a hydraulic pressure accumulator has an interior chamber containing a fire - suppressing gas such as nitrogen . the fire - suppressing gas in the accumulator is fluidly connected to a thermal device , such as a valve with a thermal fuse or a controlled valve triggered by a thermal sensor . the thermal device is designed to open a fluid connection between the accumulator &# 39 ; s interior chamber to ambient when the exterior temperature exceeds a determined safety threshold , thereby releasing the fire suppressing gas from the accumulator .