Frequently Asked Questions about MDH Air Guidance

This page provides answers to frequently asked questions about the Health Risk Values Rules. For questions or additional information, see the Air Values Table or contact the Health Risk Assessment Unit.

On this page:
What are Health Risk Values?
How are Health Risk Values Developed and Updated?
How are Health Risk Values Used?
Are the Health Risk Values Protective of Susceptible Populations?
What Other Types of Guidance Values are Developed by MDH?

What are Health Risk Values?
Health Risk Values (HRV) are concentrations of chemicals (or a defined mixture of chemicals) that are likely to pose little or no risk to human health. HRVs are stated in micrograms of chemical per cubic meter of air (µg/m3), and they are developed for a specified length of exposure (e.g., one hour, 13 weeks, a lifetime). HRVs were adopted into Rule in March 2002.

HRVs also may be expressed as micrograms of chemical per kilogram body weight per day of exposure (µg/kg-day). These values, called multi-media HRVs (HRVms), are developed for chemicals emitted to ambient air where multi-media exposures are important to public health. These values are based on oral exposures.

The HRVs are uniformly developed, science-based rules developed through a stakeholder involvement process. They are based solely on health effects information. Other factors such as the ability to detect or monitor a chemical, the cost of controlling a chemical, or background concentrations of a chemical are not considered in their development.

How are Health Risk Values Developed and Updated?
HRVs are developed using the best peer-reviewed science and public health policies available at the time of their development. The HRVs are derived using U.S. Environmental Protection Agency (US EPA) guidelines and the standard methodology used to derive US EPA's Reference Concentrations (RfCs) and California EPA's Reference Exposure Levels (RELs).

MDH does not currently have plans to revise Health Risk Values Rules. However, we update our guidance values for air and other environmental media at the request of Minnesota state agencies. For more information, see the Health-Based Guidance Development Process and Chemicals Under Review.

How are the HRVs Used?
HRVs are used by the Minnesota Department of Health and other state agencies, such as the Minnesota Pollution Control Agency (MPCA), to assist in the assessment of potential health risks from exposures to chemicals in ambient air. HRVs can be used for assessing risks in the environmental review process, issuing air permits, risk assessments and other site-specific assessments. For example, see the MPCA Air Emissions Risk Analysis process. The application of HRVs is not specified in Minnesota rule.

It is important to note that the absence of a chemical from the HRV list does not imply that there are no health risks associated with the emission of that chemical to air.

HRVs are classified as acute, subchronic, and chronic based on the length of the exposure to a chemical or mixture.

  • Acute HRVs are compared to one-hour averaged concentrations of chemicals or defined mixtures of chemicals in ambient air.
  • Subchronic HRVs are compared to a 13 week averaged concentration of a chemical or defined mixture of chemicals in ambient air.
  • Chronic HRVs are compared to an annual average concentration of a chemical or defined mixture of chemicals in ambient air.

The HRVs were not developed (and should not be used) to evaluate workplace exposures. The Occupational Safety and Health Administration, United States Department of Labor, is responsible for regulating workplace exposures.

Are Health Risk Values Protective of Susceptible Populations?
HRVs are developed using public health protective practices that protect susceptible portions of the population (including but not limited to children, pregnant women and their fetuses, individuals compromised by pre-existing diseases, and elderly persons). However, HRVs may not be protective of every individual. HRVs are not necessarily protective of hypersensitive individuals who may respond low level chemical exposures.

What Other Types of Values/Guidance are Developed by MDH?
The Minnesota Department of Health develops other types of values/guidance at the request of MDH programs and other state agencies. For a complete list of recommended values for air, see the Air Values Table.

For additional information, also see: MDH Guidance, Health-Based Guidance Development Process and Chemicals Under Review.

Updated Thursday, November 14, 2013 at 07:52AM