STUDIES OF VENTILATION EFFICIENCY IN A PROTECTIVE ISOLATION ROOM BY THE USE OF A SCALE-MODEL

OBJECTIVE: To assess the ability of a protective isolation room ventil ation system to reduce patient exposure to airborne infectious agents, using a small-scale model that permits cost-effective and unobtrusive study of relevant indices of performance. DESIGN: A one-half scale mo del of a protective isolation room at the University of Minnesota Hosp ital was constructed and equipped for tracer gas experiments to assess ventilation efficiency. MEASUREMENTS: Tracer gas (SF6) was injected i nto the model supply air. Tracer gas concentration was recorded over t ime and analyzed to determine local and room mean age of air. Age of a ir is a direct measurement of ventilation efficiency and can be used t o predict patient exposure to contamination. RESULTS: Although for the room taken as a whole, ventilation efficiency was close to 50% (a val ue corresponding to perfect mixing), the experimental results for the local mean age of air indicate that some parts of the model were venti lated much better than others. CONCLUSION: Room air exchange rate is o nly one parameter useful in assessing ventilation in patient areas. Ef fective distribution of ventilation air also is critical to the contro l of airborne contamination. Areas of the room with poor ventilation w ould be expected to have higher concentrations of airborne infectious agents and other contaminants. Patient exposure can be minimized by pl acing the patient in well-ventilated areas of the room. Improved venti lation designs may reduce patient exposure further without increasing actual airflow rate.