Posted By Graham Bullough The methane bubble experiment involving Judith Hackitt which formed the basis of the thread “Judith Hackitt set alight!” started on 30.1.09 ( currently viewable at http://www.iosh.co.uk/in...=1&thread=41873&page=481 )reminded me of a simple but very effective demonstration given to visitors by the HSE at its former Health & Safety Centre at Horseferry Road in London. A short candle was placed and lit at one end of a long metal trough. At the other end a long handled mini-ladle was used to tip a small amount of highly flammable liquid (HFL) into the other end. Nothing seemed to happen for a while until an impressive flame erupted suddenly and briefly from the entire length of the trough. What had happened was that the HFL had evaporated and flowed as an invisible vapour along the trough until it was ignited by the candle flame. This was an excellent and memorable way of demonstrating the need for strict precautions for the heavier-than-air vapours of HFLs and also liquefied petroleum gases (LPGs) such as butane and propane. If anyone thinks the demonstration is worth replicating, they should obviously consider and take appropriate simple precautions - as for any activity which involves a degree of risk. These include choosing a suitable location, control of spectators and, for indoor locations, avoidance of smoke detectors. The related precautions for storing and using HFL must include using only a SMALL amount of HFL, i.e. about a teaspoonful or so just as HSE did with its demonstrations. Another thought: Does anyone know if this demonstration is given during school and college science lessons? If not, is there any good reason why it should not be given, considering that it would be a good way of improving understanding about HFLs and LPGs as well as making science more interesting? Turning now to the subject of the former Health & Safety Centre: There seems to be very little information available on the internet about it, including anything about its origins. One notably poignant exhibit at the Centre was a glass cabinet containing numerous items of common portable electrical appliances such as kettles. The accompanying information simply explained that each appliance had had an electrical safety defect which had caused an electrocution at work. The website for Hansard (the official record of proceedings in Parliament) indicates that the Centre was closed in the 1980s during government spending cuts when it was deemed not to be cost-effective. Out of curiosity, does anyone happen to know what happened to the building and/or the display machinery and other exhibits?

Posted By Graham Bullough John is spot on about the dust explosion demonstration. My three week stint as an inspector serving as a guide/presenter at the Centre was almost 30 years ago, but I recall the model flour mill which was probably in the basement along with the HFL vapour trough. The model had transparent sides so that spectators could see a spoonful of fine combustible powder being placed inside, whirled about by some sort of impeller and then ignited by a spark plug. The resulting explosion was quite noisy and caused the hinged or chained sections of the model’s roof to blow off. Great fun: The best bit was anticipating and watching the reaction of spectators, mainly groups of bored apprentices. The somewhat stunned spectators were then asked to consider what would happen if much larger amounts of combustible dust were ignited inside a grinding machine in a real building, followed by a brief discussion about measures to try and prevent dust explosions, and also to protect people, machinery and buildings if explosions did occur. While on the topic of explosions, some are highly desirable, notably the countless vapour explosions which occur inside vehicle engines for example. It’s worth mentioning that the flaming methane bubble experiment involving Judith Hackitt is listed in “Top Ten Flash Bang Experiments”. This is available at www.whynotchemeng.com and was produced by the Institution of Chemical Engineers to encourage the inclusion of fun, safe and relevant demonstrations in secondary school science. The final experiment involves dropping coffee whitener or other combustible powders onto a burning spill to demonstrate how the combustibility of such powders is raised significantly because of their high surface area. This demonstration is unlikely to be as dramatic as HSE’s model flour mill. Nevertheless, among other things, it can play a part in developing an understanding of how the forms of substances can be relevant to fire precautions. A similar principle is shown by the difficulty of trying to set a telephone directory alight compared with how easy it is to ignite pages which have been torn from a directory and crumpled. p.s. Moderators, especially Jane – Following the reprimand I got about bad language in my response yesterday to the thread “Purpose of Risk Assessment” I’d better point out that the word “flaming” in the above paragraph is used wholly in its literal sense and not as a perjorative comment about the experiment!