Diacetyl is a component of the artificial butter flavoring found in microwave popcorn. Exposure during the manufacturing process can cause a lung disease called bronchiolitis obliterans which reduces quality of life and causes premature mortality. Unfortunately, the disease has acquired the moniker "popcorn workers lung." While Congress is pushing for the Occupational Safety and Health Administration (OSHA) to issue a new regulation, the agency has taken a positive (albeit belated) step by examining regulations already on the books which could improve the situation. Last week, OSHA announced a National Emphasis Program with the intent of reducing or eliminating exposure to the butter-flavoring chemical. Among other things, the Program instructs all manufacturers using the chemicals to assess employee exposure levels. OSHA points out in bold-faced type that employers "must conduct" the assessments under the Respiratory Protection standard (29 CFR 1910.134). But OSHA and Congress should watch out. Industry lobbyists and senior congressional Republicans are using their favorite tactic to undermine regulations: attacking the underlying science. According to Inside OSHA (subscription), Rep. Howard McKeon (R-CA) said, "There is no clear scientific evidence that diacetyl alone causes 'popcorn lung' disease." A coalition including the National Association of Manufacturers and the U.S. Chamber of Commerce claimed the bill would "completely ignore" requirements which "make sure OSHA standards reflect the best science available." McKeon and his industry allies should try reading the National Institute for Occupational Safety and Health study which found "inhalation exposure to butter flavoring chemicals is a risk for occupational lung disease."