Manual of basic techniques for a health laboratory - libdoc.who.int

3. General laboratory procedures 85● For decontamination of blood spills and other specimens with a high proteincontent: 40ml of concentrated hypochlorite solution in 360ml of water (1%available chlorine).Strong hypochlorite solutions are corrosive and can cause burns. Handle solutionsof bleach carefully: wear rubber gloves to protect the hands, and eye shields toprevent splashing in the eyes.Calcium hypochlorite is available in its solid form as powder or granules. It decomposesat a slower rate than sodium hypochlorite. A solution of 1% available chlorineis obtained by dissolving 14g of calcium hypochlorite in 1 litre of water.ChloramineChloramine (tosylchloramide sodium) is a crystalline powder which, like thehypochlorites, releases chlorine as the active disinfectant agent, although at a slowerrate. It is also used for water disinfection: chlorinated water has a concentration of0.05% chloramine. Note that chlorinated water can interfere with laboratory tests.Distilled water must therefore be used.Calcium hydroxideCalcium hydroxide solution is prepared from quicklime (calcium oxide) powder orgranules dissolved in water (1 part:3 parts w/v). Calcium hydroxide solution is notsuitable for disinfecting stools from patients with tuberculosis.Quaternary ammonium compoundsQuaternary ammonium compounds (QUATS) are effective against vegetative bacteriaand some fungi. They are not effective against spores, viruses and mycobacteria;they are not toxic and are harmless to the skin.AlcoholsAlcohols (e.g. ethanol, isopropanol, n-propanol) are fast-acting, but relatively expensivedisinfectants that are usually used for skin disinfection. They kill bacteriaand some viruses, but not fungi.IodineIodine is an excellent, fast-acting disinfectant with a wide range of action. It killsbacteria, many spores, viruses and fungi. At low temperatures iodine is more activethan other disinfectants. Some people are hypersensitive to iodine and suffer a rashon areas of skin that have been exposed to iodine solution. Their sensitivity ismuch less when iodophores (polymer solutions that bind iodine) such as polyvidoneiodine are used.3.5.5 SterilizationSterilization is defined as the destruction of all microorganisms in or about anobject. In the medical laboratory sterilization is achieved either by moist heat(autoclaving, boiling) or by dry heat (hot-air oven, flaming). Materials are sterilizedfor three main purposes in the medical laboratory:— in preparation for taking specimens (needles, syringes, tubes, etc. must besterile);— to disinfect contaminated materials;— to prepare the equipment used for bacteriological cultures (Petri dishes,Pasteur pipettes, tubes, etc.).