Setting Safety Standards "d0e1284"

The Explosion Problem

Of all the hazards associated with grain handling, the most serious one is also the most difficult for those outside the grain business to understand. It is grain dust. This dust, generated whenever grain is handled, is easier to ignite and results in a more severe explosion than equal quantities of TNT. One insurance company distributes placards with the warning "Grain dust is like high explosives." Dust explosions account for the vast majority of personal injuries and property losses in grain-handling facilities. There are thousands of small fires in these facilities every year; estimates range from 2,970 to 11,000. But the twenty to thirty explosions a year account for almost 80 percent of the property damage and 95 percent of the fatalities^[6] (see table 4). Making sense of these trends over time is complicated by the changing fortunes of the grain trade. The major explosions in 1977–78 coincided with tremendous increases in wheat exports (primarily to the Soviet Union). The comparatively low number of explosions in recent years, on the other hand, is attributable in part to decreases in grain sales.^[7] Fluctuations in trade patterns notwithstanding, the explosion problem remains the most serious hazard in grain elevators.

Contrary to popular belief, explosions in grain elevators are not caused by spontaneous combustion. To cause an explosion, the dust must be mixed with air to form a dense cloud. (Layered dust only smolders upon ignition.) The airborne dust concentrations must also be above the lower explosive limit (LEL), a condition so opaque that visibility is minimal and breathing is difficult. Concentrations above the LEL occur regularly inside most bucket elevators (described below) but seldom elsewhere in a facility. Also contrary to popular belief, grain elevator explosions are not one big blast. They usually involve a primary explosion and a series of secondary ones.^[8] The primary explosion generates shock waves throughout the elevator, often raising into sus-

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Figure 1. Terminal-Type Grain Elevator

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Table 4 Casualties Resulting from Explosions in the U.S. Grain-Handling Industry, 1976–87
		Explosions	Deaths	Injuries
1976		22	22	83
1977		31	65	87
1978		20	8	46
1979		29	2	18
1980		45	10	50
1981		21	13	62
1982		14	11	32
1983		13	0	14
1984		20	9	30
1985		22	4	20
1986		21	2	14
1987		15	0	18
	Total	273	146	474
	Average/Year	23	12	40
SOURCE : "Some Impacts of a Proposed OSHA Standard in Grain Handling Facilities" (Report prepared by Booz, Allen & Hamilton, Inc., April 1984); Petition for Partial Stay of Grain Handling Facilities Standard, In the Matter of Grain Handling Facilities , March 21, 1988, 5 n. 5.

pension layered dust on walls, rafters, equipment, and the floor. Accumulations of as little as one-hundredth of an inch will propagate the flame from an initial explosion. In other words, layered dust provides the fuel to turn a primary explosion—often itself quite minor—into a major one.

There are two basic schools of thought about how to approach the explosion hazard: one, eliminate ignition sources; two, control airborne and layered dust. Although it seems obvious that neither strategy should be pursued exclusively, the debate over safety standards is often between groups that have a strong preference for one approach.