Hot weather will be a major concern at the World Cup, but lightning may also prove a particular problem. Under US safety regulations, a strike within 10 miles (16km) of a stadium triggers a 30-minute suspension of the game, during which players must leave the pitch.
The size of the safety zone was dictated by research on the distance that lightning can strike from a storm even with no clouds overhead. This is more than a theoretical risk. During a game in the Democratic Republic of the Congo in 1998, an entire team was killed by a single bolt of lightning. There have been many other deadly incidents.
The rules say if there is no more lightning within the 30 minutes, the game can restart. But any further electrical activity resets the clock for another half an hour. If the delay lasts for more than an hour, officials may have to consider rescheduling the game.
The lightning ruling would not normally be an issue, except that some games are taking place in Florida, the lightning capital of the US. June and July are the also peak months for thunderstorms, with an average of 20 stormy days each.
