are cellphone signals hazardous?

There does seem to be truth to the fact that cellphone signals are hazardous, especially when you are putting gas in your car. Here they have warning signs telling people to turn off their cellphones while at the pump so that a fire does not start from the cellphone signal or an explosion. There had been reports of cellphone use not being good for ones health but they came back later and said there is no harm to a person by using one.