ASHRAE Journal - February 2014 - 26

TECHNICAL FEATURE

Total Microbial

contaminating the space. The room dimensions were
100
87
90
20 ft 5 in. W × 20 ft 7 in. L × 10 ft H (6.2 m W × 6.3 m L ×
80
3.0 m H).
70
Because a standardized testing method for airborne
60
contaminants in an OR does not exist, the experimental
50
design for sample collection, laboratory analysis and
40
data interpretation were derived from the United States
30
24
20
Pharmacopial Convention, USP<797> (Revision Bulletin
11
10
2008 guidelines for pharmaceutical sterile compound2
0
0
0
0
ing facilities)16 with one exception; in this experiment
Air
MDA
MDA
SLD1
SLD1
SLD2
SLD2
Curtain 30 fpm 50 fpm 30 fpm 50 fpm 30 fpm 50 fpm
samples were collected during the simulation of an
active surgical procedure as opposed to an unoccupied
FIGURE 7 Microbial results, reported as colony forming units per cubic meter (cfu/m3).
room. The mock OR was precisely measured and marked
for repeatable placement of the surgical equipment
contaminant (yeast) was introduced for each 15-minand team members, a manikin (to simulate the patient
ute experiment (as described in Reference 14) in the
on the operating table), and all particle measurement
equipment. Surgical procedures were scripted to mimic exact same quantity with steps taken in between each
experiment, including scrubbing, gowning and OR
an actual surgery as well as the process for bringing in
new instruments during a surgical operation. Each team cleaning in accordance with operating room preparation procedures, to ensure that only that
member was assigned a predesignated
TABLE 2 Recommended action levels
quantity was present in the OR for each
task to complete at a specific time durfor viable particles in air.
experiment.
ing each test conducted. The manikin
ISO
ACTIVE AIRBORNE
The microbial data collected during the
was equipped with two mock surgical
CLASS
(CFU/M 3 )*
study is summarized in Figure 7.
sites, one at the chest and one at the legs.
5
>1
No microbial contamination was
Passive samples were collected at the chest
7
>10
detected with the SLD1-50, SLD2-30 or
site and active samples were collected at
8
>100
SLD2-50 configurations which meets the
the leg site. The chest and leg sites were
heated to constant temperatures of 98°F *For each ISO Class, mitigation that may include ISO Class 5 pharmaceutical cleanroom
investigation of the contaminating source and adand 75°F (36.7°C and 23.9°C), espectively ditional cleaning is required by USP 797 standards standard (Table 2). 17 SLD1-30 met ISO
to simulate the warm air plume emitted
when the number of colony forming units per cubic Class 7, while all other designs met ISO
meter detected in the air is greater than the allow- Class 8, with greater than 10 cfu/m3. The
from a surgical site.
able number for that ISO Class.
data also indicates that at equal size and
Four different ceiling air delivery sceairflow, a one or two ISO Class improvenarios, each meeting ASHRAE Standard
ment was achieved between the MDA and SLD1 scenar170 guidelines for diffuser coverage over the patient
ios without additional energy consumption.
table, were tested (Figure 6, Page 24). The air curtain was
tested at 27 fpm (0.14 m/s) velocity from the diffuser
Conclusion
screens, and the slots were between 85 fpm and 100
Preventing airborne contaminants from settling in
fpm (0.43 m/s and 0.51 m/s) (Table 1, Page 24). The three
the desired sterile field is an important objective for the
remaining scenarios were tested at 30 fpm (0.15 m/s)
airflow system in both ORs and semiconductor/pharair velocities, with additional tests performed at 50 fpm
maceutical manufacturing facilities. What is missing for
(0.25 m/s). The MDA and SLD1 scenarios were equipped
ORs is an aerobiological standard conceptually similar
with the same diffuser face area (57 ft2 [5.3 m2]) and
airflow was delivered at the same volumetric flow rate.
to that used in manufacturing cleanrooms. The fact that
The SLD2 diffuser face area was approximately 30 ft2
an operating room presents a much more dynamic envi2) larger than the MDA and SLD 1 scenarios.
(2.8 m
ronment than a semiconductor manufacturing facility,
Each scenario consisted of three repeatable experialong with the unlikelihood that doctors, nurses and
ments, exactly 15 minutes in duration, conducted over
other OR personnel will be required to wear full coverapproximately 70 minutes. A controlled microbial
age clothing to prevent release of squames into the OR,
26

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