Making assessments

Published: 24-Oct-2002

Steve Robertson, Technical Director of Crowthorne Hi-Tec, looks at the validation of containment level 3 laboratories

The Advisory Committee on Dangerous Pathogens (ACDP) guidance* requires that all containment level 3 (CL3) laboratories are validated before operation. In the UK, the Health and Safety Executive have a specialist team of inspectors who ensure that CL3 facilities meet the requirements of the ACDP guidance. Crowthorne Hi-Tec Services provides a national service to assess designs for proposed facilities, validate new laboratories and assess existing rooms. Currently it finds that 75% of laboratories do not meet the requirements of the ACDP guidance, particularly with respect to sealability for fumigation and the subsequent safe discharge of fumigant. There is every indication that this figure is optimistic rather than pessimistic as the number of prosecutions grows. The causes of this non-compliance can usually be traced to three areas:

  •  poor design
  •  poor construction (both in terms of materials and workmanship)
  •  lack of adequate controls.
Full validation of a CL3 facility can be undertaken as a 10-stage process (Fig. 1). Closely looking at the first of these stages – reviewing detailed plans for a proposed CL3 laboratory – will be time well spent when it comes to full validation. Items to consider include fumigation procedures and discharge arrangements for fumigant, room pressure specifications, provision of services and construction materials. A frequently recurring problem is the installation of electrical sockets. Installation of standard back boxes into cavity walls will result in substantial effort being expounded to seal these when it comes to validation. Provision of sockets on a surface-mounted dado avoids most of these problems. Visual inspection of a newly built facility usually identifies most of the problems that surface during later testing. These problems could include the lack of gas tight dampers on air supply and extract systems, unacceptable crevices around bench tops and other fixed equipment, and the use of conventional air supply grilles and flexible trunking which cannot be sealed. Once all visible defects have been rectified, a negative pressure integrity test can be carried out. This involves examining the entire perimeter of the room with a smoke pencil to search for leaks around service penetrations (including electrical sockets, smoke detectors, room thermostat boxes etc), wall joints, door and window frames. In many cases the leaks found can be attributed to lack of attention to detail during construction. The room pressure and flow rates for the extract and air supply systems can then be measured and compared to the design specification. The room volume air change rate is calculated, based on the extract system, and used to estimate the purge time required following fumigation. Where necessary, dispersal tests can be carried out to ensure that fumigant does not re-enter the building via windows or air intake systems. All air extracted from the room must pass through a H14 grade HEPA filter (99.995% overall efficiency, BS EN1822-1:1998). This may be through a microbiological safety cabinet or via a bypass filter or general extract from the room. Ideally the latter should be located as close as possible to the room, such as in ceiling mounted 'terminal' filter housings, to minimise the extent of potentially contaminated ductwork. It is not necessary to HEPA filter input air, although a good grade of filtration is beneficial in prolonging the life of extract HEPAs. In most installations it is not possible to scan the downstream side of the filter to identify the source of any leaks, so only volumetric testing is carried out. It is important to use a proprietary filter housing since much time can be lost replacing filters when the leak is in the housing itself. Using safe change filter housings, perhaps at plant room or roof level, means that the extract ductwork will be contaminated between the room and the filter. In this event the ductwork must be fumigated at the same time as the room, without any access ports, such as for servicing internal fire dampers. Where fire dampers are unavoidable, external types should be considered, such as intumescent collars which swell and crush the ductwork during a fire. Where temperature control is provided via ceiling void mounted fan coil units or air conditioning units these must be totally sealed to prevent loss of fumigant into the ceiling space. In practice this is both extremely difficult to achieve and requires sealed access hatches into the ceiling space to maintain them. It is preferable to avoid such systems and to locate air conditioning units below ceiling level or on the wall.

Safety cabinets Commissioning of the safety cabinets to BS EN12469:2000 standard should be carried out with all other systems in the room, including air conditioning units. This allows the aperture protection test to be carried out under as close to 'in use' conditions as possible. Where the cabinets are used as the sole extract from the room, consider shutting these down, such as for fumigation, on room pressure. The use of cabinets having in-built bypass filters, such as the TriMAT range from Medical Air Technology, can be beneficial since these allow the room pressure to be maintained while the cabinet is being fumigated or the night door fitted. Routine fitting of the night door whenever the cabinet is not in use will reduce the frequency at which the potentially more hazardous exhaust filter within the cabinet needs to be changed. Once the performance of the room has been validated in operational mode the fumigation procedure should be tested and proved. This is carried out by sealing the room as if a real fumigation was to take place but with the release of a safer tracer to prove containment and then purging it in the normal manner. The simplest tracer is a visible smoke consisting of solid particulate that will disperse to all parts of the room. This will persist in the room for several hours and shows up leaks in door frames, around vision panels, through electrical sockets etc. The disadvantage of the method is that it does result in some load on the HEPA filters when the smoke is discharged. This is not normally significant but can be if a number of leaks are found and repeated tests are required. The use of an aerosol smoke generated from oil, such as used in the testing of HEPA filters, is not recommended. An alternative is a tracer gas such as sulphur hexafluoride. These can show up small leaks but it is often difficult or impossible to identify the source of the leak by this method. Where make up air is provided mechanically, rather than through pressure controlled transfer grilles, the systems to control the room pressure must be tested. Since the aim of the control system is to prevent positive pressure in the laboratory, it is recommended that these systems should be based directly upon room pressure monitoring rather than by indirect means, such as extract fan rotation or differential pressure sensors. Testing should be carried out by simulating failure of one or more extract devices, and checking that the supply either sets back or shuts off at predetermined room pressures. Magnehelic gauges, or other pressure indicators for reference by laboratory staff entering the facility, should be calibrated, preferably in-situ. Checks are then carried out on general requirements for the room including:

  •  ensuring that tap handles are of the hands free operation type
  •  fumigation test port
  •  suitable storage for CL3 laboratory clothing and 'external' clothing
  •  operation of fumigation power socket
  •  external control of safety cabinets
  •  access control for the facility (including access to the HVAC control panels for the room) and interlocking of the lobby and laboratory doors
  •  labelling of the laboratory and plant serving the facility.
The final part of full validation is reviewing the CL3 laboratory operating protocols, particularly the fumigation procedure. A protocol should detail all stages required in the fumigation, which can be in the form of a checklist. Contractors installing a facility should ensure that all of the information required to prepare the protocol is included in the training provided to the laboratory users.

Fig 1. Validation of a containment level 3 laboratory 1 Review of design and specifications 2 Visual inspection of facility including HVAC plant 3 Negative pressure integrity tests 4 Airflow and pressure tests 5 Exhaust HEPA filter integrity tests 6 Commissioning of microbiological safety cabinets 7 Fumigation mode (ambient pressure) smoke test 8 Testing of control systems (especially room pressure control) 9 General room requirements 10 Preparation/review of operating protocols

* 'The management, design and operation of microbiological containment laboratories' (HSE Books, 2001)

Contact: Crowthorne Hi-tech +44 (0) 1252 372 333 This paper was previously presented at Cleanrooms Ireland 2002

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