Independent ASHRAE 241 Testing for Bioaerosols and Air Cleaning Technologies
Airmid Healthgroup specialises in ASHRAE 241 testing, providing manufacturers, developers, and regulators with independent, high-quality data on air cleaning system performance.
What Is ASHRAE 241?
ASHRAE Standard 241 (published by the American Society of Heating, Refrigerating, and Air-Conditioning Engineers) establishes a test method for biological aerosol removal and defines the minimum equivalent clean air requirements to reduce airborne disease transmission in indoor environments.
ASHRAE 241 Test Method: Key Requirements
ISO 17025 Compliant Testing
Airmid operates under ISO/IEC 17025 accreditation principles, ensuring rigorous quality control throughout every test.
Biosafety Standards
All bioaerosol testing follows CDC/NIH Biosafety in Microbiological and Biomedical Laboratories (BMBL) guidelines.
Non-Pathogenic Surrogates
We use safe, EPA/ASHRAE-approved surrogate microorganisms such as MS2 bacteriophage to model airborne virus removal.
Advanced Bioaerosol Chambers
Testing takes place in precisely controlled bioaerosol exposure chambers designed to replicate real-world indoor air conditions.
Standardised Environmental Parameters
Temperature (70–75°F), humidity (50–60%), and sampling protocols are maintained to meet ASHRAE 241 specifications.
Triplicate Sample Plating
ASHRAE 241 requires at least three replicates per test condition (system OFF vs. ON) to ensure statistical reliability.
How We Conduct ASHRAE 241 Testing
- Chamber Preparation: The bioaerosol chamber is thoroughly disinfected before testing begins.
- Microbial Aerosolisation: A known concentration of test microorganisms is aerosolised into the chamber under controlled conditions.
- Baseline Air Sampling: Initial air samples are collected to determine microbial concentration before the air cleaning system is activated.
- Air Cleaning System Activation: The test system is switched on and air samples are taken at key time points (e.g. 5, 10, 15, and 30 minutes).
- Sample Analysis & Enumeration: Samples are analysed to measure microbial reduction and determine the ASHRAE 241 equivalent clean airflow rate (V-ACS).
- Control Runs: Identical tests are performed without the air cleaning system to establish baseline natural decay rates.
Industry Leadership and Collaboration
- Members of the ASHRAE 241 review process, ASHRAE 185, and the Environmental Health Committee
- Members of ISO and IEC air cleaner committees
- Working closely with AHAM on AC-5 testing
- Endorsed by the Asthma & Allergy Foundation of America (AAFA) and ECARF
- Accredited laboratory for the Verified Healthier Air programme
- Strong network of leading academics, medical schools, and applied research centres with high-impact publications
- www.iAIR.Institute — a 501(c)(6) in Washington, DC
- Active participant in the ARPA-H BREATHE project
Why Choose Airmid Healthgroup for ASHRAE 241 Testing?
- Proven Expertise: Deep scientific expertise in airborne pathogen and aerobiology research.
- Trusted by Industry Leaders: We work with HVAC manufacturers, building developers, and regulatory agencies to validate air cleaning technologies.
- Independent & Accredited: ISO 17025-accredited laboratory delivering the highest standards of accuracy and reproducibility.
- GLP-based projects
- Aerobiology Infection Control Chambers and Allergen Exposure Chambers (AECs)
- Bio-safety Level 2 testing including Flu-Virus, bacteria, and mould
- Pre-clinical and clinical studies via CRO network
- Digital twins, computational fluid dynamics, and AI mathematical modelling to enhance real-time chamber testing
Frequently Asked Questions
What is ASHRAE 241 and why does it matter?
ASHRAE Standard 241 establishes minimum requirements for controlling infectious aerosols in buildings. It sets the benchmark for how much clean air must be delivered to reduce airborne disease transmission — making it essential for manufacturers of air cleaning products seeking regulatory credibility.
What types of products can be tested to ASHRAE 241?
Any air cleaning technology designed to reduce airborne pathogens — including portable air purifiers, in-duct HVAC systems, UV-C devices, and filtration units — can be evaluated under ASHRAE 241.
What microorganism is used in ASHRAE 241 testing?
Airmid uses MS2 bacteriophage, a safe, non-pathogenic surrogate approved by the EPA and ASHRAE to model the behaviour of airborne viruses during testing.
How long does ASHRAE 241 testing take?
Timelines vary depending on the number of test conditions required, but we work efficiently to meet your development and regulatory deadlines. Contact us for a project-specific estimate.
What documentation will I receive after testing?
You will receive a full GLP-standard test report detailing the methodology, results, equivalent clean airflow rate (V-ACS), and conclusions — ready for use in regulatory submissions or marketing claims.
Related ASHRAE 241 Testing Services
- Overview of aerobiology chamber testing
- Testing Services to the ASHRAE 241 Standard
- AHAM AC-5 Testing
- ANSI/AHAM AC-1 2020
- ASHRAE 185.1-2020
- Custom Bioaerosol Protocols
Related Resources
- ASHRAE Standard 241: Control of Infectious Aerosols – Understanding its impact
- Reflections on the ASHRAE Winter Meeting: Infectious Aerosols, Standard 241, and Healthy Buildings
- Understanding MERV, HEPA, and ASHRAE Standards
