352Oil Mist Explosion in a Compressor Test Loop

This explosion, discussed by Schmitt (1973), occurred in 1959 in a compressor test facility at Ingersoll-Rand Co.'s plant in Phillipsburg, N.J., USA. The test of a centrifugal compressor was being conducted in accordance with standard procedure, which involved the use of a closed loop for containment and re-circulation of the gas used during the test. The test was nearly completed when, after approximately six hours of test opera tion, an explosion occurred. The inlet side of the loop pipe ruptured with great violence, claiming the lives of six men, severely injuring six others, and imposing minor injuries on twenty-four additional men.

The explosion was described as a heavy flash fire accompanied by shock waves. Small localized fires and smoke followed. The floor plates of the platform immediately over the test loop were ripped loose. Heavy brick walls in the immediate vicinity were blown out. The roof of the building immediately over the blast was damaged and moved approximately 30 cm. The lightweight side walls of the building were torn off. Many windows were broken, some of these being located as far as 150 m away from the explosion center. The test loop, the seal oil system, and most of the equipment on the lower level were destroyed or damaged beyond repair. The coupling spacer between the gear and the compressor was shattered, and the coupling end of the gear pinion was twisted off and thrown away to outside the building.

The centrifugal compressor involved was the high-pressure unit of a system employed for compressing natural gas in oil field re-pressuring service. Floating-ring-type oil seals were used to contain the gas within the test loop where the shaft passed through the casing. This design combined the seal with the radial bearings. The sealing medium was oil supplied at a pressure of 3-3.5 bar above the gas pressure in the loop. A small quantity of oil was permitted to pass through the seal for lubrication.

The investigating committee concluded that regardless of the details of the design of this type seal, extremely small leakages of oil into the gas stream are unavoidable. As a result of the high air velocities, which tend to atomize and mix the oil droplets with the gas flow in such a manner that they cannot be effectively drained, the concentration of oil spray in the air tends to increase with time. The definite evidence of a combustion-type explosion confirmed that there must have been enough hydrocarbon oil present within the loop system to produce an explosive oil/air mixture throughout the loop system. Oil had been found to be present when blowing out low points in the piping between test runs. The destructive pressures were produced by heat liberated by the combustion of fine oil spray being circulated by the compressor. The pressure produced by an explosion is approximately proportional to the initial absolute pressure of the explosive mixture. For mixtures of common hydrocarbon compounds in air, the ratio of explosion pressure to initial pressure can be as high as eight.

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