DECONTAMINATION, STERILIZATION, DISINFECTION

The following guidelines are intended to ensure that all biohazardous waste is processed in a safe and timely manner, as well as in accordance with all applicable regulations.

Each generator of biohazardous waste has an obligation to handle and dispose their material in a manner which affords protection from leakage and injury or exposure to anyone handling their waste material.

1. Each individual working with biohazardous material or contaminated items is responsible for their decontamination, disinfection, and appropriate preparation prior to disposal or reuse.
   
2. All laboratories, in which work with biohazardous materials is carried out, must have labeled, leak-proof, covered containers for temporary holding of infectious materials awaiting disinfection or disposal. (Keep the containers closed at all times, unless adding waste.)

DEFINITIONS

Decontamination is a term used to describe a process or treatment that renders a medical device, instrument, or environmental surface safe to handle. A decontamination procedure can range from sterilization to simple cleaning with soap and water. Sterilization, disinfection and antisepsis are all forms of decontamination.

Sterilization is the use of a physical or chemical procedure to destroy all microbial life, including highly resistant bacterial endospores.

Disinfection eliminates virtually all pathogenic non-spore-forming microorganisms but not necessarily all microbial forms on inanimate objects (work surfaces, equipment, etc.). Effectiveness is influenced by the kinds and numbers of organisms, the amount of organic matter, the object to be disinfected and chemical exposure time, temperature and concentration.

Antisepsis is the application of a liquid antimicrobial chemical to skin or living tissue to inhibit or destroy microorganisms. It includes swabbing an injection site on a person or animal and hand washing with germicial solutions. Although some chemicals may be utilized as either a disinfectant or an antiseptic, adequacy for one application does not guarantee adequacy for the other. Manufacturer's recommendations for appropriate use of germicides should always be followed.

METHODS

There are four main categories of physical and chemical means of decontamination. They are heat, liquid disinfection, vapors and gases, and radiation. Each category is discussed briefly below.

1. Heat

Wet heat is the most dependable method of sterilization. Autoclaving (saturated steam under pressure of approximately 15 psi to achieve a chamber temperature of at least 250 degrees F for a prescribed time) rapidly achieves destruction of microorganisms, decontaminates infectious waste and sterilizes laboratory glassware, media, and reagents. For efficient heat transfer, steam must flush the air out of the autoclave chamber. Before using the autoclave, check the drain screen at the bottom of the chamber and clean it, if blocked. If the sieve is blocked with debris, a layer of air may form at the bottom of the autoclave, preventing efficient operation. Prevention of entrapment of air is critical to achieving sterility. Material to be sterilized must come in contact with steam and heat.

Chemical indicators, e.g., autoclave tape, must be used with each load placed in the autoclave. The use of autoclave tape alone is not an adequate monitor of efficacy. Autoclave sterility monitoring should be conducted on a regular basis (at least monthly) using appropriate biological indicators (B.stearothermophilus spore strips) placed at locations throughout the autoclave. The spores, which can survive 250 degrees F for 5 minutes but are killed at 250 degrees F in 13 minutes, are more resistant to heat than most, thereby providing an adequate safety margin when validating decontamination procedures. Each type of container employed should be spore tested because efficacy varies with the load, fluid volume, etc.

Decontaminate all infectious materials and all contaminated equipment or labware before washing, storage or discard as infectious waste. Autoclaving is the preferred method. Never leave an autoclave in operation unattended (do not start a cycle prior to leaving for the evening). Log sheets should be available at each autoclave to record the name of the user, time of run, and amount being autoclaved.

All personnel using autoclaves must be adequately trained by their PI or lab manager. Never allow untrained personnel to operate an autoclave.

View the Recommended Procedures for Autoclaving.

Dry heat is less efficient than wet heat and requires longer times and/or higher temperatures to achieve sterilization. It is suitable for the destruction of viable organisms on impermeable non-organic surfaces such as glass, but it is not reliable in the presence of shallow layers of organic or inorganic materials which may act as insulation. Sterilization of glassware by dry heat can usually be accomplished at 160-170 degrees C for periods of 2-4 hours. Dry heat sterilizers should be monitored on a regular basis using appropriate biological indicators [B.subtilis (globigii) spore strips].

Incineration is another effective means of decontamination by heat. As a disposal method, incineration has the advantage of reducing the volume of the material prior to its final disposal. However, local and federal environmental regulations contain strigent requirements and permits to operate incinerators are increasingly more difficult to obtain. There are no incinerators here at USciences.

2. Liquid Disinfection

The most practical use of liquid disinfectants is for surface decontamination and, when used in sufficient concentration, as a decontaminate for liquid wastes prior to final disposal in the sanitary sewer. (A one time approval from EHRS must be obtained for sink disposal.) If liquid disinfectants are used, they must have been shown to be effective against the organism(s) present.

Liquid disinfectant are available under a wide variety of trade names. In general, these can be classified as: halogens, acids, alkalis, heavy metal salts, quaternary ammonium compounds, phenolic compounds, aldehydes, ketones, alcohols and amines. The more active a compound is, the more likely it is to have undesirable characteristics such as corrosivity. No liquid disinfectant is equally useful or effective under all conditions and for all viable agents.

Concentrations and exposure times vary depending on the formulation and the manufacturer's instructions for use. Therefore, always follow the manufacturer's recommended instructions for use to ensure proper decontamination. View Activity Levels of Selected Liquid Germicides for additional information.

3. Vapors and Gases

A variety of vapors and gases possess decontamination properties. Vapors and gases are primarily used to decontaminate biological safety cabinets and associated systems, bulky or stationary equipment not suited to liquid disinfectants, instruments or optics which might be damaged by other decontamination methods, and rooms, buildings and associated air-handling systems. Agents included in this category are glutaraldehyde and formaldehyde vapor, ethylene oxide gas, peracetic acid and hydrogen peroxide vapor.

When used in closed systems and under controlled conditions of temperature and humidity, excellent disinfection can be obtained. Great care must be taken during use because of the hazardous nature of many of these compounds. Vapor and gas decontamination should not be attempted by research personnel.

4. Radiation

Although ionizing radiation will destroy microorganisms, it is not a practical tool for laboratory use. Non-ionizing radiation in the form of ultraviolet radiation (UV) is used for inactivating viruses, bacteria and fungi. It will destroy airborne microorganisms and inactivate microorganisms on exposed surfaces or in the presence of products of unstable composition that cannot be treated by conventional means.

Because of the low penetrating power of UV, microorganisms inside dust or soil particles will be protected from its action, limiting its usefulness. UV is used in air locks, animal holding areas, ventilated cabinets and laboratory rooms to reduce levels of airborne microorganisms and maintain good air hygiene. Because UV can cause burns to the eyes and skin of people exposed for even a short period of time, proper shielding should be maintained when it is in use. UV lamps that are used for space decontamination should be interlocked with the general room or cabinet illumination, so that turning on the lights extinguishes the UV.

The Centers for Disease Control and the National Institutes of Health agree that UV lamps are not recommended nor required in biological safety cabinets. If UV lamps are installed and used, they must be properly maintained. They must be cleaned weekly to remove any dust and dirt that may block the germicidal effectiveness of the UV light. Additionally, because UV lamp intensity or destructive power decreases with time, it should be checked with a UV meter yearly. If the UV lamp must be used, it should be used when areas are not occupied. If the cabinet has a sliding sash, also close the sash when operating the UV lamp.

 

University of the Sciences in Philadelphia • 600 South Forty-third Street • Philadelphia, PA 19104-4495 • phone: 215-596-8800 • email: safety@usp.edu