What is the primary function of a fusible plug in a gas cylinder?

The primary function of a fusible plug in a gas cylinder is to melt at a specific temperature to prevent explosion. This safety feature is crucial in situations where a gas cylinder may be exposed to extreme heat or fire. The fusible plug is designed to operate as a thermal relief device. When the temperature rises beyond a predetermined threshold, the fusible material in the plug melts, thereby allowing the gas to escape in a controlled manner. This action helps to prevent the buildup of excessive internal pressure that could lead to a catastrophic failure or explosion of the cylinder.

By allowing the gas to vent safely, the fusible plug protects not only the integrity of the gas cylinder itself but also the safety of nearby individuals and property. This is particularly important in emergency situations involving fire, where the risk of explosion due to high pressure can pose significant dangers. In contrast, the other options do not accurately represent the function of a fusible plug, as none address its critical role in temperature regulation and safety in high-pressure environments.