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Design Guidance for Isolation Room Exhaust to Reduce Potential for Contamination

Simona Besnea and Martin Stangl, Rowan Williams Davies & Irwin, Inc.

Health care facilities are facing a number of challenges caused by the transmission of infectious diseases (i.e., tuberculosis, varicella-zoster virus, and measles) due to inappropriate air-handling systems. To provide adequate protection of both patients and caregivers, special Airborne Infection Isolation Rooms (AIIR) are designed, where the environmental conditions are controlled to minimize the potential for airborne transmission of infectious agents. There is a concern that the exhaust from these isolation rooms may be discharged near fresh air intake locations or other sensitive receptor locations, leading to re-entrainment and therefore, re-circulation of micro-organisms.

An important step in optimizing isolation exhaust design is determining the probability of infection associated with high-risk medical procedures and how it relates to the dilution of the exhaust discharged from the stack. This presentation will address the development of a range of dilution criteria for isolation room exhaust and provide design guidance to avoid potential re-entrainment issues.

We propose to present our evaluation of the probability of exposure per population associated with the abscess irrigation procedure performed on tuberculosis patients. Our evaluation is based on the mathematical model by Gammaitoni and Nucci (1997) and discusses general recommendations provided by the Centers for Disease Control and Prevention and Francis J. Curry National Tuberculosis Center for the design of isolation room exhausts. Additional infection control precautions have been recently recommended by the Centers for Disease Control and Prevention to deal with Severe Acute Respiratory Syndrome (SARS).

Based on extensive experience with exhaust and intake design, we will use a hypothetical case study to provide guidance on effective design of the isolation room exhaust and hospital intake placement. We compare designs that employ engineering controls such as UVGI and HEPA filtration to make practical recommendations that can be applied to the assessment of new or existing patient isolation rooms.

Labs21 Connection:

The World Health Organization (WHO) recently suggested that the spread of Avian Influenza could lead to the next pandemic. Patient isolation rooms will be one of the important tools used to minimize the spread of influenza and other infectious diseases. Therefore, it is important to ensure that the isolation room exhaust design is effective.

Our approach is unique in that it provides predicted levels of exposure per population in the event infectious agents are re-circulated back into the building. The range of dilution criteria that will be discussed will represent the probability of exposure associated with practically achievable designs.

This presentation directly reflects the following aspects of the Labs21 approach:

  • Adopt voluntary goals - This study provides additional resources to building designers, environmental health, and infection control practitioners to make informed decisions about the risk level associated with isolation room exhaust. Optimization of the exhaust design relies on due diligence and voluntary compliance of building designers and owners.
  • Minimize overall environmental impacts - Implementing an exhaust system that provides appropriate levels of dilution will help limit over-designing while at the same time preventing degradation of local air quality and environmental impacts.

Biographies:

Simona Besnea has a BA.Sc. in Engineering Physics from the University of Bucharest, Romania and is currently completing her M.Eng. in Environmental Engineering at the University of Guelph, in Ontario, Canada. The focus of Ms. Besnea's research is air quality and dispersion modeling.

Ms. Besnea is a Professional Engineer within the province of Ontario and is currently a Project Engineer in the Wind Air and Microclimate Division at Rowan Williams Davies & Irwin Inc. in Guelph, Ontario, Canada. She focuses primarily on numerical and physical air quality modeling, specializing in exhaust re-entrainment studies for the design of building exhaust and air intake systems for laboratory, hospital, and other related facilities.

Martin Stangl has a BA.Sc. (Eng) from University of Waterloo, Ontario, Canada. Mr. Stangl is currently a Technical Coordinator in the Wind Air and Microclimate Division at Rowan Williams Davies & Irwin Inc. in Guelph, Ontario, Canada. He focuses primarily on numerical and physical air quality modeling for different types of studies including exhaust re-entrainment and roadway emissions assessments. He specializes in exhaust re-entrainment studies for the design of building exhaust and air intake systems for laboratory, hospital and other related facilities.

 

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