Laboratory Safety



Laboratory Safety



Microbiology laboratory safety practices were first published in 1913 in a textbook by Eyre. They included admonitions such as the necessity to (1) wear gloves, (2) wash hands after working with infectious materials, (3) disinfect all instruments immediately after use, (4) use water to moisten specimen labels rather than the tongue, (5) disinfect all contaminated waste before discarding, and (6) report to appropriate personnel all accidents or exposures to infectious agents.


These guidelines are still incorporated into safety programs in the diagnostic microbiology laboratory. Safety programs also have been expanded to include not only the proper handling of biologic hazards encountered in processing patient specimens and handling infectious microorganisms, but also fire safety; electrical safety; the safe handling, storage, and disposal of chemicals and radioactive substances; and techniques for safely lifting or moving heavy objects. In areas of the country prone to natural disasters (e.g., earthquakes, hurricanes, snowstorms), safety programs include disaster preparedness plans that outline the steps to take in an emergency. Although all microbiologists are responsible for their own health and safety, the institution and supervising personnel are required to provide safety training to familiarize microbiologists with known hazards in the workplace and to prevent exposure. Laboratory safety is considered an integral part of overall laboratory services, and federal law in the United States mandates pre-employment safety training, followed by quarterly safety in-services. Safety training regulations are enforced by the United States Department of Labor Occupational Safety and Health Administration (OSHA). Regulations and requirements may vary based on the type of laboratory and updated regulations. It is recommended that the laboratory review these requirements as provided by OSHA (www.osha.gov).


Microbiologists should be knowledgeable, properly trained, and equipped with the proper protective materials and working controls while performing duties in the laboratory if the safety regulations are internalized and followed without deviation. Investigation of the causes of accidents indicates that unnecessary exposures to infectious agents occur when individuals become sloppy in performing their duties or when they deviate from standardized safety precautions.



Sterilization and Disinfection


Sterilization is a process that kills all forms of microbial life, including bacterial spores. Disinfection is a process that destroys pathogenic organisms, but not necessarily all microorganisms or spores. Sterilization and disinfection may be accomplished by physical or chemical methods.



Methods of Sterilization


The physical methods of sterilization include:



Incineration is the most common method of treating infectious waste. Hazardous material is literally burned to ashes at temperatures of 870° to 980°C. Incineration is the safest method to ensure that no infective materials remain in samples or containers when disposed. Prions, infective proteins, are not eliminated using conventional methods. Therefore incineration is recommended. Toxic air emissions and the presence of heavy metals in ash have limited the use of incineration in most large U.S. cities.


Moist heat (steam under pressure) is used to sterilize biohazardous trash and heat-stable objects; an autoclave is used for this purpose. An autoclave is essentially a large pressure cooker. Moist heat in the form of saturated steam under 1 atmosphere (15 psi [pounds per square inch]) of pressure causes the irreversible denaturation of enzymes and structural proteins. The most commonly used steam sterilizer in the microbiology laboratory is the gravity displacement type (Figure 4-1). Steam enters at the top of the sterilizing chamber; because steam is lighter than air, it displaces the air in the chamber and forces it out the bottom through the drain vent. The two common sterilization temperatures are 121°C (250°F) and 132°C (270°F). Items such as media, liquids, and instruments are usually autoclaved for 15 minutes at 121°C. Infectious medical waste, on the other hand, is often sterilized at 132°C for 30 to 60 minutes to allow penetration of the steam throughout the waste and the displacement of air trapped inside the autoclave bag. Moist heat is the fastest and simplest physical method of sterilization.



Dry heat requires longer exposure times (1.5 to 3 hours) and higher temperatures than moist heat (160° to 180°C). Dry heat ovens are used to sterilize items such as glassware, oil, petrolatum, or powders. Filtration is the method of choice for antibiotic solutions, toxic chemicals, radioisotopes, vaccines, and carbohydrates, which are all heat sensitive. Filtration of liquids is accomplished by pulling the solution through a cellulose acetate or cellulose nitrate membrane with a vacuum. Filtration of air is accomplished using high-efficiency particulate air (HEPA) filters designed to remove organisms larger than 0.3 µm from isolation rooms, operating rooms, and biologic safety cabinets (BSCs). The ionizing radiation used in microwaves and radiograph machines is composed of short wavelength and high-energy gamma rays. Ionizing radiation is used for sterilizing disposables such as plastic syringes, catheters, or gloves before use. The most common chemical sterilant is ethylene oxide (EtO), which is used in gaseous form for sterilizing heat-sensitive objects. Formaldehyde vapor and vapor-phase hydrogen peroxide (an oxidizing agent) have been used to sterilize HEPA filters in BSCs. Glutaraldehyde, which is sporicidal (kills spores) in 3 to 10 hours, is used for medical equipment such as bronchoscopes, because it does not corrode lenses, metal, or rubber. Peracetic acid, effective in the presence of organic material, has also been used for the surface sterilization of surgical instruments. The use of glutaraldehyde or peracetic acid is called cold sterilization.



Methods of Disinfection


Physical Methods of Disinfection


The three physical methods of disinfection are:



UV rays are long wavelength and low energy. They do not penetrate well, and organisms must have direct surface exposure, such as the working surface of a BSC, for this form of disinfection to work.



Chemical Methods of Disinfection


Chemical disinfectants comprise many classes, including:



Chemicals used to destroy all life are called chemical sterilants, or biocides; however, these same chemicals, used for shorter periods, act as disinfectants. Disinfectants used on living tissue (skin) are called antiseptics.


A number of factors influence the activity of disinfectants, including:



Resistance to disinfectants varies with the type of microorganism. Bacterial spores, such as Bacillus spp., are the most resistant, followed by mycobacteria (acid-fast bacilli); nonenveloped viruses (e.g., poliovirus); fungi; vegetative (nonsporulating) bacteria (e.g., gram-negative rods); and enveloped viruses (e.g., herpes simplex virus), which are the most susceptible to the action of disinfectants. The Environmental Protection Agency (EPA) registers chemical disinfectants used in the United States and requires manufacturers to specify the activity level of each compound at the working dilution. Therefore, microbiologists who must recommend appropriate disinfectants should check the manufacturer’s cut sheets (product information) for the classes of microorganisms that will be killed. Generally, the time necessary for killing microorganisms increases in direct proportion to the number of organisms (microbial load). This is particularly true of instruments contaminated with organic material such as blood, pus, or mucus. The organic material should be mechanically removed before chemical sterilization to decrease the microbial load. This is analogous to removing dried food from utensils before placing them in a dishwasher, and it is important for cold sterilization of instruments such as bronchoscopes.


The type of water and its concentration in a solution are also important. Hard water may reduce the rate of killing of microorganisms. In addition, 70% ethyl alcohol is more effective as a disinfectant than 95% ethyl alcohol because the increased water (H2O) hydrolyzing bonds in protein molecules make the killing of microorganisms more effective.


Ethyl or isopropyl alcohol is nonsporicidal (does not kill spores) and evaporates quickly. Therefore, its use is limited to the skin as an antiseptic or on thermometers and injection vial rubber septa as a disinfectant.


Because of their irritating fumes, the aldehydes (formaldehyde and glutaraldehyde) are generally not used as surface disinfectants.


The halogens, especially chlorine and iodine, are frequently used as disinfectants. Chlorine is most often used in the form of sodium hypochlorite (NaOCl), the compound known as household bleach. The Centers for Disease Control and Prevention (CDC) recommends that tabletops be cleaned after blood spills with a 1 : 10 dilution of bleach.


Iodine is prepared either as a tincture with alcohol or as an iodophor coupled to a neutral polymer (e.g., povidone-iodine). Both iodine compounds are widely used antiseptics. In fact, 70% ethyl alcohol, followed by an iodophor, is the most common compound used for skin disinfection before drawing blood specimens for culture or surgery.


Because mercury is toxic to the environment, heavy metals containing mercury are no longer recommended, but an eye drop solution containing 1% silver nitrate is still placed in the eyes of newborns to prevent infections with Neisseria gonorrhoeae.


Quaternary ammonium compounds are used to disinfect bench tops or other surfaces in the laboratory. However, surfaces grossly contaminated with organic materials, such as blood, may inactivate heavy metals or quaternary ammonium compounds, thus limiting their utility.


Finally, phenolics, such as the common laboratory disinfectant Amphyl, are derivatives of carbolic acid (phenol). The addition of detergent results in a product that cleans and disinfects at the same time, and at concentrations of 2% to 5%, these products are widely used for cleaning bench tops.


The most important point to remember when working with biocides or disinfectants is to prepare a working solution of the compound exactly according to the manufacturer’s package insert. Many think that if the manufacturer says to dilute 1 : 200, they will be getting a stronger product if they dilute it 1 : 10. However, the ratio of water to active ingredient may be critical, and if sufficient water is not added, the free chemical for surface disinfection may not be released.



Chemical Safety


In 1987, the U.S. Occupational Safety and Health Administration (OSHA) published the Hazard Communication Standard, which provides for certain institutional educational practices to ensure that all laboratory personnel have a thorough working knowledge of the hazards of the chemicals with which they work. This standard has also been called the “employee right to know.” It mandates that all hazardous chemicals in the workplace be identified and clearly marked with a National Fire Protection Association (NFPA) label stating the health risks, such as carcinogen (cause of cancer), mutagen (cause of mutations in deoxyribonucleic acid [DNA] or ribonucleic acid [RNA]), or teratogen (cause of birth defects), and the hazard class, for example, corrosive (harmful to mucous membranes, skin, eyes, or tissues), poison, flammable, or oxidizing (Figure 4-2).



Each laboratory should have a chemical hygiene plan that includes guidelines on proper labeling of chemical containers, manufacturers’ material safety data sheets (MSDSs), and the written chemical safety training and retraining programs. Hazardous chemicals must be inventoried annually. In addition, laboratories are required to maintain a file of every chemical they use and a corresponding MSDS. The manufacturer provides the MSDS for every hazardous chemical; some manufacturers also provide letters for nonhazardous chemicals, such as saline, so that these can be included with the other MSDSs. The MSDSs include information on the nature of the chemical, the precautions to take if the chemical is spilled, and disposal recommendations. The sections in the typical MSDS include:



Employees should become familiar with the location and organization of MSDS files in the laboratory so that they know where to look in the event of an emergency.


Fume hoods (Figure 4-3) are provided in the laboratory to prevent inhalation of toxic fumes. Fume hoods protect against chemical odor by exhausting air to the outside, but they are not HEPA-filtered to trap pathogenic microorganisms. It is important to remember that a BSC (discussed later in the chapter) is not a fume hood.



Work with toxic or noxious chemicals should always be done wearing nitrile gloves, in a fume hood, or when wearing a fume mask. Spills should be cleaned up using a fume mask, gloves, impervious (impenetrable to moisture) apron, and goggles. Acid and alkaline, flammable, and radioactive spill kits are available to assist in rendering any chemical spills harmless.



Fire Safety


Fire safety is an important component of the laboratory safety program. Each laboratory is required to post fire evacuation plans that are essentially blueprints for finding the nearest exit in case of fire. Fire drills conducted quarterly or annually, depending on local laws, ensure that all personnel know what to do in case of fire. Exit paths should always remain clear of obstructions, and employees should be trained to use fire extinguishers. The local fire department is often an excellent resource for training in the types and use of fire extinguishers.


Type A fire extinguishers are used for trash, wood, and paper; type B extinguishers are used for chemical fires; and type C extinguishers are used for electrical fires. Combination type ABC extinguishers are found in most laboratories so that personnel need not worry about which extinguisher to reach for in case of a fire. However, type C extinguishers, which contain carbon dioxide (CO2) or another dry chemical to smother flames, are also used, because this type of extinguisher does not damage equipment.


The important actions in case of fire and the order in which to perform tasks can be remembered with the acronym RACE:






Biosafety


Individuals are exposed in various ways to laboratory-acquired infections in microbiology laboratories, such as:



Risks from a microbiology laboratory may extend to adjacent laboratories and to the families of those who work in the microbiology laboratory. For example, Blaser and Feldman1 noted that 5 of 31 individuals who contracted typhoid fever from proficiency testing specimens did not work in a microbiology laboratory. Two patients were family members of a microbiologist who had worked with S. enterica subsp. Typhi; two were students whose afternoon class was in the laboratory where the organism had been cultured that morning; and one worked in an adjacent chemistry laboratory.


In the clinical microbiology laboratory, shigellosis, salmonellosis, tuberculosis, brucellosis, and hepatitis are frequently acquired laboratory infections. Additional infections have been reported from agents such as Coxiella burnetii, Francisella tularensis, Trichophyton mentagrophytes, and Coccidioides immitis. Viral agents transmitted through blood and body fluids cause most of the infections in non–microbiology laboratory workers and in health care workers in general. These include hepatitis B virus (HBV), hepatitis C virus (HCV), hepatitis D virus (HDV), and human immunodeficiency virus (HIV). Interestingly, males and younger employees (17 to 24 years old) are involved in more laboratory-acquired infections than females and older employees (45 to 64 years old). It is important to note that laboratory-associated infections are not a new phenomena and are based primarily on voluntary reporting. Therefore, such incidents are widely underreported because of fears of repercussions associated with such events.

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Aug 25, 2016 | Posted by in MICROBIOLOGY | Comments Off on Laboratory Safety

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