Abstract: A thermal relief device releases gas from a storage cylinder when a thermal trigger senses a predetermined temperature threshold. The thermal relief device includes a valve body which has a passage for communication with the interior of the cylinder. A pilot valve assembly is disposed within the valve body and has a popper for blocking the flow path. The poppet has a longitudinal passage extending through the popper. A metal diaphragm sealing the passage of the poppet has a first side exposed to the interior of the cylinder and a second side opposite the first side exposed to the outlet. A hollow bayonet is mounted in alignment with the passage of the popper on the outlet side of the disk and is moveable between a first position and a second position. In the first position, the bayonet is spaced from the disk in the passage, and in the second position the bayonet pierces the disk. A spring is used to biased the bayonet toward the disk.