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Efficacy of an ambulance ventilation system in reducing EMS worker exposure to airborne particles from a patient cough aerosol simulator.

Lindsley WG; Blachere FM; McClelland TL; Neu DT; Mnatsakanova A; Martin SB Jr.; Mead KR; Noti JD
J Occup Environ Hyg 2019 Dec; 16(12):804-816
The protection of emergency medical service (EMS) workers from airborne disease transmission is important during routine transport of patients with infectious respiratory illnesses and would be critical during a pandemic of a disease such as influenza. However, few studies have examined the effectiveness of ambulance ventilation systems at reducing EMS worker exposure to airborne particles (aerosols). In our study, a cough aerosol simulator mimicking a coughing patient with an infectious respiratory illness was placed on a patient cot in an ambulance. The concentration and dispersion of cough aerosol particles were measured for 15 min at locations corresponding to likely positions of an EMS worker treating the patient. Experiments were performed with the patient cot at an angle of 0 degrees (horizontal), 30 degrees, and 60 degrees, and with the ambulance ventilation system set to 0, 5, and 12 air changes/hour (ACH). Our results showed that increasing the air change rate significantly reduced the airborne particle concentration (p < 0.001). Increasing the air change rate from 0 to 5 ACH reduced the mean aerosol concentration by 34% (SD = 19%) overall, while increasing it from 0 to 12 ACH reduced the concentration by 68% (SD = 9%). Changing the cot angle also affected the concentration (p < 0.001), but the effect was more modest, especially at 5 and 12 ACH. Contrary to our expectations, the aerosol concentrations at the different worker positions were not significantly different (p < 0.556). Flow visualization experiments showed that the ventilation system created a recirculation pattern which helped disperse the aerosol particles throughout the compartment, reducing the effectiveness of the system. Our findings indicate that the ambulance ventilation system reduced but did not eliminate worker exposure to infectious aerosol particles. Aerosol exposures were not significantly different at different locations within the compartment, including locations behind and beside the patient. Improved ventilation system designs with smoother and more unidirectional airflows could provide better worker protection.
Motor vehicles; Emergency response; Ventilation systems; Emergency responders; Workers; Work environment; Exposure levels; Risk factors; Airborne particulates; Airborne particles; Aerosol particles; Aerosols; Simulation methods; Protective measures; Diseases; Respiratory infections; Influenza; Airflow; Author Keywords: Airborne disease transmission; HVAC infection control; emergency medical services; emergency vehicle; ventilation systems
William G. Lindsley, National Institute for Occupational Safety and Health, 1000 Frederick Lane, M/S 4020, Morgantown, WV 26508
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Journal Article
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Healthcare and Social Assistance
Source Name
Journal of Occupational and Environmental Hygiene
Page last reviewed: May 11, 2023
Content source: National Institute for Occupational Safety and Health Education and Information Division