Operating room ventilation system design

This is a public technology created by Kristian Kirwin (B.ENG Mechanical) and Shannon Roger (B.Ed) for Airepure Australia (Camfil Group company) entitled “Design considerations for operating room ventilation systems”. This is an excerpt from the article. Medical facility Volume 40, Issue 3, September 2017.

For more information on design objectives and risks, minimum permissible requirements in Australia, individual HEPA modules and laminar flow (UCV) systems, and low speed systems designed to meet the European DIN 1946-4 standard, https: See //www.airepure. / Operating-theatre-ventilation-system-design /.

Effect of blanking section of laminar flow system

Figures 8 and 9. CFD modeling of a laminar flow system with a blank central section: A circulating flow region is created and particles are suspended. Click here for a larger image.

Figures 8 and 9 show how the space between individual diffusers, or the blanking of sections of a laminar flow system, introduces areas of non-uniform and turbulent flow. This increases the risk of surgical site infection (SSI) by allowing uncontrolled air or air contaminated with particulate matter (such as desquamation from surgical staff or skin cells) to enter the wound site.

Levitating particles and SSI

There are many technical papers and reports related to the importance of suspended particles that contribute to SSI.

“Most of the SSI is the result of hygiene-related factors associated with the surgeon. For bacteria that infect the surgical site through the air, desquamation or skin scales are the main source of infection.”[i]

Airborne particles have been shown to be responsible for about 80-90% of microbial contamination (CDC2005).

Indoor air in the operating room can contain particles from many sources, including people, processes or activities in the operating room, and microorganisms on these air particles can cause wounds, dressings, and It is generally understood that it can become established in surgery, causing instruments and infections.

Reducing nosocomial infections can have a significant impact on improving patient outcomes and minimizing costs to healthcare facilities. While hygiene-related prevention is the most practical and proven method, aerial-related pollution control offers one area that can play a much larger role. One area of ​​ongoing discussion is the role of operating room ventilation systems and system design in air containment control to help reduce nosocomial SSI.

Operating room air quality

In 2010, Airepure used independent industry resources to conduct a review of air quality in two operating room systems. One is the traditional design of a ventilation system that incorporates four terminal HEPA filters and 20 air exchanges per hour. One is laminar theater ventilation, which exchanges air 40 times an hour (2.4 x 2.4 m).2 Laminar flow system with a surface velocity of about 0.4 m / s).[ii]

Figure 10: Layout of conventional 4-terminal HEPA module

Figure 11: Laminar Flow / UCV Theater

Traditional theaters (Figure 10) have shown high levels of particle contamination both at the operating room table level and throughout the theater. The tests were conducted in three traditional theaters in the same surgical department, with similar results in each theater.

Laminar flow theater results (Figure 11) show a dramatic reduction in airborne particulate contamination both at the operating room table level and throughout the theater.

The evaluation was performed using a calibrated particle counter using particle numbers measured and recorded in the 0.3 micron, 0.5 micron, and 5 micron particle size ranges.

In both theater ventilation systems, when measuring air quality on discharge from a diffuser under a HEPA filter, the number of particles was zero for all three particle sizes, but the result was air quality at table height. Showed a significant improvement in the measured values ​​of. In a laminar theater compared to a traditional turbulent theater.

A summary of the recorded particle number results is in Table 3.

Location Number of particles / m3 Number of particles / m3 Number of particles / m3
Size 0.3 micron Size 0.5 micron Size 5.0 micron
A traditional theater 1m below the terminal HEPA diffuser 34,500 8000 824
Traditional theater at the operating room table 304,000 119,000 6950
Traditional theater on the wall 563,000 677,000 4360
Laminar flow theater at the operating room table 0 0 0
Laminar flow theater on the outside around the laminar flow diffuser 6000 2130 706
Laminar flow theater on the wall 15,900 5300 1680

Table 3: Conventional 4x terminal HEPA module placement and laminar / UCV theater particle count results

The most interesting observation is the sharp drop in air quality under the HEPA filters in traditional theaters with separate HEPA filters.

This is due to the entrainment of particles from adjacent spaces. Compared to the principles of clean room design, turbulent placement is unacceptable. Large turbulence leads to pollution and pollution as well as surface area.[iii]

During the theater observation, there were numerous staff entries from the sterile corridor to set up for the next sequence of steps — this had no recognizable effect on the observation at the table location (zero value). Was returned).

A well-designed laminar / UCV system provides two protective effects: the inflow from an open door can prevent the theater from entering the contaminated exterior or move the surrounding area to a protected zone. There is, and the polluted air in the protected zone is rapidly replaced by clean air from the laminar / UCV system.[iv]


[i] Woods; 1996
[ii] Sutherland, A: Operating Room Ventilation System Review, Part 1: AHE Journal No. 37, December 2014, Part 2: AHE Journal No. 38, March 2015
[iii] Baumkuchen set. Al; Air Conditioning Technology Summary; Volume 1: Basics. 4th Edition Karlsruhe (Germany): 2000
[iv] CEN, Building Ventilation – Test procedures and measurement methods for delivering installed ventilation and air conditioning systems.German version EN125999; 2000
AS 1668.2: Use of ventilation and air conditioning in buildings. Part 2: Mechanical ventilation of the building: SAI Global Limited 2012

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