A common design feature of cylinders is:

• A. Temperature sensor
• B. Built-in extinguisher
• C. Anti-corrosion coating
• D. Pressure relief device

Answer: (D)

When a cylinder holds high-pressure gas, safety relies on a built-in mechanism that vent-safely releases gas if the pressure gets too high. A pressure relief device does exactly that: it automatically opens to vent gas before the internal pressure reaches a dangerous level, preventing a rupture or explosion. Different types exist, such as a fusible plug that melts at a set temperature, a frangible disc that bursts under excess pressure, or a spring-loaded valve that opens at a defined pressure, but the common thread is automatic relief to protect the vessel and nearby people.

Other features like a temperature sensor, a built-in extinguisher, or an anti-corrosion coating may appear on some cylinders or equipment, but they are not universal safety controls for overpressure. The pressure-relief device is the standard safety design feature that directly mitigates the primary hazard of compressed gas cylinders.