ASHRAE Research Project 1573
Determining a Suitable Replacement of SF6 When Used as a Tracer Gas
From ASHRAE Journal Newsletter, July 14, 2020
Using fume hoods in laboratories decreases the risk of workers being exposed to dangerous airborne chemicals, so it is important to have properly functioning fume hoods for safety purposes.
The tracer gas method from ASHRAE Standard 110, Method of Testing Performance of Laboratory Fume Hoods, uses sulfur hexafluoride (SF6), which is a greenhouse gas that is damaging to the environment. A recently completed ASHRAE research project aimed to find a more environmentally friendly tracer gas and alternative testing methods to result in better fume hood performance. Tom Smith, Member ASHRAE, discusses the research.
1. What is the significance of this research?
Smith: People working in laboratories rely on proper fume hood performance to protect themselves from overexposure to hazardous airborne chemicals generated during scientific activities. Tens of thousands of fume hoods have been tested to challenge and quantify hood containment using the ASHRAE 110 tracer gas method from ASHRAE Standard 110, Method of Testing Performance of Laboratory Fume Hoods. The results have been used to improve safety and reduce energy consumption by enabling better performance of fume hoods, laboratories and ventilation systems. The ASHRAE 110 tracer gas test specifies use of sulfur hexafluoride (SF6) that has been identified as an extremely potent greenhouse gas and reported to be 24,000 times worse that carbon dioxide (CO2).
In keeping with ASHRAE’s commitment to occupant safety and environmental health, Research Project 1573 was initiated by the ASHRAE Technical Committee 9.10, Laboratory Systems, to determine a more environmentally friendly alternative to SF6.
2. Why is it important to explore this topic now?
Smith: Use of SF6 as an air tracer is increasingly being discouraged by organizations throughout the world and has been banned in California for “as used” fume hood performance tests. An alternative tracer is required to continue testing fume hood performance and help protect people working with hazardous chemicals. It was discovered that isopropyl alcohol (IPA) and other alcohol mixtures could be vaporized and discharged from the ASHRAE 110 ejector to potentially provide an alternative to SF6 generation during ASHRAE 110 tests.
Alcohol mixtures can be vaporized and generated to investigate fume hood containment. In addition, with some minor modifications, this method can also be applied to evaluate indoor air quality, investigate intrazonal and interzonal migration of contaminants and help evaluate the effectiveness of ventilation systems to dilute and remove contaminants. These methods could be rapidly deployed to help verify how airflow systems affect airborne pathogen transmission and be used to help determine strategies to mitigate risk of exposure to aerosolized pathogens and other hazards.
3. What lessons, facts, and/or guidance can an engineer working in the field take away from this research?
Smith: Fume hood containment and safety performance can be affected by numerous factors, including the aerodynamic design of the fume hood, the configuration of the laboratory, the design and operation of the ventilation systems and the user’s work practices. Testing fume hoods with an air tracer provides a quantitative test of containment and enables identification of the factors affecting safety performance. Conducting fume hood tests with an alternative tracer will enable engineers, industrial hygienists and others the capability to evaluate and improve fume hood safety while reducing their impact on the environment.
The cost of the alternative tracer and associated test equipment is considerably less than using SF6. This may help reduce past barriers to application, resulting in greater utilization, and help facilitate improvement of airflow systems used to mitigate risk of exposure to airborne hazards.
4. How can this research further the industry's knowledge on this topic?
Smith: The work revealed that isopropyl alcohol and other alcohol mixtures can be vaporized, mixed with air, discharged from the ASHRAE 110 outlet diffuser and detected using simple, low-cost and readily available photoionization detectors (PIDs). Hundreds of tests revealed that the alternative test method provided:
- Comparable results to the current ASHRAE 110 method using SF6;
- Dramatically reduced impact of tracer generation on the environment;
- Simpler and less costly testing.
Use of air tracers also has application beyond testing fume hood performance. An alternative method to use of SF6 that is simpler, less costly and has lower environment impact could enable broader application for optimizing airflow systems used in any type of building.
5. Were there any surprises or unforeseen challenges for you when preparing this research?
Smith: There were numerous surprises and obstacles to overcome during the research project. Interestingly, there were very few previous studies undertaken to identify and utilize alternative tracers. When investigating the existing tracer gas test method, it was discovered that small differences in the tracer gas ejector could affect the tracer gas plume from the outlet diffuser. Different ejectors may pose different challenges to hood performance, and there were no obvious indicators of the differences between the ejectors. This posed a problem with determining the standard to compare the results of tests using the alternative tracer.
The study also revealed that deployment of the alternative test method would require development of a user friendly, repeatable method of vaporizing and discharging the alcohol mixture. Development of a commercially available tracer generation system was beyond the scope of the 1573 project. But once complete, the alternative tracer test using IPA or other comparable alcohol mixtures, together with low cost PIDs, may lead to broader application of ASHRAE 110 tests, further improvements in ventilation system performance and better protection for people exposed to airborne hazards.