Performing Exposure Calculations

After obtaining your estimated EPCs, you will perform exposure calculations. These calculations include:

  • Exposure doses (for ingestion and dermal contact, and inhalation under very specific circumstances).
  • Adjusted air concentrations (for inhalation).
  • Hazard quotients (HQs) for evaluating non-cancer effects.
  • Cancer risks (CRs) for assessing risks from carcinogens.

ATSDR recommends health assessors use the tools it has developed for calculating these exposure estimates: PHAST and the SHOWER Model.

Different Definitions of Dose

An exposure dose is the estimate of how much of a contaminant a person might contact based on his or her actions and habits. It is generally expressed as milligrams of contaminant per kilogram of body weight per day (mg/kg/day). Estimating an exposure dose requires identifying how much, how often, and how long a person or population might come in contact with some concentration of a contaminant (i.e., the EPC) in a specific medium. ATSDR calculates exposure doses based on acute, intermediate, and chronic exposure durations.

A dermally absorbed dose is the amount of the exposure dose that is absorbed into the body through the skin. The type and form of a contaminant, among other factors, influence how much of a contaminant is absorbed.

PHAST Exposure Calculator
Four cartoon people in a house with the text Public Health Assessment Site Tool

Use the PHAST Exposure Calculator for performing exposure calculations (exposure doses, hazard quotients, and cancer risks). Health assessors and those involved in the PHA process can request access by emailing

Faucet with a water droplet that is leaching chemicals. Text: ATSDR Shower and Household water-use exposure model

Use the SHOWER Model when evaluating inhalation and dermal exposure to indoor air concentrations of volatile and semi-volatile contaminants from household water use for showering, tub bathing, clothes washing, and other activities. You can use the EPC household water concentration (generated outside of the SHOWER Model) to develop an air concentration and inhalation dose for the inhalation pathway and a dermal dose for the dermal pathway. See how the SHOWER Model fits into the PHA process in this diagram (under development). Also refer to instructions for using the model [PDF – 3 MB] and the SHOWER Model Guidance (under development). Anyone can request a copy by emailing