Air distribution design in a SARS Ward with multiple beds

Abstract

As of 7 August 2003, severe acute respiratory syndrome (SARS) was reported in 34 countries and regions with 8422 reported probable cases and 916 deaths. The hospital care workers (HCWs) were the most severely affected professions during the SARS epidemics in Hong Kong and elsewhere between November 2002 and June 2003. 20% of the infected were HCWs worldwide. 22% of the confirmed cases in Hong Kong were HCWs. Positive engineering control, in particular ventilation design in the SARS wards has been considered important and could help in minimizing cross infections.This paper summarizes a recent study of air distribution in a SARS ward with six beds. The study was carried out between April and July 2003 by SARS Busters who is a team of professional engineers from seven professional institutes in Hong Kong, led by the Hong Kong Institution of Engineers. After examining the existing air-conditioning system design for hospitals dealing with SARS cases in Hong Kong, the SARS Busters first applied computational fluid dynamics simulations to identify a design for minimising cross infection and improving pollutant dilution in a six-bed ward. The design was then tested in a full-scale SARS ward test room in the Building Services Laboratory at the University of Hong Kong. The new system designed is found to perform well for a nearly realistic full-scale SARS ward. The new bed-head exhaust design allows some degree of local capture of the virus-laden aerosols originated from a patient’s mouth. Based on this study, a general design guideline is developed. Many of the basic principles in the SARS Busters’ design have been adopted in constructing new SARS wards for more than 1000 beds in Government and Hospital Authority hospitals in 2003.Airflow patterns are also found to be very sensitive to minor changes in supply grille design details such as the internal deflector and air distributor, and various supply air parameters such as the velocity, temperature and direction. Air distribution is shown to be a complicated turbulent process and proper design is very necessary for minimizing cross-infection between patients; and between patients and health care workers (HCWs); and for efficient and effective dilution and removal of virus-lade aerosols.

到2003年8月7日止,在全球34個國家和地區相繼出現了嚴重急性呼吸系統綜合癥(SARS或者非典),其中,共報告有8422例疑似案例,916例死亡案例。2002年11月到2003年6月間的非典流行中,醫院醫護人員受感染情況最為嚴重,世界范圍內20%的感染群體為醫護人員,香港地區22%的確診案例為醫護人員。因此,為減少交叉感染,加強有關工程控制,特別是在非典病房里進行通風設計是非常必要的。本文總結了非典病房氣流分布的最新研究。這項研究由非典特工隊于2003年4～7月間完成。非典特工隊是由香港工程師協會組織,來自7個專家協會的工程師組成的研究小組。在對香港治療非典醫院的現有空調系統進行了解后,非典特工隊首先運用計算流體力學模擬確定了在6個床位的病房里減少交叉感染和改善污染物稀釋的通風設計;接著,對新設計在香港大學屋宇設備實驗室里的全尺寸非典病房里進行了測試。測試表明,新設計方案在這個接近現實的全尺寸非典病房里運行良好。采用床頭回風口回風設計可有效地對病人產生的含病毒顆粒進行局部捕獲。根據這項研究,作者提出了原則性的設計建議。2003年里,香港政府和醫院管理局醫院采納了非典特工隊提出的設計基本原理建造了1200多個床位的可用于非典治療的新病房。另外,氣流分布是復雜的紊流過程,送風格柵結