Start with what ASHRAE 241 controls
- ASHRAE 241 infection risk mitigation
- In this article, ASHRAE 241 infection risk mitigation refers to using ASHRAE Standard 241 as the regulatory and engineering framework for reducing exposure to infectious aerosols. The standard addresses air-system design, installation, commissioning, operation, maintenance, and decisions related to infection risk management mode.1,4
ASHRAE describes Standard 241 as setting minimum requirements intended to reduce the risk of disease transmission through infectious aerosols in new buildings, existing buildings, and major renovations. CDC describes the standard as compliance-focused and connects it to equivalent clean airflow per person during infection risk management mode. CDC ventilation guidance remains voluntary unless an authority with legal jurisdiction adopts it.1,4
Match the chamber method to the installed use
| Use case | Method frame to consider | Main scoping question |
|---|---|---|
| Portable household room air cleaner | ANSI/AHAM AC-5 using an aerobiology test chamber | Does the portable unit reduce concentration and viability of experimentally generated bioaerosols in the chamber condition? |
| Commercial or industrial in-room air cleaner | ANSI/ASHRAE Standard 185.3 test-chamber method | Does the in-room system remove or inactivate microorganism bioaerosol under the chamber method and selected operating mode? |
| In-duct UV or air-handling-unit installation | ASHRAE 185.1 or ISO 15714 where applicable, plus ASHRAE 241 safety requirements | Does the in-duct configuration inactivate airborne microorganisms at the airflow, residence time, and UV exposure condition being claimed? |
| HVAC recirculation or custom recirculating chamber study | Project-specific protocol aligned to the accepted consensus method where possible | Does the chamber reproduce the recirculation path, mixing, bypass, upstream and downstream sampling, and installed operating mode? |
Addendum a to ASHRAE Standard 241-2023 added references for determining air-cleaning effectiveness and safety. In the appendix context, the addendum includes AHAM AC-5 and ASHRAE 185.3 as permitted effectiveness standards. AHAM AC-5 applies to portable household air cleaners tested in an aerobiology test chamber. ASHRAE identifies Standard 185.3 as a test method for commercial and industrial in-room air-cleaning devices and systems evaluated in a microorganism bioaerosol test chamber.2,3,5
An in-room result should not be applied directly to HVAC recirculation without first evaluating the airflow path. A recirculation protocol needs defined supply and return conditions, mixing or bypass assumptions, an air-change or clean-airflow basis, upstream and downstream sampling locations, challenge stability, and the actual operating mode used during testing.2,3,4
GLP is a data-integrity decision
The GLP status should be established during study design, not after the study produces a favorable result. EPA's GLP regulations under 40 CFR Part 160 apply to studies intended to support pesticide research or marketing permits. The current eCFR text includes expectations for the protocol, study director, quality assurance unit, raw data, equipment calibration, standard operating procedures, final report, and record retention. FDA's 21 CFR Part 58 provides a related GLP framework for nonclinical laboratory studies submitted to FDA.6,7
- If the data may support an EPA-regulated air purifier, filter, UV unit, or air treatment device with antimicrobial or public-health claims, decide whether EPA GLP applies before finalizing the protocol.6,8
- If the study supports screening, engineering development, or comparison only, the report can still use controlled methods and traceable records without representing the study as GLP-compliant.6,7
- If a sponsor needs GLP, the protocol, deviations, raw data, organism records, calibration records, chain of custody, QA inspections, and final report language should be aligned from the start.6
Safety and claim language belong in the evidence plan
Bioaerosol efficacy addresses only part of the regulatory question. EPA identifies air purifiers, filters, UV light units, and air treatment devices as examples of pesticide devices when they carry pest-control or microorganism-reduction claims. EPA also warns that device labels and advertising may be false or misleading when efficacy claims cannot be supported.8
The safety review should reflect the technology being tested. EPA and CDC discuss concerns associated with ozone and ion-generating air cleaners. CDC recommends verifying UL 2998 certification when evaluating products that may generate ozone. ASHRAE 241's addendum also connects air-cleaning effectiveness with safety-element testing when the applicable standards are used.2,4,9
Live bioaerosol work also requires laboratory-specific safety controls. CDC and NIH BMBL guidance bases biosafety on a protocol-driven risk assessment. Before challenge testing begins, the study team should define the organism, concentration, aerosol generation method, sampling train, containment, decontamination procedures, personnel protection, and waste-handling requirements.10
What to define before requesting testing
- Name the compliance target: ASHRAE 241 design support, product-development screening, EPA claim support, customer comparison, or another documented decision.1,6,8
- Define the operating configuration: portable in-room, commercial in-room, in-duct, air-handling-unit, HVAC recirculation, or custom chamber recirculation.2,3,5
- Select the measurement basis before testing, such as viable bioaerosol reduction, removal, inactivation, microbial clean air delivery, equivalent clean airflow, pressure drop, airflow, ozone, or byproduct monitoring.2,4,5,9
- Decide whether GLP applies and whether the report must include a GLP compliance statement, non-GLP statement, QA records, raw data reconstruction, and record-retention commitments.6,7