Hospital/Healthcare
Forget your budget. Here are the technologies you need to equip an operating room with the cleanest and most sterile air filtration system available
 by Scott Winfrey, P.E. |
State building and health codes dictate many of the controls that keep hospital operating suites largely free from serious infections that can cause health safety concerns and costly liability.
Yet these controls, at times, fall short. Indeed, many hospitals specify more stringent requirements. While healthcare providers must usually balance cost with infectious disease containment, in an ideal world cost would not be an issue.
Just for a moment, let's consider an ideal situation, a utopian surgical suite. Following are recommendations for above average air quality and cleanability of an air handling system, as well as steps that surpass even the most copious air quality controls.
Air-handling unit construction
The air-handling system is at the basis of all air quality operations. In general, unit construction consists of return fans, supply fans, heating and cooling coils, humidifiers and various stages of filters.
While the standard allows exposed insulation upstream of final filtration, it is highly advisable to use double wall panels throughout the air-handling unit. Double wall panels are constructed of solid galvanized steel lining separated by insulation. For cooling coils and humidifier sections, which tend to oxidize metal, a solid stainless-steel lining is recommended. Alumi num liners are another option.
 The “hospahu” illustration is a picture of typical air handling used for hospital applications with dual supply and return fans. (Illustration courtesy of HDR and Trane.) |
State health codes typically specify double wall construction downstream of high-efficiency air filters for a 90 percent efficiency filtration rating based upon American Society of Heating, Refrigerating and Air-Conditioning Engineers Inc. (ASHRAE) Standard 52.1-1992 (ashrae.org). The theory is that if the insulation flakes off, it will be caught in the liner. The problem: bacteria and mold grows in the liner itself and can be the cause of infectious contamination.
Solid surfaces are more cleanable than those with a perforated lining. Therefore, minimize the use of perforated surfaces in an air-handling unit. Paint is another matter of concern. Because paint often does not satisfactorily adhere to galvanized or stainless-steel surfaces, it can actually flake off into the air stream, and should be avoided.
While solid liners are a benefit, their use has adverse ramifications that need to be offset. For example, sound levels frequently become too high for normal procedures and sound attenuators are often necessary. It is often unavoidable that attenuators have a perforated lining and contain baffles that are filled with fiberglass insulation exposed to the air stream. Because of its potential to enter the air stream, the fill material should be encapsulated with mylar or polymer sheeting.
 Illustration of the body exhaust system by Precision Air Products Co. |
A typical air-handling unit will have drain pans within the cooling coil, humidifier and perhaps the outside air intake sections. For ideal cleanliness, however, it may be beneficial to add a drain pan in each section in the air-handling unit, including the filter, access and fan sections. Review the facility's cleaning procedures and incorporate drain pans if heavy water use is anticipated. Drain pans should be double sloped to prevent standing water and should be constructed of stainless steel.
Coils
As standard construction, the casing and support channels for cooling coils are constructed of galvanized steel. Because moistened galvanized steel can corrode over the long run, it is also suggested that coil casing and support channels are constructed of stainless steel.
 Surgery in progress (Photo courtesy of HDR.). |
Another recommendation is to locate the cooling coil in the draw-through configuration, which is upstream of the supply fans. The air leaving a cooling coil typically has a relative humidity in excess of 90 percent.
In a draw-through arrangement, the motor heat will cause the supply air temperature to rise two degrees or more, which will lower the relative humidity of the supply air from 90 percent to 70-80 percent. Reducing the supply duct's relative humidity reduces the potential of bacteria and mold growth. When using a cooling coil in a draw-through arrangement, it is critical to install properly sized P-traps at the drain pan.
Coils are typically constructed with copper tube and aluminum fins. The standard fin thickness is 0.006-0.008-inch thick, which is easy to damage while cleaning. It is recommended that the thickness of the fin be increased to 0.010 inch-a small improvement but one that may encourage maintenance personnel to do more frequent cleaning.
If a healthcare facility came by some extra funds, an extremely effective method of minimizing or nearly eliminating the potential of bacteria or mold is through ultraviolet germicidal irradiation (UVGI). UVGI systems are typically located near the cooling coils. Due to their expense, UVGI systems are not very common, but it is predicted their use will increase in the future.
Fans
As standard, steel fans come from the factory with a primed finish. These should be factory painted with a high-quality finish, such as a powder coat. It is highly recommended to specify a paint that will pass a minimum 500-hour salt spray test per American Society for Testing and Materials (ASTM) B-117. It's best to avoid standard spray enamel finishes since they can lead to flaking.
 OR with a laminar flow ceiling and a low wall return at Saint Mary’s Hospital/Mayo Clinic in Rochester, MN. (Photography courtesy of HDR. Kessler Photography) |
While belt-driven fans are common, there is a potential for belt slippage and belt dust. If the budget allows, consider a direct drive fan, where the motor is directly coupled to the fan shaft. It will take up more space, but will eliminate belt dust and prevent the airflow from being compromised due to belt slippage.
Filtration
State health codes require air-handling units to have prefilters and final filters with a respective efficiency of 30 percent and 90 percent based upon ASHRAE 52.1-1992. The code also requires that all final filters be located downstream of supply fans and exposed insulation in the air stream.
Though not mandated, HEPA filters are highly recommended for specialty surgical procedures such as orthopedic, open heart, bone marrow transplants and organ transplants. Because of their high efficiency-99.97 percent on 0.3 micron particles-these are also frequently requested for use in general operating rooms. In fact probably 80 percent of operating suites employ HEPA filters.
Also in regard to filtration, be cautious of side access housings that work by sliding filters into place. They have galvanized steel channels, which can result in leakage up to 10 percent of the airflow. Instead, use holding frame systems that incorporate gasketing and retaining clips in order to eliminate air leakage.
Ideally, air-handling units for operating rooms should be dedicated to the operating suite. The result will be higher precision control of volume, odors and contaminants, and space pressurization.
To anticipate mechanical failures and facilitate cleaning, consider redundant air-handling units to serve the operating suite. Units with dual supply and return fans may be also used for this purpose.
However, if a repair is needed the unit must be taken off-line, causing disruptions in the operating room schedule. Use of multiple air-handling units would be a welcome addition in an ideal world.
Offering high flexibility, one unit could be taken off-line for routine maintenance or due to mechanical failure. While requiring additional space and funding, these will provide “true” redundancy and will greatly facilitate the ability to keep the interior of the units clean.
Air distribution
Laminar flow diffusers are typically used but not required. These direct the air in a vertical continuous, nonturbulent airflow pattern in the recommended 70 to 90 feet per minute rate of speed. It is required that the supply air must be released at the ceiling above the operating table and around the work area.
In addition, state health codes typically require 15-25 air changes per hour, though a minimum of 25 per hour are recommended. Indeed, higher rates may be necessary to achieve necessary laminar flow based on above recommended velocity.
HEPA filters are generally used either at the air handler or at the diffuser location, but rarely at both. If money were no object they should be placed at both positions for a great advantage. First, locating the HEPA filter at the diffuser is the optimal location to remove ductwork contaminants, yet changing the filters in the operating room is cause for concern because of the dirt particles, which may be released into the air.
 A laminar flow diffuser with a gel seal frame courtesy of E.H. Price Limited. |
As a result, locating the filters at the air-handling units outside the operating suite is preferred by many building owners. Installing HEPA filters at both locations would offer the best of both worlds. The air would be as clean as possible, and changing the diffuser filters in the suite would rarely occur due to the extended life resulting from the initial HEPA prefiltering at the air handling unit.
Using the HEPA filters in this manner accords much longer periods between filter changes in the OR. The air-handler HEPA filter will need to be changed every three to five years. More importantly, the diffuser filter in the OR will only need to be changed every 10 years or more. As an additional benefit of the dual locations, HEPA filters could be replaced on an active unit without compromising HEPA filtration in the operating room.
While not required, it is encouraged to use a gasketed framing system for the diffusers and the lights. This keeps the ceiling space sealed off from the room. To maintain a pressurized room, it is critical to minimize the amount of joints in the ceiling system.
The gasketed framing system limits the paths where air can escape the room, and improves pressure control. Teardrop lighting, which is relatively rare in OR rooms, may provide improved laminar flow. These fixtures are only a few inches wide and suspend down several inches from the ceiling. Compared with lay-in lights that can break up laminar flow, teardrop lights limit interference with air circulation.
Clear containment panels around the perimeter of the work area and the laminar flow core improve the containment of the air at the operating table. In fact, the effective air change rate at the operating table can be increased to more than 200 air changes per hour with 25 air changes per hour being delivered to the room. If a state-of-the-art OR is desired, this is considered cutting edge.
Two low sidewall air return grilles located at points as distant as practical within the room are required by code. In an ideal situation, use four return grilles in each corner of the room. This requires using additional wall space, which comes at a premium, and will likely result in layout changes. Adding the extra grilles will improve airflow.
Further, low wall return grilles should be constructed of stainless steel or be factory coated with a high-quality paint finish to allow for proper cleaning. A detail that's inexpensive but effective is to specify a heavy-duty grille with 14 gage blades to reduce the risk of damage and foster clean ability.
Another small detail is to use a plaster frame for low wall grilles. This supplemental frame around the perimeter of the grille border enables the grille to be removed and cleaned without disrupting paint or caulk at the edge of the grille. It also promotes cleaning.
Two quite unconventional elements hospital planners might consider if they have a futuristic bent are body exhaust systems and conducting a mock-up of the space prior to construction. First, body exhaust systems, which are used in healthcare facilities on rare occasions, can be used by the surgical team to further reduce contaminants. Surgical staff members wear a body suit with a helmet; the helmet is then connected to an exhaust system with flexible tubing. Obviously, the probable benefits would have to be weighed by the surgical team on a case-by-case basis.
Another possibility would be to test particle levels around an operating room in a mock-up room constructed during the design process to determine optimal placement of equipment. Measuring particles around the OR is beneficial to ensure the airflow is uniform. Yet the placement of necessary equipment such as lights, gas columns and articulating arms can impede the airflow around the operating table.
It is optimal, yet seldom feasible, that a hospital has the leisure of planning in such detail. Such preplanning could minimize natural conflicts in equipment placement, staff movement and air distribution. A second “mock-up” option is computerized flow dynamics, which can simulate actual conditions, including placement of surgical equipment and an analysis of airflow patterns in multiple room configurations.
Room construction
In general, room construction should take these basics into consideration. All surfaces should be as cleanable as possible. Flooring is commonly constructed of sheet vinyl or epoxy terrazzo. Walls and ceilings should be treated with glaze-coated, water-based epoxy. Wall materials should also be impact resistant to eliminate dust, and cove, or rounded corners, should be provided at all interior corners.
Stainless-steel casework is preferred over plastic laminate casework, but it is more expensive. If building code permits (main restriction is firewall requirements), use a double-acting door surrounded with stainless-steel armor. This minimizes hardware surfaces and crevices on the doorframe that need to be cleaned.
Pressurization control
Using tracking controls to regulate both supply and return air volumes is not required, but it makes sense and it is becoming more common. Both supply and return volumes should be controlled to a fixed volume with motorized dampers. Due to natural inaccuracies of control devices, the return volume should be tracked to a fixed air quantity under the measured supply air cubic feet per minute.
Typically the return air quantity is 10-20 percent less than the supply air. For example, if 3,000 cubic feet per minute (cfm) is desired and the return is 300 cfm, or 10 percent less, use the differential as a control point.
Maintaining the differential allows a facility to turn down the air volumes of an unoccupied room, something that could not be done unless employing tracking controls. As an extra level of safety, provide room pressure monitors to ensure that tracking controls are functioning properly.
Although it is rarely architecturally feasible due to space constraints, use of an anteroom at the main operating room entrance would reduce the risk of particle contamination to the OR. The anteroom, which basically is a vestibule, would feature two sets of doors in a series and would contain a surgeon's scrub sink. For most OR suites, a sterile environment is maintained in the corridor and/or connecting room to the OR and may, in reality, function similar to an anteroom.
Conclusions
You are probably aware of required specifications such as pre- and final filters, ceiling intakes and returns at the floor, as well as requirements for between 15 to 25 air changes per hour. Beyond these mandates in maintaining a surgical cleanroom, we encourage users to eliminate exposed insulation throughout air-handling units, not just downstream of final filters.
Based upon a facility's cleaning procedures, adding drain pans throughout the air-handling unit may be beneficial. Use corrosion-resistant materials or finishes for areas susceptible to corrosion. HEPA filtration should be placed at the outlet or at the unit, and dual supply and dual return fans are highly recommended. Use of laminar flow diffusers, tracking controls and possibly pressure monitors is also highly recommended.
Superior quality controls include redundant air-handling units, a HEPA filter at both the unit and the laminar flow diffuser, UVGI systems, tear drop lighting, clear containment panels, and four low wall return grilles.
Finally, if your facility is leaning toward futuristic solutions, consider the body exhaust system, a mock-up room or an anteroom configuration.
The bottom line: No matter what your budget may be, your OR should be the cleanest and most sterile you can afford.
Scott Winfrey is a senior professional mechanical engineer with over 12 years of experience. He has performed engineering services for several hospitals across the country. He is employed by HDR in Omaha, NE, an architectural and engineering services firm. He can be reach at [email protected].