| Boiling Point No. 29 - December 1992 |
High thermal efficiency downdraught stoves have figured in BP 21, 23 and 28 and seem likely to be the subject of research by stove workers for several years to come. Brief reports, news and summaries of papers will therefore be included in our R & D section and contributions are invited.
We have a further paper from Moerman and Prasad of Wood Stoves Group, Eindhoven, on this subject which will be summarized in a forthcoming edition.
Health Effects of Biomass Smoke
Dr Kirk R Smith of the East-West Centre, Honolulu, Hawaii 96848 has provided (November 1991 ) an update of the current knowledge of this problem as reported in Boiling Point's "Smoke Pollution" edition and various other articles. We have extracted the following points.
"There is growing scientific evidence to support the numerous anecdotal accounts relating high biomass smoke levels to important health effects. More research is sorely needed, however, before reliable quantitative estimates can be made of how much ill-health would be reduced by smoke reduction activities, such as promotion of improved stoves. Given the scale of the problem, the relatively small investment necessary to conduct such research is well worthwhile."
He deals briefly with the various health dangers of smoke inhalation as follows:
Acute Respiratory Infections in Children (ARI)
ARI, as pneumonia, is or,e of the chief killers of developing country children in the world. At 4-5 million per year it is equal to or somewhat less than diarrhoea. ARI in general is also responsible for more episodes of illness than any other disease category. It is well known to be enhanced by exposures to urban air pollutants and indoor environmental tobacco smoke (ETS) at levels of pollution some 10-30 times less than typically found in village homes.
In a study of 500 children in The Gambia, girls under 5 years carried on their mother's back during cooking (in smoky cooking huts) were found to have a 6 times higher risk of ARI, a substantially higher risk factor than parental smoking. There was no significant risk, however, in young boys.
These studies are extremely suggestive, but do not yet allow quantified conclusions, because there are so many other risk factors for ARI that remain difficult to account for. 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 we reduce ARI by reducing indoor air pollution from biomass combustion?"
The only ARI study that actually measured air pollution levels was in Kenya, but unfortunately only had resources to examine 36 households (Wafula et al. 1990). They found high levels of pollutants in all houses, with little variation and thus, it was not surprising that they found no association with ARI rates".
Properties of Natural Clays and their Relevance to Stove Fabrication and Operation
From the PhD thesis submitted by A B Gaspe, Dept. of Engineering Materials, the University of Sheffield, Sheffield, September 1992
Pottery stoves made from natural clays are being introduced throughout rural areas of Africa and Asia as a cheaper and safer method for cooking than the use of open fires. Whilst stoves can be made that do not fracture in service from thermally induced stresses, stoves made in many locations suffer from this problem. The reasons for this variable behaviour have been sought in this study.
A correlation has been found between the clay/non-clay ratio of natural clays and the tendency of stoves to fail in service. With values of the ratio greater than one, stoves tend to fracture from thermally-induced stresses. It has been found in this and other studies that increasing the quartz content of a natural clay. which reduces the clay/ non clay ratio, brings about a combination of changes that could account for the correlation and should reduce the tendency for fissures to form on drying and firing.
Peter Young of ITDG has thermally shock tested complete stoves by immersion of heated stoves in cold water. He found that if the firing chamber contained a vertical cut through its entrance, the stove survived the shock treatment. The cut would not only tend to reduce residual stress but would also reduce thermal stresses and appears to be a useful practical solution to the problem of stove failure in service. However, the insertion of a vertical cut in the green stove leads to a significant distortion of the stove during drying and firing. The distortion of the rim of a stove prevents the cooking pot making a sufficiently good seal with the rim and allows the hot gases from the fire to escape rather than to pass to the second chamber to heat the second pot. A possible solution to this problem is to fabricate a separate rim in such a way that it has planar alignment of the clay. This would not be microscopically residually stressed. The rim could be attached with clay to seal the gap.
Technical Enquiries to ITDG
One of the most valuable services provided by ITDG is in answering technical enquiries. The Technical Enquiry Unit acts as a focus for the Group's information and advisory service and can respond on a wide variety of topics. The TEU has extensive contacts within the UK and Europe. The stove team and its associates are at your service in this way.
Please send all enquiries to:
Technical Enquiry Office
ITDG, Myson House
RUGBY, CV21 3HT,
Telex: 317466 ITDG G
Contributions to Boiling Point
Contributions are invited for the next three issues of Boiling Point, the main themes of which will be: Special Edition: World Bank Stove Policies - postponed until 1993 No. 30 - Marketing Methods & Subsidies No. 31 - Clays for Stoves
Articles for issues 30 and 31 should reach this office by the end of February 1993 and June 1993 respectively.
ISSN: 0263-3 167
It is with great sadness that we report the death of Toby Harrison in September 1992. As the Senior Energy Advisor at the British government's Overseas Development Administration, Toby was a long time supporter and friend of IT's Stoves and Micro-Hydro programmes, his enthusiasm, advice, and support will be sadly missed.
Editorial & Production Team
Tammy Flavell - Production Manager Ian Grant - Editor Peter Watts - Co-Editor
Peter Young - Programme Manager
Emma Crewe - Social Anthropologist
Megan Lloyd-Laney - Production Resources Manager Caroline Ashley - Socio Economist
Agnes Klingshirn - GTZ Representative Elke Metzen - GTZ Consultant
C Adam, C Ashley,
G Ballard-Tremeer, A Gaspe
A Ellegard & H Egneus
L Hongpeng, T Otiti
U Simkhada, K Smith
P Turyareeba, P Watts
Proof Reading by R Marshall
Cartoons by P Bradbrook, T Dowling
French summaries by Bois de Feu
Boiling Point is the journal of the Intermediate Technology Development Group's Stove & Household Energy Programme and the Integrated Household Energy Programme of GTZ. It is printed on recycled paper by Rugby Community Printworks (affiliated to the Rugby Youth Promotion Programme). ITDG is a registered British charity.
Contributions are welcome in the form of articles of not more than 2,000 words including line drawings, photographs, simple graphs etc., where appropriate. An correspondence should be addressed to Boiling Point, ITDG, Fuel for Food Programme, Myson House, Railway Terrace, Rugby, CV21 3HT, UK.
Opinions expressed in contributory articles are those of the authors and not necessarily those of the ITDG SHE Programme.
(Readers wishing to enter into correspondence with authors may obtain full postal addresses from the address given above.)