The hazard, or potential to cause harm during use, of a chemical must be assessed prior to working with it in the laboratory, because awareness of hazards is the first step in prevention of exposures. Before using a chemical in the laboratory, the container label, SDS, and other resources, such as chemical hazard assessments, must be reviewed to determine what hazards the chemical may pose and how best to reduce or control them. Chemical exposures can result in a wide range of effects that are categorized as physical hazards and health hazards.
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Physical hazards are classified by factors such as explosivity, flammability, reactivity, corrosivity to metal, gas under pressure, or combustible dust. The risk associated with these hazards is controlled by regulating the environmental conditions present in the laboratory and limiting the volume of the chemical in use.
Health hazards encompass effects such as acute toxicity, skin, eye, and respiratory irritation or sensitization, reproductive toxicity, carcinogenicity, target organ toxicity, and aspiration hazard. They are highly affected by the dose, frequency, duration, and route of exposure; effects may be local, at the point of contact, or systemic, occurring anywhere in the body systems or organs targeted, and onset of symptoms may be acute, delayed, or long term.
Routes of Exposure
The route of exposure is the path by which a chemical enters the body. The type of toxic effects that are observed and their time of onset are affected by the route of entry. Chemicals may have serious effects by one route and minimal effects by another. For example, a chemical that is ingested may cause different toxic effects than if it was absorbed through the skin. The route of entry may also determine whether local or systemic effects are observed. Laboratory personnel working with chemicals must be aware of possible routes of entry and should implement procedures and practices that reduce their risk of exposure.
Skin and Mucous Membranes
A common way for chemicals to enter the body is through direct contact with the skin or a mucous membrane, such as your eyes. Skin contact with a chemical may result in a local effect, such as a burn or rash at the site of contact or the chemical may be absorbed into the bloodstream and cause systemic effects at distal sites in the body. The use of gloves, lab coats, eye protection, and other PPE can reduce the risk of skin and eye contact in the laboratory.
Inhalation is the most common route of entry for chemical vapors and aerosols. For some chemicals, depending on the vapor pressure and the temperature of the chemical, volatilization may occur, thus creating a potential for inhalation to occur.
The term vapor refers to the gas phase of a solid or a liquid substance at standard temperature and pressure. Vapor will revert to a solid or liquid phase by an increase in pressure or a decrease in temperature. Substances with low boiling points volatilize quickly into vapor. Examples include mercury, benzene, and methanol.
The term aerosol refers to liquid and solid particles suspended in a gaseous medium. Aerosols can contain droplets of hazardous chemicals, dust, fumes, biological materials, or other hazardous substances, and can remain suspended in the air for long periods of time. Small aerosol particles, if inhaled, may penetrate deep within the respiratory tract.
The following activities can produce aerosols: centrifugation, homogenization (e.g., use of a blender, sonicator, grinder, or mortar and pestle), mixing, vortexing, or stirring, use of a separatory funnel, and pipetting. Inhaled substances may cause localized effects on the lungs or be absorbed into the bloodstream, causing systemic effects.
Although direct ingestion of a laboratory chemical is unlikely, an individual may ingest contaminated food or beverages, touch the mouth with contaminated fingers, or swallow inhaled particles that have been cleared from the respiratory system. Direct ingestion may occur as a result of the outdated and dangerous practice of mouth pipetting. The risk of ingesting hazardous chemicals may be reduced by not eating, drinking, smoking, applying cosmetics, or storing food in the laboratory, and by washing hands thoroughly after working with chemicals even when gloves were worn.
A chemical can be injected into some parts of the body including skin, muscle, body cavities, or directly into the blood stream. Injection may result from a needlestick or puncture with a contaminated sharp object such as broken glass. In an injection exposure, the chemical may enter directly into the bloodstream and cause both local and systemic effects. Safety procedures for handling sharps in the laboratory should be instituted to reduce the risk from an injection of a hazardous substance.
Individual susceptibilities play a significant role in effects caused by exposure to hazardous chemicals. Factors such as the age of exposed persons, the genetic background, as well as the health of an employee, including preexisting medical conditions, may affect the response to toxic chemicals. For example, laboratory personnel allergic to a sensitizing agent or allergen may experience adverse effects while those who are not allergic may not experience any adverse effect. Other individual factors such as pregnancy, smoking status, or general health status may exacerbate the exposure effect. Laboratory personnel should be familiar with the health hazards associated with toxic chemicals prior to use and should discuss their concerns with EHS or their healthcare provider.