel combusion and cigarette smoke allows the study of two pollutants (carbon monoxide and particulates). Acute exposure to carbon monoxide can result in coma and death, and moderate short-term exposure can result in dizziness, headaches, and nausea. The long-term effects of lower exposures are not clear, but they are not likely to cause mortality although there is a growing link with impaired fetal development. Carbon monoxide may also increase the carcinogenic effects of other air pollutants. In addition, risk factors (for example, oxygen deprivation) increase sensitivity to exposure to carbon monoxide. In Guatemala, carbon monoxide exposure has a greater effect on people at higher elevations.

It is difficult to interpret the data on the impact of particulate exposure. It is easier to determine the health effects of acute exposure because there are more data than for chronic exposure. Acute exposures to fossil-fuel emissions show the joint effect of particulates and sulfur oxides (wood has a low concentration of sulfur oxides). Difficulties in controlling for compounding factors (for example, smoking and socioeconomic status) make many studies suspect. Nonetheless, there is reasonable certainty that acute exposures to the particulate pollution that is typical in rural kitchens of the developing world can increase both morbidity and mortality.

Polycyclic aromatic hydrocarbons (PAM) are organic compounds that are found in biomass smoke and are both mutagenic and carcinogenic. Although no link has been established between cancer and these compounds, there is much evidence of its carcinogenic potential.

Lessening the Impact of the Burning of Biomass

Despite the dangers of exposure to biomass smoke, hundreds of millions of households will continue to burn biomass. The use of cleaner fuels, improved stoves, and better ventilation could lessen the negative effects of the burning of biomass. Some changes in behaviour could also help reduce exposure.

Cleaner Fuels -Some species of wood burn more cleanly than others, and dry wood burns more efficiently. Upgrading the biomass fuel can result in more dramatic improvements. Charcoal manufacturing creates most of the emissions of particulates and carbon monoxide. Total household exposure is lower, but overall pollution is the same or higher. Dung can be upgraded by anaerobic digestion, which yields biogas and fertilizer. Biogas emissions are similar to the emissions from natural gas. Vegetable oils can also be upgraded, and in some remote locations, they are economical as fuels. Alcohol fuels, derived from the fermentation of biomass, are thought to be clean burning.

Improved Stoves and Better Ventilation - There are many designs for stoves that promote higher thermal efficiencies and lower emission factors; however, global dissemination of improved stoves has been frustratingly slow despite many isolated successes. Problems that arise in the field but have not been considered in the laboratory include

· Lack of flexibility in variety of fuels and choice of cooking methods,

· Limited capability to accommodate a variety of utensils,

· The large area occupied by the stove in homes where space is limited, and in some cases,

· Continued high exposure to smoke because the stoves were not installed correctly, maintained adequately, or operated properly.

The thermal efficiency of stoves can be improved by controlling the airflow to increase the residence time of the flue gases. The efficiency of single-pothole stoves has been improved by using a grate, a reflective surface, a water jacket, and insulation.

Despite a lack of empirical data, improved ventilation is probably the least expensive short-term way to reduce smoke exposure. Three ways to improve ventilation are minor changes in the ventilation of existing structures, relocation of the kitchen, and major redesign of the kitchen.

Behaviour Change. -Changes in behaviour can help reduce the impact of exposure to biomass smoke without new technologies. These changes include moving the stove outdoors or to a verandah and keeping pregnant women and young children out of the cooking area as much as possible.

Costs of Exposure Control

Generally, the three categories of policy tools that governments use to address pollution problems are

· Information (for example, government-sponsored R&D programs and rural education),

· The establishment and enforcement of ambient and emissions standards (generally, traditional regulatory approaches are ill-suited for domestic smoke pollution, but standards related to house and stove design may be relevant), and

· Economic tools that include severance taxes and subsidies (subsidies can be dangerous if poorly used because they create distortions and are expensive).

Cost-benefit analyses should include the costs of an increase in smoke exposure or the benefits of a decrease. The benefits of this type of pollution-control program might include decreases in medical care and in occupational disruption minus foregone benefits, such as the value of smoke as a form of thatch preservative. In the case of fuel savings, these benefits can be added to the benefits of reduced deforestation.

A rough analysis of the net present value (NPV) of the benefits of reduced exposure to domestic smoke selected as its benefit the reduction of chronic bronchitis in 10% of the population. Even without including the benefits of reduced ARI in children, decreased medical costs, decreased fuel costs, and increased household cleanliness, NPVs of more than 100 USD for most discount rates and degrees of impairment from exposure were found. This is more than enough to justify an improved cookstove program and investments in better ventilation and fuel.