While labor organizations and public health experts argue that the agency has been lax in recent years, some industries have applauded its efforts. Construction companies, for example, are pleased that OSHA recently decided to relax the standards for handling explosives.

The agency had long been the target of businesses that criticized its rules as arbitrary, costly and confusing. Three of the biggest industries regulated by OSHA — transportation, agribusiness and construction — have given more than $630 million in political campaign contributions since 2000, with nearly three-quarters of that money going to Republicans. The Bush administration has promised to address their concerns.

Change at OSHA

“We’re also going to bring a transparency to the regulatory jungle that is unprecedented in the federal government,” Labor Secretary Elaine L. Chao told business owners in a speech on June 2002. “There are more words in the Federal Register describing OSHA regulations than there are words in the Bible. They’re a lot less inspired to read and a lot harder to understand. This is not fair.”

Until recently, Congress has provided no significant oversight of OSHA. With Democrats now back in control, House and Senate committees are holding hearings this week.

Among those who testified Tuesday was Eric Peoples, a former worker at the popcorn plant in Jasper, a small town 125 miles south of Kansas City. Once healthy, the 35-year-old Mr. Peoples has been told by doctors that he will need a double-lung transplant. Far from Washington, he finds the debate over the calculus of regulation — the costs to companies and consumers of upgrading workplaces versus the possible health benefits to workers — baffling.

“I can’t understand what it would take to get them to pass rules to make it safer to handle this stuff,” Mr. Peoples said, referring to diacetyl. “Something needs to be done.”

The Occupational Safety and Health Administration was created under President Richard M. Nixon in 1970 after Congressional hearings exposed dangerous workplace conditions. The agency was to set and enforce safety standards as well as detect health hazards before they could take a toll on workers. Since the agency’s creation, deaths and injuries on the job have steadily declined. Regulators have taken credit for much of that trend, though experts also cite pressure from insurers and lawsuits. Government records show that in 2005, more than 6,800 workplace-related deaths occurred, along with 4.2 million injuries and illnesses. OSHA officials say that since 2001, the fatality rate has declined by 7 percent and the injury rate by 19 percent.