Estimation of Risk The estimated risks shown in ARB's annual toxics summary pages are calculated using Office of Environmental Health Hazard Assessment's risk assessment guidance. They represent the inhalation (breathing) pathway and follow ARB and CAPCOA's Risk Management Policy for Inhalation Risk Assessments, and can be found in the "Risk Management Policy for Risk Assessment Using the Inhalation Pathway" section. The estimated risks are expressed as the chance per million population that people may have of developing cancer from exposure to the annual mean concentration over 70 years. For example, an estimated risk of "10" means there are an estimated 10 chances in a million (or a 0.001% chance) that people represented by that annual mean may develop cancer from exposure to the monitored air toxic.