SPECIALIST FACILITIES
There are no legal minimum containment requirements under COSHH for CL1 laboratories, which are appropriate for secondary education and undergraduate teaching. CL2 is probably the most commonly used containment level, suitable for a broad range of clinical, diagnostic, and research work. At this level, there should be a high standard of supervision and enhanced precautions, such as specific training in the handling of pathogenic agents, and limited access to the laboratory when in use.
Mycobacterium tuberculosis CL3 and above
At CL3 and above, precautions become far more complex. CL3 laboratories are the highest containment level laboratories in common use in the UK, and the point at which certain features to ensure appropriate containment must be incorporated into the design. Britain has about 600 CL3 labs. Nine sites, all in south-east England, are home to highly specialised CL4 labs, including the National Institute for Medical Research, which studies pandemic and avian flu, and Porton Down, which studies Ebola and other pathogens that could be used as biological weapons.
CL3 laboratories
A CL3 laboratory is required when handling human pathogens that may be transmitted via inhalation, that often have a low infectious dose to produce effects, and that can cause serious or life- threatening disease. These pathogens include HIV, hepatitis B, yellow fever, and rabies. CL3 containment features primary and secondary barriers to minimise the release of infectious organisms into the immediate area and the environment. Every CL3 laboratory has two physical layers of containment:
n The primary barrier, which contains the hazard at source through the use of equipment such as microbiological safety cabinets.
n The secondary barrier, which protects the people and the environment through a combination of design and operating procedures such as air- handling and restriction of access.
Airtight, gas-tight, and leak-proof The CL3 laboratory is an airtight, gas- tight, leak-proof room that uses specialised airflow design to prevent the escape of hazardous pathogens. Design and maintenance of these spaces is complex, and should only be carried out by a specialised contractor like Medical Air Technology (MAT), with a thorough and proven understanding of the myriad of requirements and regulations, and the ability to deliver a safe and compliant facility.
The design and construction of a containment laboratory has to meet the specific requirements laid out by COSHH, but in addition to all the mandatory requirements that have to be addressed, the laboratory should also be designed to take account of the recommendations in guidance or standards produced by bodies such as the ACDP, whose publications, ‘The Management, design and operation of microbiological containment laboratories’, and ‘Biological agents: managing the risks in laboratories and healthcare premises’, are both vital reference documents for anyone building containment facilities.
Key elements in the design and build of a CL3 laboratory Room structure and specialist airflow design
Surface-mounted services and a gas-tight transfer plate.
88 Health Estate Journal October 2018
In a CL3 laboratory the HVAC system is a critical part of the containment process. COSHH requires that at CL3 the workplace must be maintained at an air pressure negative to atmosphere to stop the escape of hazardous pathogens. This is achieved by the specialist airflow created by the HVAC system, which establishes and maintains the negative pressure, and thus ensures containment and operator safety. The negative
pressure is achieved by engineering controls, so that a continuous inward airflow into the laboratory is maintained, away from the user and towards the source of potential contamination, with provision made for comfort factors such as the supply of fresh air and temperature control.
The lobby is another vital element of the laboratory design. As well as significantly improving the laboratory protection factor, it provides an additional level of control of the flow of air into the laboratory when workers are entering or exiting, avoiding potentially problematic fluctuations in air patterns that can compromise containment. It also marks the start point of the controlled airflow: the HVAC monitored pressure control system supplies air to the lobby, and then draws the air through to the laboratory via a combination of safety cabinet extract and HEPA filtration of exhausted laboratory air, creating a gradation of negative pressure. Where possible, the ventilation should be dedicated to the laboratory.
HEPA filters
HEPA filters are the industry norm for this sort of controlled environment, with COSHH stating that at CL3, extracted air must be HEPA filtered (or equivalent). In the HVAC system and safety cabinets, HEPA filters, or, to give them their full name, High Efficiency Particulate Arrestors, trap hazardous bacteria to provide personnel protection. In addition to straining the air, a number of actions take place within the filter that help to trap particles, making the filters a highly effective way to remove particles from the airstream.
Conceptualising and designing a safe and compliant CL3 laboratory requires
A glass-reinforced polyester (GRP) interlocked door.
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