The NIAID Integrated Research Facility (IRF) at Fort Detrick, Maryland, is a biosafety level (BSL)-2 to BSL-4 laboratory with unique medical imaging capabilities. The facility was built in accordance with Centers for Disease Control and Prevention (CDC) and National Institutes of Health biosafety standards. Extensive high-efficiency particulate air (HEPA) filtration, custom air pressure-resistant doors, state-of-the-art biological safety cabinets, multiple levels of access control and security, effluent decontamination, and multiple redundant systems provide a state-of-the-art facility dedicated to safe BSL-4 research. What distinguishes the NIAID IRF at Fort Detrick from all other existing high-containment facilities is the capability to apply clinical diagnostic imaging tools to advanced animal models under BSL-4 conditions, thus facilitating the advanced development of medical countermeasures for biodefense.
The IRF is a partner of the National Interagency Biodefense Campus (NIBC) at Fort Detrick. The IRF features BSL-2, -3, and -4 level laboratories with unique BSL-4 imaging capabilities. Research emphasis is on Category A viral pathogens in addition to newly emerging infectious diseases, which all require high levels of biocontainment. Traditional research methods are supplemented with multi-modal medical imaging.
Multi-modal medical imaging equipment is used to systematically evaluate the clinical course and pathology of infectious disease processes in experimentally infected animals at the IRF. The IRF imaging suite includes the following integrated imaging modalities: Magnetic Resonance Imaging (MRI), X-ray (XR), Computed Tomography (CT), Positron Emission Tomography (PET), Single Photon Emission Computed Tomography (SPECT), and ultrasound.
The Bioshield containment tube concept developed by CUH2A Smith Carter and Philips Healthcare specifically for the NIAID IRF separates the imaging suite into two sides: a biologically “hot” side (pathogens present) and a biologically “cold” side (pathogens not present). Each of the imaging modules utilizes a transparent biocontainment Lexan tube (Philips Bioshield), which extends the hot side of the imaging suite into the bores of the imaging system machines on the cold side (Figure 1). The animal is placed on a patient table in the hot side of the barrier wall, which then cantilevers it into the biocontainment tube to be imaged (Figure 2). The imaging machines themselves are located outside of containment on the cold side of the barrier wall and are thus accessible for adjustments, servicing and routine maintenance without requiring technicians to enter the hot side. The clear tubes also allow scientists to observe the animals being imaged from the cold side (Figure 3).
In addition to providing biocontainment, the barrier wall and containment tube arrangement separates and protects the imaging equipment from the decontamination gases and chemicals used to sterilize the hot side (Figure 4). This division also eliminates the need for electronic components on the hot side, as all electrical signals are sent through an airtight patch panel to instruments in a computer control room on the cold side. The placement of the imaging equipment had to be carefully planned for electromagnetic and radiation shielding, vibration, structural integrity, security and access control, temperature, communications, utility service penetrations, decontamination and maintenance, as well as imaging throughput, effective circulation, and animal transport and care considerations. To save space on the containment level, the imaging support rooms that contain the electronics, transformers, and controls, as well as the MRI liquid helium supply, are located in the HEPA level above. The entire imaging suite is located near the building exterior wall, which has knock-out panels that allowed for the initial installation and will permit future replacement of the imaging equipment.
Level 2: BSL-4 Laboratory and Peripherals
The IRF biocontainment laboratory was built in accordance with containment standards and requirements defined by the CDC Biosafety in Microbiological and Biomedical Laboratories (BMBL) handbook for BSL-4 Suit and Class III cabinet laboratories. The BSL-4 laboratory building consists of three dedicated levels. Essential features of this unique design are illustrated in Figure 5.
Level 3: Mechanical Mezzanine and HEPA Filtration Deck
Level 3 consists of the mechanical mezzanine and the HEPA deck. Its main purpose is to provide the HEPA filtration units that filter any potential contaminants in the supply and exhaust air of the maximum containment laboratory. Breathing air and back-up air systems, chemical shower systems, a dedicated lab vacuum, an air pressure resistant (APR) door and access control, fire protection, communication, imaging support equipment, centralized animal watering systems, air handlers, and other mechanical, electrical, and plumbing systems are also located on the HEPA level. All of the mechanical systems operate at less than 100 percent capacity and have one or more layers of redundancy, so that maintenance can be performed without affecting overall system performance. This design redundancy guarantees that there is always back-up to mitigate system failures.
HEPA filters remove 99.97 percent of all particulate material from incoming and discharged air from the laboratory spaces. Supply air is filtered once, and exhaust air is filtered by two HEPA filters in series, a standard BSL-4 practice. The HEPA filters are “bag in/bag out” units enclosed in stainless steel housings: exhaust housings contain two filters in series, and supply housings contain one (the supply is HEPA filtered to ensure that no unfiltered room air can ever be exhausted by positive room pressure through the supply ductwork). For overall flexibility, each individual enclosed room in the containment lab has its own dedicated supply and exhaust HEPA assemblies. This, coupled with strategically located APR doors in corridors, allows the IRF to be segmented and configured in several different biocontainment operating zones. It also allows for a room or series of rooms to be isolated and taken down for decontamination without requiring the entire containment lab be taken out of service. As a result of these dedicated HEPA units, the IRF has a total of 77 sets of supply and exhaust HEPA filtration units. A schematic of the HEPA laboratory exhaust filtration system is illustrated in Figure 6.
Breathing air for use in biocontainment suits is filtered two more times after initial filtration. Once it is filtered by a laboratory HEPA filter, it passes through the HEPA filters in the breathing air system and subsequently through dedicated HEPA filter cartridges prior to supplying the biocontainment suits.
Level 2: Laboratory Suites
Air Pressure Differential and APR Doors
The containment laboratory has a negative air pressure atmosphere and is surrounded on its perimeter by a positive pressure “buffer” corridor, which provides access to all areas for movement of materials, animals and personnel. It also acts as an environmental and security barrier to the high containment laboratory.
The air pressure gradient becomes progressively more negative toward the central laboratory suites. A constant air volume system (CAVS) creates a negative pressure atmosphere in a suite by maintaining a higher exhaust to intake ratio. The progressively negative atmosphere of a laboratory suite creates a positive-to-negative pressure gradient that directs air into a laboratory when one of its doors is opened. This ensures containment of potentially contaminated air.
APR door systems maintain the pressure differential between rooms when a door is opened or closed by signaling trim valves to modulate the pressure exchange in combination with the CAVS. Magnahelic air pressure gauges register the exchange of air across the doorway in inches of water column (IWC) to ensure the pressure differential is being maintained (Figure 7). When an APR door is closed, pneumatic inflatable seals prevent the exchange of air between rooms. A door control system detects door positions, permits only one door to be opened in a room at one time, and controls the pneumatic inflatable seal and the access control security devices.
Class III Biosafety Cabinets
Negative pressure gas-tight Class III biosafety cabinets provide maximum protection when working with highly infectious microbiological agents. Chemical grade Hypalon gloves attach to ports in a non-opening view window and prevent contact with hazardous materials. Materials are sterilized and passed in and out of a cabinet through a double door autoclave or a dunk tank. Materials may also be exchanged between laboratory suites through a sample transfer port. The control panel ensures that the negative pressure atmosphere is maintained. Dedicated control panel HEPA filters decontaminate the air prior to reaching the magnahelic pressure sensors.
The cabinets have their own HEPA filtration system that bypasses the general laboratory exhaust system. Incoming air from the laboratory is filtered once, and outgoing air is filtered twice before being discharged. Dual exhaust filters are staggered to allow easy access for maintenance. Filters are exposed to an aerosol challenge periodically to maintain optimal filter performance. Once the aerosol is introduced, integrated scanning wands are connected to a particle counter that checks for leaks in the filter media. A schematic representation of a Class III BSC is illustrated in Figure 8.
Level 1: Effluent Decontamination Systems
All fluid waste from the second level containment laboratory is routed to the effluent decontamination system (EDS) on the first level through stainless steel pipes. The system consists of four tanks with integral steam jackets: three 1,500-gallon tanks that treat all liquids from the containment lab and one 300 gallon tank that is dedicated to a designated autoclave (Figure 9). The three 1,500-gallon tanks are an example of the IRF’s “n+1” configuration: one tank receives waste, a second tank sterilizes a batch, and the third tank is on stand-by. Effluent waste is sterilized by heating it with steam at 250 degrees for one hour. A schematic of an EDS is illustrated in Figure 10.
The Ft. Detrick garrison has a zero-tolerance radiation sewage policy, and all effluent waste is tested for radioactivity before discharge. Standard operating procedures should preclude any radioactivity from ever entering the waste stream, but in the unlikely event this occurs, radioactive waste would be held in radioactive effluent holding tanks and decayed through multiple half-lives before being drained to containers for off-site handling. Once the effluent waste has been sterilized and tested to be radiation-free, it is mixed with the building sanitary waste in a 10,300-gallon blending tank located below the first floor ground level. The blended effluent is pH-neutralized and cooled, and any solids are macerated by a recirculating grinder pump. When the blending tank reaches full capacity, it discharges the effluent waste into the sewage system.
Tissue waste is sterilized in a high-capacity tissue digester or designated autoclave on the second level. The condensate from the tissue digester and from the designated autoclave flows through stainless steel pipes to the dedicated 300-gallon cook tank on the first floor, where it is sterilized, tested for radiation, piped to the blending tank, and ultimately discharged to the sewage system.
The design of the IRF incorporates all of the lessons learned from years of experience working safely with BSL-4 pathogens and complies with all applicable regulations. The unique challenges of incorporating medical imaging modalities into the BSL-4 environment have been innovatively addressed. Real time imaging of infectious disease processes will facilitate the development of medical countermeasures for biodefense agents by providing insight into pathophysiological processes as required by the FDA Animal Efficacy Rule. Imaging will also reduce the number of animals required for natural history studies by permitting sequential sampling of individual animals and will refine the data quality by permitting each animal to serve as its own control, thus satisfying two of the three “Rs” (reduction, refinement, and replacement) required by animal care and use committees. While the engineering and design of the IRF have been the focal points of this article, it is important to note that this unique facility is essentially an intensive care unit for animals experimentally infected with biodefense pathogens. We welcome inquiries from all interested entities to develop collaborative agreements to fully realize the potential of this unique national resource.