A properly maintained cylinder should have no problem coping with normal ambient temperatures if kept in a ventilated area, lots of cylinders can be found stored outside buildings. They should be fitted with a safety valve that will vent off surplus gas if the pressure does get too high, but again provided there is ventilation the gas will dissipate without causing a danger. If the venting gas did catch fire, it would not pose a risk to the tank itself.
The only real risk of a tank exploding is if it gets caught in an external fire, and the heat is sufficient to weaken the structure of the tank.