While the approach to defining hazardous chemicals varies by regulatory agency, the symbols used to denote hazards should be the same. The Globally Harmonized System (GHS) is a universally accepted system of labeling and communicating hazards. There are nine symbols you may come across when reviewing the hazards of a chemical:

Flammable

Material that will burn or ignite, causing fire or combustion. An ignitable chemical has a flashpoint less than 100° F. A combustible material will burn but requires a flame or elevated temperature plus a spark, and it has a flashpoint greater than 100° F but less than 200° F.

Corrosive

Chemical that causes visible destruction of, or irreversible alterations in, living tissue by chemical action at the site of contact. pH < 2 and pH > 12.5

Examples: acetic acid, sodium hydroxide, photographic fixer

Explosive and Oxidizer

Reactive: Material that reacts violently or explodes under either ambient conditions or when in contact with air, water, or other chemicals. (There are two symbols that may designate a reactive chemical or solution)

• Explosive - designed to explode violently
• Oxidizer - react strongly with organic materials, sometimes enough to start a fire
• Organic peroxides - form friction and/or shock-sensitive explosives
• Water reactive - reacts violently with water
• Air reactive (pyrophoric) - react violently with air

Examples:

• Explosive: TNT, picric acid
• Oxidizer: nitric acid
• Organic peroxides: benzoyl peroxide, methyl ethyl ketone peroxide
• Water reactive: sodium metal, sodium borohydride
• Air reactive: silane, t-butyl lithium

Toxic

Toxic: Material that may cause harm to an individual if it enters the body. (There are two symbols that may designate a toxic chemical or solution)

• Carcinogen - a substance or agent that may cause cancer
• Mutagen - an agent that can induce or increase the frequency of mutation in an organism
• Poison - any substance that can impair function, cause structural damage, or otherwise injure the body
• Sensitizer - a substance that causes hypersensitivity or reactivity to an antigen, such as pollen, especially by a second or repeated exposure
• Teratogen - an agent that causes malformation of an embryo or fetus

Examples:

• Carcinogen: benzene, carbon tetrachloride
• Mutagen: bromine
• Poison: sodium azide, powdered pigments and inks (may contain toxic metals such as chromium and barium)
• Sensitizer: formaldehyde, phenol
• Teratogen: PCBs, mercury

Irritant

Material that can cause harm to an individual in the following ways:

• Irritant - a substance that can irritate the skin or eyes
• Skin sensitizer - a substance which can cause an allergic response following skin contact
• Acute toxicity (harmful) - a substance that may be fatal or cause organ damage from a single short-term exposure
• Narcotic effect - a substance that can cause drowsiness, lack of coordination, and dizziness
• Hazardous to ozone layer (this is a non-mandatory designation that may use this symbol)

Examples include many powdered substances. This hazard class is often appropriate for very dilute acids that no longer exhibit corrosivity.

Environmental Hazard

Toxic or hazardous to aquatic animals or environment

Example: oils and oily debris can be in this class of hazards

Compressed Gas

These materials always exhibit physical hazards associated with pressurized containers, but chemical hazards, such as toxicity, may also be a factor.

Examples: compressed helium, compressed nitrogen, compressed hydrogen, compressed argon

Routes of entry describes the way in which a hazardous material enter the body. In a laboratory, the primary route of entry is through inhalation and dermal contact. With proper ventilation such as a chemical fume hoods and proper personal protective equipment, like nitrile gloves, you can reduce the risk of exposure to hazardous chemicals. Good hygiene habits, such as washing your hands after using hazardous chemicals, and using mechanical means to pick up sharps, will reduce your risk of exposure through ingestion or injection. Make sure to report any exposure, or possible exposure, or Risk Management & Safety.

Absorption (Skin/Eye Contact)

Absorption may occur when not using proper engineering controls, work practices/procedures, and/or personal protective equipment (PPE). It may also occur when handling containers, etc. that have been contaminated without wearing PPE.

Reduce your Risk of Exposure through Injection:

• Wear appropriate gloves and other protective gear
• Remove PPE when entering common spaces and hallways
• Well label areas that require PPE
• In the event of an accidental exposure, wash the affected area with soap and water and seek medical attention

Inhalation

Inhalation may occur when working with volatile materials without appropriate engineering controls, work practices, and/or PPE.

Reduce your Risk of Exposure through Injection:

• Use appropriate engineering controls, work practices, and protective gear to control for the inhalation hazards
• In the event of an accidental inhalation seek medical attention for instructions

Ingestion

The gastrointestinal tract is another possible route of entry for hazardous materials. Although direct ingestion of laboratory substances is unlikely, exposure can occur as a result of ingesting contaminated food or beverages, touching the mouth with contaminated fingers or pens, or swallowing inhaled particles.

Reduce your Risk of Exposure through Ingestion:

• Do not eat, drink, smoke, or store food or drink in labs
• Wash hands thoroughly after working with hazardous materials, even when gloves are worn
• In the event of accidental ingestion, seek medical care for instructions
• Do not induce vomiting unless directed to do so by a health care provider

Injection

Injection effectively bypasses the protection provided by intact skin and provides direct access to the bloodstream, and thus, to internal organ systems. Injection may occur through mishaps with needles, wires, when handling biting animals, or through accidents with broken glass or other sharp objects that have been contaminated.

Reduce your Risk of Exposure through Injection:

• Wear appropriate gloves and other protective gear
• Caution should be taken when working with and around sharp objects
• In the event of an accidental injection, wash the affected area with soap and water and seek medical attention

• Dose (see below)
• Route of exposure (see above)
• Physical properties of the chemical (see above)
• The susceptibility of the individual receiving the dose. No two people are alike - each person's body will react differently upon exposure. Exposure to a hazardous material may affet one person more than others.

The toxic effects of hazardous materials may be local or systemic, acute or chronic.

• Local injuries involve the area of the body in contact with the hazardous material and are typically caused by reactive or corrosive chemicals, such as strong acids, alkalis, or oxidizing agents.
• Systemic injuring involve tissues or organs unrelated to or removed from the contact site when toxins have been transported through the bloodstream. Certain hazardous materials may affect a target organ.
• Acute toxicity results from a single, short exposure, and the effects usually appear quickly and may be reversible.
• Chronic toxicity results from repeated exposure over a long period of time. Effects are usually delayed and gradual, and may be irreversible.

Dose

The dose is the amount of a chemical that actually enters the body. This dose of a chemical that a person receives is dependent on the concentration of the chemcial and the frequency and duration of exposure. Relatively safe chemicals may become toxic if the dose is high enough, and even potent, highly toxic chemicals may be used safely if exposure is kept low enough. 

The actual health risk of a given chemical is a function of both the toxicity of the chemical and dose (or exposure) someone has to that chemical:

Risk = Dose x Toxicity

No matter how toxic a chemical may be, there is little risk involved unless it enters the body. It is important to be aware of the routes of exposure (see above) for each chemical, and to protect those routes using appropriate control measures.

Evaluating Toxicity Data

Most estimates of human toxicity are based on animal studies, which may or may not relate to human toxicity. In most animal studies, the effect easure is usually death. This measure of toxicity is often expressed as LD50 (lethal dose 50), which is the dose required to kill 50% of the test population. The LD 50 is measure in milligrams of material per kilogram of body weight of the test animal. The LC50 (lethal concentration 50) may be used to determine the concentration in air that is lethal to half the population. 

Many factors influence the susceptibility of an individual to the effects of toxic substances:

• Nutritional habits,
• Physical condition,
• Medical conditions,
• Drinking and/or smoking,
• Pregnancy, etc,

Due to individual variation and uncertainties in estimating human health hazards, it is difficult to determine a dose of chemical that is completely risk-free. Regular exposure to some substances can lead to the development of an allergic rash, breathing difficulty, or other reactions. The phenomenon is referred to as sensitization. Over time, these effects may occur with exposure to smaller and smaller amounts of the hazardous material but may disappear soon after the exposure stops.

• OSHA's Permissible Exposure Limit (PEL) (regulatory level)
• ACGIH's Threshold Limit Value (TLV)* (recommended)
• NIOSH's Recommended Exposure Limit (REL) (recommended)

*TLVs may be found on Safety Data Sheets or in the ACGIH book (updated annually).

Most exposure limits are expressed as a time-weighted average (TWA). The TWA is the total amount of a substance that a person may be exposed to averaged over an 8-hour work day. Some substances may have a ceiling, which indicates the maximum dose of a substance a person can be exposed to at any time. If a person excedes the ceiling, but doesn't exceed the TWA, there has still be an unacceptable exposure. Similar to a ceiling, there may also be a short-term exposure level (STEL). The STEL indicates the maximum dose of a substance a person can be exposed to in a 15-minute period.

Both regulatory and recommended exposure limits are based on exposures to the "average individual." Your personal reaction to a chemical may differ from that of the average person based on your medical history, circumstances of the exposure, your susceptibility, etc. Therefore, it is important that you familiarize yourself with the signs and symptoms of exposure to the chemicals you use. This way, you will be able to recognize if the symptoms start occurring.

So, why are some of the regulatory limits different than recommended limits?

OSHA regulations have not changed much since their effective date. As new research and data become available, the ACGIH have published new recommendations for exposure limits. While OSHA's PELs are the regulatory limits, UVM strives to keep exposures to any hazardous material as low as possible.

UVM labs are required to have copies of Safety Data Sheets (SDSs) available for fast review, either in the lab safety notebook or on a lab computer in a digital file that is available to all lab personnel. Lab personnel should be trained to review SDS information before using a chemical in the lab. SDSs may be audited during a lab inspection.

The Hazard Communication Standard (29 CFR 1910.1200(g), revised in 2012, requires that chemical manufacturers, distributors, or importers must provide SDSs for each hazardous chemical to users to communicate hazard information. Information contained in the SDS is required to be presented in a 16-section format with the following types of information:

• Properties of the chemical or solution
• Physical, health, and environmental hazard information
• Protective measures
• Safety precautions for handling, storing, and transporting the chemical

All hazard symbols and phrases should be consistent with the Globally Harmonized System of Classification and Labeling of Chemicals (GHS). Always check for a revision date to ensure the information is as updated as possible.

The SDS Quick Link above links to a resource that may help you find a Safety Data Sheet for materials used in the lab.