Public Citizen Health Research Group v. Tyson

Ethylene oxide (EtO) was a chemical widely used in manufacturing and hospital instrument sterilization. The Occupational Safety and Health Administration (OSHA) (defendant) assessed the risks of low-level EtO exposure. OSHA used evidence submitted by a significant portion of the scientific community to determine that exposure to one part per million (ppm) of EtO posed a significant risk to human health. OSHA modeled EtO’s health effects using assumptions about the relationship between EtO exposure and biological response, including the assumption that EtO exposure and biological response vary proportionately and that there is no threshold level below which EtO exposure produces no adverse health effects. In 1984, OSHA issued a final rule that required employers to limit employee exposure to EtO. The final rule required that employers ensure that their employees were not exposed to an airborne concentration of EtO in an excess of one ppm as an eight-hour time-weighted average. If EtO was detected at 0.5 ppm, employers were required to engage in regular employee monitoring. The Association of Ethylene Oxide Users (AEOU) (plaintiff) challenged OSHA’s model and petitioned the court of appeals for review. AEOU argued that the model unlawfully assumed that there was no threshold level of EtO exposure and that EtO was harmful at low doses because the model was based on probable or suspected risks and OSHA’s assumptions were not unequivocally scientifically proven.