All LP gas containers must have their pressure relief valve in direct communication with which part of the container?

The pressure relief valve on LP gas containers must be in direct communication with the vapor space of the container. This is essential because the vapor space is where the gaseous form of propane exists, allowing any excess pressure to be properly vented. When the pressure within the container increases beyond safe levels, the relief valve opens to release vapor, thus preventing a dangerous build-up of pressure that could potentially lead to rupture or explosion.

Having the pressure relief valve located in the vapor space ensures that the gas is expelled rather than liquid propane, which could occur if it were in the liquid space. This separation is critical for safety, as venting liquid could lead to other hazards, such as frostbite or fire risks when it evaporates. Furthermore, proper placement of the pressure relief valve within the vapor space helps to maintain the integrity of the LP gas system, ensuring the safe operation of appliances that rely on propane.