The Safe Working Environment


Basic Levels 1 and 2 laboratories

Although Containment Levels 1 and 2 laboratories are considered to be adequate with microorganisms which offer minimal risk to the worker. The potential for such risks is enough to merit design features additional to school laboratories and offices. A safe working environment implies enough working space. In the UK, it is recommended by the DHSS that each worker should have at least 18.6 m2 of space. It is now generally accepted that each worker be given 3 m run of benching and 24 m of free air space (ACDP). Access to laboratory areas by people who do not work in them should be strictly limited. Members of the general public should get no further than the reception areas or waiting rooms.

In the interest of safety, floors should be slip resistant, seamless, be impermeable to liquids and resistant to most, if not all chemicals that are normally used in laboratories. The surfaces of walls and partitions should be smooth, impervious and easily cleaned. Windows should be sealable and fitted with blinds. Doors should be fire resistant and fitted with vision panels. Ceilings also need to be impermeable and should be coved to the walls. Openings in walls and ceilings for the entry of pipes etc. should be sealed around such pipes. Bench surfaces should be impervious to liquids, and not easily corroded or stained by chemicals. Electricity and gas supplies to the benches are needed, water and waste plumbing is optional. Each laboratory should have a hand basin and disposable paper towels provided.

Ventilation systems designed to prevent the distribution of infectious airborne particles were developed during the Second World War based on the "Clean-to-Dirty" airflow principle, where more air is extracted from the rooms where hazardous materials are handled than from any other area. Close-fitting doors are used and thereby resulting in a pressure gradient so that air always flows from clean to potentially contaminated areas ie. from corridors to laboratories and not in the opposite direction. The air extracted from contaminated areas may be ducted directly to the atmosphere. It is important that adequate lighting is provided. It is not usually necessary to fit microbiological safety cabinets into Levels 1 and 2 laboratories.

Level 3 laboratories

The object of level 3 laboratories is to confine, or contain the organisms so that only a minimum number of people are exposed to them. Hence the policy of designating a whole microbiology department as a level3 laboratory is fatuous. A true level 3 laboratory is suitable for one or two persons only. If the amount of work merits more staff, than separate Level 3 laboratories should be provided. All the design features advocated for Level 2 laboratories apply. Although Level 3 laboratories may open off non-public corridors, it is best if access is from other laboratories of a lower Containment Level. Access to Level 3 laboratories should be strictly limited and controlled and the doors should be locked when the rooms are not in use. Microbiological safety cabinets are essential features of these laboratories. Care is needed in siting those in relation to airflows and staff movements. An incubator room could open directly from a Level 3 laboratory and there should be enough storage space e.g. refrigerators and deep-freezers so that Hazard Group 3 organisms need not be kept elsewhere.

Level 4 laboratories

Work with Hazard Group 4 agents is usually severely restricted in most countries by government decree. Therefore a great deal of consultation and supervision is necessary in the planning and building of these laboratories. The laboratory should be isolated or physically separated from other parts of the same building so that access is difficult. It should be airtight and access is through airlocks. The ventilation system should be completely controlled so that air flows via air locks into the laboratory. Class III safety cabinets should be maintained at a lower pressure than the room. All effluent air is passed through double banks of HEPA filters before discharge to the atmosphere. A double-ended autoclave is essential to ensure that nothing passes outside the room without being sterilized.

Specimen reception rooms

A specimen reception room should be separated from offices and treated as a potentially infected area. The floors and surfaces must likewise to leak-proof and amenable to decontamination procedures. A hand basin is essential and access should be restricted to authorized persons.

Preparation or utility rooms

One or more of these rooms should be designated for the reception, treatment and disposal of contaminated waste. The design features should be those of a Level 2 laboratory equipped with autoclaves, a sluice, a waste disposal unit plumbed to a public sewer, deep sinks, glassware washing machines, drying ovens, sterilizing ovens and large benches. These should be arranged to preclude any mixing of contaminated and decontaminated materials.

Walk-in incubators and refrigerators

The microbiological hazards associated with these concern firstly, their distance from the laboratories, and secondly raised thresholds. Spillages and breakages of cultures in corridors are much more hazardous than in rooms. Raised thresholds are sometimes fitted to incubator and refrigerator rooms to accommodate floor insulation. There is little need for floor insulation since the average concrete floor will not lose or gain enough heat to affect an incubator or cold room.

Microbiological Safety Cabinets