Air-tight silos hold high-quality lime silica materials used in manufacturing the asbestos-free porous mass. A computer-controlled automated filling system maintains a constant temperature while mixing the raw materials that form the rigid porous filler. Moderate temperature box ovens cure and dry the porous filler. Norris requires 100% inspection to be sure the overall shrinkage between the porous mass and the steel shell of the Norris acetylene cylinder does not exceed .0789” top and bottom clearance combined. As a safety feature, acetylene cylinders are fitted with one or more fusible safety devices, which employ a fusible alloy having a normal melting point of 212 F (100 C). The fusible device may be a filled channel in the cylinder valve, or it may be a plug in the cylinder itself. The purpose of these fusible devices is to release the contents of the cylinder before excessive high pressure can build up from heat caused by an external fire.