Wet heat sterilization (autoclaving) uses saturated steam under pressure of approximately 15 pounds per square inch to achieve a chamber temperature of at least 250°F (121°C) for a prescribed time (usually 30–60 minutes) to destroy all forms of microbial life.
Dry heat is less efficient than wet heat and requires longer times and higher temperatures to achieve sterilization.
- Typical uses: Sterilization of glassware by dry heat can usually be accomplished at 160°–170°C for periods of 2 to 4 hours.
- Precaution: Monitor wet and dry heat sterilizers on a regular basis using appropriate biological indicators [spore strips].
Liquid disinfectants can be generally classified as halogens, quaternary ammonium compounds, phenolics, aldehydes, and several other chemical compounds.
Liquid disinfectant effectiveness varies with the organism, concentration, contact time, and other conditions of use. Select only liquid disinfectants that are confirmed to be effective against the organism(s) present.
- Typical uses: Liquid disinfectants are used for surface decontamination and to decontaminate liquid wastes prior to disposal in the sanitary sewer.
- Precautions: The more chemically reactive a compound is, the more likely it is to be toxic and corrosive.
- Consult Summary of Disinfectants for recommended disinfectants, their uses, and requirements.
- Also see How to Disinfect Tissue Culture Media in Vacuum Flasks.
Vapors and gases, when used in closed systems and under controlled conditions of temperature and humidity, provide excellent disinfection. Agents in this category include the aerosol, vapor, or gas phase of chlorine dioxide, glutaraldehyde, para-formaldehyde, ethylene oxide, peracetic acid, and hydrogen peroxide.
- Typical uses: Vapors and gases are primarily used to decontaminate biosafety cabinets, animal rooms, and their associated systems, bulky or stationary equipment not suited to liquid disinfectants, instruments or optics that might be damaged by other decontamination methods, and rooms, buildings, and associated air-handling systems.
- Caution: Due to their hazardous nature, contact EH&S Biosafety, (858) 534-5366, for special monitoring requirements if these compounds will be used.
Ionizing radiation will destroy microorganisms, but is not a practical tool for laboratory use.
The UV-C band of ultraviolet (UV) radiation contains wavelengths (250-270 nm, 265 is optimum) that effectively destroy most microorganisms in air and water and on surfaces. Organisms must be directly exposed to the UV light; dirt, dust, and shadows can shield organisms, limiting UV lamp effectiveness.
Ultraviolet radiation is typically used to reduce levels of airborne microorganisms in healthcare, food handling, and pharmaceutical production settings. UV is also used in biological safety cabinets and in some laboratory rooms to reduce surface contamination.
UV can cause burns to the eyes (photokeratitis) and skin of people exposed for even a short period of time. Use these precautions:
- Activate UV lights only when the area is unoccupied.
- Use proper shielding when UV lamps are in use.
- Interlock UV lamps used for space decontamination with the general room or cabinet illumination, so turning on the lights turns off the UV.
- Warn new and visiting personnel about the hazardous affects of UV radiation and the appropriate precautions to take.
Because UV lamp intensity (its destructive power) decreases with time, proper maintainance is critical for decontamination purposes. Perform this regular maintenance:
- Check lamp efficiency monthly with a UV meter or monitoring strip.
- Clean UV lamps every few weeks to prevent dust and dirt from accumulating that drastically reduces UV lamp effectiveness.