ENGINEERING INSIGHTS | Why Doesn't the Empire State Building Mind Being Struck by Lightning?
Because the current has somewhere to go.
The US National Weather Service puts it at about 23 strikes a year. In one storm, according to NYC Emergency Management, it was hit eight times in 24 minutes.
So much for lightning never striking twice.
Tall buildings get hit because of their height, shape and isolation. Not because they're full of metal. Metal doesn't attract lightning. It only gives the current a path, and a good path is exactly what you want.
In the 1930s, General Electric's lightning researcher Karl McEachron spent three summers photographing strikes on the building. His pictures showed something new: some bolts didn't come down from the cloud at all. They started at the top of the tower and forked upward.
Time magazine summed up his work in 1938. A big building's steel frame "acts as a lightning rod, carrying off the charge", so the people inside are well protected.
That protection isn't luck. It relies on an unbroken path from the roof to the ground.
In Australia, that path is designed under AS/NZS 1768: air terminals on the roof, down conductors, an earthing system and surge protection for the equipment inside. Break one link and the rest can't help. A damaged down conductor, a corroded earth connection or new rooftop plant that was never bonded in, and the current finds its own way down.
The strike lasts a fraction of a second. The route it takes was decided long before, on the drawings.
A question for building owners and facility managers: when was your lightning protection last inspected, and has anything gone on the roof since?
