Hazard, Keefe & Leane Engineering, Inc. 
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Mapp Gas Torch Explosion


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4604 no 86.jpg (31550 bytes)  
X-Ray of Valve Showing Internal Components

An explosion occurred when a man attempted to light a Mapp Gas torch attached to a hand-held propane cylinder. Our investigation revealed that the valve stem of the pressure regulator assembly of the torch had been tampered with and substantially modified, which caused a leak.

A slotted round-head brass screw had been installed in the threaded hole for a set-screw, in the top of the valve stem of the torch. This threaded hole was originally designed to contain a factory installed set-screw, used to control the maximum factory-set pressure of the pressure regulator valve of the torch. The brass screw was not an original component of the torch, and had been installed some time after the torch had been placed in use.

Nondestructive inspection of the interiors of the subject torch and an exemplar torch were conducted by means of X-rays. The radiographs of the subject torch showed that a slotted round-head screw had been installed in the top of the valve stem of the pressure regulator valve. The original factory-installed set-screw had been driven downward, past the threaded portion of the valve stem, and into the spring bonnet for the pressure regulator valve. When the foreign round-head screw was installed, the bottom end of the dislodged set-screw had been driven against the valve spring with great force, so as to drive the bottom spring guide completely through the diaphragm and cause it to leak gas.



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