A highly charged performance
In July, Milan's climate can be rather oppressive, to say the least, hot and very humid, and so a summer thunderstorm can offer a welcome cooling respite. Swathes of giant raindrops, wind gusting through the streets, claps of thunder that set car alarms off, and lightning that, if it hits the lightning conductor on the building next to you, makes a very loud bang.
The people of Milan have a constant reminder of the power of lightning, in the shape of Filarete's tower over the main gate of the Castle. On 23 June 1521, the tower was struck by lightning, and this caused the gunpowder stores inside to blow up, destroying the tower completely. At that time, Milan was under French rule, and from then on the Castle started its gradual disintegration. Only in the late 19th century did restoration begin, including the tower, which was redesigned using period paintings and prints to get an idea what Filarete’s long-forgotten original looked like.
And something similar
happened over 200 years later in nearby Brescia. Early on 17 August 1769, a
stroke of lightning hit the church of San Nazaro, which was still under
construction, and was located near one of the city gates. The bolt ignited eight
tons of gunpowder stored in the fortifications nearby, and the explosion
projected enormous blocks of masonry into the air. They fell onto the city over
a mile’s diameter, causing devastation over what was then about a seventh of the
city. The sound of falling shards of glass woke the whole city. 200 houses had
been destroyed, and 500 damaged by falling rubble. The number of fatalities was
variously estimated by writers of the day at between 400 and 2,500.
Even without
help from gunpowder, lightning is a powerful phenomenon. A single lightning bolt
reaches a temperature of about 30,000° C, or five times hotter than the surface
of the sun. Its voltage ranges from 1 million to 1 billion volts, at between
10,000 and 200,000 amps, which means that the average lightning bolt, which
lasts 30 microseconds, could light a 100 watt bulb for 3 months. Lightning
causes objects to explode because it instantly turns any water to steam. This
includes concrete, trees, asphalt and clothes. According to statistics, about a
thousand people are killed by lightning worldwide annually. In Italy, there are
probably around 800,000 strokes of lightning every year, and these cause about
7-10 deaths per year.
The potentially damaging nature of lightning has led to a considerable amount of research in this field, starting with Benjamin Franklin who was interested in determining what lightning actually was. His first idea was to use a spire that was being built in Philadelphia, but he became impatient waiting for the builders to finish it, and so decided to use a kite to bring the electric charge of a thunderstorm to earth. He survived his experiments: many others who tried to emulate him didn't. They were, truly, playing with fire.
Today, CESI, Centro Elettrotecnico Sperimentale Italiano, based in Milan, is the structure that runs SIRF, the Italian lightning detector system, recording each stroke of lightning by means of a network of sensors all over the country. The map at www.fulmini.it gives you an idea of the system. There are analogous networks in other countries, and they all meet once a year to compare ideas (I suppose that “brainstorming” would be an appropriate term!) Another structure, ERSE, runs a laboratory designed to produce artificial lightning, the largest of its type in Europe to be inside a building. This makes it easier to control atmospheric conditions, and in fact a specific climate can be set for each experiment. The laboratory is a 35x35x40 (h) metre building in which a high voltage impulse generator is operated. The machine simulates a stormcloud and charges up to 5 million volts. This equipment is used to study the effects of lightning on industrial and agricultural plant, insulators, aircraft etc.
The CESI website also provides the rules to be followed if there's a thunderstorm nearby. Some of these are familiar – is there still anyone who would think of sheltering under an isolated tree in a thunderstorm? – but others less so. For example, if you're outdoors, and you can't get to a building, it's best not to stand up, but crouch, keeping your feet together. Don't lie on the ground. If you're in a group, don't huddle together, but spread out. The danger is less in a forest, as long as you keep away from the trunks. Place any metallic object you're carrying a few dozen yards away, and keep away from any metal structures such as pylons. If you're on a beach, move away, because umbrellas and the masts of boats tend to attract lightning. Stay away from the water, and if you're swimming when the storm starts, return to shore. Put away your fishing rod, especially if it's in carbon fibre. Your car is an excellent refuge, because the metal bodywork conducts a strike to earth through the wet tyres. If you're at home, close the windows, and disconnect electrical devices. Don't touch radios, telephones, computers etc. And if there’s a lightning strike nearby, don’t think that this offers you sure protection through the old adage “lightning never strikes in the same place twice,” because it’s not true!
Henry Neuteboom