Health impact review of toxic air pollution

Updated air toxics rule

Amendments to Controls for New Sources of Toxic Air Pollutants (Chapter 173‑460 WAC) became effective in December 2019. This rule includes air quality permit requirements for businesses that emit toxic air pollutants. The amendments updated the list of toxic air pollutants and the emission thresholds using the best available health effects information in 2019.

We started a related, but different, process we call exploratory rulemaking to assess possible changes to the rest of Chapter 173-460 WAC. This rulemaking is on hold.

Air toxics

We review emissions of toxic air pollutants (sortable list) from new or modified stationary air pollution sources. This review is part of the Notice of Construction permit process.

The purpose of the health impact review is to:

• Prevent air pollution by controlling emissions of toxic air pollutants from new sources.
• Reduce toxic emissions as much as possible.
• Maintain healthy air quality.

There are up to three levels of review for making permit decisions about projects that emit toxic air pollutants.

First tier review

Most new projects only need a first tier review (toxic screening) before getting a permit. First tier review compares the expected level of toxic air pollutants to established health-based acceptable source impact levels (ASILs). If the estimated impacts are less than the acceptable source impact levels, then health risks are considered insignificant and the clean air agency might issue a permit.

Second tier review

Some projects — like data centers — require a second tier review that includes a health impact assessment. If a project emits more of a toxic air pollutant than is allowed by the acceptable source impact levels (ASILs), then the applicant must submit a health impact assessment. This review determines the increase in lifetime cancer risk and other health effects for people who are exposed to increased amounts of the toxic air pollutant from the proposed project. The cancer and health risks are then compared to the maximum risk allowed by a second tier review to see if they are within allowable limits.

Third tier review

Third tier review is rarely needed. If the emissions of a toxic air pollutant result in a risk higher than allowed by the second tier review, a business can ask us to do a third tier review. In that review, we decide whether the risk of the project is acceptable based on:

• Whether available preventive measures can reduce emissions enough to protect human health.
• The estimated environmental benefits.