An Explosion Could Have Been Avoided If Gasket Specifications Were Utilized

An Explosion Could Have Been Avoided If Gasket Specifications Were Utilized 

An i/8-inch thick compressed asbestos gasket failed on a 20-inch (50.8 cm) Class 6(X) ASM flange after a regular semiannual turnaround. About 66 pounds (30 Kg) of hydrogen leaked from the manway flange on a compressor knockout drum, ignited, and exploded. Two employees died and two other employees were injured in this incident in a Canadian styrene plant. [15] 

The explosion resulted in construction trailers having their sides bowed inward and significant window damages at a distance of 365 meters (1,200 ft.) and as far away as 900 meters (3,(XK) ft.). The explosion occurred on a plant holiday. If it had been a regular workday, many more injuries could have occuired within the unit and in a neighboring office building located 500 ft. (150 m) from the epicenter of the blast. 

Investigations revealed that the specified gasket for this installation was a spiral wound asbestos-filled gasket with a centering ring. However, the maintenance personnel did not know the specifications, as they recalled that a compressed asbestos fiber (CAP) gasket had been used for 7 or 8 years. 

Typically at this plant, substitution of a gasket is authorized only after calculations ensure that the substitution is acceptable. No calculations or authorizations were found. The substitution of a CAP gasket was probably intended as a one-time substitute and it was replaced in kind on each turnaround that followed. The 1/8-inch GAP gasket was theoretically acceptable in this service, but conditions would have required a foil pre.s-sure test to ensure that the 24 bolts had sealed the gasket properly. Unfortunately, the risk of the gasket disintegrating under a high-pressure leak was not considered. 

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