| Boiling Point No. 30 - April 1993 |
Kirk R. Smith, Program on Environment, East-West Centre, Honolulu, Hawaii, prepared for the African Development Perspectives Yearbook, Volume 3, 1993. Editorial Summary
Although not nearly as prevalent as wood and charcoal, there is some use of coal as a household fuel in parts of Sub Saharan Africa, particularly in the southern portion of the continent where there are significant coal resources. Botswana is in this category and in the Republic of South Africa about 40% of households rely on coal (Terblanche/Nel/Opperman, 1992). In addition, serious consideration is being given in several countries to encouraging substantial expansion of coal use to relieve pressures on forests from wood gathering and to assist those many households that must spend excessive time gathering woodfuels. Among those nations considering this option are Zambia and Zimbabwe (AFREPREN, 1990). Although Mozambique has some coal resources, it is considering imports for household use from South Africa (Ellegard and Lopes, 1990).
Biomass Smoke Health Effects
Most of the SSA indoor pollution measurements quoted below were taken in conjunction with ongoing investigations of acute respiratory infections (ARI) in children. ARI is the general term for respiratory diseases produced by a range of infectious organisms and indeed ARI, mostly as pneumonia, is the chief killer of developing-country children in the world.
In Zimbabwe, 244 children under 3 years old reporting with lower respiratory disease at Marondera Hospital were compared to 500 children with similar disease reporting to a Well-Baby Clinic (Collings/Martin/Sithole, 1990). Pollution monitoring showed kitchen particle concentrations to be four times higher in a sampling of homes of ill children.
In a study of 500 children in The Gambia, girls under 5 years old carried on their mother's back during cooking (in smoky cooking huts) were found to have a six times higher risk of ARI, a substantially higher risk factor than parental smoking (Armstrong and Campbell, 1991). Oddly, there was no significant risk for young boys, perhaps because they tended to be carried for shorter periods than their sisters. For infants, however, the risk for boys and girls together was almost three times (Campbell/Armstrong/Byass, 1989).
Unfortunately, however, there are so many other risk factors for ARI that it is difficult to make sure they have all been taken into account in these studies. What is most needed is a study measuring both ARI and air pollution levels in households before and after introduction of some smoke-reduction measure, such as improved stoves. Only this kind of intervention study can provide the scientific information needed for answering the policy-relevant question of "How much can ARI be reduced by controlling indoor air pollution from biomass combustion?" At the time of writing, the World Health Organisation is planning a series of such studies around the world, including Africa.
Coal Smoke Health Effects
One set of African exposure measurements has been reported related to household coal use for cooking and heating in the Vaal Triangle of South Africa (Terblanche/Nel/Opperman,1992). Twelve-hour exposures of 124 pupils aged 8-12 showed average particulate exposures of 6201330 microgram/m³). The primary, but not sole, source of these exposures was household coal burning, which affected both indoor and outdoor concentrations.
Over a period of 7 months in the mid-1980s, a coal-burning residential area of Soweto was found to have outdoor particulate concentrations that frequently exceeded standards, although there were marked seasonal variations (Turner/Aneegarn/ Snyman, et al., 1986). Concentrations of nitrogen and sulphur oxides, on the other hand, were not excessive.
Children living in homes with wood or coal-cooking stoves in the coal triangle were found to have upper respiratory infections 2.2 times more often than those using electricity or gas. For lower respiratory tract infections, there was a similar difference between households using solid fuels and those using kerosene, but not between solid fuels and electricity/gas.
The vast bulk of studies on the health effects of indoor coal smoke have been done in China. They have focused on several health endpoints including interference with immunological function, acute and chronic carbon monoxide poisoning, loss of lung function, respiratory illness symptoms, chronic lung diseases and stroke. Associations of various statistical strength have been found in all these cases.
These findings are disturbing enough, but pale beside the depth and strength of evidence linking household coal use and lung cancer in China. There are difficulties in finding a connection between exposures and health effects that may be decades apart. Basically, the lung cancer appearing today is related to environmental conditions 10-40 years ago. Nevertheless, with so many studies using different methods for reconstructing these histories and all but one finding significant effects, it is difficult to argue that the finding is due to methodological biases. The extra risk of lung cancer due to past household use of coal seems to be at least 2-6, but could be as high as 9- 16 in some particularly smoky circumstances (Smith and Liu, 1992). These are significant risks and should lead to a critical look at any plans to expand household coal use in Africa.
Assuming that people will still be cooking in their homes, there are basically three approaches to reducing smoke exposures: changes in fuel, stoves and ventilation.
The historical solution to poor household fuel quality has been to move up the 'energy ladder' to the higher quality fuels such as kerosene or gas. Although by no means perfectly clean, these fuels produce orders of magnitude less pollution than unprocessed solid fuels. Such household fuel transitions have been more difficult in recent years because of the cost and balance-of-payment concerns raised by turning to these petroleum-based fuels. Nevertheless, accelerated movement up the ladder is probably the surest way to reduce indoor smoke.
Some relief from wood smoke can also be achieved by choosing less-polluting wood species or avoiding the use of wet wood (Mutere, 1991). One way of dealing with the cost of moving to modern fuels is to consciously insert a new step on the energy ladder: clean coal. Depending on costs, clean coal/ stove combinations may be a reasonable interim stage in the energy ladder for some communities.
Charcoal making, of course, is a way of dramatically cleaning woodfuel. In terms of the health effects discussed earlier, charcoal stoves are much less polluting (Bormann/Smith/Bormann, 1991). Unfortunately, however, there are several counterbalancing disadvantages to charcoal, such that an overall evaluation of its impacts is difficult. Related to the typically low efficiency with which wood is changed to charcoal in African kilns is that such kilns seem to produce rather large releases of non-CO2 greenhouse gases, such as methane (Smith and Thorneloe, 1992).
From a health standpoint, charcoal may greatly reduce the potential for chronic ill-health, but it raises an acute hazard. It is quite rare to hear of accidental deaths from carbon monoxide (CO) poisoning due to wood burning, even though it emits more than enough CO to be fatal. The reason is that the irritation from the many hydrocarbons and other pollutants in the woodsmoke awakens people before they succumb from the CO. Charcoal burning, however, does not produce much hydrocarbon, although it still releases substantial CO. Because it is colourless and odourless, CO does not give such warnings on its own.
In areas of the world (e.g., China, Korea, Iran) where households use processed (low-hydrocarbon) solid fuels, such as charcoal or clean coal, acute CO poisoning is a serious threat, leading to thousands of deaths annually.
A redesigned stove can potentially reduce smoke exposures in two ways: by using a chimney or flue to take pollutants form the house or by improving the combustion efficiency such that fewer pollutants are created (Baldwin, 1987). Although designing and successfully disseminating such stoves have turned out to be more difficult than first thought, there has been much success in SSA and elsewhere with stoves taking one or both of these tacks (Ramakrishna, 1991; Wickramagamage, 1991).
Improving household ventilation can reduce smoke levels when cooking is done indoors, although not by as much as one might hope. Thus, making changes to cooking behaviour and household architecture are other ways of reducing cookstove smoke exposures. In the long term, of course, merely putting the smoke outdoors is not a solution, particularly where households are close together. The smoke will simply enter someone else's home.
There is clearly more to be learned about the health effects of household use of biomass and coal. It would seem, however, that donor agencies, governments and charitable organizations seek ways to measure and reduce exposures wherever possible (Smith, 1992b).
Ed Note: Details of health effects of biomass smoke worldwide have been described in several recent editions of Boiling Point. ITDG's Stove and Household Energy programme is carrying out preparatory work on the measurement of smoke levels in kitchens in Sri Lanka and is seeking funding for longer scale field work. Derails of references available from BP editor.