Finding a More Environmentally Friendly Tracer Gas for Fume Hood Performance Tests
From ASHRAE Journal Newsletter, Oct. 12, 2021
Sulfur hexafluoride (SF6) is specified by ASHRAE Standard 110-2016, Method of Testing Performance of Laboratory Fume Hoods, during tracer gas tests to quantitatively test and challenge the ability of the fume hood to provide adequate containment. But, it has been identified as one of the most potent greenhouse gases (GHG).
It has been estimated as being a 24,000 times stronger GHG than carbon dioxide and is increasingly being banned from use. This has increased the importance of finding an environmentally friendly alternative tracer to SF6. That was the purpose of RP-1573—Determination of Suitable Replacement of SF6 When Used as a Tracer Gas In Accordance With ANSI/ASHRAE Standard 110.
ASHRAE Journal spoke with researcher Tom Smith, Member ASHRAE, about this completed research project.
What lessons, facts and/or guidance can an engineer working in the field take away from this research?
The method of generating SF6 specified in the existing standard creates potential for some variability in the challenge to hood containment. The research project identified how the volume and concentration of the challenge plume can be better controlled and how less expensive tracers and detectors can be used to provide a comparable challenge to hood performance and potentially eliminate the variability.
How can this research further the industry's knowledge on this topic?
The results identify the issues associated with challenging fume hood containment and the need to have a consistent and replicable tracer gas challenge to hood containment. Common issues associated with quantitative hood containment tests include:
- Generating a sufficient volume of the air tracer through the ASHRAE Standard 110 ejector;
- Generating the air tracer at a constant concentration throughout the duration of the five-minute challenge tests; and
- Detecting the concentrations outside the fume hood with sufficient speed, precision and accuracy.
The research indicated that the ability to consistently generate the tracer at a rate of 4 L/m, producing a plume inside the fume hood of comparable concentration and the capability of the detector to accurately detect the tracer at a rate or 1 Hz are critical to achieving comparable results.
As for a new tracer, the research project indicated that a common material like isopropanol or isopropyl alcohol can be vaporized, mixed with air and discharged from the ASHRAE ejector diffuser to provide an equivalent tracer challenge to hood containment. The ASHRAE Standard 110 committee is reviewing the feasibility of using isopropyl alcohol as an alternative air tracer for fume hood testing.
Were there any surprises or unforeseen challenges for you when preparing this research?
There were many challenges identified during the investigation. The most significant finding was the potential for the existing method to produce inconsistent challenges to hood containment. This variability resulted in difficulties getting repeatable results to serve a standard for comparing results using alternative tracers. Other challenges included finding the right combination of tracer and detector that provided an equivalent challenge with the sensitivity required to detect escape from the fume hood. Furthermore, the investigation revealed that generation of a consistent tracer plume is difficult and slight variations in outlet plume concentration and turbulence can affect the consistency of results.