Fire is a real danger around propane tanks so any containers have to be kept away from fire or significant heat. This is because extreme heat or fire reduces the integrity of the unit containing the propane. Once flames or heat affect it enough, it will no longer be safe if something impacts it and an explosion will occur.
Human error is another cause of propane tank explosions. They need to be stored properly by their users and treated responsibly. Things like leaving a bleeder valve opened so that the propane leaks and smoking a cigarette around the gas can ignite it causing a fire. If the tank is stored with other propane tanks that fire will reduce the integrity of the other tanks and the small fire due to unthinking human error could become a much larger problem.
Sometimes humans can be responsible and fire is kept away from propane tanks but they still explode. This is because of some type of deficiency in the tanks. These tanks could possess things like defective gas control valves, have leaks or even be insufficiently labeled to instruct in their proper usage.
The effects of a propane explostion are devastating. Since it is a flammable and explosive gas it is capable of causing death. Lesser effects could be injuries still severe enough to threaten life, multiple burns in every degree or a loss of limbs. Even if these are avoided it will cause burning of the eyes and nausea. Caution around anything containing propane is an absolute necessity to protect life and limb.