Prevention

Location

A thimble connection (see Figure 3) is used with Class II type A2 BSC that is ducted to the outside. The thimble fits over the cabinet’s exhaust housing, sucking the air expelled from the cabinet into ducts that lead outside. A small opening (usually 5 cm wide) is maintained between the thimble and the cabinet’s exhaust housing. This opening enables room air to be drawn into the exhaust ducting system. The capacity of the exhaust system must be sufficient to capture both room air and the cabinet’s exhaust.

Class II BSCs differ from Class I cabinets in that they allow only air from a HEPA-filtered (sterile) supply to flow over the work surface.

A Class II type A2 BSC is shown in Figure 2. An internal fan draws room air (supply air) into the cabinet through the front opening and then into the front intake grill. After passing through the grill, the supply air is drawn upwards and through a HEPA filter before flowing downwards over the work surface.

• All procedures must be performed in such a way as to minimize or prevent the formation of aerosols and droplets (see Box 2).
• Mouth pipetting must be strictly prohibited.
• No materials should be placed in the mouth.

Gloves must be worn for all procedures that involve direct contact, or may involve accidental contact, with sputum, blood, body fluids and other potentially infectious materials. After use, gloves should be removed aseptically and hands washed.

Contaminated gloves (and unwashed hands) may be a source of infection for other staff members if they are used to handle or operate equipment in the laboratory (such as a centrifuge or telephone).

In general TB laboratories that perform diagnostic tests, an autoclave that uses saturated steam under pressure is the most efficient means of sterilizing instruments, glassware and media solutions; it is also used for decontaminating biological material (such as mycobacterial cultures). Two factors are essential for an autoclave to function optimally: (1) all of the air in the chamber should be replaced by steam; and (2) the temperature must be 121 °C.

Similar to the moderate-risk laboratory, there are two levels of containment in a high-risk laboratory: the BSC (primary containment) and the laboratory itself (secondary containment).

In addition to the safety elements required for a moderate-risk laboratory, a high-risk (or TB-containment) laboratory requires the following additional enhancements.