Dr Robin Allen - firewalking expert from the Wessex Skeptics - gives the pre-walk lecture. He explains why a bunch of physicists have organised a spectacle usually associated with Eastern mystics, religious nuts and blatant con-artists. Apparently there is no mystery about why one can walk over coals at temperatures of several hundred degrees C without coming to any harm, and its all down to the physics of heat conduction.

"Its like opening the oven to take out a baked cake", he says. "Everything in the oven is at the same temperature, the air, the metal cake tin and the cake. You have no fear of putting your hand in the oven - that's because the air is a poor conductor of heat and doesn't immediately burn you. But the metal cake tin will!"

The wood is a poor conductor of heat - it only causes burns if your feet stay in contact for long enough for the heat energy to be transferred. There are many other factors involved, such as the length of the pit, the thickness of the soles of your feet, how quickly you walk and the type of wood being used. Dr Allen has a confession to make - tonight is going to be a bit of an experiment as the wood being used is beech, and he has only ever used oak before. One hundred and fifty people, a mixture of physicists, other students and the general public, all laugh although somewhat nervously. All the reassurances seem to be scaring people even more so as a distraction he shows a video clip of a guy who licks red-hot iron bars for fun. Compared to that the task in hand seems a doddle and everyone is out of the physics building like a shot, swarming around the bonfire site.

While the lecture was in progress a quarter of a ton of beech and rosewood has been set alight, with the help of some paraffin and copies of the Daily Mirror. By the time we arrive the leaping flames have died down and red hot embers are being raked out evenly over the pit. People start to remove their shoes and socks, following the lead of Dr Allen. The tension mounts, the embers are given a final prod and the firewalking physicist carefully wipes his feet on a towel. Hot embers stick to wet feet, and the way to avoid nasty burns is to make as little contact with the hot stuff as possible.

The crowd holds its breath as Dr Allen crunches his way across the far-from-cool pit, following his own advice of brisk light steps, with toes curled upwards and no hanging around. After five strides he's onto the sopping wet blanket at the far end. The gathered throng burst into applause and he runs back and has a second go at it. Amazement and relief show on peoples' faces - it is possible. There is a short pause before some guy decides this is not a cruel trick and has a go himself. Suddenly everyone wants a go. As the pensioners leave, having seen what they came to see, a constant stream of willing volunteers donate their pound to the Wessex Cancer Trust and make the journey across the 600 degrees C terrain.

To the flash of the press' cameras people go across alone, three-legged, in a conga and generally very quickly. No one attempts a handstand, cartwheel, forward roll or backflip, and especially no the Monkees walk. After an hour of this application of thermodynamics most of the experimenters have grown tired of this amazing feat that was actually quite easy to perform. Only a few die-hard physics students remain, trying to set a record for going across the most times. At 10pm the security guards decline the offer to be the last ones to go over and the once-quarter-of-a-ton of wood is finally extinguished.

At the recovery session in the Union bar everyone is busy lying about how brave they were. No-one seemed to have any injuries - the only casualty of the evening was a packet of Hob-Nob biscuits that had fallen from the pocket of a firewalker. The profit for charity adds up to 100 and people are looking forward to being in the papers. Riding high on a wave of firewalking-induced self confidence I was confronted by a guy who says "So you walked across hot embers, what's so amazing about that?" This was a bit deflating to say the least and I realised that some people don't need a sound demonstration of the application of physics to remove the mysticism from the spectacle of walking on fire.

N.B. Don't try this one at home.

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Assembled by Jim Champion j.d.champion@physics.org Created 10 June 1997 Last updated 16 June 1999