by Dr. John McKeon, Medical Director, Airmid Healthgroup. Over 20 years in aerobiology and IAQ research and member of the ASHRAE Environmental Health Committee
The ASHRAE “185 series” encompasses standards designed to evaluate the performance of various air-cleaning technologies, primarily focusing on their effectiveness in removing or inactivating microorganisms and particles in different settings.
ASHRAE 185.1 – Method of Testing UV-C Lights Installed in Air-Handling Units
- Scope: Assesses the effectiveness of UV-C lamps installed in air-handling units (AHUs) for inactivating airborne microorganisms.
- Test Environment: Full-scale AHU setups with UV-C lamps positioned to treat the moving airstream.
- Organisms: Standardized microbial challenges, such as Serratia marcescens.
- Output: Percentage reduction of viable microorganisms in the treated air.
- Primary Use Case: Validation of UV-C disinfection performance in central HVAC systems.
ASHRAE 185.2 – Method of Testing UV-C Lights in Ducts
- Scope: Evaluates the microbial inactivation performance of UV-C systems installed within ductwork.
- Test Environment: Simulated or actual duct systems with controlled airflow conditions.
- Organisms: Utilizes specific test microorganisms to assess efficacy.
- Output: Determines the percentage of microorganisms inactivated as air passes through the UV-C treatment zone.
- Primary Use Case: Assessment of in-duct UV-C systems aimed at improving indoor air quality.
ASHRAE 185.3-2024 – Method of Testing In-Room Air-Cleaning Devices and Systems for Microorganism Bioaerosol Removal or Inactivation
- Scope: Provides a chamber-based test method to evaluate commercial and industrial in-room air-cleaning devices and systems for their ability to remove or inactivate airborne microorganisms.
- Test Environment: Controlled environmental chambers where bioaerosols are introduced, and the device’s performance is measured.
- Organisms: Specified indicator microorganisms are used to standardize testing.
- Output: Measures elimination efficiency, indicating the percentage reduction of viable microorganisms; results can inform calculations similar to microbial Clean Air Delivery Rate (CADR).
- Primary Use Case: Benchmarking the microbial reduction capabilities of various in-room air purification technologies, including but not limited to filtration, UV-C, ionization, and photocatalytic oxidation systems.
Note: While 185.3-2024 is part of the 185 series, which traditionally focuses on UV-C technologies, this standard is technology-agnostic, applicable to any air-cleaning technology designed for in-room use, regardless of the specific method employed.
ASHRAE 185.5P – Proposed Method of Testing HVAC-Duct Mounted Devices and Systems and In-Room Devices for Particle and Microorganism Removal or Inactivation in a Chamber with a Recirculating Duct System
- Scope: Establishes a test method for evaluating both HVAC-duct mounted devices and in-room air-cleaning devices and systems for their effectiveness in removing or inactivating particles and microorganisms within a chamber equipped with a recirculating duct system.
- Test Environment: Utilizes a chamber with a recirculating duct system to create a controlled setting for consistent and repeatable testing.
- Particles and Organisms: Specifies procedures for generating specific particles or selected indicator microorganisms to challenge the air-cleaning devices.
- Output: Calculates elimination efficiency for each specific particle or microorganism, providing a clear measure of device performance.
- Primary Use Case: Offers a standardized method to assess and compare the performance of various air-cleaning technologies, applicable to both in-duct and in-room systems.
Note: ASHRAE 185.5P is currently a proposed standard (denoted by the ‘P’ suffix), indicating it is under development and not yet finalized. Once published, it will provide a comprehensive test method applicable to a broad range of air-cleaning devices and systems.
Distinguishing Between the Standards
While the ASHRAE 185 series originated with a focus on UV-C technologies (as seen in 185.1 and 185.2), recent developments have expanded the scope:
- 185.3-2024 is technology-neutral, applicable to any in-room air-cleaning device or system aimed at microorganism removal or inactivation, not limited to UV-C solutions.
- 185.5P further broadens the scope by including both HVAC-duct mounted and in-room devices, evaluating their performance in removing or inactivating particles and microorganisms within a recirculating duct system.
These expansions reflect ASHRAE’s commitment to providing comprehensive evaluation methods that accommodate the diverse range of air-cleaning technologies available in today’s market.
For more detailed information on ASHRAE Standard 185.5P, including its development status and committee activities, you can visit the ASHRAE 185.5 Project Committee page.
And finally…. What is RAST?
There is two schools of thought on this…
One is the quite reasonable assumption that when referring to ‘RAST’ with 185.5 you are referring to Recirculating Aerosol Test System (RAST). The idea is that a Recirculating Aerosol Test System (RAST) is a controlled chamber setup with a recirculating duct loop that aerosolizes particles or bioaerosols (including viable microorganisms), allows them to recirculate through the system, and can also sample the air at different intervals to assess the performance of an air-cleaning device or system installed within the loop.
Therefore a RAST setup would enable: Uniform mixing and distribution of the test challenge (particles or microbes), repeatable time-based sampling (to measure decay or reduction curves) and simulation of real-world recirculating HVAC systems, particularly in commercial or institutional settings.
However I am afraid that this is “LLM nonsense”!
RAST is not an official acronym defined in all ASHRAE literature yet, but in committee and technical discussions like those for ASHRAE 185.5P R.A.S.T. does in fact mean; Reactive Air and Surface Technologies.
That is to say, “a category of technologies that actively interact with air or surfaces to neutralize, inactivate, or remove contaminants. Often contrasted with passive filtration methods like HEPA or MERV filters”.
ASHRAE and other regulatory bodies (like the EPA and CDC) are increasingly using “reactive air cleaning technologies” as an umbrella term for technologies that produce reactive species, photons, or other mechanisms that act on pathogens or pollutants or devices where the mode of action is not purely physical filtration.
This terminology helps differentiate performance expectation as well a highlighting potential byproducts or occupant safety issues (e.g., ozone, secondary chemistry) and also encourage fit-for-purpose evaluation in standards like 185.3 and 185.5P.
Written by Dr John McKeon; subject matter expert and author for Airmid Healthgroup’s thought leadership blog due to his extensive expertise in medicine, entrepreneurship, and indoor air quality innovation. His diverse background and thought leadership make him an invaluable contributor to advancing health-focused conversations within the indoor environment sector
Relevant External Links
View the official ASHRAE 185 series standards
Use for: Referencing any of the official 185.x standards directly
EPA guidance on air cleaning technologies and indoor air quality
Use for: Supporting your explanation of reactive vs passive technologies, CADR, and safety considerations.
Learn more about the AHAM AC-5 microbial CADR standard
Use for: Linking to the consumer-side CADR testing methodology to contrast with ASHRAE 185.3.
Related Resources on the Airmid Web Site
Advancing the Science of UV Disinfection: Insights from the IUVA & NIST Workshop
Understanding MERV, HEPA, and ASHRAE Standards
Related Case Studies
Fresh-Aire UV’s APCO Air Purifier
- Overview: Airmid Healthgroup conducted tests on the APCO air purifier, manufactured by Fresh-Aire UV, demonstrating its effectiveness in inactivating microorganisms and reducing volatile organic compounds (VOCs).The results showed significant reductions in bacteria (98.85%), viruses (99.03%), and mold (78.80%) in a simulated HVAC environment.
- Relevance to ASHRAE 185: This case study exemplifies the application of ASHRAE 185.1 and 185.2 standards, which focus on testing UV-C lights installed in air-handling units and ducts for microbial reduction.
Air Sniper’s Germicidal UVGI Technology
- Overview: Air Sniper collaborated with Airmid Healthgroup to validate the effectiveness of its germicidal ultraviolet germicidal irradiation (UVGI) technology in reducing airborne pathogens. The study provided scientific evidence supporting the technology’s role in enhancing indoor air quality.
- Relevance to ASHRAE 185: This case study aligns with the objectives of ASHRAE 185.3-2024, which provides a method for testing in-room air-cleaning devices and systems for microorganism bioaerosol removal or inactivation.
Related Services
Custom Bioaerosol Protocol Development: Explore our custom bioaerosol test method development services.
Test Method for UV-C Disinfection in Air-Handling Units and Air Ducts: The ANSI/ASHRAE 185.1-2020 standard defines a test method for evaluating UV-C technologies in HVAC systems to determine their effectiveness in inactivating airborne microorganisms.
ASHRAE 241 Testing Services: Independent Bioaerosol Testing for Air Cleaning Technologies
Helpful Research Phrases
ASHRAE 185 microbial testing standards, air cleaner microbial efficacy testing, commercial equivalent to AHAM AC-5, ASHRAE 185.3 air purification validation, UV-C and non-UV air cleaning standards.
Key Words
ASHRAE 185 series, germicidal UV testing, in-room air cleaners, ISO 15714, bioaerosol test chamber, microbial CADR, air disinfection standards, ionization efficacy testing, UV-C performance validation, air cleaning device certification
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