Petrol stations too
I know this drifts away slightly from the main point of the thread, but anyhow....
Mobile phones are not supposed to be used in petrol stations either (same goes in the vicintiy of aircraft refuelling), due to the apparent 'risk' of explosion. Yet a few years ago in the UK press it was revealed that some mobile phone masts were actually located in the signage outside the petrol station forecourt.
So the explosion 'risk' was obviously not a huge concern when the petrol companies were being paid to have masts in the signs.