Isolation Room Ventilation Design Case Studies
Duncan A. Phillips, Ph.D., P.Eng.
Associate Member ASHRAERay J. Sinclair, Ph.D.
Glenn D. Schuyler, P.Eng.
ABSTRACT This paper discusses the design of ventilation systems for negatively and positively pressurized patient isolation rooms. The paper focuses on how to quantify and achieve target levels of protection for either the patient (positively pressurized rooms) or health care workers and other hospital occupants(negatively pressurized rooms). Attention is paid to the influence of ceiling supply diffuser selection. Thermal comfort issues are also discussed, and an alternative to “age-of-air” techniques using age-of-contaminant calculations is recommended for use in patient isolation room design. Practical considerations are illustrated through the presentation of two case studies. The first case study ofa TB isolation room includes a CFD model analysis of different air distribution systems including an assessment of ventilation effectiveness and patient thermal comfort. This work includes simulation of a cough from a patient toward a health care worker and throughout the isolation suite. The second case study of a positive pressure isolation room assesses the throw of supply air around a patientbed in terms of providing protection for the patient while maintaining comfortable conditions. INTRODUCTION Challenges to health services around the world from monkey pox, severe acute respiratory syndrome (SARS), and continued cases of tuberculosis have meant that hospitals have had to deal with, and prevent the spread of, contagious diseases. Additionally, health care facilities are providingfor people afflicted with diseases that suppress a patient’s immune system, either through the treatments (e.g., cancer) or due to
the illness itself (HIV/AIDS). To provide adequate protection of patients and caregivers, special purpose patient isolation rooms are designed with ventilation systems that maintain a negative pressure to protect caregivers or positive pressure to protect patients.While positive or negative pressurization can be used as a containment strategy, it leaves the occupants within the room (caregivers and patients) with risks from each other. Proper ventilation design can help to reduce those risks by providing either deflection of contaminated air or at least efficient removal of contaminants. The momentum from the supply diffuser can be used beneficially in thisregard or, as often happens without careful design, can aggravate the problem. The case studies that follow illustrate some of the effects of supply momentum, buoyancy, and room dimensions on ventilation within the space. BACKGROUND The purpose of this section is to review the means by which airborne infections spread, using tuberculosis (TB) as an example, and then present methods by whichpatient room ventilation systems are assessed. In that review, comparisons between the different methods are provided. TB Isolation Rooms (Case 1) Infectious diseases can spread from one person to another by aerosol droplets. The spread of tuberculosis (TB), for example, occurs when an otherwise healthy individual inhales a sufficient number of tubercle bacilli that are expelled by a patient infectedwith pulmonary TB. An infected patient continuously expels these particles when coughing, sneezing, talking, or spitting (Gammaitoni and Nucci 1997). The infec-
Duncan Phillips is an associate and senior specialist, Ray Sinclair is a principal and project director, and Glenn Schuyler is a principal and vice-president of research at Rowan Williams Davies and Irwin, Inc., Guelph, Ontario, Canada....