The Labor Department's Occupational Safety and Health Administration is circulating a draft of what it calls its "highest priority standard," the one that is designed to reduce the number of grain elevator explosions. Already, three months before the formal proposal of the rule, a major item of controversy has emerged: how to deal with loose combustible dust in open areas of the elevators, dust that can act like gunpowder when conditions for an explosion are right. About 130 explosions in the last five years have killed 102 people.

One union safety expert said that unless OSHA sets a minimum level for grain dust on the open surfaces of the nation's 15,000 grain elevators, the standard has little more meaning than a simple command not to let the elevator blow up. But Barry White, an OSHA safety expert, counters that setting a standard would imply that lesser levels of dust are safe, when, he says, no levels are safe. Setting an unrealistic minimum level, he continued, would encourage a scofflaw attitude.

The minimum level being discussed is one-eighth of an inch -- or the minimum amount of dust that can hold a footprint. White says tests show explosions are possible with dust levels as low as 1/100th of an inch. "Our strategy," White said, "is to deal with ignition sources" -- smoking in the elevators would be banned and welding would require an OSHA permit -- "then to make them clean and clean and clean and ventilate and ventilate and ventilate."