Environmental odors: What's that smell?

Odors in the environment can come from many sources, including human activities, animals, nature, vehicles, and industrial activities. Click here for a link to the Centers for Disease Control website of various odors/vapors in the environment and what they smell like.

Vapors Sources

Gases or vapors generated by the tank waste accumulate in the tank headspace (area between the waste surface and the tank dome). From time to time, chemical vapors may potentially enter a worker's breathing zone.

Static operations

Hanford’s waste tanks are vented to the atmosphere through pipes that extend above ground from the tank dome. Double-shell tanks are actively ventilated with exhaust systems. Single-shell tanks are passively ventilated, allowing the tanks to “breathe” with changes in atmospheric pressure, temperature differences between the inside of the tank and the surrounding atmosphere, and wind.

Active operations

In addition, much of the work at tank farms consists of “waste-disturbing activities,” potentially resulting in a greater possibility to stir up vapors that may vent to the atmosphere. During work planning additional controls are put in place to protect workers and their health against potential hazards.

Leading indicators

This is a brief summary of PNNL- 27449, Leading Indicator Phase 2 Report, released 4/23/2018.

Some of the chemicals in the tank farm headspace vapors have Occupational Exposure Limit (OEL) levels that are lower than the ability to detect and measure with real-time instruments. Ideally, the measurements of one chemical will tell us something about the levels of the more difficult-to-measure Chemicals of Potential Concern (COPCs). When such relationships exist, the measurable chemicals are called leading indicators (LIs).

Pacific Northwest National Laboratories (PNNL) released a study in April 2018, entitled, Leading Indicator Phase 2 Report, which describes a process for identifying LIs for use across the tank farms. While the 2016 Phase 1 report relied on pairs of analytical sampling data from the Tank Waste Information Network System (TWINS) and Site Wide Industrial Hygiene Database (SWIHD), the Phase 2 report took advantage of additional data that was not previously available, including data from the respirator cartridge filter testing program, and the RJ Lee Mobile Laboratory collected from both static and tank disturbing work activities. The Phase 2 report also adopted a different statistical process for determining the confidence level for an LI to predict whether one or more COPCs are present above or below their OEL levels.

The PNNL researchers reported that the trio of ammonia, nitrous oxide, and mercury may together serve as LIs for up to 45 of the 61 total COPCs (at the time of this report) and 21 of 24 COPCs found on Tank Vapor Information Sheets (TVIS) for individual tank farms. Fortunately, all three of these candidate compounds can be and are routinely monitored in real-time using direct reading instruments in the tank farms. For more information, please click here.


This is a summary from October 2016 of the PNNL-25533 Leading Indicators Process Development report, developed to provide an overview to inform and educate the reader of the report contents and a list of frequently asked questions on the subject matter.

Tank farm vapors are a mix of gases, and some gases in the mix are more easily detected than others. The more easily detected gases can be monitored by Industrial Hygiene technicians in real-time using handheld instruments. Monitoring for one or two chemicals (a leading indicator also referenced as a limiting chemical) can indicate the presence of other chemicals that cannot be monitored in real-time. It is possible to protect against potentially harmful tank vapors by monitoring for leading indicators. An October 2016 study, (PNNL-25533), concluded that two tank farm gases, ammonia and nitrous oxide, were the best candidates to use as leading indicators. The analysis will be updated next year after more data is collected.


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Waste Transfers

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