The killing action of disinfectants depends on the population of organisms to be killed, the concentration used, the duration of contact, and the presence of organic debris.
Proprietary disinfectants recommended as suitable for use in TB laboratories are those containing phenols, chlorine or alcohol. These are usually selected depending on the material to be disinfected.
Phenol should be used at a concentration of 5% in water. However, inhalation and dermal exposure to phenol is highly irritating to the skin, eyes and mucous membranes. Ingestion of phenol is considered to be toxic. Because of its toxicity and odour, phenol derivatives are generally used in place of phenol.
Phenol solutions are used for decontaminating equipment and single-use items prior to disposal.
Chlorine is widely available. Sodium hypochlorite solutions (domestic bleach) contain 50 g/l available chlorine, and should therefore be diluted to 1:50 or 1:10 in water to obtain final concentrations of 1 g/l or 5 g/l. Bleach, either in stock or in solution, must be stored in a well ventilated, dark area. In good storage conditions, the 50g/l solution may last as long as 3 months; diluted solutions should be prepared daily.
Bleach can be used as a general purpose disinfectant and for soaking contaminated metal-free materials; because it is highly alkaline, it can corrode metal.
Alcohols, ethanol (denatured ethanol, methylated spirits) or isopropyl alcohol are used at a 70% solution. Alcohols are volatile and flammable, and must not be used near open flames. Solutions should be stored in proper containers to avoid evaporation. Bottles with alcohol-containing solutions must be clearly labelled so they are not autoclaved.
A solution of 70% alcohol can be used on laboratory benches and BSCs for routine decontamination. A major advantage of aqueous solutions of alcohols is that they do not leave any residue on treated items. When hands become contaminated, a rinse with 70% ethanol or isopropyl alcohol followed by thorough washing with soap and water is effective.
Peracetic acid is characterized by rapid action against all microorganisms. Special advantages of peracetic acid are that it lacks harmful decomposition products, enhances removal of organic material, and leaves no residue. Working solutions (2% concentration) are stable for 48 hours after preparation.