The integrity of the directional air inflow is fragile and can be easily disrupted by air currents generated by people walking close to the BSC, by open windows or air-supply registers, and by the opening and shutting of doors. Ideally, BSCs should be situated as recommended by the manufacturer in a location away from traffic and rom potentially disruptive air currents. Whenever possible, a clearance of 30 cm should be provided behind and on each side of the cabinet to allow easy access for maintenance. A clearance of 30–35 cm above the cabinet may be required to accurately measure air velocity across the exhaust filter, and to change exhaust filters.
If BSCs are not used properly, their protective benefits may be greatly diminished; in some instances improper use can even result in increased risk to the laboratory worker. Written protocols, as well as a biosafety manual, should be issued to laboratory staff and they should sign a form to confirm that they have read and understood the required protocols. All individuals working in BSCs should be observed to ensure they follow correct working practices before they routinely perform testing in the BSC. Operators need to maintain the integrity of air flowing through the front opening when moving their arms into and out of cabinets. They should move their arms slowly and ensure they are perpendicular to the front opening. Staff should wait about 2 minutes after placing their hands and arms inside the BSC before they begin manipulating materials; this will allow the airflow within the cabinet to adjust and the air to sweep the surface of their hands and arms. The number of movements made across the front opening should be minimized by placing all necessary items into the cabinet before beginning manipulations.
The front intake grill of Class II BSCs must not be blocked with paper, equipment or other items. It is recommended that all work be performed on disinfectant-soaked absorbent towels arranged to capture splatters and splashes. All materials should be placed as far back in the cabinet as practical – that is, towards the rear of the work surface – without blocking the rear grill. Aerosol-generating equipment (such as vortexes and centrifuges should be placed towards the rear of the cabinet. Bulky items (such as biohazard bags and discard containers) should be placed to one side of the interior of the cabinet. Active work should flow from clean areas to contaminated areas across the work surface. Paperwork should never be placed inside BSCs. The cabinet must not be overloaded because overloading may affect the efficiency of the airflow (see Figure 4).
Ultraviolet lights are not recommended in BSCs used in TB laboratories.
Open flames must be avoided in BSCs because heat disrupts the patterns of airflow within the cabinets. To sterilize bacteriological loops, microincinerators or electric furnaces are available, and their use is preferable to open flames. The use of disposable loops and disposable transfer pipettes is preferred.
A copy of the laboratory’s protocol for handling spills should be posted, read and understood by all laboratory staff. When a spill occurs inside a BSC, clean up should begin immediately and the cabinet should continue to operate. An effective disinfectant should be used and applied in a manner that minimizes the generation of aerosols. All materials that come into contact with the spilled agent should be disinfected and disposed of properly.
The functional operation and integrity of each BSC should be certified to national or international performance standards at the time it is installed, following any relocation with the laboratory, and regularly thereafter (at least annually) by qualified service technicians, according to the manufacturer’s specifications. An evaluation of the effectiveness of the cabinet’s containment capability should include tests of the cabinet’s integrity; tests for HEPA filter leaks; assessments of the down flow velocity profile, face velocity, negative pressure and ventilation rate, airflow smoke pattern, and alarms and interlocks.
The velocity of air flowing through the front opening into a BSC should meet the manufacturer’s specifications. Optional tests may also be conducted for electrical leakage, lighting intensity, ultraviolet light intensity, and noise level and vibration. Special training, skills and equipment are required to perform these tests, and it is highly recommended that they are undertaken by an experienced professional. The professional should be familiar with and trained in all aspects of BSCs.
Cleaning and disinfecting the work area
When work is completed, all items within a BSC, including equipment, should have surfaces decontaminated and be removed from the cabinet.
The interior surfaces of BSCs should be decontaminated before and after each use. Work surfaces and interior walls should be wiped with a disinfectant that will kill any microorganisms that might be found inside the cabinet. At the end of the workday, the final surface decontamination should include wiping down the work surface, and the sides, back and interior of the glass. A second wiping with sterile water is needed when a corrosive disinfectant, such as bleach, is used.
Before it is switched off, the BSC should be left to run for 15 minutes after work is completed in order to purge the atmosphere inside.
BSCs must be thoroughly decontaminated before filters are changed and before the cabinet is moved; decontamination must include plenums and filters. See standard NSF/ANSI 49 – 2008 for procedures and details of decontamination.²⁰ Decontamination should be performed by a qualified professional.
BSCs can be equipped with one of two audible alarms. Sash alarms are found only on cabinets with sliding sashes. The alarm sounds when the laboratory worker has moved the sash to an improper position. When this alarm sounds, the sash must be returned to the proper position. Airflow alarms indicate a disruption in the cabinet’s normal airflow pattern. This alarm represents an immediate danger to the worker or product. When an airflow alarm sounds, work should cease immediately and the laboratory manager should be notified. Manufacturers’ instruction manuals should provide further details about how to address this type of alarm. Training in the use of BSCs should include information on how to respond to this type of alarm.