The Occupational Safety and Health Administration proposed long-awaited rules on Friday to limit crystalline silica, a move it said would prevent nearly 700 deaths a year by reducing exposure to these very small particles that can cause lung cancer and other diseases.

OSHA faced heavy pressure from labor leaders, who argued that the current exposure limits, adopted four decades ago, were lax and should be strengthened to prevent silicosis, an irreversible respiratory disease that can be fatal. But business groups lobbied against the proposal, questioning whether it would be feasible to carry out and noting that silicosis deaths were declining.

“Exposure to silica can be deadly, and limiting that exposure is essential,” said David Michaels, the assistant secretary of labor in charge of OSHA. He estimated that the proposed rule would prevent 1,600 new cases of silicosis each year.

Dr. Michaels said the rules — issued after two and a half years of delay — would affect 534,000 businesses, 90 percent of them in construction. He said it would cost industry $640 million to comply with the new rules, averaging $1,242 a company — but he estimated that the total benefits would exceed $4 billion.

Crystalline silica — tiny particles no more than one-hundredth the size of grains of sand — is created during work with stone, concrete, brick or mortar. It can occur during sawing, grinding and drilling and is common in glass manufacturing and sand blasting. One government study found that many workers in hydraulic fracturing, known as fracking, were exposed to 10 times the permissible level of silica.

Dr. Michaels said, “Every year, exposed workers not only lose their ability to work but also to breathe. This proposal is expected to prevent thousands of deaths from silicosis — an incurable and progressive disease — as well as lung cancer.”

He said the public would have 90 days to submit written comments before public hearings would be held.

Marc Freedman, executive director of labor law policy at the United States Chamber of Commerce, questioned the need for the rules. For general industry and maritime, the proposed permissible exposure levels will be cut to 50 micrograms a cubic meter of air from 100 micrograms. The construction industry’s exposure levels will be cut 80 percent, to 50 micrograms from 250 in a cubic meter of air.

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