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Written by Robert E. Sheriff, MS, CIH, CSP, President
April 4, 2020; Updated November 2021
Sulfur Hexafluoride (SF6): A Common Tracer Gas Used for Ventilation Studies
Sulfur Hexafluoride, also known as SF6, is by far the most common tracer gas used for ventilation studies. The primary reason is that it is easy to detect at low concentrations (even in the parts per billion (ppb) or parts per trillion (ppt) range) and has very low toxicity. The best instrument to detect SF6 is an Infrared Spectrophotometer (IR Spec). Although the portable units are still a bit heavy, it allows direct reading measurements in real-time. There are other detection instruments, but they don’t have the IR Spec sensitivity and can have potential interferences.
Gas Bag / Tedlar Bag
An alternate to direct reading is to collect air samples in a gas bag (the best is a Tedlar bag) that will be transported to a laboratory for analysis. The problem with this approach is that you are starting at an unknown point and finishing at an unknown point. Taking multiple samples over various times makes this approach a little more reasonable, but it is still not as effective as real-time measurements.
Although not as sensitive as an IR Spec, a Flame-Ionization Detector (FID) is also useful. Its weakness is that in the presence of other VOCs, it can give uncertain readings or is subject to readings involving other VOCs.
Measuring Air Changes Per Hour (ACH)
The most common use of SF6 tracer gas in ventilation application is as a tracer gas to measure Air Changes Per Hour (ACH) in a commercial building. This is usually done for locations that primarily use general ventilation rather than local exhaust ventilation to move air in and out of the building.
Another use of SF6 is as a leak detector in closed air systems and it can even be used to detect leaks in an open duct system.
It is important to note that a Photo-Ionization Detector (PID) cannot be used to detect SF6 since the ionization potential of SF6 is above the detection range of the standard detector and even the expanded range of the PID.
Tracer gas is often the recommended method of measuring Air Changes Per Hour (ACH) over actual airflow measurements where the access points in the HVAC System are very numerous or are difficult to access.
It is also useful where a building is classified as a “safe haven” in the event of a release of hazardous chemicals or gases into the atmosphere.
For more information, contact Atlantic Environmental.
Our primary service areas for Sulfur Hexafluoride Ventilation Testing are New Jersey NJ, New York NY, (New York City), Pennsylvania PA, Connecticut CT, Delaware DE, Massachusetts, (Boston) MA, Rhode Island RI, Washington DC, Wisconsin WI, Maryland MD, Michigan MI, Illinois (Chicago) IL, Virginia VA, Indiana IN, Georgia (Atlanta) GA, Alabama AL, North Carolina NC, South Carolina SC, Tennessee TN, Texas (Dallas, Ft Worth) TX, Oklahoma OK, DC, Arkansas AR, Florida FL. We can service most other areas of the U.S. but additional travel charges will be applied.