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Oleh: Dawn Berkelaar
Terbit: 20 Oktober 2004

The majority of people in developing countries cook over open fires. In many countries in sub-Saharan Africa, over 90% of the population cook their food with biomass (plant material). The smoke from such fires can be a nuisance, and it can also lead to severe health problems. The Intermediate Technology Development Group (ITDG) has issued a document called “Smoke—the Killer in the Kitchen” that shares statistics on indoor air pollution caused by burning solid fuels like wood, charcoal, and crop residues. The document also suggests steps that can be taken to minimize health risks. Unless otherwise indicated, the information below is summarized from the ITDG document (Warwick and Doig, 2003. Download from - now “Practical Action” –

Dangers from Wood Smoke

Smoke from burning biomass fuels inside the home is the fourth leading cause of death and disease in the world’s poorest countries. The indoor air pollution that results from burning solid fuels kills more than 1.6 million people, mostly women and children, each year. This works out to more than three people per minute. It is a higher death toll than that caused by malaria!

The poor, especially poor women and children, are most affected by indoor air pollution. Of the 1.6 million people who die each year because of indoor air pollution, 56% are children under five years of age. Most of these children die from acute lower respiratory infections. Young children tend to spend most of their time with their mothers, meaning they are near the cooking fire a lot. The ITDG document states, “The impact this length of exposure has on small children is exacerbated by a number of factors. Children’s airways are smaller, therefore more susceptible to inflammation. Their lungs are not fully developed until they are teenagers, so they breathe faster. Also, their immune systems are not fully developed—a process that may be further delayed by malnutrition.”

According to the ITDG document, the United Nations Development Programme claims that “the use of poorly ventilated, inefficient stoves ‘can have the same adverse health impacts as smoking two packs of cigarettes a day.’” Throughout the developing world, poor people are exposed in their own homes to levels of pollutants that are 100 times higher than accepted safety levels! (see Figure 1, next page)

In December 1952, a smoke-laden fog called The Great Smog hung over London for six days. Deaths that resulted were estimated at 4,000. Deaths from bronchitis and pneumonia increased by seven times. Yet in developing countries, women and children are exposed to similar levels of particulate pollution for up to seven hours a day, every day.

The ITDG document includes a quote from a review by Professor Kirk Smith from the University of California: “Biomass fuel smoke contains significant quantities of several pollutants for which many countries have set outdoor air quality standards— for example, carbon monoxide, particles, hydrocarbons, and nitrogen oxides.”

Indoor air pollution can cause illnesses including acute lower respiratory infection, such as pneumonia (35.7% of cases caused by exposure to smoke from solid fuels); diseases such as chronic bronchitis causing “progressive and incompletely reversible obstruction of the airflow”; lung cancer (in China and India, around two thirds of women with lung cancer are non-smokers); tuberculosis; asthma; and cataracts. Recently there have been many health studies demonstrating a link between indoor air pollution and illness or death.

Figure 1: Comparison of typical levels of particles less than 10 micrometers in size in developing country homes (represented by gray and black boxes in middle and on right) with WHO guidelines (small gray box on left). Figure used with permission from ITDG.
Figure 1: Comparison of typical levels of particles less than 10 micrometers in size in developing country homes (represented by gray and black boxes in middle and on right) with WHO guidelines (small gray box on left). Figure used with permission from ITDG.

Even in countries whose economies are in transition, people are reverting back to the use of solid biomass fuels. With economic downturns, infrastructures sometimes collapse and people can lose access to the power grid and to cleaner fuels. In Tajikistan, where just such a thing has happened, there was a 35% increase in cases of acute respiratory infection between 1991 and 2000, largely because of burning wood indoors.

In addition to suffering from exposure to smoke, women carry the burden of having to find firewood or other fuel. Estimates for the time they spend collecting fuel range from two to twenty hours per week!

A few years ago we learned of a study by Dr. Wayne Bragg and Dr. Gene Shultz, Professor Emeritus at Washington University in St. Louis. We contacted Dr. Shultz to find out more information. Dr. Shultz and Dr. Bragg worked with local colleagues in northeast Brazil and central Mexico. They investigated indoor air pollution in rural households, caused mainly by burning wood and other household fuels in cook stoves. They measured the concentrations of very fine particulates (that are associated with certain respiratory and eye diseases) in smoky atmospheres typical of the homes of the rural poor.

Dr. Shultz told ECHO, “Instead of measuring smoke particulates at fixed locations in the home, we were interested in the particulate burden that a typical woman might breath [while conducting] a task such as preparation of a meal, using her own cooking equipment in her own kitchen, and cooking her own foods. Therefore, we asked each cook to wear a small belt-mounted battery-operated air pump that sucks room air at approximately the rate of breathing, through a flexible tube, with the opening located on her shoulder. The air was passed through a micro filter system to entrap fine particles from the room air—particles that are usually deeply respired into the lungs.

“The cook would wear this equipment during preparation of a typical meal, following her normal patterns of behavior. At times she would be hovering over a smoky stove. At other times she might be on the other side of the room cutting up food. She might even walk outside to throw something to the chickens. We did not interfere with her normal patterns of behavior. She wore the equipment just for the length of time required to complete the preparation of the meal.

“We were interested in measuring the weight of very fine particles that she is likely to collect in her lungs during meal preparation. The particles entrapped on the micro filters were weighed by special equipment available at a world-class air pollution lab at the University of Sao Paulo, Brazil.

“As part of our program of research, we worked with a team of indigenous researchers who carried out a survey of fuel usage patterns. Typically, they would interview the cook and other members of the household in their own language to better understand the types of wood that were preferred and why, the types of wood that the cooks actually used and why, etc. In addition, the interviewers asked questions to all the members of the household about the incidence of certain smoke-related illnesses in their homes (for example, respiratory illnesses and cataracts).

“In brief, we found a great diversity of results. Some women were able to minimize the smoke in their homes. Usually these were younger women who could walk the longer distances to gain access to less-smoky wood species. Older women often had to accept the more smoky species nearby that had been passed over by those who could walk farther. “Most women were relatively unaware of the hazards of smoke. But, remarkably, some had figured it out on their own and had successfully enlisted their husbands with handy skills, in the tasks of cutting down on household air pollution by fixing the stove and chimney or by learning to use ventilation. These women with “exemplary” kitchens were definitely in the minority. We were discouraged to find that most men were unwilling to help their wives. It was [the wives’] problem, not the men’s problem. Also, knowledge [about] the hazards of smoke and how to mitigate them did not diffuse easily from one family to another, even when the families were closely related and in daily touch. Of course, in many cases we were dealing with those who were so poor that they had to scramble to survive. Their priorities did not include household smoke or chimney repair.

“In Brazil we found many examples of chimney flues that exited the kitchen horizontally, or nearly horizontally, and never turned up vertically outside the kitchen wall. Thus no draft was being generated, and so no smoke was being eliminated from the kitchen. There was widespread ignorance of this simple principle in several villages, even though a very few women understood this problem and managed to avoid it. “Clearly, the problem is at least as much a social problem as a technical problem, and we are of the opinion that it is best studied and solved by interdisciplinary teams and methods. “Although we aren’t medics, we were aware of a high incidence of respiratory problems in children, women and elderly, even in the case of non-smokers. There was also a high incidence of cataracts in the elderly, men as well as women, since elderly men spend a lot of their time indoors. Kitchen smoke isn’t confined to the kitchen. It migrates throughout the houses we saw. No one escapes it.”

Switching to a Cleaner Fuel

There are ways to reduce people’s exposure to such high levels of smoke. Switching to a cleaner fuel is a good option for the relatively few people who can afford it. Examples of such fuels include liquid petroleum gas, kerosene, or biogas. Biogas is made from dung and other organic waste materials. It is very effective and results in a gaseous, clean fuel. In Asia, the introduction of biogas is proving very successful (with 120,000 bio-gasifiers in Nepal alone), but it is harder to introduce biogas in Africa for cultural reasons.

There are ways to reduce people’s exposure to such high
levels of smoke. Switching to a cleaner fuel is a good option for the relatively few people who can afford it. Examples of such fuels include liquid petroleum gas, kerosene, or biogas. Biogas is made from dung and other organic waste materials. It is very effective and results in a gaseous, clean fuel. In Asia, the introduction of biogas is proving very successful (with 120,000 bio-gasifiers in Nepal alone), but it is harder to introduce biogas in Africa for cultural reasons.

Removing Smoke from the House

Another good option for reducing exposure to high levels of smoke is to use well-designed chimney stoves or to use smoke hoods. These can reduce indoor air pollution by up to 80%.

Smoke hoods and improved ventilation, introduced by an ITDG project in Kenya, resulted in a nearly 80% reduction of particulate and carbon monoxide pollution in homes. Unlike chimneys, smoke hoods are freestanding and are not attached to the stove.

Enlarging eave spaces in a traditional house in Kenya resulted in a 60% reduction of respirable particulates. Enlarging windows did little to reduce air pollution, but windows are necessary in houses that have smoke hoods, so that air can flow through the house.

[Ed (MLP): I have read of unexpected side effects from removing the smoke too. Examples include loss of protection from insects that harm thatched roofing material or grains stored on the ceiling, or from insects that cause human illness. I wonder if this might be true of the insect in the Andes Mountains that causes Chagas disease. It drops from the ceiling at night onto the bed and bites a person. Years later the individual might experience heart disease as a result.]

Improved Stoves

Of the energy from a kilogram of wood that is burned in a three-stone wood-fired stove, about 18% of the energy goes into the pot, 8% into the smoke, and 74% into wasted heat. Not surprisingly, most work on stove design has been done to improve energy efficiency and to save fuel. However, these modifications are not necessarily effective at reducing indoor air pollution. In fact, according to the ITDG document, “Studies have shown a small decrease [in emissions] from certain improved stoves, although many stoves in fact increase emissions if air flow to the fuel is restricted.”

Stoves that incorporate a flue or chimney are often very effective at reducing the amount of smoke in a house. Two stoves with these features are the rocket stove and the Ecostove, both of which are being used in Central America (see below for more details about these). However, there are potential problems with chimney stoves. In order to work, they need to be properly designed and installed. Sometimes they are expensive. Soot can also make them ineffective without regular cleaning.

Reducing Need for Fire

One very simple technology that can reduce the amount of fuel necessary for cooking is the “hay box.” Food is heated to boiling, then it is placed in a box that has been filled with insulating material (e.g. dried grasses or crumpled newspaper). The food will continue to cook slowly. The concept is similar to that of a slow cooker. In Nairobi, the development organization Winrock found that hay boxes were proving as popular as improved stoves with women’s groups.

In areas that are consistently sunny, solar water heaters can be used to provide warm water (around 60°C) and this can reduce the need for fire to heat water. Solar water heaters can be made very simply from black pipe and plastic [or metal] drums painted a dark color.

Solar cookers can also be used to reduce the need for a fire. They can be made very inexpensively (e.g. from cardboard and aluminum foil) and work by concentrating sunlight directly onto the food. They can be extremely effective, but according to the ITDG document, they have had limited success in practice. One reason for this is that, in many cultures, the main family meal is eaten in the evening, whereas solar cooking is best done in the middle of the day when the sun is highest [though combined with the hay box, this obstacle could be overcome]. Another reason for limited success is that in order to use a solar cooker the cook must work out of doors, which reduces privacy. As with many projects, solar cookers need to be developed with input from the intended users if they are to be accepted and used widely. Stan Doerr, a new ECHO staff member with years of experience in Africa, says he has seldom seen a situation where solar cooking became popular over a long term. One reason that he cited is the important social structure for women that centers around preparing food. Still, information on this type of technology abounds.

Look for Species with Less-Smoky Wood

Dr. Schultz (whose work was described above) suggested growing and using trees with less-smoky wood. He wrote to ECHO, “Shrubs and fast-growing trees that create minimal smoke would be highly desirable, but little seems to be known about such species, especially about local shrub species. What is needed is something that is similar to oak (low smoke production), but grows rapidly. Local women know the best and the worst species, and where to find them. Species that do NOT contain the resinous materials that produce a lot of smoke still exist, farther from the villages. But these are accessible only by the younger women, and especially by women still able to walk long distances and who also have children old enough to walk with them and help them carry and collect fuel.

“Older women are definitely disadvantaged. Fast growing shrubs and trees that produce little smoke when properly dried might be planted close to their homes. Although this is a bit out of my field, I imagine that the better species could be identified by interviewing women to get the common names, and using botanists in local universities to match the common names with Latin names and to identify the best propagation methods.

“Ideally, this initiative to encourage the use of better wood fuels should be matched with local efforts to repair stoves, flues and chimneys, and to arrange kitchens such that prevailing winds can be used to clear most of the smoke from kitchens. One obvious step would be to place the stove under a window on the leeward side of the kitchen [i.e. on the side toward which the wind is blowing], so air movement from the windward side of the kitchen would push the smoke out the leeward window.”

Changes in Behavior

Sometimes simple changes in behavior can reduce women’s exposure to smoke. “For example, making sure that fuel wood is dry cuts emissions. The use of a pot lid can reduce the fuel consumed during simmering by a factor of three and overall emission levels by almost a half” (ITDG document). Keeping children away from the fire (if possible) will reduce their exposure to smoke. Though not a concern in many areas of the tropics, in some places an open fire is used not only to cook meals but also to heat the home. Efficient stoves are typically well insulated, meaning that less heat will enter the room. Likewise, chimneys help remove smoke, but also conduct heat away from the home. ITDG summarized, “Cooking is a deeply cultural and domestic task and communities themselves, particularly the women, must be directly involved in developing solutions that suit their circumstances….Experience has indicated that there is no point trying to dictate a solution to a community.”

With that said, solutions have been found in different communities, and there is much to learn from them. Many, many stoves have been designed to operate more efficiently. A few success stories are highlighted below.

The Ecostove in Nicaragua

Three-stone fires often result in burns; can lead to acute respiratory illnesses that are the second highest cause of death in young children in Nicaragua; and are inefficient, requiring lots of wood. The Ecostove, an efficient enclosed stove that was developed in Honduras, has been found to reduce wood consumption and smoke by half. In the Ecostove, the cooking fire is enclosed in a ceramic box encased by an insulated material (such as pumice rock). A metal griddle sits above the fire, and smoke leaves the stove via the chimney. The unit is sealed, so no air pollution enters the building. The stove works well in Central America, where tortillas are a common part of the diet. Tortillas can be cooked on the flat surface of the stove, with no contamination from smoke.

An article in ITDG Food Chain that described the Ecostove also shared two case studies of women who prepare and sell food out of their homes. They have benefited financially (because they need to purchase less fuel wood) and health wise (because the smoke from the fire is carried out of the house). (Cameiro de Miranda, ITDG Food Chain 31:23-25).

Kenya Smoke and Health Project

An ITDG project involved 50 rural households in Kenya. To reduce smoke in the house, the households were introduced to smoke hoods, enlarged eaves (to improve ventilation), windows and improved fuel-efficient stoves.

“Without these aids, smoke particles in the air exceeded 5526 micrograms per cubic metre of smoke; with them pollution is reduced by approximately two-thirds. Personal monitors on cooks showed that exposures to [potentially toxic] carbon monoxide were reduced by 35 per cent.

“’The project identified that the levels of smoke particles in these rural homes is, in most cases, more than 100 times greater than the acceptable level of 50 micrograms of smoke particles per cubic meter suggested by the US Environmental Protection Agency’, says Dr. Liz Bates, co-ordinator of ITDG’s Smoke and Health Project.”

“ITDG is disseminating the ideas to urban areas in Kenya and other countries like Sudan and Nepal.” (Smoke Gets in Their Eyes, Appropriate Technology

Other Examples of Stoves

Exposure to smoke is best reduced with stoves that have chimneys, but these stoves are not always feasible. Below are examples of some very inexpensive stoves that result in fewer emissions

The Jiko is a bucket with a ceramic lining that can be made for US$2.00. Alternatively, a ceramic insert alone can be set in the fireplace and surrounded by mud and stones. The insert can be made for less than US$1.00. More information can be found at… .html.

Aprovecho developed the Rocket Stove, which consists of a small tin can inside a large tin can, with the space between filled with ashes. Information (including how to make one) can be found at


Aprovecha developed the Rocket Stove, which consists of a small tin can inside a large tin can, with the space between filled with ashes. Information (including how to make one) can be found at
Aprovecha developed the Rocket Stove, which consists of a small tin can inside a large tin can, with the space between filled with ashes. Information (including how to make one) can be found at

Cite as:

Berkelaar, D. 2004. Indoor Air Pollution from Cooking Fire Smoke. ECHO Development Notes no. 85