The predictive risk equation developed by Naugle and co-workers is based on four general equations. These equations relate source factors, activity patterns, dose factors, and dose response to risk. The equations are:
Exposure
Concentration x Duration = Exposure
Dose
Exposure x Dosimetry factors = Dose
Individual risk
Dose x Dose-Response relationship = Individual Risk
Population Risk
Individual Risk x Exposed population = Population risk
The framework subdivides the four components of the risk assessment process into ten elements to provide a refined and systematic way of describing the risk estimation process. These elements are:
The starting point for the risk analysis. The estimation of risk can be based on the study of a single source emitting one or more pollutants of concern or the study of a pollutant or mixture that is emitted from one or more sources.
The pollutant concentration of interest depends on the effect that is of interest. The concentration may be the peak concentration, the average concentration, or some threshold concentration.
The exposure duration and setting combines the setting in which exposure occurs and an estimation of the time spent in that environment.
The outcome of exposure duration and setting is individual exposure.
The dosimetry factor addresses factors which influence how much of the exposure to a pollutant is available to the body. For many air pollutants the major factor is inhalation rate.
Dose represents the amount of a substance available for interaction with metabolic processes or biologically significant receptors.
Response factor describes the magnitude of the response of an individual to a given dose of the substance.
Individual risk represents the risk of an individual exposed at the given concentration, duration, etc. For cancer risk the individual risk is expressed as lifetime individual risk.
Exposed population is the number of individuals that are exposed to the conditions covered by the risk assessment.
The risk calculation framework can be placed in a spreadsheet format for ease of calculation. RISK uses the spreadsheet format shown in Figure 2. The IAQ model calculates the concentration, duration, and exposure. The user must independently provide the dosimetry factors, the response factors, and the population.