Elimination of Airborne Microorganisms Using Compressive Heating Air Sterilization Technology (CHAST): Laboratory and Nursing Home Setting

Abstract

Background: Airborne transmission of bacteria, viruses, and fungal spores poses a major threat in enclosed settings, particularly nursing homes where residents are highly vulnerable. Compressive Heating Air Sterilization Technology (CHAST) applies compressive heating to inactivate microorganisms without reliance on filtration or chemicals.

Methods: CHAST efficacy was evaluated in laboratory and deployed for a feasibility and performance validation study of air sterilization in a nursing home environment. Laboratory studies tested prototypes (300-5000 CFM; 220-247 °C) against aerosolized surrogates including Bacillus globigii (Bg), B. stearothermophilus (Bst), B. thuringiensis (Bt), Escherichia coli, and MS2 bacteriophage. Viral inactivation thresholds were further assessed by exposing MS2 to progressively lower treatment temperatures (64.5-143 °C). Feasibility and performance validation evaluation involved continuous operation of two CHAST units in a nursing home, with pre- and post-treatment air samples analyzed for bacterial and fungal burden.

Results: Laboratory testing demonstrated consistent microbial inactivation, with most prototypes achieving > 6-log (99.9999%) reductions across bacterial spores, vegetative bacteria, and viruses. A 5000 CFM prototype achieved > 7-log (99.99999%) elimination of B. globigii. MS2 was completely inactivated at 240 °C, with modeling suggesting a threshold for total viral elimination near 170 °C. In the feasibility study, baseline sampling revealed bacterial (35 CFU/m³) and fungal (17 CFU/m³) contamination, dominated by Bacillus, Staphylococcus, Cladosporium, and Penicillium. After 72 h of CHAST operation, discharge air contained no detectable viable organisms, and fungal spore counts showed a 93% reduction relative to baseline return air. Units maintained stable operation (464 °F ± 2 °F; 329-335 CFM) throughout deployment.

Conclusion: CHAST reproducibly and scalably inactivated airborne bacteria, viruses, and fungi under laboratory and feasibility field studies, supporting its potential as a chemical-free strategy to improve infection control and indoor air quality in healthcare facilities.

Keywords: air sterilization; compressive heating; healthcare associated infection; long-term care facility; volatile organic compounds.

Figure 1

Schematic representation of the Compressive Heating Air Sterilization Technology (CHAST) system. Ambient air enters the unit via an intake blower and flows through the untreated intake duct (red), where it undergoes rapid compression and thermal elevation to sterilization temperatures (~240 °C). The heated, sterilized air then passes through a heat exchanger, where it is cooled to near-ambient levels before entering the discharge duct (blue). The cooled sterile air is released into the room through a horizontal return vent and distributed via the Sterilized Air Return Duct (green). Real-time monitoring of temperature, flow rate, and pressure is continuously conducted through an integrated LabVIEW interface to ensure operational stability and reproducibility. Color coding indicates airflow states: Red = intake air, Blue = heated air, Green = sterile air.

Figure 2

Temperature-Dependent Inactivation of MS2 Bacteriophage Using CHAST Technology. To evaluate the thermal sensitivity of viral inactivation via CHAST, aerosolized MS2 bacteriophage was subjected to treatment temperatures of 143 °C, 103 °C, 91 °C, and 64.5 °C. At each temperature setting, continuous aerosolized samples were collected over a 30-min test interval using an SKC BioSampler. Samples were subsequently cultured overnight, and viral inactivation was quantified the following day. Complete inactivation of MS2 was determined through extrapolation of viral titers to a theoretical zero point. Based on the operating flow rate of the CHAST unit, the calculated residence time of viral particles within the treatment zone was approximately 0.15 s, indicating rapid and effective thermal inactivation under the tested conditions.

Figure 3

Operational Assessment of CHAST Devices Deployed at Schoellkopf Health Center Under the Clean Air Initiative. As part of a collaborative pilot implementation with Rethink WNY and the City of Niagara Falls, two CHAST units with 300 CFM capacity were installed in the recreational space of the extended care facility at Niagara Falls Memorial Medical Center (NFMMC) to assess real-world operational performance. (A) Photograph showing the physical installation of a CHAST device within the Schoellkopf Health Center. (B) Screenshot of the custom LabVIEW interface used for real-time monitoring and data acquisition of critical operational parameters. (C) Representative time-series plot demonstrating inlet air temperature and the time required to reach the optimal treatment temperature of 240 °C. (D) Correlation plot illustrating the relationship between CHAST internal treatment temperature and outlet air temperature during ramp-up. (E) Longitudinal monitoring of temperature stability, displaying the steady-state maintenance of treatment and outlet temperatures over an 11-h operational period. (F) Quantitative analysis of the mean ± standard deviation (SD) of airflow rates (in CFM) at the outlet of both units, as measured using calibrated handheld flowmeters. (G) Mean ± SD of outlet air temperatures recorded inside the facility using handheld infrared thermometers, validating temperature consistency across units.