Glossary of Terms

Glossary of Terms

Alphabetical Listing of Terms



Acute Exposure – a short-term exposure usually occurring at high concentration.

Acute Health Effect – an effect that develops either immediately or a short time after exposure.

Autoignition Temperature – the minimum temperature required to initiate or cause self-sustained combustion, in the absence of a spark or flame.


Biohazardous Infectious Material – a material that contains organisms and the toxins produced by these organisms that have been shown to cause disease or are believed to cause disease in either humans or animals.

Boiling Point – the temperature at which a liquid changes from a liquids to a gas, at normal atmospheric pressure.


Carcinogens – agents/compounds that may induce cancer in humans.

CAS Registry Number – a number assigned to a material by the Chemical Abstracts Service (CAS) to provide a single unique identifier.

Chemical Formula – sometimes called the molecular formula, indicates the elements that make up a chemical.

Chemical Name – a proper scientific name for the active ingredient of a product.

Chronic Exposure – a long-term exposure, usually occurring at low concentrations.

Chronic Health Effects – an effect that appears a long time after exposure.

Coefficient of Oil/Water Distribution – the ratio of the solubility of the chemical in an oil to its solubility in water.

Combustible Liquid – a liquid which has a flash point above 37.8 C.

Compressed Gas – a material which is a gas at normal room temperature (20 C) and pressure but is packaged as a pressurized gas, dissolved gas or gas liquified by compression or refrigeration.

Condensation – the process of reducing from one form to another denser form such as steam to water.

Controlled Products – Under the Controlled Products Regulation, a controlled product is defined as a material, product or substance which is imported or sold in Canada and meets the criteria for one or more of the following [WHMIS1988] classes: –

  • Class A – Compressed Gas
  • Class B – Flammable and Combustible Material
  • Class C – Oxidizing Material
  • Class D – Poisonous and Infectious Material
  • Class E – Corrosive Material
  • Class F – Dangerously Reactive Material

Corrosive Material – a material that can attack (corrode) metals or cause permanent damage to human tissues such as skin and eyes on contact.

Cryogenics – materials which exist at extremely low temperatures, such as liquid nitrogen.


Dangerously Reactive Materials – materials that may undergo vigorous condensation, decomposition or polymerization. They may react violently under conditions of shock or increase in pressure or temperature. They may also react vigorously with water or water vapour to release a toxic gas.

Decomposition – the breakdown of a substance, often due to heat, decay or other effect, with the release of other compounds such as vapours or gases that may be flammable or toxic.

Density – the weight of a material in a given volume. It is usually given in grams per millilitre (g/ml).

Dilution Ventilation – dilution of contaminated air with uncontaminated air in a general area, room or building for the purposes of health hazard or nuisance control, and/or for heating and cooling.

Dose – amount of the agent that has entered the body through the various routes of entry.


Evaporation Rate – the rate at which a liquid changes to vapour at normal room temperature.

Explosive (Flammable) Limits – the lower explosive (flammable) limit (LEL) is the lowest concentration of vapour in air which will burn or explode upon contact with a source of ignition. The upper explosive (flammable) limit (UEL) is the highest concentration of vapour in air which will burn or explode upon contact with a source of ignition.

Explosive (Flammable) Range – the range between the lower explosive limit (LEL) and the upper explosive limit (UEL).

Exposure Limits– established concentrations which, if not exceeded, will not generally cause adverse effects to the worker exposed. Exposure limits differ in name and meaning depending on origin. For example:

  1.  The exposure levels for the hazardous chemicals that are included in the Regulation respecting the Control of Exposure to Biological or Chemical Agents – made under the Occupational Health and Safety Act of Ontario, are expressed as follows:

TWAEV Time-Weighted Average Exposure Value: The average airborne concentration of a biological or chemical agent to which a worker may be exposed in a work day or a work week.

STEV Short Term Exposure Value: – The maximum airborne concentration of a chemical or biological agent to which a worker may be exposed in any 15 minute period, provided the TWAEV is not exceeded.

CEV Ceiling Exposure Value: The maximum airborne concentration of a biological or chemical agent to which a worker may be exposed at any time.

SKIN: This notation indicates that direct or airborne contact with the product may result in significant absorption of the product through the skin, mucous membranes or eyes. Inclusion of this notation is intended to suggest that preventative action be taken against absorption of the agent through these routes of entry.

2. Threshold Limit Values (TLVs) are exposure guidelines developed by the American Conference of Governmental Industrial Hygienists (ACGIH). They have been adopted by several Canadian governments and others as their legal limits. They are expressed as follows:

TLV-TWA Threshold Limit Value – Time-Weighted Average: The time-weighted average concentration for a normal 8 hour work day and a 40 hour work week, to which nearly all workers may be repeatedly exposed, day after day, without adverse effect.

TLV-STEL Threshold Limit Value – Short Term Exposure Limit: a 15 minute time-weighted average exposure which should not be exceeded at any time during a work day even if the 8 hr TWA is within the TLV. Exposures at the STEL should not be repeated more than 4 times a day and there should be at least 60 minutes between successive exposures at the STEL.

TLV-C Threshold Limit Value – Ceiling: the concentration that should not be exceeded during any part of the working exposure.

Other exposure limits include the Permissible Exposure Limits (PEL) which are legal exposure limits in the United States.


Flammable Limits – See “Explosive Limits”.

Flammable Substance – one that will readily catch fire and continue to burn in air if exposed to a source of ignition.

1. Flammable Aerosol– a material that is packaged in an aerosol container which can release a flammable material.

2. Flammable Gas– a gas which can readily catch fire and continue to burn.

3. Flammable Liquid – a material that gives off a vapour which can readily catch fire and continue to burn. A flammable liquid has a flashpoint below 37.8 C.

4. Flammable Solid– a material which can readily catch fire and continue to burn vigorously and persistently. This may occur from friction, absorbing moisture, from spontaneous chemical change, or by retaining heat from manufacturing or processing.

5. Reactive Flammable Material– a material which is a dangerous fire risk because it can react readily with air or water.

Flashback – this occurs when a trail of flammable material is ignited by a distant source of ignition. The flame then travels back along the trail of gas, vapour or aerosol to its source.

Flashpoint – the lowest temperature of a liquid at which it gives off enough vapour to form an ignitable mixture of vapour and air immediately above the liquid surface.

Freezing Point – the temperature at which a liquid becomes a solid, at normal atmospheric pressure.


Hazard– the potential for harmful effects.

Hazardous Combustion Products – chemicals which may be formed when a material burns. These chemicals may be flammable, toxic or have other hazards.

Hazardous Decomposition Products – formed when a material decomposes (breaks down) because it is unstable, or reacts with materials such as water or oxygen in air.

Hazardous Ingredient – Under the Hazardous Products Act, a chemical must be listed in the Hazardous Ingredients section of a MSDS if:-

* it meets the criteria for a controlled product;

* it is on the Ingredient Disclosure List;

* there is no toxicological information available; or

* the supplier has reason to believe it might be hazardous.

Hazardous Polymerization – Polymerization is a process of forming a polymer by combining large numbers of chemical units or monomers into long chains (polyethylene from ethylene or polystyrene from styrene). Uncontrolled polymerization can be extremely hazardous. Some polymerization processes can release considerable heat or can be explosive.


Ingestion – means taking a material into the body by mouth (swallowing).

Inhalation – means taking a material into the body by breathing it in.

Irritant – some sort of aggravation of whatever tissue the material comes in contact with.


LC50 – the concentration of a material in air which causes death in 50% of a group of test animals. The material is inhaled over a set period of time, usually 4 hrs. LC stands for lethal concentration.

LD50 – the weight of material which causes the death in 50% of a group of test animals. It is usually expressed in weight of material per weight of test animal. LD stands for lethal dose.

LEL (Lower Explosive Limit) – See “Explosive Limits”.

Local Exhaust Ventilation – involves the capture of pollutants at the source.


Material Causing Immediate and Serious Toxic Effects – classified under “Poisonous and Infectious Material” as toxic or very toxic based on information such as the LD50 or LC50.

Material Causing Other Toxic Effects – classified under “Poisonous and Infectious Material” as a material causing toxic effects such as skin or respiratory sensitization, carcinogenicity, mutagenicity, etc.

Melting Point – the temperature at which a solid material becomes a liquid.

Mutagen – an agent that affects the genes or cells of the exposed people in such a way that it may cause cancer in the exposed individual or an undesirable mutation to occur in some later generation.


NA Number – See “UN number”.


Odour Threshold – the airborne concentration, usually in part per million, at which an odour becomes noticeable.

Oxidizing Material – gives up oxygen easily or can readily oxidize other materials.


Permissible Exposure Limits (PEL) – legal limits in the U.S.A. set by the Occupational Safety and Health Administration (OSHA).

pH – a measure of the acidity or basicity (alkalinity) of a material when dissolved in water.

Polymer – a natural or man-made material formed by combining units, called monomers, into long chains.

Polymerization – a process of forming a polymer by combining large numbers of chemical units or monomers into long chains.

Parts Per Million (ppm) – represents the concentration of gases or vapour in air. For example, 1 ppm of a gas means that 1 unit of the gas is present for every 1 million units of air.


Sensitization – the development, over time, of an allergic reaction to a chemical.

Solubility – the ability of a material to dissolve in water or another liquid.

Solvent – a material which is capable of dissolving another chemical.

Specific Gravity – the density of a liquid compared to the density of an equal amount of water.

Stability – the ability of a material to remain unchanged in the presence of heat, moisture or air.


Teratogen – agents or compounds that a pregnant woman takes into her body that generate defects in the fetus.

TLV – See “Exposure Limits”.

Toxicity – ability of a substance to cause harmful effects.

Trade Name – the name under which a product is commercially known.

TWA – See “Exposure Limits”.


UEL (Upper Explosive Limits) – See “Explosive Limits”.

UN Number – a four digit number assigned to a potentially hazardous material or class of materials. UN (United Nations) numbers are internationally recognized and are used by fire fighter and other emergency response personnel for identification of materials during transportation emergencies. NA (North American) numbers are assigned by Transport Canada and the US Department of Transport to materials they consider hazardous and to which a UN number has not been assigned.


Vapour – a gaseous form of a material which is normally solid or liquid at room temperature and pressure.

Vapour Density – the density of a vapour compared to the density of an equal amount of air.

Vapour Pressure – the pressure of a vapour in equilibrium with its liquid or solid form.

Ventilation – the movement of air.

Volatility – the ability of a material to evaporate.