SURVEY OF DESIGN PRACTICES OF HOSPITAL OPERATING ROOM
AIR CONDITIONING AND VENTILATION SYSTEM
Vinson R. Oviatt, M.P.H., F.A.P.H.A.
Survey questionnaires, similar in many
respects to those sent to hospital main-
tenance engineers, were directed to 287
individuals and firms identified as being
active in the field of hospital air con-
ditioning and ventilation design.
only did the survey sheets attempt to
collect design practice data suitable for
tabulation and comparison, but the re-
spondents were encouraged to contribute
any original information bearing on de-
sign practice and theory in the follow-
ing health or safety related areas:
1. Air quality within the operating room
from a bacteriological point of view.
2. Physical comfort of operating room oc-
3. Removal of flammable anesthetic vapors
4. Control of electrostatic hazards.
The discussion and tabulated material
below summarize the information con-
tained in the 99 replies received from
The survey indicated a multiplicity
of sources for design standards, ranging
from original design by the respondent to
56 of the respondents reported that ele-
ments in their designs were based on
standards. Whether or not the remain-
ing 43 consider recognized standards
as being significant enough to use or
mention could not be determined.
the 56 referring to standards, USPHS
standards were listed
28 times,1 ASHRAE ("Guide") stand-
ards were listed 17 times,2 NFPA Code
56, 17 times,3 and various state codes,
that only 23 of the respondents indi-
official or quasi-official
is of particular interest to note
cated that the hospital staff had been
consulted about the design.
consult the hospital staff, but at least
only 23 felt that this item was signifi-
cant enough to check on the question-
naire. This indication can lead to several
conclusions, one of the more important
being that there appears to be a mini-
mum of communication between the de-
sign group and the hospital staff who
will use the facilities.
Almost unanimous agreement on two
design considerations was elicited from
the survey returns. The first was that
98 of the 99 respondents replied that
both supply and exhaust ventilation are
used; one respondent failed to reply to
this question. The second was to supply
clean air to the operating room.
significant to note that there were a
number of requests for information re-
ceived in the returned questionnaires
as to the degree it is considered neces-
sary to clean the air. Other comments
and the enforcement of standards for
Air Intake and Exhaust Outlet Location
The numerical preferences for gen-
eral locations for fresh-air intakes and
exhaust air outlets are summarized in
As shown, sidewall locations for fresh-
air intakes are strongly favored.
largest number of designers prefer the
roof level for exhaust air outlets. Since
sources occur at grade level, the com-
mittee was gratified to note that grade
level locations for fresh-air intakes are
rarely used today.
An examination of Table 2(B), which
summarizes design practice with respect
VOL. 51. NO. 12. A.J.P.H.
OPERATING ROOM AIR CONDITIONING AND VENTILATION SYSTEMS
Intake and Exhaust Outlets
Sidewall and grade
Roof level and side-
to minimum vertical and horizontal dis-
tances separating fresh-air intakes and
exhaust outlets, shows the wide range
of values found in current practice. By
their comments, a number of the de-
signers showed an awareness
need to achieve the maximum separa-
tion possible. One inference drawn from
the number of returned questionnaires
which did not furnish answers on fresh
air and exhaust separation is that there
is a large element of uncertainty or lack
of understanding in this area of design.
As mentioned earlier, the design en-
gineers, as a group, exhibited consid-
erable interest in methods for supplying
a bacteriologically clean
reflected by the number of combinations
of air cleaning methods reported.
the face of an absence of standards for
the degree of air cleaning required, the
availability of project funds appeared
in other instances to be the determinant
in the selection of surgery air cleaning
methods (s) .
Other Design Factors with Air
One of the simplest design concepts
which can be used to reduce air con-
tamination within enclosed spaces is to
increase the number of
It was considered
whether air change rates currently being
specified are influenced by this con-
Generally, from 8 to 12 air
changes per hour are required in United
structed for comparison with Table 6
in the preceding survey.
survey data to tabular form, the con-
vention was followed
which extended over more than one
range in the table, to the range em-
bracing its mean.
From a review of the table it appears
are probably based on thermal load re-
quirements, rather than on air quality
of assigning a
Temperature and Humidify
prevailing temperature and relative hu-
midity design practice, shows a close
adherence on the part of the design
group to published standards for both
The extent to which flexi-
which summarizes the
Distance Between Any Supply
and Exhaust Outlet
"As conditions indi-
Table 3(B)-Rates of Air Change in Surgery
No. of air
bility in temperature adjustment is being
designed into operating room systems
to meet individual preferences on the
part of the surgeons and other members
of the surgical team could not be ascer-
tained from the questionnaires.
Type of System
various types were designated by
However, many indicated the
use of room package units with only
This appears to indicate that the selec-
tion of the type of system is often in-
fluenced by cost and whether the system
is a new or remodeled project. A few
respondents have employed panel cool-
distribution systems of
Fresh Air Supply and Exhaust
Air Outlet Locations in
A great variety of air supply grilles or
diffusers and exhaust register designs
are used for operating rooms and a
systematic study of the rationale for
Sidewall supply grilles
or diffusers were listed in 69 replies
(28 nonaspirating, 36 aspirating); 72
replies mentioned ceilingsupplydiffusers
(14 nonaspirating and 54 aspirating);
while 20 indicated perforated
panels for the supply.
Though aspirating-type air diffusers
patterns, an indication of the designers'
intents with regard to air movement is
shown in Table 5(B).
is complicated by cost
Table 4(B)-Temperature and Humidity Design Practice
VOL. 51. NO. 12. A.J.P.H.
OPERATING ROOM AIR CONDITIONING AND VENTILATION SYSTEMS
Generally, it may be concluded that
designers attempt to follow codes which
require low exhausts or low exhausts
in combination with high exhausts.
Following a review and study of the
data in the above surveys, the Com-
APHA Engineering and Sanitation Sec-
tion has issued the following interim
features of hospital operating room air
A number of the medical, bacterio-
logical, and engineering studies of oper-
ating room air conditioning4-10 have
been reported and others are still in
Some of these may throw
further light on such fundamental issues
as the relative amounts of pathogenic
sources or locations within the operating
room.8 Further information upon which
more specific recommendations can be
made is needed. In consideration of
mittee's two surveys, it is recommended
that the practices in designing operating
greater emphasis upon furnishing the
1. Effective temperatures which will, by pro-
viding the maximum comfort for the surgeon
and the surgical team, help assure optimum
conditions for conducting the surgical pro-
2. An air flow pattern designed to displace,
or accelerate the removal
borne contamination immediately above the
operating table in particular and the operating
room in general.
3. An air supply free of biological
4. An absence of backflow of contaminated
air into the operating room from less critical
areas, to be achieved, for example, by one or
more of the following procedures:
(a) Imbalancing the air supply quantities
to the room and the exhaust from the room so
as to maintain a positive pressure condition
within the room sufficient to cause air to move
5(B) - Supply
Supply high, exhaust low
Supply high, exhaust high and low
Supply high, exhaust high
Supply low, exhaust high
out of the room through the entire area of
openings under all conditions.
(b) Providing an air lock between the room
and the more contaminated adjacent areas for
the use of personnel who must leave the op-
erating room during surgical procedures in
the performance of their duties.
(c) Simultaneous with (a) and (b), pro-
viding the same temperatures in adjoining less
critical areas as are maintained in the operat-
ing room to eliminate air movements set up
by air density currents.
5. Outdoor air supply inlets properly located
with respect to all forms of exhaust originat-
ing within the hospital as well as other con-
6. Biological particulate air cleaning devices
placed downstream from all other mechanical
elements in the air conditioning system and
located as near as possible to the point of
entry of supply air to the operating room.
7. Locating devices for the removal of bio-
highly contaminated sources in the hospital
environs as near as possible to their point of
ACKNOWLEDGMENTS-The committee wishes
to thank all those respondents to its two sur-
veys for making these reports possible.
Richard G. Bond, professor, School of Pub-
lic Health, and public health engineer, Uni-
versity Health Service, University of Minne-
Slagle, assistant director, Division of Hospital
Health, were members of Mr. Michaelsen's
G. A. Weidemier, American
Hospital Association, gave valuable assistance
to Mr. Michaelsen in supplying a mailing list
of hospital maintenance engineers.
James C. Barrett, chief of the Ventilation
Techniques Section, Division of Occupational
served as a member of Mr. Oviatt's subcom-
Refrigerating and Air Conditioning Engineers
kindly gave its permission for the committee
to indicate the society's interest in the survey
air conditioning engineers and
associates in the Division of Hospital and
Medical Facilities of the Public Health Serv-
ice, Department of Health, Education, and
Welfare, were largely responsible for assem-
bling the names of the group surveyed by Mr.
The American Society of Heating,
P. Gaulin and his
DONALD L. SNOW, M.S., National Insti-
tutes of Health, Bethesda 14, Md.,
JAMES C. BARRETT
RICHARD G. BOND, M.P.H.
RICHARD P. GAULIN
LAWRENCE B. HALL
LOUVA G. LENERT
GEORGE S. MICHAELSEN, M.S.
VINSON R. OVIATT, M.P.H.
ELMER C. SLAGLE, M.P.H.
1. Public Health Service Regulations. Part 53 pertain-
the Hospital Survey and Construction Act,
1960. New York, N. Y.: American Society of Heat-
and Air Conditioning Engineers.
3. Code for the Use of Flammable Anesthetics. NFPA
56. Boston, Mass.: National Fire Protec-
tion Association (May), 1960.
4. Blowers, R.; Mason, G. A.; Wallace, K. R.; and
Thoracic Surgery Unit. Lancet 269:786-794 (Oct. 15),
B., and Colebrook,
Ibid. 250:601-605 (Apr. 27), 1946.
6. Shooter, R. A.; Taylor, Gerard W.; Ellis, George;
and Ross, James Paterson. Postoperative Wound Infec-
Surgery, Gynec. & Obst. 103:257-262 (Sept.),
7. Greene, V. W.; Bond, R. G.; and Michaelsen, G. S.
Air Handling Systems Must Be Planned to Reduce
the Spread of Infection. Mod. Hosp. 95:2,136 (Aug.),
9. Lidwell, 0. M., and Williams, R. E. 0. The Ven-
Staphylococcus aureus. Hospitals 35,6:57-64 (Mar.),
L. Air Hygiene
Marvin, M.; and Hall,
Mr. Michaelsen is associate professor and industrial health engineer, School
of Public Health, and University Health Service, University of Minnesota,
Mr. Oviatt is Hospital Consultant, Engineering Division,
Michigan Department of Health, Lansing, Mich.
This report was presented before the Conference of Municipal Public Health
Engineers, the National Association of Sanitarians, and the Engineering and
Sanitation Section of the American Public Health Association at the Eighty-
Eighth Annual Meeting in San Francisco, Calif., November 1, 1960.
VOL. 51, NO. 12, A.J.P.H.