The Court's opinion indicates that risk assessments, which may involve mathematical estimates with some inherent uncertainties, are a means of demonstrating the existence of significant risk.
Some risks are plainly acceptable and others are plainly unacceptable.
If, for example, the odds are one in a billion that a person will die from cancer by taking a drink of chlorinated water, the risk clearly could not be considered significant. OSHA has always considered that a working lifetime risk of death of over 1 per 1000 from occupational causes is significant. This has been consistently upheld by the courts. Counterpart risk figures for 20 years of exposure are excess cancer risks of 4.5 per 1,000 workers and an estimated asbestosis incidence of 2 cases per 1,000 workers. OSHA's current estimates of employee exposure in the various operations covered by these standards are referenced in the Regulatory Impact Analysis found later in this document.