International Journal of Automotive and Mechanical Engineering
ISSN: 2229-8649 (Print); ISSN: 2180-1606 (Online)
Volume 16, Issue 4 pp. 7447–7463 Dec 2019
© Universiti Malaysia Pahang, Malaysia
Enhancement of Airborne Particles Removal in a Hospital Operating Room
K. Y. Wong, H. M. Kamar* and N. Kamsah
Faculty of Engineering, Universiti Teknologi Malaysia,
81310 Skudai, Johor, Malaysia
*
Email: haslinda@mail.fkm.utm.my
ABSTRACT
This article presents the results of a numerical study to examine the transport of particles
in an operating room equipped with an Econoclean ventilation system. Its aims are to
reduce the number of particles falling onto the operating table. A simplified CFD model
of the operating room was developed and validated based on the measured air velocity
distribution. An SST k-ω turbulent flow model was used to simulate the airflow, while a
discrete phase model was used to simulate the movement of the airborne particles. The
effects of the standing posture of the surgical staff on the settlement of the particles on
the operating table were examined. Results show that under the present ventilation
system, when the surgical staff bend forward at an angle of 45°, the number of airborne
particles that tend to fall onto the operating table increased by 1.4-fold. Adding an exhaust
grille to the operating room does not have any significant effects on the distribution of
the airborne particles. However, when a larger air supply diffuser is also used, the number
of airborne particles that settled on the operating table was reduced 4-fold. More airborne
particles are transported towards the exhaust grilles, and more airborne particles
accumulate below the operating table. The present study shows that the usage of large air
supply diffuser in the operating room is capable of reducing the number of airborne
particles fall onto the operating table. Also, it enhances the efficiency of airborne particle
removal.
Keywords: Numerical method; bacteria-carrying particles; hospital operating room;
surgical site infection; air supply system.
INTRODUCTION
Hospitals require a high level of cleanliness, particularly inside the operating rooms where
surgeons perform surgical procedures on patients. Such requirements will protect patients
from possible surgical site infection (SSI). Studies have shown that out of 100 operations,
approximately seven patients (Sweden), fifteen patients (Brazil), five patients (Europe &
USA) and eleven patients (Vietnam) were infected with SSI [1-3]. The U.S. Department
of Health and Human Services (HHS) estimated that there were more than 290000
incidences of SSI, and more than 13000 infected patients died annually [4]. SSI cause an
undue financial burden, as the costs for post-surgical treatment are high, ranging from
$400 to $30,000 depending on the types of infection [1]. SSI could occur either through
direct contact or through the deposition of airborne bacteria-carrying particles (BCP) into
the patient's wound. The probability of patients contracting an SSI through direct contact
is quite low since all surgical instruments are sterilised before they are used. The
deposition of airborne particles is hence identified as the primary cause of SSI. Studies
have found that about 98% of infections in surgical wounds resulted from bacteria carried
7447
Enhancement of Airborne Particles Removal in a Hospital Operating Room
by airborne particles [5]. Staphylococcus aureus has been found to be the dominant SSIcausing bacteria species present in the operating room (OR) [6-8]. Methicillin-resistant
Staphylococcus aureus (MRSA), Pseudomonas aeruginosa and Acinetobacter species
have also been identified as causes of SSI [8]. Bacteria-carrying particles have sizes in
the range of 10 μm [9]. Particle sizes ranging from 5 μm to 10 μm can be considered as
infectious particles inside the OR [10]. Hansen et al. (2005)[11] state that there is a close
relationship between colony-forming units (CFUs) and particles of diameter larger than
5 μm. Subsequently, people tend to assume that particles with diameters of 5 - 10 μm are
infectious particles in the context of the OR [12-14].
In recent times, the majority of operating rooms equipped with mixed turbulent
systems have inclined towards the use of cleanroom ventilation systems. Such systems
use the laminar airflow (LAF) air-supply system together with high-efficiency particulate
air (HEPA) filters or ultra-low penetration air (ULPA) filters. HEPA filters are capable
of filtering out 99.97% of particles with diameters of 0.3 μm and larger, whereas ULPA
filters are capable of filtering out 99.999% of particles with diameters of 0.12 μm [15,
16]. The use of these filters is found to be very effective in eliminating airborne particles
in a unidirectional clean air supply condition [16]. Operating rooms in many developing
countries use ultraclean ventilation systems with ULPA filters [1, 14]. Such systems are
capable of supplying clean air and provide high levels of comfort for medical staff [17].
However, perhaps because of the high construction and maintenance costs, ORs in
Malaysian hospitals do not widely employ such systems. Instead, Econoclean systems
with HEPA filters, which have lower capital and maintenance costs, are found in most
ORs in Malaysia [18].
The guidelines for "Design and Construction of Hospital and Health Care
Facilities" state that the air distribution pattern in the operating room is equally important
as the air change rate per hour (ACH) [19]. The performance of two types of air supply
system, namely vertical and horizontal systems, has been investigated by Sadrizadeh et
al. (2014) [12]. They claimed that the horizontal air supply systems performed much
better in removing airborne particles from the vicinity of the operating table. Sadrizadeh
and Holmberg (2015) [1] also found that the addition of a portable ultraclean air supply
system could further reduce the accumulation of airborne particles in the area close to the
operating table.
This article presents a numerical study to investigate the transport of airborne
particles inside an OR furnished with an Econoclean system in a private hospital in
Malaysia. The phrase “Econoclean system” refers to one of the classifications of the aircooling system for the OR. So far, most of the studies have replaced the airborne particles
as gaseous (fluid phase) during the simulation. In the present study, solid particles
(discrete phase) were utilised in the simulation. The purpose is to reflect a more realistic
condition of airborne particles’ movements in the OR. The particles were assumed to be
discharged from the exposed faces of the surgical staff at a given mass flow rate. The first
objective is to examine the transport paths and concentration of the particles in the vicinity
of the operating table. The second is to identify a ventilation strategy that will improve
the removal of the particles from the OR. A simplified model of the operating room was
developed using Fluent Computational Fluid Dynamics (CFD) software and validated for
flow analysis. The CFD method has been used by many researchers as a tool to carry out
flow analyses and predict airflow patterns inside hospital ORs. An SST k-ω turbulent
model was employed to simulate the airflow, while a discrete phase model (DPM) was
used to simulate the transport of the airborne particles. The study also proposed the
ventilation strategy to reduce particle concentration in the area of the operating table.
7448
Wong et al. / International Journal of Automotive and Mechanical Engineering 16(4) 2019 7447–7463
METHODOLOGY
Field Measurement
The field measurement was carried out when there was no surgical procedure taking place
inside the operating room. The objective was to quantify the variation of airflow velocity
inside the operating room. The data will also be used for validating the CFD flow models.
The field measurement was conducted according to the procedures described in the ISO
14644-1 (1999) [20], IEST (1997) [21] and NEBB Procedural Standards for Certified
Testing of Cleanroom (2009) [22] to ensure the reliability of the measured data. The
operating room was set in fully functional condition 30 minutes before the field
measurements was performed to assure steady-state operating conditions was achieved.
All doors of the operating room were closed to avoid any changes in the airflow velocity
and direction. The operating conditions were set to comply with the ISO 14644 standards,
where the airflow velocity is 0.45 m/s +/- 20%, air change rate is greater than 20 per hour,
relative humidity is 55% +/- 10%, air temperature is 20○C +/- 2○C, and a room air
pressure of greater than 5 Pa. An Alnor EBT 731 micro-manometer with an error of +/3% was used to measure the airflow velocity, as shown in Figure 1. The manometer is
capable of measuring the mean airflow velocity at a large nominal face area of the supply
air diffuser.
Figure 1. An Alnor balometer (EBT 731)
Before taking the measurement, a tape was used to mark the sampling points
according to the generated grid. A total of 12 sampling zones were specified on one
horizontal plane that is at the height of 1.2 m from the floor of the operating room. This
zone is shown in Figure 2. Measurements of the airflow velocities were carried out
according to the procedure described in IEST standards. Data sampling point was set at
the center of each zone which has an area of 30 m2 [23]. The airflow velocity was recorded
at every 1 minute time interval. A tripod was used to hold the measuring instrument to
eliminate error due to any movement of the device.
7449
Enhancement of Airborne Particles Removal in a Hospital Operating Room
Figure 2. Sampling zones on the horizontal plane of 1.2 m from the floor. The numbers
indicate the exact locations where the airflow velocity measurements were made.
Description of The CFD Model
Figure 3 shows a simplified CFD model of the hospital OR. The model includes a surgical
lamp, an operating table, air supply diffusers and air exhaust grilles [24]. Although the
surgical lamp was included, the effects of heat generated by the lamp on the airflow and
particle movement were not considered. For simplification, other surgical equipment and
furniture were not included in the CFD model. The air supply diffusers measure 1.2 m
(W) 0.6 m (L), while the exhaust air grilles have dimensions of 0.22 m (W) 0.46 m
(L). The size of the surgical lamp is 0.45 m (D) 0.155 m (H). The major dimensions of
the components are tabulated in Table 1. There is a total of six air supply diffusers located
at the ceiling of the operating room, directly above the operating table. They are designed
such that the downward airflow covers the entire area of the operating table with a 305
mm offset on all sides of the table. This feature is to fulfil the requirement of the ASHRAE
Standard 170 (2008) [25]. There are two entrances refer to the operating room: one for
the surgical staff, which measures 0.9 m (W) 2.1 m (H), and the other for the patient,
which measures 2.0 m (W) 2.1 m (H). Each of the exhaust grilles has an effective area
of 0.084 m2. They are located in the middle of the four sides of the room wall, at a height
of 0.25 m from the floor.
Table 1: Major dimensions of the components
Component
Operating room
Exhaust grilles
Surgical lamp
Patient entrance
Personnel entrance
Dimension
6.0 m × 6.9 m × 3.0 m (Length × width × height)
0.22 m × 0.46 m (Width × height)
0.45 m × 0.15 m (Diamter × height)
2.0 m × 2.1 m (Width × height)
0.9 m × 2.1 m (Width × height)
The operating room is furnished with a vertical downward cooling air-flow
system, which is in compliance with Standard 170. This standard requires that the air
supply diffusers be equipped with HEPA filters mounted on the ceiling, directly above
the operating table, while the exhaust air grilles are to be installed on the corner walls, at
7450
Wong et al. / International Journal of Automotive and Mechanical Engineering 16(4) 2019 7447–7463
least 203 mm above the floor. Additionally, less than 30% of the operating room's ceiling
grid area must be spared to occupy the boom mounts and lighting.
Figure 3. Simplified CFD model of the operating room with major dimensions.
Meshing the Computational Domain
The ANSYS ICEM software was used to mesh the computational domain of the CFD
model. Tetrahedral elements of three different sizes were used: coarse, medium and fine.
The fine elements were utilized in areas where there are significant variations in the
airflow field, while coarser elements were employed in areas with relatively little change
in the airflow. The element size in regions where there is a large variation in the results
should be ten times smaller than the element size in the surrounding areas [26]. In this
study, elements with finer size were used in the area close to the air supply diffusers, the
exhaust air grilles, the operating table and the surgical lamps. Larger elements were
utilized in the region surrounding these areas. Medium size elements were used in the
remaining sections of the computational domain. The skewness of the meshing grid is
0.9. The minimum and maximum element sizes are 3.85 × 10-4 m and 7.25 × 10-2 m,
respectively.
A grid independence test (GIT) was carried out, and a grid convergence index
(GCI) was determined to establish the number of elements that would minimize the
effects of meshing on the results of the simulations. For the GIT, five sets of element
numbers were tested, namely from 220,000 up to 3,520,000 elements. The airflow
velocity for 100 points uniformly distributed on an x-axis line at 1.2 m above floor level
was selected in the model. The airflow velocity magnitude versus the distance along the
x-axis line was plotted, as shown in Figure 4. It can be seen that the airflow velocity was
nearly unchanged when 880,000 elements were used to mesh the computational domain.
7451
Enhancement of Airborne Particles Removal in a Hospital Operating Room
Figure 4. The variation of airflow velocity versus the distance along a line.
The determination of the GCI was based on Sadrizadeh et al. [27], Kwasniewski
[28] and Karimi et al. [29], as given in Eq. (1) below:
𝐺𝐶𝐼 (𝑢) =
𝐹𝑠 ɛ𝑟𝑚𝑠
(1)
𝑟 𝑝 −1
where Fs is the safety factor, with a value of 3, ɛ is the relative difference between
subsequent solutions, p is the order of convergence, with a value of 2, and r is the ratio of
the amount of the fine grids to that of coarse grids. The safety factor Fs was arbitrarily set
based on the accumulated experience on CFD calculations [28]. It represents 95%
confidence for the estimated error bound. The ɛ was defined as given by Eq. (2)[27]:
ɛ𝑟𝑚𝑠 = √
∑𝑛
𝑖=1((𝑢𝑖,𝑐𝑜𝑎𝑟𝑠𝑒 −𝑢𝑖,𝑓𝑖𝑛𝑒)/𝑢
𝑛
𝑖,𝑓𝑖𝑛𝑒
)2
(2)
where f is the airflow velocity. The values of the GCI for meshing with 440,000, 880,000,
1,760,000 and 3,520,000 elements were found to be 6.2%, 3.3%, 0.5% and 0.3%,
respectively. Thus, 880,000 tetrahedral elements with non-structured meshing were
considered adequate for the airflow and particle movement simulations. To further ensure
that the mesh was sufficiently fine, the dimensionless wall distance (y+) was kept below
five.
Selection of Airflow and Particle Movement Models
The governing equations that describe the fluid flow and particle concentration within an
enclosure are all based on the conservation of mass, momentum, energy and species
concentration within the enclosure. Several flow models are available in the CFD
software to simulate the airflow inside the computational domain. These are ReynoldsAveraged Navier- Stokes (RANS) family equations, which include the k-ɛ, k-ω, transition
SST, detached eddy simulation (DES) and large eddy simulation (LES) models. The
application of DES and LES for flow simulation in an indoor environment requires high
computational power and longer computation time as compared to the RANS family
models. For a steady-state simulation of airflow, many studies found in the literature
7452
Wong et al. / International Journal of Automotive and Mechanical Engineering 16(4) 2019 7447–7463
indicate that the RANS model is adequate to give sufficiently reliable results [1, 12, 27,
30-32].
In this study, all the above flow models were examined under a steady-state
condition to find out which flow model is the most suitable to be used in the proceeding
airflow simulations. This analysis was done by performing the simulations on the base
case model of the operating room using each of the flow models. Airflow velocity of 0.45
m/s was prescribed at all the air supply diffusers as the boundary conditions. A zero gauge
pressure boundary condition was specified at all the air outlet grilles. The air temperature,
density, dynamic viscosity and kinematic viscosity are at 19°C, 1.209 kg/m3, 1.816 ×105
Ns/m2, and 1.502 × 10-5, respectively. A no-slip condition was defined at all the wall
surfaces. Airflow simulations were performed on the CFD model repeatedly, using
different flow models. The boundary conditions applied to the CFD model of the
operating room are tabulated in Table 2.
Table 2: Boundary conditions applied to the CFD model of the operating room.
Location
Air supply diffuser
Type
Velocity inlet
Exhaust grille
Pressure outlet
Floor
Wall
All walls
Wall
Door
Wall
Surgical staff
Wall
Setup
Velocity magnitude: 0.45 m/s
Direction of airflow: Normal to the boundary
Turbulence intensity: 5%
DPM: Escape
Gauge pressure: 0 Pa
DPM: Escape
DPM: Trap
Wall motion: Stationary wall
Wall condition: No-slip
DPM: Trap
Wall motion: Stationary wall
Wall condition: No-slip
DPM: Trap
Wall motion: Stationary wall
Wall condition: No-slip
DPM: Escape
Injection setup: 1.31 × 10-12 kg/s
Wall motion: Stationary wall
Wall condition: No-slip
Figure 5 shows the comparison of the airflow velocity magnitudes at all the
measuring points on the horizontal plane at a height of 1.2 m from the floor, obtained for
the flow models. The results were compared with the airflow velocities obtained from the
field measurement at all the measuring points. It was found that the Realizable k-ε flow
model has an average deviation of about 10% compared to the measured airflow
velocities. The SST k-ω flow model has an average difference of about 8%, while the
SST k-kl-ω and SST transition models both have an average deviation of about 10%.
Finally, the standard k-ω flow model has an average difference of about 16%. These
findings suggest that the k-ω family flow models produced smaller average deviations in
the airflow velocity magnitudes compared to the k-ε family models. Among all flow
models, the SST k-ω produces airflow velocities closest to the measured values.
Therefore, this model was chosen and used in the proceeding CFD simulations.
7453
Enhancement of Airborne Particles Removal in a Hospital Operating Room
Figure 5. Comparison between the measured and predicted airflow velocity variation on
a plane of 1.2 m height from the floor, using the k-ε and k-ω family flow models.
The governing equations for the SST k-ω model are given by Eq. (3) and Eq. (4) below
[33]:
∂(ρk)/∂t + ∂(ρkúi)/∂xi = ∂(Γk∂k/∂xj)/∂xj + Ĝk - Yk + Sk
(3)
∂(ρω)/∂t + ∂(ρωúi)/∂xi = ∂(Γω∂ω/∂xj)/ ∂xj + Gω - Yω + Dω + Sω
(4)
where ρ is fluid density, t is time, úi is velocity component, xi is the coordinate, µ is fluid
viscosity, k is kinetic energy, ω is the specific rate of dissipation, Γ is effective diffusivity,
G is the generation of turbulence kinetic energy, Y is dissipation due to turbulence, D is a
cross-diffusion term and Si is a source term.
A pressure-based segregated algorithm was adopted in this study since the airflow
is assumed to be incompressible and with relatively low velocity. Also, a coupled
algorithm was selected for the pressure-velocity coupling, since it is suitable to handle
single-phase and steady-state flow conditions. Additionally, a double-precision option
was chosen for the numerical scheme, since it promotes less iterative error. In this study,
the simulation was performed in a steady-state condition with a second-order upwind
discretization scheme. The discretization scheme was selected as second-order upwind to
reduce the effects of numerical diffusion on the solution, as this would help to improve
the accuracy. The field variables (stored at cell centres) were interpolated to the faces of
the control volumes. An absolute residual value for all equations was set to 1 × 10-5 for
all the conservation equations. The convergence of the airflow velocity is shown in Figure
6.
7454
Wong et al. / International Journal of Automotive and Mechanical Engineering 16(4) 2019 7447–7463
Figure 6. Convergence history.
Two models are available for simulating the movement of airborne particles,
namely the discrete phase model (DPM) and the multiphase model. Both models calculate
the flow field according to the Eulerian framework, while the particle phases are solved
differently. The particle phases of DPM are solved based on the Lagrange approach. In
this study, this model was used for simulating the movement of airborne particles in the
computational domain. In this model, the fluid phase was treated as a continuum that was
analysed by solving the time-averaged Navier-Stokes equations. The discrete phase was
resolved by tracking a large number of particles through the calculated flow field. The
DPM is appropriate for particles that occupy a volume fraction of less than 10%
regardless of its mass fraction [34]. Many studies have shown that this model is reliable
to be used in modelling particle movement [1, 6, 12].
In this study, the aerodynamic diameter of the particles was chosen as 5 µm, and
their density was 2 g/cm3 [30]. The particles were considered to be released from the
frontal exposure area of the surgical staff at a rate of 1.31 × 10-12 kg/s. The particles
released rate was acquired by Liu et al. [30]. For the particle boundary conditions, an
escape condition was specified at the air supply diffusers and exhaust grilles, while a trap
condition was set on the expose surfaces of the operating table, walls and surgical lamps.
The trap boundary condition means that once a particle touches the area, it is caught, and
the particle tracking process stops. The escape boundary condition means that when the
particle exit through the area, the trajectory calculations are terminated. The DPM model
is capable of handling the effects of diverse forces such as Brownian force, gravitational
force, Saffman lift force, etc. [33]. The effect of Saffman force was disregarded in this
study, since the airborne particles are relatively small in (5 μm), as reported in Saidi et al.
(2014) [35]. The Saffman force is only significant when the particles involved in the flow
simulation are sufficiently large (greater than 10-6 m).
The Brownian motion force was also abandoned due to its non-significance in
comparison to turbulent diffusivity [12, 14, 36]. Forces such as gravitational force and
drag, which have been reported to have important effects on micro-sized particles, are
considered [37, 38]. The discrete random walk (DRW) model was incorporated to
simulate the stochastic airflow velocity fluctuations. This model assumes that the
fluctuating velocities follow a Gaussian probability distribution. The force balance
equation for discrete phase model then becomes [1, 12],
dup/dt = FD(u - up) + g(1 - ρ/ρp) + Fa
(5)
7455
Enhancement of Airborne Particles Removal in a Hospital Operating Room
where FD(u - up) represents the drag force, u is fluid velocity, up is particle velocity, g is
gravity force, ρ is fluid density, ρp is particle density, and Fa is the additional force.
Proposed Modification of The Ventilation System
The presently installed ventilation system in the actual operating room was designed
based on an ISO 14644 Standard 170-2013 - Minimum Guidelines for a Modern
Operating Room. In this study, a minor modification to the present ventilation system is
proposed in an attempt to improve the particle removal capability of the system,
particularly from the vicinity of the operating table [4]. Two minor modifications are
proposed: the first is the addition of one air exhaust grille mounted on one of the room’s
walls and the second is the use of a much larger ceiling-mounted air supply diffuser. The
airflow velocity at the diffuser remains the same, at 0.45 m/s. With the larger area, the air
volume flow rate will increase. Figure 7 shows a simplified CFD model of the operating
room which incorporates the two proposed modifications to the ventilation system.
Figure 7. A simplified CFD model of the operating room with the proposed
modifications on the ventilation system.
RESULTS AND DISCUSSION
Variation of Airflow Velocity
Figure 8 shows the effects of the proposed modification of the ventilation system on the
airflow distribution in the same vertical plane when both the surgical staff are bending
forward. Figure 8 (a) shows the variation of airflow velocity under present ventilation.
Whereas, Figure 8 (b) shows the variation of the airflow velocity when the operating room
is furnished with an additional air exhaust grille. It can be seen from this figure that there
are no noticeable changes in the airflow velocity resulting from this modification. The
magnitudes of the airflow velocity at the rear of both surgical staff and in the area between
them appear to be similar to those shown in Figure 8 (a). However, when a combination
7456
Wong et al. / International Journal of Automotive and Mechanical Engineering 16(4) 2019 7447–7463
of a new exhaust grille and a larger air supply diffuser is employed, the airflow velocity
distribution shows a very significant increment. The airflow velocity at the rear of both
surgical staff rises to about 0.23 m/s, while the airflow velocity in the area between the
staff increases to 0.2 m/s. This represents a two-fold increment when compared to the
same case under the present ventilation system. In summary, the first proposed
modification to the ventilation system does not have any appreciable effects on the airflow
distribution. However, when that change is combined with a larger air supply diffuser, a
significant increase in the airflow velocity distribution is achieved, especially in between
the surgical staff who are bending forward, which is not desired.
(a)
(b)
7457
Enhancement of Airborne Particles Removal in a Hospital Operating Room
(c)
Figure 8. Variation of airflow velocity magnitude in a vertical plane with the proposed
modified ventilation system, when both surgical staffs bend forward (a) with the present
ventilation system, (b) with an additional exhaust grille, and (c) with a combination of
additional exhaust grille and larger air supply diffuser.
Variation of Particle Concentration
Figure 9 shows the variation in the concentration of the airborne particles in a vertical
plane that passes through the two surgical staff standing at the head-end of the
operating table under the present ventilation system. It can be observed from Figure
9(a) that the particles fell from all the surgical staff and were transported away towards
the exhaust air grilles. A larger number of particles appear to be washed away from
the left surgical staff member compared to the one on the right. The concentration of
particles around the two surgical staff reached a peak value of about 2.5 × 10-5 mg/m3.
It can also be observed from Figure 9(b) that larger numbers of airborne particles fall
onto the operating table when two surgical staff are bending forward. These findings
indicate that the accumulation of airborne particles on the operating table is affected
by the standing posture of the surgical staff. High accumulation of airborne particles
in this area is undesirable, as this would increase the possibility that the particles
would settle on the patient. In the actual surgical procedure, this would increase the
risk of the patient being infected by the bacteria carried by the falling particles.
(a)
7458
Wong et al. / International Journal of Automotive and Mechanical Engineering 16(4) 2019 7447–7463
(b)
Figure 9. Variation of particle concentration on a vertical plane under (a) six surgical
staff standing upright, (b) two surgical staff bending forward at 45°.
In summary, with the present ventilation system, when all the surgical staff are
standing upright, almost no airborne particles appear to fall onto the operating table.
However, when two surgical staffs who are standing opposite to one another bend
forward, the number of particles that fall onto the operating table increases
dramatically. The present ventilation system is incapable of washing away the
airborne particles from the area of the operating table when the surgical staff are
bending forward.
Figure 10 shows the variation in the concentration of airborne particles in the
same vertical plane when two surgical staff are leaning forward at a 45° angle under
the proposed modified ventilation system. It can be observed from Figure 10(a) that,
when an additional air exhaust grille is placed in one corner of the room, the variation
in concentration of the airborne particles around the surgical staff is not greatly
affected. Also, the transport paths of the particles appear very similar to those found
under the present ventilation system. However, when a larger air supply diffuser is
combined with the additional air exhaust grille, fewer particles are transported
towards the exhaust grille on the left side of the room, as observed in Figure 10(b).
Also, more particles appear to accumulate below the operating table. These particles
can be transported upward and end up settling on the operating table, which is not
desirable. The concentration of particles around the two surgical staff is reduced. With
higher airflow velocity in this area, more particles tend to be transported away towards
the exhaust air grilles. The most important effect is that the number of particles that fall
onto the operating table is significantly reduced, but more particles are accumulating
under the operating table.
7459
Enhancement of Airborne Particles Removal in a Hospital Operating Room
(a)
(b)
Figure 10. Variation of particle concentration on a vertical plane with two surgical
staffs bend forward: (a) with additional air exhaust grille and (b) with the
combination of additional air exhaust grille and a large air supply diffuser.
CONCLUSION
A computational fluid dynamic method was used to carry out simulations to predict the
airflow distribution and the movement of airborne particles in a hospital operating room
equipped with an Econoclean ventilation system. The goal was to reduce the
accumulation of airborne particles on the operating table. Results show that under the
present ventilation system, when the surgical staff bend forward at a 45° angle, the
number of airborne particles that tend to fall onto the operating table increases. Modifying
the present ventilation system by adding an exhaust grille to the operating room does not
have any significant effects on the distribution of the airborne particles. However, when
this modification is combined with the use of a larger air supply diffuser, more airborne
particles are transported towards the exhaust grilles. The number of airborne particles
falling onto the operating table appears to be decreased, as a larger proportion of them are
accumulating below the operating table.
7460
Wong et al. / International Journal of Automotive and Mechanical Engineering 16(4) 2019 7447–7463
ACKNOWLEDGEMENT
The authors would like to express their appreciation for the support of Ainuddin Wahid
Scholarship throughout this study under the Vot No. A.J10000.5900.06000.
REFERENCES
[1]
[2]
[3]
[4]
[5]
[6]
[7]
[8]
[9]
[10]
[11]
[12]
[13]
[14]
[15]
Sadrizadeh S, Holmberg S. Effect of a portable ultra-clean exponential airflow
unit on the particle distribution in an operating room. Particuology, 2015, 18:170178.
Melhado MA, Hensen J, Loomans M. Review of ventilation systems in operating
rooms in view of infection control. In: Proceedings of the 6th Int. Postgraduate
Research Conf.. in the Built and Human Environment, Technische Universiteit
Delft, 2006; pp. 478-487.
Nguyen D, MacLeod WB, Phung DC, Cong QT, Nguyen VH, Hamer DH.
Incidence and predictors of surgical-site infections in Vietnam. Infection Control
& Hospital Epidemiology, 2001. 22: 485-492.
Wagner JA, Schreiber KJ. Improving operating room contamination control.
Ashrae Journal, 2014, 56, 18.
Whyte W, Hodgson R, Tinkler J. The importance of airborne bacterial
contamination of wounds. Journal of Hospital Infection 1982; 3: 123-135.
Sadrizadeh S, Holmberg S, Tammelin A. A numerical investigation of vertical
and horizontal laminar airflow ventilation in an operating room. Building and
Environment 2014; 82: 517-525.
Whyte W, Cleanroom technology: fundamentals of design, testing and operation:
West Sussex: John Wiley & Sons; 2010.
Buang S, Haspani M. Risk factors for neurosurgical site infections after a
neurosurgical procedure: a prospective observational study at Hospital Kuala
Lumpur. Medical Journal of Malaysia 2012; 67, 393-398.
Memarzadeh F, Manning AP. Comparison of operating room ventilation systems
in the protection of the surgical site. ASHRAE Transactions 2012; 108: 3-15.
Memarzadeh F. Reducing risks of surgery, ASHRAE Journal 2003; 45: 28.
Hansen D, Krabs C, Benner D, Brauksiepe A, Popp W. Laminar air flow provides
high air quality in the operating field even during real operating conditions, but
personal protection seems to be necessary in operations with tissue combustion.
International Journal of Hygiene and Environmental Health 2005; 208: 455-460.
Sadrizadeh S, Tammelin A, Ekolind P, Holmberg S. Influence of staff number
and internal constellation on surgical site infection in an operating room.
Particuology 2014; 13: 42-51.
Emmerich SJ, Heinzerling D, Choi J, Persily AK, Multizone modeling of
strategies to reduce the spread of airborne infectious agents in healthcare facilities.
Building and Environment 2013; 60: 105-115.
Chow TT, Wang J, Dynamic simulation on impact of surgeon bending movement
on bacteria-carrying particles distribution in operating theatre. Building and
Environment 2012; 57: 68-80.
Wong KY, Kamar HM, Kamsah N, Zawawi FM, Tan H, Musa MN, et al.,
Correlation between particulate matter and microbial counts in hospital operating
rooms. Advances in Environmental Biology 2018; 10: 1-4.
7461
Enhancement of Airborne Particles Removal in a Hospital Operating Room
[16]
[17]
[18]
[19]
[20]
[21]
[22]
[23]
[24]
[25]
[26]
[27]
[28]
[29]
[30]
[31]
Kamsah N, Kamar HM, Alhamid MI, Wong KY. Impacts of temperature on
airborne particles in a hospital operating room. Journal of Advanced Research in
Fluid Mechanics and Thermal Sciences 2018; 44: 12-23.
Wong KY, Kamar HM, Nazri K, Alia SN. Effects of surgical staff turning motion
on airflow distribution inside a hospital operating room. Evergreen 2019; 6: 5258.
Kamar HM, Kamsah N, Wong KY, Musa MN, Deris MS. Field measurement of
airborne particulate matters concentration in a hospital's operating room. Jurnal
Teknologi (Science & Engineering) 2015; 77: 63-67.
Ninomura P, Rousseau C, Bartley J, Updated guidelines for design and
construction of hospital and health care facilities. ASHRAE Journal 2006; 48:
H33, 2006.
Standard ISO, ISO 14644-1, Cleanrooms and associated controlled environments,
in classification of air cleanliness vol. ISO 14644-1, Cleanrooms and associated
controlled environments, ed. United Kingdom: Institute of Environmental
Sciences and Technology, 1999.
Standard IEST, IEST-RP-CC006.2, in testing Cleanrooms vol. IEST-RPCC006.2, ed. USA: Institute of Environmental Sciences and Technology, 1997.
Standard NEBB, Procedural standards for certified testing of cleanrooms, in
Adjusting. and Balancing of Environmental Systems vol. Procedural standards for
certified testing of cleanrooms, ed. USA: National Environmental Balancing
Bureau, 2009.
Xu T, Lan CH, Jeng MS, Performance of large fan-filter units for cleanroom
applications. Building and Environment 2007; 42: 2299-2304.
Woloszyn M, Virgone J, Mélen S, Diagonal air-distribution system for operating
rooms: experiment and modeling. Building and Environment 2004; 39: 11711178.
Standard ASHRAE, Standard 170 - 2008, in Ventilation of health care facilities
vol. Standard 170 - 2008, ed. USA: The American Society of Heating,
Refrigerating and Air-Conditioning Engineers, 2008.
Villafruela J, Olmedo I, De Adana MR, Méndez C, Nielsen PV, CFD analysis of
the human exhalation flow using different boundary conditions and ventilation
strategies. Building and Environment 2013; 62: 191-200.
Sadrizadeh S, Holmberg S, Nielsen PV. Three distinct surgical clothing systems
in a turbulent mixing operating room equipped with mobile ultraclean laminar
airflow screen: A numerical evaluation. Science and Technology for the Built
Environment 2016; 22: 337-345.
Kwaśniewski L. Application of grid convergence index in FE computation.
Bulletin of the Polish Academy of Sciences: Technical Sciences 2013; 61, 123128.
Karimi M, Akdogan G, Dellimore KH, Bradshaw SM. Quantification of
numerical uncertainty in computational fluid dynamics modelling of
hydrocyclones. Computers & Chemical Engineering 2012; 43: 45-54.
Liu J, Wang H, Wen W. Numerical simulation on a horizontal airflow for airborne
particles control in hospital operating room. Building and Environment 2009; 44:
2284-2289.
Sadrizadeh S, Afshari A, Karimipanah T, Håkansson U, Nielsen PV. Numerical
simulation of the impact of surgeon posture on airborne particle distribution in a
7462
Wong et al. / International Journal of Automotive and Mechanical Engineering 16(4) 2019 7447–7463
[32]
[33]
[34]
[35]
[36]
[37]
[38]
turbulent mixing operating theatre. Building and Environment 2016; 110: 140147.
Tao Y, Inthavong K, Petersen P, Mohanarangam K, Yang W, Tu J. Experimental
visualisation of wake flows induced by different shaped moving manikins.
Building and Environment, 2018, 142: 361-370.
Fluent A, Ansys fluent 12.0 users guide, in Ansys Inc vol. Ansys fluent 12.0 users
guide, ed. USA: ANSYS, 2009.
Rui Z, Guangbei T, Jihong L. Study on biological contaminant control strategies
under different ventilation models in hospital operating room. Building and
Environment 2008; 43: 793-803.
Saidi M, Rismanian M, Monjezi M, Zendehbad M, Fatehiboroujeni F.
Comparison between Lagrangian and Eulerian approaches in predicting motion
of micron-sized particles in laminar flows. Atmospheric Environment 2014; 89:
199-206.
Chen Q, Zhang Z, Prediction of particle transport in enclosed environment, China
Particuology 2005; 3: 364-372.
Tao Y, Inthavong K, Tu J, Computational fluid dynamics study of human-induced
wake and particle dispersion in indoor environment. Indoor and Built
Environment 2016; 26: 185-198.
Wang J, Chow TT. Influence of human movement on the transport of airborne
infectious particles in hospital. Journal of Building Performance Simulation 2015;
8: 205-215.
7463