What is the primary hazard associated with improperly maintained pressure relief valves?

The primary hazard associated with improperly maintained pressure relief valves is the risk of explosion. Pressure relief valves are critical safety devices designed to prevent excessive pressure buildup in gas storage systems. When these valves are not maintained properly, they may fail to open at the designated pressure, allowing gas to accumulate to dangerous levels. This accumulation can create a highly explosive environment, especially if there is an ignition source present.

Each of the other options does present potential risks related to gas storage and handling, but they do not capture the immediate and severe danger posed by a failure of the pressure relief system. For instance, leakage of propane can occur, but it's the unchecked pressure buildup that primarily leads to explosion risks. Similarly, overheating and corrosion are concerns that may lead to equipment failure, but they do not directly relate to the critical function of pressure relief valves in preventing explosive incidents. Therefore, the risk of explosion stands out as the most significant consequence of neglecting the maintenance of these essential safety devices.