Earlier this month, 120 sceptics gathered in Southampton
to prove that anyone can
walk over red-hot coals and come away with their feet intact. The "firewalk" was
organised by Wessex Skeptics, one of a network of sceptics' groups around the
country.
Few people initially thought they would be able to walk on fire, but more than
100 of the sceptics, including university students, staff and friends, crossed
the coals at temperatures of up to 593 °C (1,100°F) - nearly hot enough to melt
aluminium. None had had any "spiritual training" but all were able to walk
home comfortably.
Firewalking is such a spectacular defiance of common sense
that throughout history it has been used as evidence of spiritual
superiority. There are references to it in the Bible, and it has been reported in such different places as South Africa, Japan
and Bali.
In 1984 tens of thousands of Californians paid hundreds of dollars each for "fear
seminars", at which firewalks were promoted as the cure for everything from drug
addiction to insomnia.
In
fact, firewalking has little to do with mind over matter and everything to do with
the laws of physics concerning heat capacity and conductivity. To set up this
month's event, the Wessex Skeptics raked the embers of a bonfire of storm-damaged
oak and beech into a bed about 1 metre wide by 3.5 metres long.
Firewalkers were warned to
walk briskly and avoid letting their toes sink into the embers. Wet
blankets and buckets of water were positioned at the end of the walk, so
they could cool their feet down quickly afterwards.
Physicist Robin Allen, a research fellow at Southampton
University and president of
the Wessex Skeptics, gave a prior talk on the physics involved.
A substance may be hot but will transfer that heat slowly. To take a commonplace
example, think of a cake baking in a tin in an oven at 200 °C. The air in the
oven, the tin and, after a while, the cake, are at the same high temperature. If
you put your hand in the oven, the air will feel hot but won't burn you in the
time it takes to remove the cake. Similarly, you won't I get burned touching the
cake. But you will get burned if you touch the cake tin or the metal oven
racks.
Metal holds large amounts of heat energy and transfers it
quickly, whereas air and cake have
low heat capacity and poor thermal conductivity. For firewalking, wood and its ash
behave like the cake. In some parts of the world, porous rocks are used
instead of embers — they are also poor conductors of heat. And, because feet
have a high heat capacity, the embers actually cool down when walkers step on
them. The trick is not to spend too long on the embers — the effects are
cumulative.
It takes an average four or five steps to cross a 3.5 metre bed of coals. At the
recommended brisk pace, each foot is in contact with the embers for no more than
a second or a second and a half, not long enough to cause burns.
At the Wessex Skeptics firewalk, a few blisters did appear, but they were caused
by embers sticking to walkers' feet. Experienced firewalkers recommend drying
the feet carefully first to avoid this.
"The only mind over matter," says Mr Allen, "is finding the courage to take the
first step." But don't try it at home. Fire is still fire — and still dangerous.
