DEPARTMENT OF ENVIRONMENTAL AND OCCUPATIONAL HEALTH 

                                                                                                   SCHOOL OF PUBLIC HEALTH AND HEALTH SERVICES 

              January 16, 2007

              Keith Umemoto
              Executive Officer
              Occupational Safety and Health Standards Board
              2520 Ventura Oaks Way, Suite 350
              Sacramento, CA 95833

              Dear Mr. Umemoto,

              Tomorrow, the Occupational Safety and Health Standards Board will consider the question of
              an Emergency Temporary Standard to protect workers exposed to the chemical diacetyl, which
              has been implicated as a cause bronchiolitis obliterans, a debilitating and sometimes fatal lung
              disease. It is possible that at the meeting, individuals may question the evidence concerning
              diacetyl’s toxicity, and call for more research instead of protective action.

              In a letter to US Secretary of Labor Chao sent July 26, 2006, a group of prominent scientists
              and physicians wrote that there was “compelling evidence” of the link between diacetyl and
              bronchiolitis obliterans. As the letter describes, the number of cases among exposed workers
              is increasing and there is powerful animal evidence that exposure to diacetyl causes respiratory
              tract damage among laboratory animals. The letter and additional materials on diacetyl can be
              downloaded from:

              Complete evidence of diacetyl’s toxic effects on humans is limited by a problem we often face
              in epidemiology: we do not have (and cannot have) controlled studies of humans exposed to
              the chemical, while not exposed to other potential toxins. There are multiple chemical
              exposures at factories where diacetyl is used. We must rely on these studies of the patterns of
              disease in workplaces, in addition to evidence gathered in experiments with laboratory

              Since writing our letter in July 2006, we have obtained additional powerful evidence of the
              effects of diacetyl exposure. This evidence is an unpublished study entitled “Respiratory
              effects in workers of a diacetyl production plant with a special focus on bronchiolitis
              obliterans: An evaluation among currently working and retired workers.” The study finds
              three cases of bronchiolitis obliterans, among the workers in a Dutch factory where diacetyl
              was manufactured. We have posted the study on the website of the Project on

                                                 THE PROJECT ON SCIENTIFIC KNOWLEDGE AND PUBLIC POLICY 

                                         2100 M STREET, NW ∙ WASHINGTON, DC 20037 ∙ 202‐994‐0774 ∙ FAX 202‐994‐0011 

Scientific Knowledge and Public Policy (SKAPP):

Although this study alone does not prove conclusively that the cases were caused by
diacetyl, three cases of the rare condition bronchiolitis obliterans at a factory where
diacetyl is manufactured provides strong additional support for the need for immediate
action to protect workers from this dangerous chemical.

Thank you for your consideration.

David Michaels, PhD, MPH
Director, The Project on Scientific Knowledge and Public Policy
Research Professor and Acting Chairman
Department of Environmental and Occupational Health

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