CITI Program

    Courses Records CE/CMEs Support

Search
Bruce Lickey
ID 8841906
Disinfection and Sterilization

University of Vermont - BSL-1 Basic Course
Disinfection and Sterilization

    Content Author

        Benjamin Fontes, MPH, CBSP
        Yale University

Introduction

    This module provides an overview of the processes and options associated with disinfection.

    Learning Objectives

    By the end of this module, you should be able to:

        Identify different ways to disinfect work surfaces and contaminated items.
        Describe the parameters of the liquid decontamination process including selecting the most appropriate chemical, identifying an appropriate concentration, and determining the required contact time.
        Explain the parameters of physical decontamination methods, such as autoclaving, dry heat, and incineration for the inactivation of biohazards.

Disinfect Work Surfaces and Contaminated Items

    All items contaminated by biohazards, including equipment, work surfaces, and supplies, must be decontaminated after the experiment, prior to reuse, or before disposal.

Antisepsis

    A chemical applied to living tissue that will control or arrest the growth of a microorganism. Hand washing with antibacterial soap and water is an example of this application.

Disinfection

    The intent of disinfection is to free from infection and reduce the contaminant load to a safe level. It does not imply total destruction of all microorganisms. This process will not always inactivate spores.

Sterilization

    The destruction of all forms of microbial life. This is difficult to achieve, but there is a low probability of microorganism survival.

Physical Methods of Sterilization
Autoclave

    Employs steam under pressure, using moist heat to lower the time needed to destroy microorganisms. In general, a temperature of 121 ºC (250 ºF) can be achieved using 15 psi of pressure. Run times of 30 to 60 minutes may be needed for complete sterilization, but it will depend on the parameters of the load within the autoclave.

    Autoclave runs can be verified with chemical indicators, which can indicate if appropriate temperature has been reached; with digital data-loggers that can record and track temperature in various locations within the autoclave and check for cold spots; and with biological indicators, usually containing spores of Geobacillus stearothermophilus, which will survive at 121 ºC (250 ºF) for 11 to 13 minutes.

    Care must be taken in autoclaving liquids that can present a hazard of boil over if a slow-exhaust setting is not used. Always use a slow-exhaust setting when autoclaving liquids to allow appropriate cooling before the autoclave can be opened. Capped containers can also over pressurize and burst, making it important to ensure that caps are loosely positioned on bottles or not at all during the autoclave run. To avoid this potential during the use of the autoclave, follow these safety work practices:

        Never place hazardous chemicals within the autoclave.
        Position items in the autoclave to allow for effective steam penetration (in other words, do not overload the autoclave, as much longer residence times will be required for sterilization).
        Do not place tightly stoppered or sealed bottles or tubes within the autoclave as pressure build up within them may lead to explosions during or after the autoclave cycle.
        Wear appropriate clothing, long pants, solid cover shoes, in conjunction with a lab coat, an impact resistant full-face shield, and long sleeved insulated gloves when operating the autoclave. A rubberized apron can be used for additional protection.
        Allow the load to fully cool before opening the autoclave door following the run.
        When opening the autoclave door at the end of the full cycle, open only .5" or 1 cm and wait. This will allow any steam to be removed through the small opening and not towards the operator. Allow the door to sit only slightly opened for 5 to 10 minutes before fully opening. This will protect the operator from exposure to any over-pressurized bottles inside which could burst after the run.

Dry Heat

    Dry heat (provided in an oven) will require higher temperatures – 160 to 170 ºC (320 to 338 ºF) – for longer times (up to 2 to 4 hours). Caution should be taken with loads as even thin layers of inorganic or organic material may insulate surfaces and longer residence times may be required.

Incineration

    Burning of contaminated materials, generally involves a two-stage burn cycle, with temperatures ranging from 760 to 982 ºC (1400 to 1800 ºF).

Gases Can Also be Used to Achieve Sterilization
Formaldehyde Gas

    Boiling formalin or heating paraformaldehyde at prescribed concentrations can create formaldehyde gas. As this is an extreme chemical hazard, only trained and authorized experts should perform this procedure. Exposure times up to eight hours may be needed. Since formaldehyde is a suspect carcinogen, residual formaldehyde vapor can be neutralized with ammonia gas (created by heating solid ammonium bicarbonate) following the residence time. Temperature and humidity are important considerations for successful sterilization with formaldehyde and each must be controlled during the procedure. Temperature must be maintained at 21 ºC (70 ºF) or above and humidity must be above 70 percent.

Ethylene Oxide

    Ethylene oxide is also a significant chemical hazard and known carcinogen. Ethylene oxide sterilizers must be evaluated by an Industrial Hygienist or other qualified safety professional and used only by trained and authorized personnel. This gas is commonly used for sensitive equipment in healthcare settings. Concentrations between 400 and 800 mg per liter (with temperature between 35 to 60 ºC [95 to 140 ºF] and 30 to 60 percent Relative Humidity) for a 4-hour contact time have been used as a successful gas sterilant.

Hydrogen Peroxide

    At the higher concentrations required for space decontamination, hydrogen peroxide is a potent oxidizer and should only be utilized by trained and authorized personnel. Generally, designated personnel are trained to use commercialized systems with built in safety features for the decontamination of equipment or space. Hydrogen peroxide, which can be vaporized from aqueous hydrogen peroxide, is gaining favor as a space decontaminant, as it breaks down to harmless substances after use.

Liquid Disinfectants

    The most common application of disinfectant is the use of disinfectant solutions to decontaminate potentially contaminated work surfaces and equipment. Surfaces must be cleaned and disinfected at the end of the experiment or workday, and after any spills of biohazards. A successful disinfection involves the selection of an appropriate disinfectant; the use of the proper disinfectant concentration; applying the disinfectant for an appropriate contact time; and knowledge of the limitations of the chemical used. Factors that may interfere with disinfection include temperature; pH; humidity; and the presence of organic material, such as blood or sputum. One way of formatting a successful disinfection process is to follow the 3 C's of disinfection as described below.

    • Chemical: Select a chemical that can inactivate the microorganism of concern. • Concentration: Follow the manufacturer's preparation instructions for dilution as the label will identify the effective concentration range or use the concentrations provided in the “Summary Overview of Common Laboratory Disinfectants” section below. • Contact Time: The Environmental Protection Agency (EPA) uses a 10-minute contact time to test the effectiveness of disinfectants. Use this time period or another reference to apply the disinfectant for the appropriate contact period.

Disinfection Work Practices

        Select appropriate combination of chemical, concentration, and contact time.
        Keep working solutions of disinfectant available at bench and in the work area.
        Use work surface covers or bench pads and replace them frequently.
        Promptly clean/decontaminate work surfaces and equipment, and biohazard waste (and spills).
        Have concentrated disinfectant available in the lab for spill response.
        Decontaminate all work surfaces with an appropriate disinfectant after completion of a procedure, when surfaces are overtly contaminated, and after any spill of biohazards.
        Decontaminate equipment used for work with biohazards after each use and before any service work is performed on the equipment.
        Decontaminate all bins, pails, or other receptacles that could become contaminated periodically or as soon as feasible after they become visibly contaminated.
        Decontaminate reusable tools and instruments before reuse or reprocessing.

    Some items may require cleaning to remove excess debris before application of the disinfectant. Whenever feasible, remove all visible contamination with disinfectant-soaked towels before applying the disinfectant.

Summary Overview of Common Laboratory Disinfectants

    This information has been adapted from the 1979 NIH Laboratory Safety Monograph, A Supplement to the NIH rDNA Guidelines.

Chlorine (Household Bleach)

    The effective concentration of chlorine is a minimum of 500 ppm. Chlorine can be used to target a wide spectrum of microorganisms, including vegetative bacteria, enveloped (lipid viruses), non-enveloped (non-lipid) viruses, and bacterial spores. Review notes about chlorine.

Iodine

    The effective concentration of iodine is 75 to 1600 ppm. Iodine can be used to target a wide spectrum of microorganisms, including vegetative bacteria, enveloped (lipid viruses), non-enveloped (non-lipid) viruses, and bacterial spores. Review notes about iodine.

Alcohol

    The effective concentration of alcohol is 70 to 85 percent. Alcohol can be used to target microorganisms, including vegetative bacteria, enveloped (lipid) viruses, and some non-enveloped (non-lipid) viruses. Review notes about alcohol.

Quaternary Ammonium Compounds

    The effective concentration of quaternary ammonium compounds is 0.1 to 2.0 percent. Quaternary ammonium compounds can be used to target microorganisms, including vegetative bacteria and enveloped (lipid viruses). Review notes about quaternary ammonium compounds.

Phenol

    The effective concentration of phenol is 1.0 to 5.0 percent. Phenol can be used to target microorganisms, including vegetative bacteria, enveloped (lipid) viruses, and some non-enveloped (non-lipid) viruses. Review notes about phenol.

Formaldehyde

    The effective concentration of formaldehyde is 0.2 to 8.0 percent. Formaldehyde can be used to target a wide spectrum of microorganisms, including vegetative bacteria, enveloped (lipid viruses), non-enveloped (non-lipid) viruses, and bacterial spores. Review notes about formaldehyde.

Hydrogen Peroxide

    The effective concentration of hydrogen peroxide is 3.0 to 25.0 percent. Hydrogen peroxide can be used to target a wide spectrum of microorganisms, including vegetative bacteria, enveloped (lipid viruses), non-enveloped (non-lipid) viruses, and bacterial spores. Review notes about hydrogen peroxide.

        Using Disinfectants

Summary

    This module has provided an overview of the principles of decontamination, disinfection, and sterilization. It has also summarized the factors required for successful decontamination using liquid disinfectants and physical treatment methods for biohazard inactivation. Work practices associated with disinfectant use were also reviewed as part of this module.

Reference

        U.S. Department of Health, Education, and Welfare. 1979. “Laboratory Safety Monograph: A Supplement to the NIH Guidelines for Recombinant DNA Research.” Accessed December 20, 2018.

Additional Resources

        Centers for Disease Control and Prevention (CDC). 2016. “Disinfection and Sterilization.” Accessed December 20, 2018.

        Rutala, William A., David J. Weber, and the Healthcare Infection Control Practices Advisory Committee (HICPAC). 2017. “Guideline for Disinfection and Sterilization in Healthcare Facilities, 2008.” Accessed December 20, 2018.

Original Release: February 2010
Last Updated: January 2019

This module has a quiz.
Support

    888.529.5929
    8:30 a.m. – 7:30 p.m. ET
    Monday – Friday
    Contact Us

Legal

    Accessibility
    Copyright
    Privacy and Cookie Policy
    Terms of Service

CITI Program