The ASHRAE 241 Standard at a Glance
ASHRAE stands for American Society of Heating, Refrigerating and Air-Conditions Engineers who establishes industry recognized standards for HVAC&R framework.
The ASHRAE Standard 241 stipulates a biological aerosol removal test method and provides the minimum equivalent clean air requirements to reduce airborne diseases in commercial/residential settings. The application of the standard helps bring forward safer and healthier indoor environments.
Requirements of the ASHRAE 241 Test Method
- Laboratory is compliant with the requirements of ISO/IEC 17025 or equivalent.
- All bioaerosol testing and microbial procedures are conducted in accordance with the current version of the CDC/NIH Biosafety in Microbiological and Biomedical Laboratories.
- Microchem’s upmost priority is the safety of the performing scientists by following the guidelines set forward by the CDC and NIH. Microchem does not aerosolize highly infectious microorganisms. For example, MS2 bacteriophage is a non-pathogenic EPA/ASHRAE approved surrogate virus used in bioaerosol testing.
- Testing takes place in a bioaerosol chamber more than 800 ft3.
- Microchem offers two bioaerosol chambers. Our Negative Pressure Aerosol Chamber (NPAC) measures at 10’ x 10’ x 8.5’ (~850 cubic feet) and our Large Aerosol Chamber measures at 4,980 ft3.
- Parameters for environmental and airflow conditions must be identical between test and control runs.
- Microchem follows the parameters set forward in ASHRAE Standard 241 (e.g., 70-75 degrees temperature, 50-60% relative humidity, samples collected between 48 and 50 inches above floor level and greater than 2 feet from walls, and triplicate sample plating).
Note: ASHRAE 241 requires a minimum of three replicates for each test condition (Air cleaning system OFF and Air cleaning system ON) to be performed, i.e., 3 control chamber runs and 3 test chamber runs.
Summary of Bioaerosol Test method following ASHRAE 241:
- The bioaerosol chamber(s) are cleaned and disinfected before use with validated disinfection methods.
- A microbial suspension of the test microorganism(s) is prepared and placed into two aerosol nebulizers.
- Prior to aerosolizing, the chamber is adjusted to be following ASHRAE 241 requirements (Placing of the air cleaning system, sampling heights, environmental conditions, triplicate sample plating etc.).
- The aerosolization phase starts, filling the chamber with bioaerosols.
- At the end of aerosolization the microbial concentration in air is determined using air samplers.
- At the end of initial sampling, the air cleaning system is turned on and samples are taken at times that are best representative of the air cleaning system (e.g., 5 minutes, 10 minutes, 15 minutes, and 30 minutes).
- The collected samples are enumerated using standard techniques and are plated in triplicate per the standard
- After testing, the microbial population collected at each specified time is compared with the initial control concentration to determine percent reduction, log reduction, and ASHRAE 241 air cleaning system equivalent clean airflow rate (V-ACS).
- An identical control run is also performed in the same manner described above except for the air cleaning system not being active. The control run provides the effectiveness of the air cleaning system when the system is active compared to absence of the air cleaning system.
Contact Microchem today to discuss ASHRAE 241 testing for your air cleaning system.
