A previous article in this series discussed disinfection of surfaces with hydrogen peroxide. We turn our attention now to bleach as another very effective treatment agent.
Most people understand that ordinary household bleach – a 5.5% solution of sodium hypochlorite (NaOCl) in water – is a strong disinfecting agent. In neutral or slightly acidic solutions the active species responsible for the bactericidal action is HOCl, hypochlorous acid. It has been proposed that the HOCl breaks down the cell walls of pathogenic organisms and causes the proteins in these organisms to lose their necessary three-dimensional structure. Furthermore, bleach solutions have a well-established reputation for killing spores, allowing the product to be classified as a sterilant (destruction of all forms of microbial life, including spores), not just as a disinfectant. In health care applications, a working concentration of 0.5% sodium hypochlorite in water is sufficient to act as a sterilant on critical surfaces.
The procedure for applying bleach solutions in controlled environments is similar to that provided previously for hydrogen peroxide solutions. It is included here for convenience.
A major concern is that bleach come into contact with bare surfaces in order to kill the bacterial organisms. If there are any soils on the surface, they must be removed with detergent, then the surfaces rinsed with deionized water prior to applying bleach. Residual soils or detergents on the surfaces will consume bleach and will limit bactericidal or sporicidal action. If the surfaces are soil-free then direct application of bleach is fine. It is essential that all surfaces be wiped thoroughly with bleach using the recommended linear wiping strokes. After wiping, surfaces should be allowed to air dry for a minimum of 10 minutes to allow the liquid bleach to accomplish surface sterilization.
There are two concerns with using bleach as compared to hydrogen peroxide. In contrast to hydrogen peroxide which is odorless, bleach carries a pungent odor and cleanroom personnel should avoid the area after the bleach has been applied. Also, hydrogen peroxide breaks down harmlessly to oxygen and water and thus cause no surface residue issues; bleach, however, leaves behind a corrosive residue (especially if stainless steel surfaces are involved) which must be removed after the 10 minute contact time has elapsed. Since these residues are ionic in nature, wiping with deionized water will be most effective for removal. A final wipedown with 70%IPA-30% deionized water is recommended to hasten drying of the surfaces.