Diacetyl (2,3-butanedione) is a chemical used to add favor and aroma to food and other products. Diacetyl and its substitutes are commonly manufactured in microwave popcorn and favoring production plants, and they also are used in the making of beverages, snack foods, baked goods, prepared canned and frozen foods, and candy (OSHA, 2010a, b). Food and Drug Administration (FDA, 2011) classifies diacetyl and its substitutes as "generally recognized as safe (GRAS)."

While the substance may be safe to consume, that does not mean it is safe to work around. Through extensive research and case studies, NIOSH has found that diacetyl is a standard air contaminant in the popcorn and favoring industry (OSHA, 2010a, b). Numerous jobs may expose workers to diacetyl, including mixing, weighing, pouring, transferring or other handling activities, as well as during cleaning and maintenance operations, quality assurance and laboratory work (OSHA, 2010a, b).

In May 2000, numerous workers at a microwave popcorn processing facility displayed similar respiratory symptoms and, ultimately, developed bronchiolitis obliterans (OSHA, 2011a, b, c). Since bronchiolitis obliterans is an uncommon lung disease, the local health department (Missouri Department of Health and Senior Services) launched an investigation and requested NIOSH's assistance. NIOSH (2003a, b; 2006) linked the development of bronchiolitis obliterans to occupational exposure to diacetyl. Bronchiolitis obliterans be-came known as popcorn workers' lung due to the correlation of the disease with the butter favoring of microwave popcorn (Kanwal & Kullman, 2007; NIOSH, 2003a, b). Many lawsuits from popcorn and favoring plant workers, as well as regulatory concerns, soon followed.

NIOSH's investigations sparked OSHA's inter-est. The agency added microwave popcorn processing plants to its national emphasis program (NEP) in 2007 (OSHA, 2007a, b; 2011a, b, c). OSHA launched this program to address controls required to reduce and eliminate occupational exposure to diacetyl. In addition, OSHA (2007a, b) added the industry to the targeted inspection list and offered compliance assistance to processing plants.

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