Indoor air quality is an important
issue in health care facilities such as hospital
operating theatres. The outbreak of avian influenza
and SARS has given much warning to the community
about the importance of minimizing the infection
risk through airborne and/or direct-contact routes.
In hospitals, the specialized ventilation systems
for operating theatres and isolation wards are to
provide comfortable and healthy environment for the
patient and the surgical team. In Hong Kong, their
design and construction are mostly based on the UK
Health Technical Memoranda (HTM), the US Centres for
Diseases Control and Prevention requirements, as
well as the supplementary guideline of the
Architectural Services Department of the Hong Kong
Government.
Dr. Chow Tin Tai and his research
team member Dr. Lin Zhang studied the ventilation
provisions at the operating theatres in a sample of
hospitals in Hong Kong. It was observed that the
ventilation designs in some hospitals were not fully
complied with the recommended specifications. "In
most cases, these were because of the continuing
revisions and tightening of the required standards,
and the physical constraints of the building itself
in the older hospitals," said Dr. Chow.
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Numerical simulations were used
to examine the importance of full compliance with
the above mentioned technical specifications. The
outcomes help to understand the limitations and the
proper applications of the spec-ialized ventilation
systems, and give a detailed evaluation of its
health effects on people. For example, in some
ultraclean ventilation systems, the velocity of the
supply air at the perforated ceiling diffuser was
found lower than the design specification.
Comparative air flow studies were performed to
examine the effects of changed supply airflow rate
as well as the main and auxiliary medical lamp
positions. Through computational fluid dynamics
(CFD) analysis, the dispersions of infectious
particles from both the surgical team and the
patient were examined. The variations in supply
velocity and medical lamp positions in practice were
found to affect very little the thermal comfort
environment. But on occasions, these may have severe
effects on the movement of infectious particles, and
hence on the cross infection risk.
It was also reckoned that full
compliance with engineering standards not necessary
implies a risk-free environment, as in the case of
unpredictable SARS cross-infection. When treating a
SARS patient, the protection of the surgical staffs
and others outside the operating theatre is equally
important. In 2004 a negative pressure operating
theatre was made ready in one hospital of Hong Kong
for the treatment of suspected or confirmed airborne
infection cases. This was converted from a
conventional operating theatre designed for positive
pressure originally for stopping the particulate
ingression from the outside. In the absence of
relevant design guide, site measurements and
numerical airflow study were performed. The
simulation results show that the physical
environment and the bacteria dispersion in this
negative pressure operating theatre are as good as
those in the one originally designed for positive
pressure. The research outputs provide useful
references for related installations in other
hospitals.
Dr Chow Tin-tai
Division of Building Science and
Technology
City University of Hong Kong
bsttchow@cityu.edu.hk |
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