Chemical Hazards

Identifying the Chemical Hazards

The hazard associated with a chemical depends on:

  • what the specific chemical is
  • what chemical(s) it is mixed with, if any, and
  • the relative proportion of the chemical, if it is in a mixture or solution.

Always consider not only what the chemical is, but what concentration you are using when evaluating the hazard.  This is important when reviewing chemical safety reference information such as technical data sheet or Safety Data Sheet (SDS). 

Safety Data Sheets

Types of Chemical Hazards
Routes of Entry
Toxic Effects of Chemical Exposure
Exposure Limits

Types of Chemical Hazards

While the approach to defining hazardous chemicals varies by regulatory agency, consider these four basic types of chemical hazards:

Hazard Types




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 require a flame or elevated temperature plus a spark to start them; and has a flashpoint greater than 100° F but less than 200° F. Flammables: methanol, acetonitrile, spray adhesive/mount

Combustible: diesel fuel, mineral spirits


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

acetic acid, sodium hydroxide, photographic fixer


Material that reacts violently or explodes under either ambient conditions or when in contact with air, water, or other chemicals.

Oxidizers: materials that react strongly with organic materials, sometimes strongly enough to start fires

Organic Peroxides:  form friction and shock-sensitive explosives

Water Reactive:  react violently with water

Air Reactive (pyrophoric):  react violently with air

Explosive:  designed to explode violently

Oxidizers: nitric acid

Organic Peroxides: benzoyl peroxide, methyl ethyl ketone peroxide

Water Reactive: sodium metal, sodium borohydride

Air Reactive: silane, t-butyl lithium

Explosive: TNT, picric acid



Material that may cause harm to an individual if it enters the body.

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.

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




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 (Non-Mandatory)

Powdered substances often have the irritant symbol.



Environmental Hazard


Toxic to aquatic animals. Oils and oily debris can be in this class of hazards.

Contact with questions and concerns regarding hazardous chemicals used in your laboratory.

Routes of Entry

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.

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

Reducing 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.
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 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.

Reducing 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.

Contact with questions and concerns regarding exposure to chemicals used in your laboratory.

Toxic Effects of Chemical Exposure

The effects of exposure to a chemical is dependent on many factors. Those factors include:

  • The dose is the amount of a chemical that actually enters the body. The dose of a chemical that a person receives is dependent on the concentration of the chemical and frequency and duration of the exposure.
  • Route of exposure.  How the hazardous chemical enters the body determines how the material may travel through the body and effect organs or systems.
  • Physical properties of the chemical
  • The susceptibility of the individual receiving the dose. No two people are alike, therefore each person’s body will react differently upon exposure. Exposure to a hazardous material may affect one person more than others.

The toxic effects of hazardous materials may be local or systemic. 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 injuries 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.

The effects materials have upon the body also depend on the acute or chronic toxicity. Acute toxicity results from a single, short exposure and the effects usually appear quickly and are often reversible. Chronic toxicity results from repeated exposure over a long period of time. Effects are usually delayed and gradual, and may be irreversible.


Poisonous and toxic are not interchangeable terms.  All chemicals induce some type of adverse effect at some dose, so all chemicals may be described as toxic.  So what chemicals are considered toxic and which are safe?  BOTH!  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.  All chemicals are toxic at some dose and may produce harm if the exposure is sufficient, but all chemicals produce their harm under prescribed conditions of dose or usage. 

Risk = Dose x Toxicity

The actual health risk of a chemicals is a function of both the toxicity of the chemical and the actual dose (or expsoure) someone has to that chemical. No matter how toxic a chemical may be, there is little health risk involved unless it enters the body.  It is important to be aware of the routes of exposure for each chemical and protect that route through appropriate control measures (e.g. fume hood, biosafety cabinet, limiting quantity in use, personal protective equipment).

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 measured 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 LD50 is measured in milligrams of the material per kilogram of the body weight of the test animal. The LC50 (lethal concentration 50) may be used to determine the concentration in air that kills half of the population.

Susceptibility of Individuals

Factors that influence the susceptibility of an individual to the effects of toxic substances include:

  • nutritional habits
  • Physical condition
  • obesity
  • medical conditions
  • drinking and smoking
  • pregnancy

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

Where to Find Toxicity Information

  • Safety Data Sheets, under the "Health Hazard Data" Section
  • Product Labels
  • Registry of Toxic Effects of Chemical Substances

Exposure Limits

After becoming informed about the toxicity and health hazards of a chemical, you need to know the safe level for exposure.  There are both regulatory levels and recommended guidance, including:

*TLVs may be found on a Safety Data Sheet or in the ACGIH Book, which is updated annually.

Most of these exposure limits are expressed as a time-weighted average.  The average is the total amount of a substance that a person is exposed to averaged over an 8-hour work day.  Some substances may have ceiling levels (C), which indicate the maximum dose of a substance a person can be exposed to at any time.  There may also be a short-term exposure level (STEL), which indicates the maximum dose of a substance a person can be exposed to in a 15- minute period. 

Both the regulatory and recommended exposure limits are based on exposures to the "average individual".  Your personal reaction to a chemical exposure may differ from that of the average person based on  your medical history, the circumstances of the exposure, your suseptibility, etc.  Therefore it is important that you be familiar with the signs and symptoms of exposure to the chemicals you use so that you can be aware if those symptoms start occurring.  Signs and symptoms of exposure can be found on the SDS for these chemicals.

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 has become available, the ACGIH and NIOSH have published new recommendations for exposure limits.  While OSHA's PELs are the regulatory limit, UVM strives to keep exposures to any hazardous material as low as possible.


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