RISK IAQ model

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The text on this page is taken from an equivalent page of the IEHIAS-project.

The Indoor Environment Management Branch of the US-EPA has developed an IAQ model for analyzing the impact of sources, sinks, ventilation, and air cleaners on indoor air quality. The RISK model incorporates the latest results from EPA research on sources, sinks, ventilation, and air cleaners. The latest published version of the computer model, called RISK, is designed to allow calculation of individual exposure to indoor air pollutants from sources. The model is designed to calculate exposure due to individual, as opposed to population, activity patterns, and source use. The model also provides the capability to calculate risk due to the calculated exposure. RISK is calculated using a risk calculation framework developed by Naugle and Pierson (1991).

The model uses data on source emissions, room-to-room air flows, air exchange with the outdoors, and indoor sinks to predict concentration/time profiles for all rooms. The concentration/time profiles are then combined with individual activity patterns to estimate exposure. The model allows analysis of the effects of air cleaners located in either/or both the central air circulating system or individual rooms on IAQ and exposure. The model allows simulation of a wide range of sources including long-term steady-state sources, on/off sources, and decaying sources. Several sources are allowed in each room. The model allows the analysis of the effects of sinks and sink reemissions on IAQ.

Model description


The RISK model was designed in order to support the overall mission of the US-EPA IAQ engineering research, namely ‘to develop cost-effective tools, techniques, technologies, and guidance necessary to prevent or reduce individual exposure to indoor air pollutants’. In this respect, RISK was developed and aims at:

  • Providing tools to integrate the results of IAQ research
  • Providing tools for analysis of the effects of IAQ control options on individual exposure
  • Providing tools for improving understanding of interactions of sources, sinks, ventilation, building parameters, air cleaners, and individual activity patterns on individual exposure to indoor air pollutants.

Data related to source characterization were developed as part of EPA’s indoor air source characterization program. These data were used to develop source emissions models which are incorporated in the RISK IAQ model. The source models in RISK are continuously being updated, whenever new information is developed by the source characterization research program of EPA.

RISK is designed using the concepts of buildings and scenarios. The model consists of 1) fixed information about building, the number of rooms, the room dimensions, and the arrangement of rooms in the building, and 2) changing information on sources, sinks, air exchange and room-to-room flows.


Fields of model: exposure, risk assessment

Spatial Resolution: the RISK model assumes homogenous concentration distribution within each room of the building enveloppe (assume all rooms in a building are well mixed)

Temporal Resolution: defined by user, depending on emission source (down to seconds); activity patterns defined within a 24 h time span

Pollutants/Stressors/Agents covered: VOCs, PM and O3, other pollutants. The model has recently been revised to allow improved analysis of particulate matter and multiple pollutants.

Health effects: The model also provides the capability to calculate risk on health effects due to the calculated exposure. RISK is calculated using a risk calculation framework developed by Naugle and Pierson (1991) and involves instantaneous, peak and cumulative exposure, individual and population risk.

Population subgroups considered: can be specified by activity pattern

Source type of emissions/sectors: The RISK model has 2 sub modules focusing on the modelling of emission from sources, the IAQX toolkit (Simulation Tool Kit for Indoor Air Quality and Inhalation Exposure) and the PARAMS toolkit.


IAQX version 1.0 consists of five stand-alone simulation programs:

  • GPS.EXE is a general purpose IAQ simulation program with a rich library of indoor source models. It also handles chemical reactions.
  • VBX.EXE implements four models for VOC emissions from solvent-based indoor coating materials. The built-in VOC property database simplifies the simulation process.
  • SPILL.EXE contains three models for unstrained, small-scale solvent spills in the indoor environment.
  • SLAB.EXE implements a mass transfer model for VOC emissions from building materials.
  • PM.EXE is for indoor particulate matter (PM). It considers such factors as penetration of outdoor PM, emissions from indoor sources, deposition, ventilation, and filtration.


This Microsoft Windows-based computer program PARAMS 1.0 implements 30 methods for estimating the parameters in indoor emissions source models, which are an essential component of indoor air quality (IAQ) and exposure models. These methods fall into eight categories:

  • the properties of indoor air,
  • the first-order decay rate constants for solvent emissions from indoor coating materials,
  • gas-phase, liquid-phase, and overall mass transfer coefficients,
  • molar volume,
  • molecular diffusivity in air, liquid, and solid materials,
  • solid-air partition coefficient,
  • vapor pressure and volatility for pure organic compounds and petroleum-based solvents, and
  • the properties of water. Potential users include those who develop or use IAQ and exposure models, and those who develop or use quantitative structure-activity relationship (QSAR) models. In addition, many calculations are useful to researchers in areas other than indoor air quality. Users can benefit from this program in two ways: first, it serves as a handy tool by putting commonly used parameter estimation methods in one place; second, it saves users time by taking over tedious calculations.


The model consists of fixed information about the building, the number of rooms, the room dimensions, and the arrangement of rooms in the building (can not be changed within scenarios). Scenario definitions require as input the presence/location/emission of indoor sources and sinks, air exchange, and room-to-room flows, and individual activity patterns. Properties of pollutans (molecular weight, diffusivity, toxicological reference values for non-cancer, cancer and irritation) are needed.


Data output: The RISK model calculates as output 1) concentration versus time, 2) instantaneous exposure versus time, 3) cumulative exposure versus time, 4) total exposure for each activity pattern, and 5) time exposed to irritant concentration for each activity pattern, 6) risk related to the exposure. The RISK model provides its output both as graphs and tables.

Output format: tab delimited file

Description of processes modelled and of technical details:

We refer to the EPA website for further information and downloads of the software and manual.

Time required for a typical run: seconds

Operating system: MS Windows

Degree of mastery: intermediate expertise

Developed by: Indoor Environment Management Branch, US-EPA

Cost for using the model: free

See also

Integrated Environmental Health Impact Assessment System
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