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close this book Boiling Point No. 02 - May 1982
View the document Editorial
View the document News from Shinfield
View the document Stove Programmes in Kenya
View the document Fuelwood and Stoves in Zimbabwe
View the document Strengthening Clay by Traditional Methods
View the document Study of the Thai Charcoal Stove
View the document Firewood Consumption Survey in Sri Lanka

Boiling Point No. 02 - May 1982

IT Intermediate Technology

 

 

Editorial

Over the past three years, a great deal of information and knowledge has been gained on the theory and practice of stove design and testing. However, very little is known on methods for widespread dissemination of stoves. If the deforestation problem is to be tackled quickly it will be necessary to introduce at least 10,000,000 stoves into Africa alone in the next 10 - 20 years. Greater efforts are needed now to collate the existing experiences of stove extension, and from them to develop models to assist the increasing number of people planning and implementing stove programmes.

During the Woodstoves Meeting in Leuven, Belgium, 4-5th March, this problem was considered by people involved in stove programmes. The proceedings of this meeting will be published in the near future and will be available from the Katholieke Universiteit, Leuven. We would like to maintain this interest in stove dissemination by devoting an entire future issue of "Boiling Point" to this subject.

ITDG has identified the following as some of the factors which influence the adoption of new stoves:

Technical attributes of the new stove: e.g. does it use less wood; is it portable or fixed; is it to be made by the user or an artisan; can it be mass produced?

Methods of its generation and development: e.g. did the stove programme arise from expressed needs of villagers or urban people; from perceived needs of government officials or donors?

Economic Cost/Benefits, financial or non-financial e.g. labour or time; direct or indirect e.g. needing new cooking pots to fit a new stove; the time over which costs are incurred, or benefits realised.

Rural/urban infrastructure:e.g. can stoves be transported; are there artisans who can produce the stove?

Needs, attitudes and personality traits of individual adopters e.g. perceived fuelwood shortage.

Overall social structure: who controls the money and makes decision to purchase or construct a stove.

We would like to hear of the experience of other people and their analysis of the factors that affect the dissemination of stoves. We would welcome case studies and/or theoretical contributions for publication in "Boiling Point"

Technical Editors:

Contributors:

Stephen Joseph

Yvonne Shanahan

Jaz Gill, J. Bialy

Poonsab Samootsakorn

Peter Dunn, Norman Joyce

Jenny Trussell

Artwork: Jenny Trussell

Production Co-ordinator: Karen Mallik

"Boiling Point" is the newsletter of the I.T.D.G. Stoves Project and appears three times a year. Contributions in the form of articles of about 700 words would be welcome, and where appropriate line drawings and simple graphs etc.

 

 

News from Shinfield


FIGURE

The first issue of Boiling Point was distributed in the relative calm of last January while both Stephen Joseph and Yvonne Shanahan were overseas with our collaborators. Yvonne and Stephen have been working with Dian Desa on an evaluation survey of their stove programme in three villages in Central Java and Bill Stewart has been carrying out a similar exercise in Sri Lanka on the Sarvodaya Programme. The results of the surveys were analysed and written up as discussion papers for a meeting in London on evaluation studies at which Martin Creeley and Mick Howes of the Institute of Development Studies acted as advisers to help refine the ITDG evaluation methodology. In Sri Lanka it was found that of -199 users interviewed 55% said they used their new stove all the time and an additional 18% said they used it for everything except making tea. Only 19.5% of those interviewed did not use their stove, or used it infrequently. 69% of those who used their stoves most or all of the time had Tungku Lowon stoves. The single most important factor that affects the frequency of use of a stove is the accuracy of construction which suggests that emphasis must be placed on field worker training so that they can build stoves accurately. The results of the Indonesian survey have not all been analysed yet. However it would appear that of 10 households where there was a Tungku Lowon stove, 7 were in constant use and were saving fuelwood. Only 5 of the 10 Katesan type stoves that had been introduced before the Tungku Lowon stoves were still being used.

 


Figure 1 Tungku Lowon


Figure 2 Katesan stove

 

Stephen and Yvonne also went together to Leuven, Belgium, to the 7th Woodstove meeting hosted this time by Dr. Guido de Lepeleire of the Katholieke Universiteit of Leuven. Stephen Joseph presented two papers, one on dissemination and the other on field testing. It was agreed that Stephen Joseph, Guido De Lepeleire, Tim Wood and Paul Bussman would try and develop a standard procedure for carrying out field testing. A position paper on field testing is being prepared by Stephen Joseph and Peter Dunn of Reading University.

Stephen Joseph paid a short visit to Kenya to meet with the Kenya Clay Stoves Working Group. He was assessing their application to I.T.I.S. for funding for the manufacture of improved clay jikos.

Meanwhile, testing in Shinfield has been continuing. Jon Loose who did the testing of the Tungku Lowon has now moved onto materials testing on extruded clay samples. Peter Young, formerly of the UNICEF Appropriate Technology Centre, Embu, Kenya, has taken over the stoves testing and has been optimising the performance of the Indonesian Tungku Mein Chong stove.


FIGURE Stoves

 

Peter has also built a mould for making mud/clay samples and a rig for thermal cycling and testing them. The test rig is now housed in the new improved Stoves Testing Workshop which has been totally enclosed and now includes a permanent exhibition of mud, clay and metal stoves. Jenny Trussell has been working on a training manual for Sri Lanka based on information supplied by Bill Stewart. She has also been making a series of fired clay charcoal-burning stoves that have been developed in Kenya and which will be tested here in Reading.

Yvonne recently went to Sri Lanka to help Bill Stewart with the second stage of his evaluation survey. She and Bill Stewart are now both back in Shinfield and Bill is working for the Stoves Project as Field Project Officer. He will divide his time between the ITDG collaborators helping them with all aspects of their programmes. Stephen Joseph will not be travelling overseas again for some months due to the recent arrival of his second child Benjamin on April 16.

GRET SEMINAR IN DECEMBER IN FRANCE

In December, Ian Grant and Yvonne Shanahan were invited to a meeting in France hosted by the Groupe de Recherche et d'Echanges Technologiques (GRET). Yvonne presented a paper and slideshow on the ITDC stoves programme strategy and our experience in implementing with overseas collaborators. The meeting was attended by representatives of various European organisations concerned with fuelwood, forestry and wood-burning stoves, including Eindhoven University. France is particularly anxious to provide technical support for programmes in the Sahel which will help to reduce deforestation. A public awareness campaign is planned for Paris during the Spring to highlight the near crisis situation for the Third World's primary fuel - wood and there will be another meeting in Marseilles in May.

 

 

Stove Programmes in Kenya


Stoves in Kenya

 

A great deal of activity has been generated to help solve the fuelwood crisis in Kenya, as a result of the Nairobi Energy Conference in August, 1981. Both government and non-governmental organisations have initiated stove programmes. Charcoal is used extensively in urban and pert-urban regions and accounts for much of the stripping of forests in Kenya. Therefore, most of the activity has centred around the improvement of the existing charcoal-burning metal jiko. The jikos are made by tin smiths, who purchase scrap metal and fashion it into a very simple brazier. See Fig.1. There are two main problems with this stove design. During use the halls may reach a temperature of 300 degrees C which is dangerous to the user and a waste of heat. Secondly, the performance of the stove is relatively inefficient when compared to other charcoal stoves such as the Thai Bucket. At present two groups are attempting to design and disseminate improved metal jikos. They have tried to cut charcoal consumption and improve safety by insulating the combustion chamber.


Stoves in Kenya

The Kenya Clay Stoves Working Group has developed three models, (See Fig. 2). The simplest model involves slipping an extruded clay cylinder into the existing jikos, the second consists of an inner clay cylinder, an outer metal cladding and an insulating layer of ashes added between the inner and outer layers. Both cylinders are extruded The third model is an adaptation of the Thai bucket. The inner clay liner is made on a pottery wheel and tapers inwards at the bottom. Tests are being carried out at the Kenyatta University College on both the existing and the new models of jiko stoves. On completion of these tests the group hopes to carry out field trials on all the models and the results will be published. About 2,000 of these stoves (all three models) will be introduced.


Stoves in Kenya

 

Phil Hassrick of UNICEF has designed an improved jiko in which the pot sits into the stove. It has an outer metal cladding, a sloping inner combustion chamber and an ash layer between the inner and outer metal layers. The author questioned a user living in a village in Karai district, 30 kilometres from Nairobi, on the fuel efficiency of this jiko. She claimed that with the old jiko stove a bag of charcoal lasted three weeks: with the new UNICEF stove a bag 1asted two; months.

In the same district work has been carried out- by UNICEF on developing wood burning stoves. One of the two models being introduced, the Karai stove, Figure 3, was designed by a few local people. A group of 12 women construct these stoves on Wednesdays each week. The owner of the stove participates in the construction. It is an adaptation of a stove they had seen at the UNICEF Appropriate Technology Centre at Karen. It is made from mud, has two pot holes and a metal chimney which is surrounded by a water jacket. The user must contribute 100 shillings, about 3 U.S.$, towards the construction of the stove and UNICEF pays another 100 shillings as a subsidy. The author carried out tests on this stove two years ago and found that it used less wood than an open fire to heat water from 25 to 100 degrees C. Users seemed to think that the stove did save some wood but the main advantage was ease of use and the fact that there was less soot in the kitchen. The author feels that the fuelwood consumption of this stove could be reduced significantly by minor modifications. For example, placing a baffle underneath the second pot hole would increase the heat to the second pot.


FIGURE

In the same village, Mr. Waclaw Micuta of the Bellerive Foundation, built demonstration stoves with grates and metal heating plates - the Pogbi (Figure 4) and the Nomad stove (Figure 5). Tests have indicated that these stoves could save a considerable amount of firewood. The stoves are built by local craftspeople and are transported to users houses. They cost 200 shillings. The author was unable to interview the owners of these stoves.


Nomad stove (Figure 5).

 

In the same village, Mr. Waclaw Micuta of the Bellerive Foundation, built demonstration stoves with grates and metal heating plates - the Pogbi (Figure 4) and the Nomad stove (Figure 5). Tests have indicated that these stoves could save a considerable amount of firewood. The stoves are built by local craftspeople and are transported to users houses. They cost 200 shillings. The author was unable to interview the owners of these stoves.


the Pogbi stove (Figure 4).

 

Finally, another innovative metal stove (Figure 6), has been designed in Kenya by Maxwell Kinyanjui. It is being made by tinsmiths in Nairobi and Mombassa. The; stove can burn twigs and if it is used properly, it can produce charcoal from these twigs at the same time as cooking a meal.

ITDG hopes to undertake testing of these metal and metal/fireclay jikos over the next two months, and will present reports of this work in the next issue of "Boiling Point".

Stephen Joseph


FIGURE

 

 

Fuelwood and Stoves in Zimbabwe

An energy shortage is widely perceived to exist in the non-industrialized countries especially relating to cooking activities, and is expected to become more acute. In addition, traditional cooking stoves used in such countries are said to be very inefficient. In view of this, a trip was undertaken to Zimbabwe (October 1981 January (1982) for an assessment of the actual situation in the field regarding rural domestic energy and related issues, e.g. fuel collection and use, and modes of cooking.

Direct measurement of the daily firewood consumption and a questionnaire survey, covering perceptions of tasks, agricultural activity, seasonal variations in fuel use and consumption were undertaken in two study villages. One village experienced a slight and the other a moderate fuel problem. A questionnaire survey was conducted in a village in a third study area where there was an acute firewood- shortage. The results of the questionnaire survey are presented here.

It was found that there were seasonal variations. in the consumption and collection of fuel; an increase in consumption was reported during winter and in some cases immediately after harvesting, whilst generally firewood was not collected during the rainy sason. Firewood was said not to be collected during the rains because once wood got wet it became very heavy and hence difficult to carry, as well as being virtually impossible to burn. Hence the practice was to aim to collect sufficient firewood during dry season such that the supply would last through to the end of the rains. The wood would be stored outside in a pile close to the cooking hut.

Mealie cobs were generally used as a fuel supplement during August and September. Of the three villages visited, it was only in the fuel-scarce area that animal manure was used as a cooking fuel, as well as being used as a fertilizer; manure could only be collected during the dry season, since the rains would wash it away. However, manure from the cattle kraal (the enclosure where the cattle were kept) was used as a fertilizer, and only manure found outside these kraals was used as cooking fuel.

A shift from the traditional 3-stones fireplace for cooking to either 4-stones, or a commercial iron frame stove was observed. The vast majority used the iron frame which is produced by urban based artisans. According to the villagers themselves, the iron frame used 1.5 to 3 times as much fuel as the traditional 3-stone fireplace. The primary reason given for the adoption of this "stove" was that it enabled the users to heat several pots simultaneously. In this respect more than one pot was reported to be heated simultaneously during the months October through to April (the rainy season) whilst pots were heated sequentially during the other months. This appeared to be linked to the variation in agricultural labour demand over the year. The months October through to April were regarded as being the busiest months owing to agricultural tasks e.g. ploughing, planting, weeding, and harvesting. Hence the time available for activities such as cooking would be less than during the other months.

Other perceived benefits included the production of less smoke, more space heat, faster cooking, stabler pots, and a "modern" image. Users of this new technology were prepared to sacrifice fuel economy and bear the extra labour cost (which was high in areas of fuelwood scarcity) for these benefits. This was possible because fuel was collected in the slack agricultural season whilst fast cooking was required during peak labour demand.

The 4-stone fireplace was user built and consisted of 4 mounds of clay (soil), linked by 4 metal bars in the shape of a square. Two additional metal bars formed the diagonal supports. Similar benefits were perceived by users of both 3-stones and iron frame stoves. However, the 4-stone fireplace had to be repaired periodically e.g. about every 6 months, owing to cracks developing in the clay mounds causing them to break up. Fuel consumption was said to be about 1.5 time' that of the 3-stones fireplace.


FIGURE

 

One possible reason for the widespread adoption of the new modes of cooking may be due to the increase in the work burden of rural women. However, the workload of rural women is multifaceted and connected (certainly in this case) also to issues such as male migrant labour, the degree of contact of women farmers with agricultural extension workers, the introduction of cash cropping and the provision of formal education facilities for children, and not just fuel collection.

Fuel efficiency is therefore not the main determinant of choice of cooking method in Zimbabwe and stove programmes are unlikely to succeed unless they take into account factors such as those mentioned above.

Jaz Gill, Open University


FIGURE

 

 

Strengthening Clay by Traditional Methods

A primary factor in designing ceramic stoves is the suitability of the clay available. Close observation of local potters will give clues as to how to improve its qualities as these people have learnt through traditions how to adapt the clay for the pots they make. Clay used for cooking pots is not necessarily going to be suitable for ceramic stoves but because clay cooking pots have to withstand localised thermal stress and a fair amount of pounding, it will come some way to meeting the demands and provides a good starting point.

Observation of a group of Voltaic potters working on the edge of the Sahara desert found them mixing the following with their clay: 15% grog (crushed fired pots), 15% millet husks, 5% charcoal and 5% ash (percentages of total volume). They also added a small amount of dried donkey dung to the clay used to shape the neck of the pot.

The strength of the final product will be a function of both firing temperatures and the addition. The addition of grog a is widespread practice. In a study of two Ethiopian pottery villages Roel Hakemulder (1980) writes:

"Broken bricks are acquired from the Nicola Brick factory....The potters consider the powdered brick to be indispensable for it makes the pots strong. The bricks are powdered in several ways; using mortar and pebble, beating them to pieces with metal staves and milling small pieces of brick between rocks. The powder is seived and the fine powder sprinkled on the clay after which the clay is pounded and kneaded.- There is no standard quantity of brick powder to be mixed with the clay; the potters judge by feeling, adding a little water whenever they think it is necessary."

Other potters add ground broken up fired pottery in various sizes. The addition of grog serves several functions, firstly in a very fine plastic clay it opens out the body making it stronger for building larger shapes and less likely to shrink and warp excessively which could cause cracking in drying and in firing. The type of firing typically used by potters i.e. bonfire firing will only just serve to harden the clay into a biscuit stage with temperatures ranging from 600 - 850 degrees all in one firing. Grog additions especially in the case of high fired particles such as bricks will strengthen the weaker low fired body.

Charcoal and ash additions also act to strengthen the clay. The addition of amorphous silica in the form of grass stem ash or rice husk ash is a common ingredient in the clay used by the Thai Bucket stoves makers in Thailand. There they add up to 40% ash to their mix making a non-plastic clay which has to be moulded into shape. The silica addition will lower the maturing temperature of the clay. The tiny honeycomb structure makes an incredibly light pot which has some insulating qualities. Charcoal additions make a more porous body and the finer and more even the distribution, the stronger it will be as small pores tend to stop cracks propagating. It also serves as a localised fuel especially useful if the fuel for the firing itself is scarce. The Voltaian addition of millet husks would serve to some extent the points mentioned above with an emphasis on the increased burning during the firing.

Dung is well known in mud mix for increasing the binding strength of the mix by breaking down some clay particles into a bacterial ooze . The reasons for adding dried dung to clay are debatable. In the Voltaic potters case, one can only hazard a guess that adding dung to the neck of a pot, would increase the burning and so raise the temperature locally, thus creating a stronger area of fired clay where it is most likely to get knocked.

Sand is also widely used as an addition. It is a plentiful and easily added form of silica. Its gritty texture adds strength to the wet clay when building shapes and in firing it helps to lower the sintering temperature of the clay because of its high silica content although this only happens with any real effect at temperatures above 900 degrees C. The addition of sand also lowers the porosity of the fired clay thus improving its resistance to thermal stress.

Most typical firings are in the range of 600 - 800 degrees where the maximum "positive dimensional change" occurs: that is to say the pores increase in number and size rather than contract and glassify as at a higher temperature. This, along with the fired grog addition and honeycomb structures seems to improve resistance to the effects of thermal cycling. However open pores on the surface of a pot will weaken the structure if water is allowed to penetrate and turn to steam on heating. Primitive potters seem to have an answer to this as well: they finish their pots with a highly polished, almost impermeable surface. Whilst in the "leather hard" stage, the pots are beaten and tempered into shape. This treatment consolidates the surface layers and aligns particles. The mica, prevelant in many primitive potters clays responds well to that treatment, helping the thermal shock resistance and surface texture. Sometimes a fine clay slip is applied before the whole outside surface is burnished by rubbing with bone or pebbles to a high gloss. This then closes the surface pores of the pot giving it a hard impermeable skin and honeycombed granular structure within. Charcoal, however, would burn through the burnishing in the firing, making a pitted surface.

Increased additions of all or some of the materials above, plus beating and burnishing should, with experiment produce an acceptable body for ceramic stoves. Here at Shinfield we are carrying out a testing programme to find suitable refractories for ceramic stove making. We would be interested to hear of any unusual additions readers have seen or heard of. In the future, "Boiling Point" will be carrying an article on clay testing methods, procedures and results from our refractories programme so far.

By Jenny Trussell

Biscuit ware - clay which has been fired once and is still porous. Firing temperature can vary between 600 and 1100 degrees C.

Burnishing - surface treatment of leather hard clay rendering it highly polished by rubbing with a smooth hard object.

Sintering temperature - the temperature at which the clay particles start to fuse together.

Slip - fine particles of clay suspended in water to form a liquid.

Tempering - beating and thus flattening clay particles to create a stronger surface.


FIGURE

 

Study of the Thai Charcoal Stove

Wood and charcoal used for cooking account for nearly 50% of the energy consumption in Thailand. Deforestation has become a problem and the continuing population growth puts ever increasing demands on the wood and fuel supply. Any reduction in the fuel used in the cooking process is a factor of considerable importance. This report looks at the performance of a typical Thai charcoal stove used under 18 different operating conditions and identifies the major heat losses.

A typical Thai charcoal stove is shown in Figs. 1 and 2 and the dimensions of the stove used in this study are given in Figure 3. The measurements included the burning rate, air flow, exhaust gas analysis together with temperature measurement on the walls, combustion bed, inlets and exhaust gas and cooking pan as shown in Figure 4. Simulated cooking tests were carried out using water; the heat to the water and heat lost as steam were measured. The transducer outputs were fed to a minicomputer via a multiplexer and processed online. A theoretical model was used to predict the heat balance.


FIGURE

 

The following stove parameters were varied:

Area of the air aperture (A)

A1 = 2,500 mm

A2 = 5,000 mm

A3 = 10,000 mm

Distance between the charcoal bed and the bottom of the pan (V)

V1 = 100 mm

V2 = 150 mm

V3 = 170 mm

Number of holes in the grate (G)

G1 = 16

G2 = 37

Diameter of holes 15 mm


FIGURE

 

The best configuration of these tested was A1V1G1, i.e. the stove with the smallest air aperture, the smallest distance between the charcoal bed and the pan bottom and the grate with the fewest holes.

There was a 40% increase in the charcoal used from the best test (AlV1G1) to the worst test (A3V3G2). The heat input into the pan did not vary much from test to test. The difference in heat output from the charcoal between A1V1C1 and A3V3G2 was 3,015 kJ and 2,532 kJ of this extra heat appears in the flue gas of A3V3G2 as seen by comparing the two sankey diagrams of Figures 5 and 6. With this configuration, the two main heat losses were, the heat to generate steam and the heat stored in the stove wall. The loss by steam could be reduced by using the air control to reduce the heat input-to the pan after the water has reached boiling point. It is however, typical Thai cooking practice to boil away a large amount of water while cooking the rice.

The other major loss to the stove wall could be reduced by making the stove smaller; the test stove was made large to accommodate the changes in dimension between the charcoal bed and the pan bottom. The distance of 100 mm between the charcoal bed and the pan used in the best configuration is about the minimum that can be used without losing some of the stove's versatility e.g. for cooking large quantities of food and sometimes wood is used instead of charcoal

The Thai stove, as developed over the years, is probably not far from the best that can be achieved using readily available local materials. It is much superior to the simple metal charcoal stove found in Africa (Openshaw 1979) which is little more than a metal "radiator": There can be little doubt that a stove could be built using heat shields, modern materials and insulators which would be superior to the Thai stove, but the cost would put it out of the reach of most users and the local material content would be largely lost.

The heat input to the pan is not sensitive to dimensional changes. If sensible use is made of the air aperture control by closing it down after the fire has become established, the charcoal used can be reduced by at least 30% without any significant reduction of the heat input into the pan.

The economic use of charcoal is very much in the hands of users. Recommendations can be made, such as:

1 Proper use of air control

2 Do not overload the stove with charcoal

3 Keep the stove away from draughts

4 Keep the bottom of the pan black

However, the real spur to economy will be price and scarcity. While charcoal is available at affordable prices, old practices are not likely to change.

Heat stored in the stove walls is significant if the stove is only used for a short period. Over 50% of the heat produced during the 30 min test period when starting from cold goes into heating the stove walls, a modified-design which reduces the heat capacity of the stove without any loss of its insulating properties might be worth pursuing.


FIGURE

 

Firewood Consumption Survey in Sri Lanka

As part of ITDG's programme to develop suitable field testing procedures, Jan Bialy surveyed fuelwood consumption in a village in Sri Lanka.

"This survey was carried out at the home of a farming family in a small village near Anuradhapura where the writer had worked three years previously. The cooking place consisted of the common '3-stones' arrangement, made in fact with 6 bricks placed two high as shown in Figure 1.

The quantities of wood used for each cooking operation, the quantities of food cooked and the vessels used were recorded over a period of 23 hours from 1500 hr on Friday, 17th July. The results are presented in Table 1. All weighings were made with a Salter plastic kitchen scale weighing up to 4.5 kg by 25 g divisions. This scale was not really suitable for weighing firewood or heavy ceramic vessels as the reading was particularly sensitive to the positioning of the weight on the pan. Besides, some ceramic vessels, when filled with food, were too heavy to be weighed, so that some of the food had to be removed and weighed separately. A spring balance would have been more suitable and would have lessened the disturbance to the cook. The full co-operation of the family is essential in making a survey of this kind and every effort must be made to minimise the inconvenience caused in carrying out the necessary measurements. It is very easy to forget to use wood only from the measured pile, or to add wood to the pile without informing the researcher. It is necessary for the researcher to be present in the kitchen the whole time, because the fire is frequently used outside the normal cooking times for minor operations like boiling water for tea, reheating tea, roasting chillis prior to grinding them or boiling buffalo milk to make curd.

The summarized results on the survey given in Table 2 (6.4) reveal that about 20% of the total weight of wood burnt was not in fact used for any cooking operation, but was consumed when the fire was shouldering between operations. The quantity of wood consumed when the fire was burning without any vessel on top came to only 1% of total weight used, but it is likely that if the writer had not been making measurements, the quantity consumed in this way would have been higher. It is worth noting that changing the design of the stove would probably have little effect on the quantity of wood lost in smouldering, in this case 1.3 kg a day.


FIGURE

Of the quantity of wood used for cooking, that is 5.3 kg in the day, 60% was used for cooking the rice and curry for lunch and dinner, and almost a quarter was used in boiling water for tea and reheating tea. It has been suggested that information about the quantities of wood used for different cooking operations could be obtained by measuring the duration of each operation and by assuming an approximately constant burning rate. Unfortunately, the burning rate does vary in some operations such as cooking rice, because the rice is usually allowed to simmer for some time on the remains of the fire after the flames have been put out. Thus it can be seen from the second half of Table 2 that of the total time spent cooking, the cooking of the main meals (rice and curry) accounted for only 45% (compared to 60% of the total weight of wood used for cooking). Similarly, because the fire used for making tea is generally smaller than that used for cooking food, the percentage of the total time spent cooking which is devoted to making tea is over 30%.

Exerpt from report by J. Bialy


FIGURE