A chemical risk assessment uses toxicology, epidemiology, and exposure data to estimate how much of a chemical a person can safely be exposed to before experiencing health effects. The process has two steps: hazard identification (does the chemical cause harm?) and dose-response assessment (how much causes harm?). Independent risk assessments, like those produced by IRIS, create a firewall between the science of how dangerous a chemical is and the policy decision of how to regulate it. When the same agency writes both the science and the regulation, critics say industry influence can distort both.