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Developing safe paraffin appliances in South Africa by Philip Lloyd
[top] [end]IntroductionA paper, “We live in paraffin and burn in it: Fire, fuel use and social dislocation in an East London Township” (Bank and Mlomo 1996) described how, in the township of Duncan Village, there had been fires almost every week which often destroyed tens of homes. Some inhabitants had lost their meagre possessions every year for four years in a row. There was a drop in the extent of damage after the community enforced a 2m separation between adjacent buildings, but population pressures soon forced skin-to-skin houses with a consequent return to the previous pattern of damage. We therefore set out to see if there was a common cause.[top] [end]Identifying the problemThere were many reports that fires were caused by the ‘explosion’ of paraffin stoves used for cooking. The reports of ‘explosions’ suggested that the stoves were pressurised and of the ‘Primus’ type. However, the majority of stoves in use in these lower-income households were wick-type stoves. The pressure stoves retailed for upwards of R70, whereas a wick stove could be bought for as little as R25. The market for wick stoves was of the order of 1 million units per year, where as less than 100,000 pressure stoves were sold annually. Clearly the wick stoves were the most likely source of the problem. So how did a wick stove, which operates at atmospheric pressure, explode?Many tests were carried out. Even when the appliance was knocked over and leaked copious quantities of paraffin, it took several minutes for a fire to develop. Figure 1 shows the result of a typical test. The spilled paraffin can be seen seeping from the appliance, which only ignited a few seconds later and then burned quite gently and was easily extinguished.
Eventually we carried out a test in which the appliance was used to cook for some time, and then knocked over. There was a dramatic change. It ‘exploded’ with a ‘Woomf’ and the flame was so luminous that in the test photograph, shown in Figure 2, the background appears dark even though it was taken on a bright sunny day.
Repeated tests showed that, when the stove was used, the paraffin in the fuel tank became hot. Once it exceeded its flash point (the lowest temperature at which it can form an ignitable mixture in air), for paraffin about 50ºC, it would burst into flames when shaken. The rate of combustion was in excess of 1MW. We therefore examined the construction of this type of appliance and Figure 3 shows the essential features of the stove. In use, the inner and outer elements become red-hot and the radiant heat then evaporates paraffin from the wick. The paraffin vapour mixes with hot air drawn through the holes on the elements and burns. The elements are a push-fit into indentations in the upper surface of the fuel tank, and can be readily dislodged (see Fig. 1). Nevertheless, the contact between the elements and the fuel tank is good enough for heat to be transferred efficiently. It is therefore inevitable that the paraffin will get hot in appliances of this design.
Could such a simple design fault be the cause of so much damage? To demonstrate that this was indeed the case, several homes were built and filled with a typical collection of possessions. Attempts to burn them down using a candle soon showed that it was remarkably difficult! Usually the candle went out. If it stayed alight, the wax ran clear until the wick ran out of fuel. Eventually we succeeded in igniting a fire, which took approximately 15 minutes to gain hold, by which time the house was burning fairly fiercely. In contrast, when the house was set alight by a stove containing hot paraffin, the fire spread instantly, and was burning fiercely within 30 seconds. This proved what we had suspected when we first determined that these appliances could give a heat output of 1MW - they were almost certainly the source of the really devastating, rapidly spreading fires that had been reported. The next question was what to do about the problem. The Department of Minerals and Energy agreed to support the development of national standards that could be made mandatory. In other words, it would illegal to sell appliances that failed to meet the standard. With this support assured, the existing standards were reviewed. [top] [end]Revision of standardsThe critical standard, SANS 1906 (SANS 1998), was reviewed. The SA Bureau of Standards set up a Technical Committee, which in turn established an informal Working Group comprising manufacturers, technical experts, and representatives of relevant Government departments.The second edition of SANS 1906: Non-pressure stoves and heaters (SANS 2006), was gazetted on 31 January 2006 and it became mandatory a year later. It appeared to resolve all the safety issues that had been identified in the earlier versions of the standard. In particular, it said:
The latest revision has also cut out the “particulate matter” requirement, partly because it was so ill-defined and partly because, being ill-defined, it was impossible to measure. More work is obviously necessary in this area. The latest revision also does away with specific power requirements. Instead, it requires the manufacturer to set a “rated power” for an appliance. Most of the tests are then run at the manufacturer’s rated power. The use of the ratio of CO2: CO to allow for the variable power now makes sense, because the CO2 emissions are directly related to the power. A new test has also been introduced, namely a maximum power, which should not be greater than 20% above the rated power. The need for this became apparent when it was shown that CO levels tended to drop as the power was reduced, so that a designer could, in principle, meet the required CO specification by under-rating the appliance. The final change in the latest revision is to shorten the time for extinguishing from 30 to 10 seconds. Manufacturers developed techniques for rapid shut-down that made the longer period unnecessary. Thus the stage has been reached where appliances that appear capable of meeting the revised standard for non-pressure stoves are available. The standard for pressure stoves, SANS 1243, is similarly being revised prior to making it mandatory. [top] [end]Experience in trying to enforce the mandatory standardIt is unfortunate that designs meeting the revised standard were not available when the standard was made mandatory. What then happened was that locally manufactured appliances were removed from the market and they were replaced by imported appliances - that were just as dangerous, if not more so. The imports had not previously been competitive but now, with the local appliances removed from the market, the imports could be priced at levels that made the cost of importation worthwhile. As a result the market was flooded with sub-standard equipment and the danger persisted. At the time of writing, methods for stopping the imports were being examined.A further change was the introduction of ethanol gel as a substitute for paraffin. This happened with the active encouragement of the Department of Minerals and Energy, who were concerned at the apparent lack of progress in getting safe paraffin appliances. It seemed that, because ethanol gel could not be spilled, and because any fire could be extinguished with water, then it would be safer than paraffin. Unfortunately these hopes were not realized. One problem that soon emerged was that the emissions from the gel appliances were exceptionally high (Lloyd & Visagie 2006). This arose from the fact that in order to burn efficiently, fuel and air must be intimately mixed before combustion. It is very difficult to achieve this when the fuel is a gel. A further difficulty was that there were no standards for ethanol gel. Gels containing less than 70% ethanol reached the market, some of which contained so much water that it would condense on the base of a cold cooking pot, and droplets would fall back and put the flames out. Other gel manufacturers forgot that it was essential to add a denaturant, to make it unfit for human consumption, and salesmen would demonstrate the “safety” of their gel by eating a few spoonfuls! Ultimately it seems that economics rule. Ethanol gel was sold at a price similar to that of paraffin. A gel of reasonable standard has a calorific value of around 19MJ/kg; paraffin is about 44MJ/kg (lower heating value in each case). The users soon found cooking on gel too costly to be sustainable. Government has insisted that there should be national standards for gel appliances. They are being developed, but few fuels and no devices that meet even the draft standards are yet available. The other change that has happened is that the global increase in the price of liquid fuels has made paraffin less affordable. As a result, many users have switched to cooking on electricity. There is a general policy in South Africa to make the first 50kWh/month of electricity free to the poor. In terms of energy, that is the thermal equivalent of about 4 litres of paraffin. It is too little for a household to cook on, but it reduces the average cost of cooking on electricity to slightly less than that of paraffin. This has, however, had a knock-on effect. There has been a rapid increase in the peak demand for electricity, which has now exceeded generating capacity when a margin of safety is included. Modelling studies have shown that if there is wider use of liquid fuels for cooking then as much as 4,000MW of peak power, about 10% of the total, could be saved. [top] [end]ConclusionsThe use of paraffin-fuelled appliances has long been the primary source of household energy in lower income homes in South Africa. However, the problems caused by sub-standard appliances have given paraffin a bad name. Safe appliances are known internationally, and some of those which we have tested appear to meet the revised standards more than adequately. However, those appliances are relatively costly; the market is used to a 5 USD stove, and hopes its safer replacement will not cost much more than 10 USD. We have reason to believe that 15 USD is achievable, but we recognise that 80 USD, which is typically the cost of a safe appliance internationally, is unlikely to prove attractive in the short- to medium-term. It is too early to show conclusively that the problem has been resolved, but we believe we have gone a long way towards achieving it.[top] [end]ReferencesBank L and Mlomo B 1996 We live in paraffin and burn in it: Fire, fuel use and social dislocation in an East London Township, 1986-96, J Energy in SA 7 pp118-123.SANS 1906 Safety of non-pressure stoves and heaters, First Ed 1998, Pretoria. SANS 1906:2006 Non-pressure paraffin stoves and heaters. ISBN 0-626-17542-9, Pretoria. Lloyd, PJD and Visagie, E, 2006, The testing of gel fuels, and their comparison to alternative cooking fuels. Paper D5-1, Int. Conf. Domestic Use Energy, Cape Peninsula University of Technol., Cape Town, March 2006 [top] [end]Download the original article Developing safe paraffin appliances in South Africa by Philip Lloyd (149 KB)[top] [end]Contents: Boiling Point 56 - Liquid fuels in the household
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29 January 2009; Last edited:
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Pagename: BP56:DevelopingSafeParaffinAppliancesInSouthAfrica @HEDON: KXPA | |||||||||||||
