As distinguished from acute. Chronic respiratory disease A persistent or long-lasting intermittent disease of the respiratory tract. CO Carbon monoxide. COD Chemical oxygen demand. A measurement of visibility interference in the atmosphere.
Cohort study See prospective study.
Combustion nucleus Condensation nucleus formed as a result of industrial or natural combustion processes. Any comparison among the risks of two or more hazards with respect to a common scale. Common mode failures Several errors in a technological system occurring simultaneously. The ratio of the concentration of a compound or radionuclide in an organism or its tissues to the concentration in the surrounding under equilibrium, or steady-state conditions. As with significance levels, confidence levels are commonly chosen as 0.05 or 0.01, the corresponding confidence coefficients being 0.95 or 0.99.