Cooking smoke: a silent killer

Posted: 18 August 2000

Author: Dietrich Schwela

Thousands of articles have been written about air pollution, from cities choked with traffic to forest burning in Asia. But an even greater killer is indoor air pollution, as Dietrich Schwela reports.

Wood, stubble, dung and grass are used daily in about half of the world's households as energy for cooking and heating. In most parts of the Third World they are burnt in open fires or inefficient stoves in poorly ventilated kitchens. The result is a toll in death and ill health far greater than the more often discussed outdoor air pollution.

Biomass smoke contains many harmful constituents such as respirable particulates and carbon monoxide (CO), exposure to which can cause or contribute to acute respiratory infections (ARI), pneumonia, tuberculosis, lower birth weights cataract, and nervous and muscular fatigue. Smoke, especially coal smoke, also contains sulphur and nitrogen oxides and hydrocarbons which can lead to cancer. Women and children are most exposed to high levels of harmful smoke and suffer the most serious health damage;respiratory infections alone cause between 4 and 5 million deaths per year among small children, which is equal to or marginally less than deaths from diarrhoeal diseases. WHO has estimated that about 2,500 million people in the world are exposed to excessive levels of indoor air pollution, largely due to burning biomass and coal indoors in ovens that are badly designed and lack proper chimneys. Some 1.9 million additional deaths each year are blamed on rural indoor pollution through suspended particulate matter and another 450,000 deaths are attributed to urban indoor air pollution. These figures are over and above the 500,000 excess deaths worldwide due to concentrations of suspended particulate matter and sulphur dioxide in the atmosphere.

African countries and India have the worst record for suspended particulate matter in rural homes, while Latin America, India again and China are worst for suspended particulate matter in urban interiors. Again, most monitoring is being carried out on ambient (outdoor) air, whereas many health problems potentially linked to indoor air pollution still go unrecognized. For example, several studies in China found that coal smoke was a strong risk factor for lung cancer among non-smoking women, while another study in Japan has related lung cancer to the past use of biofuels in cooking. In Gambia it was found that girls aged under five carried on their mother's back during cooking (in smoky cooking huts) had a six times higher risk of ARI - a substantially higher risk factor than if their parents smoked. At the 7th International Conference on Indoor Quality and Climate, "Indoors Air '96", held in Nagoya, Japan, participants were told that a shift of focus was needed to ensure that the health hazards from indoor air pollution were accorded the importance they deserve. This series of conferences - which started two decades ago - continued with "Indoor Air '99" in Edinburgh in August 1999.

Smokeless stoves

Unfortunately, while the health problems are all too clear, the solutions are as many as grains of sand in the desert. The issues involved are culturally diverse since they relate to such basic traditional patterns as how people live and cook and eat. The literature abounds with designs for 'simple' smokeless stoves or 'elementary' chimneys, hoods and smoke removal appliances. But persuading people to build, install, maintain and use such devices en masse is a thorny issue; indeed the first step is probably to persuade the millions exposed to biomass smoke that it does actually pose a health hazard. Although carbon dioxide, the principal gas produced by biomass combustion, is the best-known greenhouse gas, it is by no means the only one. Essentially, all the products of incomplete combustion produced by biomass fires with less than 100 per cent efficiency (virtually all of them) are also greenhouse gases, and include methane, carbon monoxide and non-methane hydrocarbons. It is the products of incomplete combustion, mostly in the form of carbon monoxide, particulates and gaseous organic compounds that comprise the chief health-threatening materials in coal and biomass smoke. The WHO Air Management Information System (AMIS) has recently been initiated to report trends in air pollution concentrations in many of the world's mega-cities. But much additional research is also needed on the relationships between indoor smoke and respiratory diseases, and on the linkages between housing design, fuel, stoves, water, food and health - taking into account social, economic and cultural factors as well as the appropriate technologies that are locally available. At present, great emphasis and attention is placed on controlling industrial emissions, prevention air pollution from road traffic through farsighted transport policies and urban planning, the phasing out of leaded petrol and obligatory emission control in new cars. But no less effort needs to be put into the actions required to reduce indoor air pollution both in cities and in villages.

Dr Dietrich H. Schwela is a Scientist with WHO's Urban Environmental Health Unit, Division of Operational Support in Environmental Health, in Geneva.

Improved stoves halve chest and eye disease

A 1993 study in Limuru area of Kenya showed that acute respiratory infection (ARI) and conjunctivitis is lower in households using an improved jiko stove than in those households using the traditional three-stone stove, writes Isabel Mbugua.

Looking at a one-week prevalence among young children and mothers of the two health conditions, the study found ARI to be 23 per cent in the households using the jiko stove, compared to 59 per cent prevalence in households using the traditional stove. Households using the traditional stove were 2.5 times more likely to have children with conjunctivitis.

The Stoves and Household Energy Programme of the Intermediate Technology Development Group (ITDG) in Kenya collaborates with the government, bilateral agencies and women's groups to promote the use of improved stoves, which are more efficient, use less firewood and emit less smoke.

"We look at the issues from all angles and we do not simply go to a community and sell the stove idea. The programme usually will marry the stove technology with other ideas and concepts that will help a given community evaluate their energy needs and how to meet these locally," says Stephen Gitonga of ITDG's regional Household Energy project.

Gitonga's major responsibility since 1994 has been to share the experiences from Kenya's activities in the energy sector with other partners in the region.

"Over the years we have done a lot of research on stove production and use ­ from clay selection to mixing, design as well as use of chimneys, hoods, ventilation and improved kitchens. This is what we hope to disseminate in the rest of the countries of the region," says Gitonga.

According to the ITDG 1996 Annual Report, "over 30 partners have received some form of technical assistance. Through the provision of information and training, their capacity to implement effective household energy programmes has been significantly enhanced. It is hoped that by developing local capacities the project has reached more people than if IT were implementing activities directly."

Gitonga feels that household smoke as a pollutant needs to be addressed at all levels.

"When you look at it, the improved stove is a concern of those interested in health care of women and children; it is a concern for those interested in conservation of trees; it is a gender issue because it is women who spend most time in the smoky kitchens, causing their health to suffer, and women spend hours looking for firewood."

Research among 50 households in Kenya, published in February 2002, showed that the introduction of smoke hoods reduced the average smoke in the house by 70 per cent and carbon monoxide by 77 per cent. ITDG is now planning to spread the lessons learnt to urban Kenya, Sudan and Nepal.

Isabel Mbugua is Kenyan journalist who specialises in development issues.