Prevention

Personal protective equipment and clothing may act as barriers to minimize the risk of exposure to aerosols, splashes and accidental inoculation. The choice of clothing and equipment depends on the nature of the work. Protective clothing should be worn whenever staff work in the laboratory (see Box 6). Before leaving the laboratory, staff should remove their protective clothing, and wash their hands. Table 5 summarizes the types of personal protective equipment used in laboratories and the protection each type offers.

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.

During the centrifugation process, aerosols may be produced. Consequently, safety measures must be strictly followed when operating the centrifuge.

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.

Class I BSCs work by drawing unfiltered room air in through a front opening, passing it over the work surface, and then expelling it through an exhaust duct.

Class I BSCs protect workers but do not protect work products (such as specimens or cultures) against contamination because unsterilized room air is drawn over the work surface.

The two types of BSCs described below are best suited for use in moderate-risk laboratories and in high-risk laboratories (TB-containment laboratories).

Class I

• This type of BSC provides personal and environmental protection but does not offer product protection. This lack of product protection may contribute to increased contamination rates, especially when preparing and inoculating liquid cultures (see Figure 1).

Class II

Owing to their small size, droplet nuclei aerosols may be generated by certain laboratory procedures without the laboratory worker’s knowledge; this may result in the inhalation of infectious agents or cross-contamination of work surfaces or materials. BSCs are designed to protect people and the environment from infectious agents and, depending on their classification, offer varying degrees of protection from contamination of specimens and cultures.

Safety equipment may be used to eliminate or reduce certain risks in TB laboratories (Table 4). Such equipment offers no assurance of protection unless the operator is competent and uses proper techniques. Equipment should also be tested regularly to ensure that it continues to perform safely.