Nail Chemistry Glossary

NFPA Hazard Rating

Before handling chemicals in your salon, it is important that you're able to read and understand the NFPA hazard symbol.

The NFPA Fire Diamond. The NFPA Fire Diamond is divided into four parts listing the health hazards, flammability concerns, and reactivity of a compound, along with recommended protective equipment. Each section is rated on a scale of 0 (minimal hazard) to 4 (extreme).

Position Reference

Position A (Blue) - Health Hazard. Degree of hazard; level of short-term protection
  • 0 = Ordinary Combustible Hazards in a Fire
  • 1 = Slightly Hazardous
  • 2 = Hazardou
  • 3 = Extreme Danger
  • 4 = Deadly
Position B (Red) - Flammability. Susceptibility to burning
  • 0 = Will Not Burn
  • 1 = Will Ignite if Preheated
  • 2 = Will Ignite if Moderately Heated
  • 3 = Will Ignite at Most Ambient Conditions
  • 4 = Burns Readily at Ambient Conditions
Position C (Yellow) - Reactivity, Instability. Energy released if burned, decomposed, or mixed
  • 0 = Stable and Not Reactive with Water
  • 1 = Unstable if Heated
  • 2 = Violent Chemical Change
  • 3 = Shock and Heat May Detonate
  • 4 = May Detonate
Position D (White) - Special Hazard.
  • OX = Oxidizer
  • W = Use No Water, reacts!
  • 0 = Will Not Burn
  • 1 = Will Ignite if Preheated
  • 2 = Will Ignite if Moderately Heated
  • 3 = Will Ignite at Most Ambient Conditions
  • 4 = Burns Readily at Ambient Conditions

A chemical substance relatively free of impurities, e.g., absolute alcohol.


To soak up. The incorporation of a liquid into a solid substance, as by capillary, osmotic, solvent, or chemical action. See Adsorb


American Coference of Governmental Industrial Hygienists. An organization of professionals in governmental agencies or educational institutions engaged in occupational safety and health programs. ACGIH develops and publishes recommended occupational exposure limits for chemical substances and physical agents (see TLV and BEI). (1330 Kemper Meadow, Cincinnati, OH 45240; [513] 742-2020.)


An inorganic or organic compound that is usually corrosive to human tissue and must be handled with care. Has a pH of less than 7.0. Neutralizes bases (alkalis) to form salts. Dissociates in water yielding hydrogen or hydronium ions. May react with metals to yield hydrogen. Turns litmus paper red.


A condition of decreased alkalinity of the blood and tissues. Symptoms may include sickly sweet breath, headache, nausea, vomiting, visual disturbances; usually the result of excessive acid production. Tissues and CNS functions are disturbed.


Irritating and bitter (referring to smell).


American Chemical Society. Professional society that establishes standards of purity for a number of reagents, e.g., the ACS Reagent Grade. They publish Chemical Abstracts and a host of professional journals and magazines dealing with various areas of chemistry, chemical engineering, and allied sciences. (1155 Sixteenth St., N.W., Washington, DC 20036; [202] 872-4567.)

Action Level

The exposure level (concentration in air) at which OSHA regulations to protect employees take effect (20 CFR 1910.1001.1052); e.g., workplace air analysis, employee training, medical monitoring, and record keeping. Exposure at or above action level is termed occupational exposure. Exposure below this level can also be harmful. This level is generally half the PEL.

Acute Exposure

Exposure of short duration, usually to relatively high concentrations or amounts of material.

Acute Health Effect

An adverse effect on a human or animal body, with symptoms developing rapidly. See Chronic Health Effect.

Active Ingredient

The ingredient of a product that actually does what the product is designed to do.

Acute Lethality

The death of animals immediately or within 14 days after a single dose of or exposure to a toxic substance.

Acute Toxicity

Adverse health effects resulting from brief exposure to a chemical (e.g. seconds, minutes, hours).


Acceptable Daily Intake.

Administrative Controls

A number of measures used to reduce worker exposure, including work practices, labeling and warning devices, training, environmental monitoring, assignment scheduling, housekeeping, maintenance, and management.


To attract and retain gas or liquid molecules on the surface of another material. See Absorb.


A fine suspension in air or other gas of liquid (mist, fog) or solid (dust, fume, smoke) particles small enough to stay suspended. See Smoke; Fog; Mist


Any substance, force, radiation, organism, or influence affecting the body. The effects may be beneficial or injurious.


American Institute of Chemical Engineers (800-242-4363, Web site:


American Industrial Health Council (202-833-2131).


Abbreviation for the Australian Inventory of Chemical Substances. This list contains chemical substances which can be used commercially in Australia. It is similar to TSCA Chemical Substances Inventory in the U.S.

Airborne Release

Release of any chemical (gas, vapor, mist, dust) into the air.


An inorganic or organic chemical that: Is usually corrosive to human tissue and must be handled with care; Has pH of more than 7.0; Neutralizes acids to form salts; Dissociates with water yielding hydroxide ions; Turns litmus paper blue

May also be called a base or caustic. Examples are oxides of hydroxides of certain metals belonging to group IA of the periodic table (Li, Na, K, Rh, Cs, Fr). Ammonia and amines may also be alkaline. Common commercial alkalis are sodium carbonate (soda ash), caustic soda and caustic potash, lime, lye, waterglass, regular mortar, Portland cement, and bicarbonate of soda. See Acid; Base; pH.


A substance that causes an allergic reaction.


A condition in which an initial symptomless exposure to a specific allergen later gives rise to a sensitivity to further exposure. Symptoms may be exhibited in a variety of ways, sneezing and skin eruptions are common. In more serious instances the throat swells, leading to respiratory distress.


Usual or surrounding conditions of temperature, humidity, etc.


A compound derived from another compound (e.g., an acid) by removing the elements that compose water, i.e., hydrogen and oxygen.


"Without water." Describes a substance in which no water molecules are present in the form of a hydrate or as water or crystallization.

Annual Report on Carcinogens

Published annually by the National Toxicology Program (NTP) and available from NTIS, this report list substances either known or anticipated to be carcinogens.


Loss of appetite.


Loss of the sense of smell.


A lack of oxygen in the blood or tissues (literally, "without oxygen"). See Hypoxia.


American National Standards Institute. A privately funded organization that identifies industrial/public national consensus standards and coordinates their development. Many ANSI standards relate to safe design/performance of equipment and safe practices or procedures. (1430 Broadway, New York, NY 10018; [212] 642-4900.)


When the effect of one chemical or material counteracts (works against) the effect of another.


A remedy to counteract a poison’s toxic effects; it may act to eliminate, absorb, or neutralize the poison.


American Public Health Association (202-789-5600 Web site:


A material’s physical state (solid, gas, or liquid), its color, and other visual attributes. If there is a difference between a material’s appearance and that listed on the MSDS, contact your supervisor.

Aqueous (AQ)

Describes a water-based solution or suspension. Frequently describes a gaseous compound dissolved in water.


The mineral content remaining after complete combustion of a substance.


A vapor or gas that can cause unconsciousness or death by suffocation (lack of oxygen). Most simple asphyxiants are harmful to the body only when they become so concentrated that they reduce (displace) the available oxygen in the air (normally about 21%) to dangerous levels (18% or lower). Examples of simple asphyxiants are carbon dioxide, nitrogen, hydrogen, and helium. Chemical asphyxiants like carbon monoxide (CO) reduce the blood's ability to carry oxygen, or like cyanide, interfere with the body's utilization of oxygen.


A condition that causes asphyxia or suffocation. Asphyxiation is one of the principal potential hazards of working in confined spaces.

Aspiration Hazard

The danger of drawing material into the lungs, leading to an inflammatory response that can be fatal.


American Society for Testing and Materials. An organization that devises consensus standards for materials characterization and use. (100 Barr Harbor Dr., W. Conshohocken, PA 19428; [610] 832-9500.


Not exhibiting symptoms


Atmosphere. A unit of pressure equal to the average pressure that air exerts at sea level. 1 atm =1.013 x 10 5 N/m2, or 14.7 lb/in. 2, or 760 mm Hg or 101 kPa. Generally used in connection with high pressures.


To break up a liquid into very fine droplets by forcing it through a small orifice.


Agency for Toxic Substances and Disease Registry (800-447-1544, Web site: 8080)

Autoignition Temperature

The minimum temperature at which a substance ignites without application of a flame or spark. Do not heat materials to greater than 80% of this temperature.


An alkali. See Alkali.

Baume (BE)

A scale of specific gravities devised by the French chemist Antoine Baume' (c. 1800; pronounced bo-may) that indicates concentration of materials in a solution. Baume' degree increases as specific gravity decreases.

Biological Exposure Indexes (BET)

Numerical values based on procedures to determine the amount of a material the human body absorbs by measuring the material or its metabolic products in tissue, fluid, or exhaled air. See the ACGIH publication Documentation of the Threshold Limit Values and Biological Exposure Indices.




The accumulation of a substance, such as a pesticide, in a living organism.


The process by which a chemical is passed through the food chain from soil to plants and animals where it accumulates and is ultimately passed to humans.


An organic material's capacity for decomposition as a result of attack by microorganisms. Sewage-treatment routines are based on this property. Biodegradable materials do not persist in nature.

Biological Monitoring

Analysis of body substances, such as blood or urine, to determine the extent of hazardous material absorption or accumulation.

Bureau of Labor Statistics (BLS)

(202-219-5000, Web site:

Body Burden

The total toxic material a person has ingested or inhaled from all sources over time and retained in the body. For example, lead can be ingested from drinking water channeled through lead-soldered pipes, lead glazes on dishes, or flakes from painted surfaces, as well as from many industrial operations.

Boiling Point (BP)

The temperature at which a liquid substance turns into a gas, or at which a gaseous substance condenses to a liquid. Also, the temperature at which a liquid's vapor pressure equals the surrounding atmospheric pressure so that the liquid rapidly vaporizes. Flammable materials with low BPs generally present special fire hazards [e.g., butane, BP = 0.5 C (31 F) gasoline, BP = 38 C (100 F)]. For mixtures, a range of temperature is given. Sometimes present as a temperature range if an exact value is unavailable. Sometimes accompanied by a note such as dec (decomposes) or expl (explodes).

British Thermal Unit (BTU)

The quantity of heat required to raise the temperature of 1 lb of water from 17 C (63 F) to 18 C (64 F). Compare to Calorie.


A substance that reduces the change in hydrogen ion concentration (pH) otherwise produced by adding acids or bases to a solution. A pH stabilizer.

Bulk Density

The mass (weight) per unit volume of a solid particulate material as it is normally packed, with voids between particulates containing air. Usually expressed as lb/ft 3 or g/cm 3.

CAS Registry Number

A unique accession number assigned by the Chemical Abstracts Service, a division of the American Chemical Society. Other than being guaranteed unique to a given compound, this number has no particular meaning. CAS Registry Numbers are assigned to every uniquely-identifiable substance, so 'cis-2-hexene', 'trans-2-hexene', and '2-hexene' (a mixture with unspecified cis/trans composition) are all assigned separate CAS Numbers.


Unit of heat. The amount of heat required to raise 1 g of water 1 C. See Btu.


An abnormal multiplication of cells that tends to infiltrate other tissues and metastasize (spread). Each cancer is believed to originate from a single "transformed" cell that grows (splits) at a fast, abnormally regulated pace, no matter where it occurs in the body.


Carcinogen or carcinogenic.

Carbon Dioxide

See CO2.

Carbon Monoxide

See CO.


A material that either causes cancer in humans, or, because it causes cancer in animals, is considered capable of causing cancer in humans. A material is considered a carcinogen if 1) the International Agency for Research on Cancer (IARC) has evaluated and found it a carcinogen or potential carcinogen; 2) the National Toxicology Program's (NTP) Annual Report on Carcinogens lists it as a carcinogen or potential carcinogen; or 3) OSHA regulates it as a carcinogen.




A malignant tumor or cancerous growth.


A substance that modifies (slows, or more often quickens) a chemical reaction without being consumed in the reaction.


See Alkali.

Caustic Soda

Sodium hydroxide. Strong alkaline substance used in cleaning products, detergents.

Caustic Lime

Calcium hydroxide.

Caustic Potash

Potassium hydroxide

Ceiling Limit

The concentration not to exceed at any time. "An employee's exposure [to a hazardous material] shall at no time exceed the ceiling value" (OSHA).


Celsius is now this temperature scale's preferred name.

Centimeter (cm)

1/100 meter. A cm = 0.4 in.

Centipoise (cP)

A metric (cgs) unit of viscosity equal to 1/100 poise. The viscosity of water at 20 C (68 F) is almost 1 centipoise.

Central Nervous System (CNS)

The brain and spinal cord.

Central Nervous System (CNS) Depression

Drowsiness, dizziness, and headache caused by a chemical acting on the brain; higher doses can cause unconsciousness, coma, or death.

Canada Environmental Protection Act (CEPA)

Federal legislation, administered by Environment Canada, designed to protect the environment.

Chlorofluorocarbon (CFC)

Associated with damage to the Earth's ozone layer.

Code of Federal Regulations (CFR)

A collection of the regulations established by law. Contact the agency that issued the regulation for details, interpretations, etc. Copies are sold by the Superintendent of Documents, Government Printing Office, Washington; DC 20402; (202) 512-1800.

CFR 29 Section 1910.1200

The OSHA regulation known as the Hazard Communication Standard.

Chemical Family

A group of single elements or compounds of a common general type. For example, acetone, methyl ethyl ketone (MEK), and methyl isobutyl ketone (MIBK) are of the ketone family; acrolein, furfural, and acetaldehyde are of the aldehyde family.

Chemical Formula

The number and kind of atoms comprising a molecule of a material. Water's chemical formula is H2O. Each water molecule consists of 2 atoms of hydrogen and 1 atom of oxygen.

Chemical Hygiene Officer

Per 29 CFR 1910.1450; OSRA regulation, "Occupational Exposures to Hazardous Chemicals in Laboratories." The designated, qualified employee who assists in the development and implementation of the CHP. See CHP.

Chemical Inventory

List of hazardous materials in a workplace, reflected by a collection of matching MSDSs, generally for compliance with OSHA and SARA.

Chemical Name

A chemical's scientific name. Complex chemicals may have more than one name, corresponding to different naming systems.

Chemical Pneumonitis

Lung inflammation caused by inhaling a chemical that is irritating or otherwise toxic to the lungs.

Chemical-protective Clothing (CPC)

Personal protective clothing, suit, apron, gloves, etc. that is manufactured to be resistant to penetration by specific chemicals for a certain period of time.

Chemical Reactivity

A chemical's tendency to react with other materials. Undesirable and dangerous effects such as heat, explosions, or production of noxious substances can result.


Emission of light during a chemical reaction other than burning.

Chemical Transportation Emergency Center (CHEMTREC)

Established in Washington, DC, by the Chemical Manufacturers Assoc. (CMA) to provide emergency information on materials involved in transportation accidents. 24-hr No.: (800) 424-9300

Chronic Exposure

Continuous or intermittent exposure extending over a long time period, usually applies to relatively low material amounts or concentrations.

Chronic Health Effect

An adverse effect on a human or animal body with symptoms that develop slowly over a long time period and persist or that recur frequently. See Acute Health Effect.

Chronic Toxicity

Adverse health effects resulting from long-term exposure to a chemical (e.g. months, years, decades)

Chemical Manufacturers Association (CMA)

(703-741-5000, Web site:

Carbon Monoxide (CO)

A colorless, odorless, flammable, and very toxic gas produced by incomplete combustion of carbon compounds and as a byproduct of many chemical processes. A chemical asphyxiant, it reduces the blood’s ability to carry oxygen. Hemoglobin absorbs CO 200 times more readily than it does oxygen.

Carbon Dioxide (CO2)

A dense, colorless, gas produced by combustion and decomposition of organic substances and as a by-product of many chemical processes. CO2 does not burn and is relatively nontoxic and unreactive. High concentrations, especially in confined places, can crate hazardous oxygen-deficient environments that can cause asphyxiation. CO2 is 1.5 times as dense as air, making it useful as a fire-extinguishing agent to block oxygen and smother a fire.


A materials that will burn under most conditions and may ignite easily depending on its flash point. The DOT defines combustible liquids as a liquid with a flash point above 141 F (60.5 C) and below 200 F (93 C). NFPA and OSHA generally define combustible liquid as a liquid with a flash point at or above 100 F (38 C) but below 200 F (93.3 C).


An exothermic chemical reaction due to rapid oxidation or burning, which releases heat and light. A source of air pollution.

Common Name

A designation for a material other than its chemical name, such as code name or code number or trade, brand, or generic name. May be used as the "product identifier" in Canadian law [Workplace Hazardous Materials Information System (WHMIS) regulations].


Meeting the requirements of law and regulations.

Compressed Gas

Any material which is a gas at normal temperature and pressure, and contained under pressure as a dissolved gas or liquefied by compression or refrigeration.

Consumer Products

Products regulated by the Consumer Product Safety Act. They are not required to carry label information.

Consumer Product Safety Commission (CPSC)

Consumer Products Safety Commission. Per the Hazardous Substances Act and Poison Prevention Packaging Act of 1970, a Federal agency responsible for regulating hazardous materials used in consumer goods per the Hazardous Substances Act and Poison Prevention Packaging Act of 1970.

Contingency Plan

Documented plan for the course of action to be taken in the event of a fire, spill or other emergency involving the potential for exposure of humans to health-threatening conditions.


To hold back a spilled material with dikes or absorbent material so as to prevent further spillage and contamination.

Critical Pressure/Critical Temperature

A temperature above which a gas cannot be liquefied by pressure. The critical pressure is that pressure required to liquefy a gas at its critical temperature.


Relating to extremely low temperature. For example, refrigerated gases are cryogenic materials that can cause frostbite on contact.

Chemical Specialties Manufacturing Association (CSMA)

(202-872-8110, Web site:

Chemical Testing and Assessment Research Commission (CTARC)

Cubic Feet per Minute (CFM)

Means of quantifying the volume of air exchanged in a workplace in a period of time.


Pertaining to the skin (dermal).

Cutaneous Hazards

A chemical that affects the skin by causing rashes, irritation, or defatting. Examples include ketones and chlorinated compounds.

Dangerously Reactive Material

A material that can react by itself (e.g., polymerize) or with air or water to produce a hazardous condition. Preventive measures can be taken if you know what conditions may cause the dangerous reaction.

Dec, Decomp

Decompose, Decomposition. Breakdown of a material (by heat, chemical reaction, electrolysis, decay, or other processes) into parts, elements, or simpler compounds.

Defatting Agent

A material, that upon repeated exposure or skin contact can remove fat causing in some instances drying, irritation and/or redness.


Generally refers to the destruction or decomposition of material through the corrosive effects of chemicals, oxidation, heat, ultraviolet exposure, abrasion, etc.


A term used to characterize water-soluble salts (usually powdered) that tend to absorb moisture from the air and to soften or dissolve as a result. See Hygroscopic; Hydrophilic.


A material capable of soothing or protecting inflamed, irritated mucous membranes.


Ratio of weight (mass) to volume of a material, usually in grams per cubic centimeter or pounds per gallon. See Specific Gravity and Bulk Density.


The process by which a chemical substance is obtained actually or theoretically from parent substance(s).


Pertaining to the skin (cutaneous).

Dermal Toxicity

Adverse effects resulting from a material's absorption through skin. Ordinarily used to denote effects on experimental animals.


Skin rash; inflammation of the skin.

DFG (Germany) MAK

Deutsche Forschungsgemeinschaft (DFG), Federal Republic of German, Commission for the Investigation of Health Hazards of Chemical Compounds in the Work Area establishes MAK (maximum concentration values) for substances found in the workplace. MAKs are expressed as time weighted averages (TWAs) and peak exposures.


A chemical that kills pathogenic organisms. Chlorine is often used as a disinfectant.


Chemical agent with the property of separating concentrations of organic material, e.g., detergent on oil.

DOT Number

Codes for use in the commercial transportation of hazardous materials, as mandaetd by 49 CFR 172 and the U.S. Department of Transportation. A single substance may have multiple codes, depending on its concentration, physical state, etc.


Solid particles suspended in air, often produced by some mechanical process such as crushing, grinding, abrading, or blasting. Dusts may be inhalation, fire, or dust-explosion hazards.


Difficulty in speaking clearly.


Impaired sense of smell.


Difficulty in swallowing.


Abnormal growth or development of organs or cells.


A sense of difficulty in breathing; shortness of breath.


A skin rash characterized by redness, itching, sometimes blistering; may become scaly or crusty.

European Inventory of Existing Chemical Substances (EINECS)

A list of chemical substances identified by CAS and EINECS numbers that were marketed in the European Community between January 11971 and September 18, 1981.


A list of approximately 400 chemicals identified by EINECS numbers, established with the European Community from September 18, 1981 to June 30, 1990. The list was published on May 29, 1991 and is a supplement to EINECS. Additional supplements will be added as necessary.


A substance (as an acid, base, salt) that dissociates into ions when in aqueous solution and that provides ionic conductivity. Electrolytes are lost from the body through perspiration as salts, causing impairment of CNS functions if not adequately replaced.

Emergency Overview

A brief summary usually found in Sec. 3 of a MSDS that describes a material's appearance and gives an overview of the most significant immediate concerns for emergency personnel.


An irreversible lung condition in which the alveolar walls lose resiliency, resulting in excessively reduced lung capacity.


A chemical reaction that absorbs heat.

EPA Code

The 4-character codes used by the U.S. Environmental Protection Agency to designate regulated contaminants in waste. A single substance may have multiple codes, depending on its concentration, physical state, etc.

Evaporation Rate

The rate of evaporation for a liquid, in unitless values relative to butyl acetate, which is assigned an evaporation rate of 1. The rate at which a material vaporizes (volatilizes, evaporates) from the liquid solid state when compared to a known material's vaporization rate. Evaporation rate can be useful in evaluating a material's health and fire hazards. The known reference material is usually normal butyl acetate (N-BuAc or n-BuAc), with a vaporization rate designated as 1.0. Vaporization rates of other solvents or materials are then classified as

Fast evaporating if greater than 3.0, e.g., methyl ethyl ketone (MEK), 3.8; acetone, 5.6; hexane, 8.3;

Medium evaporating if 0.8 to 3.0, e.g., 190-proof (95%) ethyl alcohol, 1.4; VM&P naphtha, 1.4; MIBK, 1.6;

Slow evaporating if less than 0.8, e.g., xylene, 0.6; isobutyl alcohol, 0.6; normal butyl alcohol, 0.4; water, 0.3; mineral spirits, 0.1.


A material that produces a sudden, almost instantaneous release of pressure, gas, and heat when subjected to abrupt shock, high temperature, or an ignition source.

Explosive Limits

See Flammable Limits.

Exposure Limits

The concentration in workplace air of a chemical deemed the maximum acceptable. Meaning that most workers can be exposed at given levels or lower without harmful effects. Exposure limits in common use are; 1) TLV-TWA (threshold limit value - time-weighted average); 2) STEL (short-term exposure limit); and 3) C (ceiling value).


Refers to an employee possibly endangered by a chemical because the chemical may have been permitted to enter that employee through some route of entry.


A chemical reaction that gives off heat.

Extinguishing Media, Agents. The type of fire extinguisher or extinguishing method appropriate for a specific material. Some chemicals react violently in the presence of water, so other methods, such as the use of foam or CO2, should be followed.

Eye Hazards

Chemicals that affect the eye or visual capacity. Examples include acids and organic solvents.

Federal Emergency Management Agency (FEMA)

(800-480-2520, Web site:


Forced expiratory volume in 1 sec (L). A measurement of lung function.

Federal Food, Drug, and Cosmetic Act (FFDCA)


A basic form of matter, usually crystalline, with a high ratio of length to diameter. Examples: animal (wool); vegetable (cotton); mineral (asbestos, steel); and synthetic (rayon, carbon, high polymers).


Finely crushed or powdered material or fibers; especially those smaller than the average in a mix of various sizes.

Fire Diamond (NFPA Hazard Rating)

The National Fire Protection Agency (NFPA) visual rating system that addresses the health, flammability, reactivity, and related hazards of a material that may exist due to a short-term, acute exposure caused by a fire, spill, or similar emergency. Per "NFPA 704" publication.

First Aid

Immediate measures that can be taken by the victim or others in order to reduce or eliminate the potential effects of a chemical exposure or other injury.

Flammability Classification

Per OSHA 29 CFR 1910.106, criteria to classify combustible and flammable liquids.


Describes any solid, liquid, vapor, or gas that ignites easily and burns rapidly. See Combustible and Inflammable.

Flammable Gas

A gas that at normal atmospheric pressure forms a flammable mixture with air at a concentration of 13% by volume or less; or over a concentration range greater than 12% by volume, regardless of lower limit.

Flammable Limits (Flammability Limits, Explosive Limits)

Minimum and maximum concentrations of flammable gas or vapor between which ignition can occur. Concentrations below the lower flammable limit (LFL) are too lean to burn, while concentrations above the upper flammable limit (UFL) are too rich. All concentrations between LFL and UFL are in the flammable range, and special precautions are needed to prevent ignition or explosion.

Flammable Liquid

A liquid that gives off vapors readily ignitable at room temperature. The DOT defines a flammable liquid as a liquid with a flash point of not more than 141 F (60.5 C). The NFPA and OSHA generally define a flammable liquid as a liquid with a flash point below 100 F (37.8 C).

Flammable Solid

A solid, other than an explosive or blasting agent, that ignites readily and continues to burn so vigorously and persistently that it creates a serious hazard. Flammable solids are liable to cause fires under ordinary conditions or during transportation, through friction, as a result of spontaneous chemical change, or from retained heat from manufacturing or processing, or moisture absorption.

Flash Back

Occurs when a distant spark or ignition source ignites a trail of flammable material (e.g., gasoline vapor). The flame then travels along the trail of the material back to its source.

Flash Point (FP)

Lowest temperature at which a flammable liquid gives off sufficient vapor to form an ignitable mixture with air near its surface or within a vessel. Combustion does not continue. FP is determined by laboratory tests in cups. See Fire Point.

Flash Point Method

The means by which a flash point is obtained. If possible, flash point temperature is to be based on a closed cup (CC) method; see TCC, TCT, Setaflash Closed Tester, and Pensky-Martens closed cup (PMCC). Any flash point based on the Tag Open Tester (TOC) or the Cleveland Open Cup (COC) will be identified by (OC).

Fire Point

The lowest temperature at which a liquid produces sufficient vapor to flash near its surface and continues to burn, - usually 10 to 30 C higher than the flash point.

Flash Point (FP)

The temperature at which the vapor of a liquid can be made to ignite in air.


A visible suspension of fine droplets of liquid in a gas; e.g., water in air.

Food and Drug Administration (FDA)

Branch of the federal government responsible for enforcing the Food, Drug and Cosmetic Act, including matters of consumer safety involving related products. Those products subject to the Act are not subject to labeling requirements of hazardous materials. (800-532-4440, Web site:


Colorless, intensely irritating, flammable gas with pungent smell, used as a preservative and chemical feedstock. Probable human carcinogens.

Formula Mass

The sum of atomic weights of the atoms in a molecule. For example, water (H2O) has formula mass of 18.0, the atomic weights being [hydrogen: 2(1.0) + oxygen: 16] = 18.0.

Freezing Point (FP)

The temperature at which a material changes from a liquid to a solid state upon cooling. This information is important because a frozen material may burst its container or the hazards could change.


Tiny solid particles formed by the vaporization of a solid which then condenses in air; particles are usually of a size which readily reach the air sac (alveoli) of the lungs.


Chemical compounds used to prevent or destroy fungi.


A formless fluid which disperses in air; often found in tanks or cylinders and may be created by a chemical reaction. It can be changed to its liquid or solid state only by increased pressure and/or decreased temperature.


Any compound that kills disease-causing microorganisms.

General Ventilation

Also known as dilution ventilation. The removal of contaminated air and its replacement with clean air from the general workplace area as opposed to local ventilation, which is specific air changing in the immediate area of a contamination source. An example of local ventilation is a laboratory fume hood.

Generic Name

A common, possibly chemical, name applied generally to a substance. For example, bleach is the generic name for the chemical sodium hypochlorite. Chlorox(Tm) is a tradename for bleach. A chemical name may be used as a generic name, but tradenames are not generic names.


Generally recognized as safe. A phrase applied to food additives approved by the Food and Drug Administration (FDA).


A material is defined as harmful (defined as a chemical with a low degree of toxicity) if it falls into any of the following two categories:

Has a median lethal dose (LD50) of more than 500 mg/kg but no more than 2000 milligrams per kilogram of body weight, when administered orally to albino rats;

Has a median lethal dose (LD50) of more than 1000 mg/kg, but no more than 2000 mg/kg of body weight, when administered by continuous contact for 24 hours with bare skin of albino rabbits.

Hazard Communication Rule

Requires chemical manufacturers and importers to assess the hazards associated with the materials in their workplace (29 CFR 1910.1200). Material safety data sheets, labeling, and training are all results of this law. You are urged to acquire and become familiar with these regulations. Contact your local OSHA office. See OSH Act.

Hazardous Chemical, Material

In a broad sense, any substance or mixture of substances having properties capable of producing adverse effects on the health or safety of a human. In 1971 OSHA adopted the following definition in regulations affecting employers operations subject to the Federal Longshoremen's and Harbor Worker's Compensation Act. "The term Hazardous Material means a material which has one or more of these characteristics:

Has a flash point below 140 F (60 'C), closed cup, or is subject to spontaneous heating;

Has a threshold limit value below 400 ppm for gases and vapors, below 15 mg/m3 for fumes, and below 25 mppcf (million particles per cubic foot) for dusts;

Has a single dose oral LD50 below 500 mg/kg;

Is subject to polymerization with the release of large amounts of energy;

Is a strong oxidizing or reducing agent;

Causes first-degree burns to skin [from a] short time exposure, or is systemically toxic by skin contact;

In the course normal operations, may produce dusts, gases, fume, vapors, mists, or smokes which have one or more of the above characteristics." Included are substances that are carcinogens, toxic, irritants, corrosives, sensitizers, and agents which damage the lungs, skin, eyes, mucous membranes, etc.

Hazardous Combustion Products

Hazardous products released when a material is burned.

Hazardous Decomposition

A breaking down or separation of a substance into its constituent parts, elements, or into simpler compounds accompanied by the release of heat, gas, or hazardous materials.

Hazardous Decomposition Products

Hazardous products resulting from decomposition of a material. For example, vinyl chloride, a compound used to make plastics, releases poisonous hydrogen chloride, carbon monoxide, and phosgene gases when burned.

Hazard Warning

Defined by OSHA as "any word pictures, symbols, or combination thereof appearing a label or other appropriate form of warning which convey the hazard(s) of the chemical(s) in the container(s)".

Hazardous Waste Number

An identification number assigned by the EPA, per the RCRA law (40 CFR 261.33, 40 CFR 302.4), to identify and track wastes.

Health Hazard

For OSHA purposes refers to a material considered hazardous to human health due to at least one statistically significant study conducted in accordance with scientific principles.

Health Surveillance

The continuing scrutiny of specific individuals for the purpose of identifying disorders or health states, especially those which may relate to exposure to hazardous materials.

Henry's Law Constant (H)

The equilibrium ratio of concentrations of a material in air and in water. Materials with a high H are more volatile.


High-efficiency particulate air filter. Also called absolute. Has a 99.97% removal efficiency for 0.3-micron particles.

Highly Toxic

A material is classified as highly toxic (a poison) if it falls into any of the following four categories:

Has a median lethal dose (LD50) of 50 milligrams or less per kilogram of body weight when administered orally to albino rats.

Has a median lethal dose (LD50) of 200 milligrams or less per kilogram of body weight when administered by continuous contact for 24 hours with the bare skin of albino rabbits.

Has a median lethal concentration (LC50) of gas or vapor in air of 200 parts per million (ppm) or less by volume, or 2 milligrams per liter or less of mist, fume, or dust, when administered by continuous inhalation for 1 hour to albino rats.

Is a liquid having a saturated vapor concentration (ppm) at 68 F (20 C) equal to or greater than its LC50 (vapor) value (ppm), if the LC50 value is 3000 parts per million (ppm) or less when administered by continuous inhalation for 1 hour to albino rats.

Hazardous Materials Identification System (HMIS)

A system developed by the National Paint and Coatings Association (NPCA) to provide information on the acute health, reactivity, and flammability hazards encountered in the workplace. This system also includes temperatures under fire conditions (especially for flammability and reactivity). A number is assigned to a material indicating degree of hazard, from 0 for the least up to 4 for the most severe. Letters designate personal protective equipment. (Details from Labelmaster, 5724 N Pulaski Rd, Chicago, IL 60646; [312] 478-0900.) See NPCA.

Hazardous Substance Data Bank (HSDB)

A data bank focusing upon the toxicology of potentially hazardous chemicals. Built, maintained, reviewed, and updated by the National Library of Medicine.

Hydrocarbons (HCs)

Chemical compounds - most often combustible fuels - that contain only hydrogen and carbon.

Hydrogen Sulfide (HS)

A by-product of oil refining, and natural emission from rotting organic matter. Smells like rotten eggs. Highly flammable. Highly toxic by inhalation and strong irritant to eyes and mucous membranes.


Process by which chemical compounds are decomposed by reaction with water.


Describing materials having large molecules that tend to absorb and retain water, causing them to swell and frequently to gel. See Deliquescent.


Readily adsorbing available moisture in any form. See Deliquescent.


Capable of burning or causing a fire.

Ignition Temperature

The lowest temperature at which a combustible material ignites in air and continues to burn independently of the heat source.


Describes a material that does not allow another substance to penetrate or pass through it; impermeable.


Describes materials that could cause dangerous reactions and the release of energy from direct contact with one another.

Inert Ingredients

Anything other than the active ingredient in a product; not having active properties. Inert ingredients may be hazardous. For example, the propellant gas in aerosol spray, such as hair spray, may be flammable.


Capable of being easily set on fire and continue burning, especially violently. Do not confuse with nonflammable. See Combustible and Flammable.


A local response to cellular injury due to trauma, infection, or chemical irritation; symptoms include swelling, redness, pain, tenderness, and loss of function.


Swallowing a chemical substance; may inadvertently result from eating, drinking, or smoking in the workplace or with contaminated hands.


Entry of a chemical substance to the lungs by breathing.


A material added to another to prevent an unwanted reaction; e.g., polymerization.

Inorganic Materials

Compounds derived from other than vegetable or animal sources that do not generally contain carbon atoms. Some simple carbon compounds are considered inorganic (e.g., CO2, carbonates, cyanides).




An electrically charged atom or radical.

Ionizing Radiation

Radiation (e.g., alpha, beta, and gamma radiation) that has the effect of removing electrons from atoms leading to the formation of free radicals.


Inflammation of the eye's iris and its ciliary body.


A substance capable of causing a reversible or irreversible inflammatory effect on living tissue by chemical action at the site of contact as a function of concentration or duration of exposure.


Chemical compounds with the same molecular weight and atomic composition but differing molecular structure; e.g., n-pentane and 2-methylbutane.


A variant of an element characterized by having the same atomic number but a different mass because of its neutrons

Job Hazard Analysis

A process by which work place hazards are determined and safe work practices are instituted to adequately protect workers.

Liter (L)

Basic metric unit of volume. One liter a water weighs 1 kg and is equal to 1.057 quarts.


Any written, printed, or graphic sign or symbol displayed on or affixed to containers of hazardous chemicals. A label should identify the hazardous material, appropriate hazard warnings, and name and address of the chemical manufacturer, importer, or other responsible party.

Latency Period

Time that elapses between exposure and first manifestations of disease or illness. Latency periods can range from minutes to decades, depending on hazardous material and disease produced.


Rinse with water.

Lay Language

Language that is easily understood by the general public without specialized training.


See Lower Explosive Limit, Lower Flammable Limit


See Lower Flammable Limit, Lower Explosive Limit

LFM or lfm

Linear feet per minute.

Lipid Solubility

Measure of the maximum concentration of a chemical that will dissolve in fatty substances. Lipid-soluble substances will disperse through the environment via living tissue.


Changing a solid into a liquid.

Lowest Observed Adverse Effect Level (LOAEL)

Local Ventilation. The drawing off of contaminated air directly from its source. This type of ventilation is recommended for hazardous airborne materials. Treatment of exhausted air to remove contaminants may be required.


Lowest Observed Effect Level.

Meter (m)

The basic metric measure of length equivalent to 39.371 in.


A vague, generalized, ill feeling.



Material Safety Data Sheet (MSDS)

A fact sheet summarizing information about material identification; hazardous ingredients; health, physical, and fire hazards; first aid; chemical reactivities and incompatibilities; spill, leak, and disposal procedures; and protective measures required for safe handling and storage. OSHA has established guidelines for descriptive data that should be concisely provided on a data sheet to serve as the basis for written hazard communication programs. The thrust of the law is to have those who make, distribute, and use hazardous materials responsible for effective communication. See Hazard Communication Rule, 29 CFR, Part 1910.1200, as amended, Sec. g. See also Schedule I, Sec. 12, of the Canadian Hazardous Products Act. The CMA has recently drawn up a set of guidelines for developing a consistent MSDS format. This standard format has been accepted by ANSI.


Methyl Ethyl Ketone.

Melting Point

The temperature at which a solid substance becomes a liquid, or at which a liquid substance solidifies. Listed in Celsius degrees on the ChemFinder WebServer. Assumed to be at standard pressure unless otherwise indicated. Sometimes present as a temperature range if an exact value is unavailable. Sometimes accompanied by a note such as dec (decomposes) or subl (sublimes).

Milligram (mg.)

(1/1000, l0-3 of a gram).


Milligram per kilogram. Dosage used in toxicology testing to indicate a dose administered per kg of body weight.


Milligram per cubic meter of air. mg/m3 = ppm x MW/24.45 at 25 C.


Methyl Isobutyl Ketone.


Methyl Isocyanate.

Microgram (ug)

One-millionth (10-6) of a gram.

Micrometer (um)

One-millionth (10-6) of a meter; often referred to as a micron.

Micron (u)

See micrometer.

Milliliter (mL)

One thousandth of a liter. A metric unit of capacity, for all practical purposes equal to 1 cubic centimeter. One cubic inch is about 16 ml.

Millimeter (mm)

1/1000 (10-3) of a meter.


When two liquids or two gases are completely soluble in each other in all proportions. While gases mix with one another in all proportions, the miscibility of liquids depends on their chemical natures.


Suspended liquid droplets in the air generated by condensation from the gaseous to the liquid state or by mechanically breaking up a liquid by splashing or atomizing.


Japanese Ministry of International Trade and Industry.


A heterogeneous association of materials that cannot be represented by a chemical formula and that does not undergo chemical change due to interaction among the mixed materials. The constituent materials may or may not be uniformly dispersed and can usually be separated by mechanical means (as opposed to a chemical reaction). Uniform liquid mixtures are called solutions. "If a hazardous chemical is present in the mixture in reportable quantities (i.e., 0.1% for carcinogens and 1.0% for other health hazards; it must be reported unless the mixture has been tested as a whole" (OSHA CPL 23-02.38A).

mm Hg

A measure of pressure in millimeters of a mercury column above a reservoir, or difference of level in a U-tube. See atm.


Moderate irritation effects.

Moderate irritation effects.

The quantity of a chemical substance that has a mass in grams numerically equal to the formula mass. For example, table salt (NaCl) has a formula mass of 58.5 (Na, 23, and Cl, 35.5). Thus, one mole of NaCl is 58.5 g.

Molecular Weight

See Formula Mass.


Smallest representative particle of a covalently bonded chemical compound.

Momentary Value (DFG)

A level which the concentration should never exceed.


Millions of particles per cubic foot of air, based on impinger samples counted by light-field techniques (OSHA).


Mass Spectrometry.

Maximum Safe Storage Temperature (MSST)

See SADT (Self-Accelerating Decomposition Temperature).

Mucous Membrane

The mucous-secreting membrane lining the hollow organs of the body, i.e., nose, mouth, stomach, intestine, bronchial tubes, and urinary tract.


A material that induces genetic changes (mutations) in the DNA of chromosomes. Chromosomes are the "blueprints" of life within individual cells. Mutagens may affect future generations if sperm or egg cells are affected.


See Molecular Weight.

Newton (N)

The metric unit of force, approximately equal to the weight of a 102.5 g mass.


Normal. A chemical name prefix signifying a straight-chain structure; i.e., no branches.


Not applicable, not available; not determined.

NA Number

See DOT Identification Numbers.


To render less chemically reactive; to change the pH to about 7 (neutral) by adding acid to a basic compound or base to an acidic compound.

National Fire Protection Association (NFPA)

An international voluntary membership organization formed to promote and improve fire protection and prevention and establish safeguards against loss of life and property by fire. Best known for the National Fire Codes, 16 volumes of standards, recommended practices, and manuals developed (and periodically updated) by NFPA committees. NFPA 704M publication is the code for showing hazards of materials using the familiar diamond-shaped label with appropriate numbers or symbols (NFPA hazard rating). See Fire Diamond. (Batterymarch Park, Quincy, MA 02269; [800] 344-3555, [617] 770-3000, Web site:

NFPA Hazard Rating

The NFPA Fire Diamond. The NFPA Fire Diamond is divided into four parts listing the health hazards, flammability concerns, and reactivity of a compound, along with recommended protective equipment. Each section is rated on a scale of 0 (minimal hazard) to 4 (extreme).

NFPA 704 System



Nanogram. One billionth, l0-9, of a gram.


National Institute for Chemical Studies.


National Institutes of Health (Web site:


National Institute of Occupational Safety and Health. The agency of the Public Health Service that tests and certifies respiratory and air-sampling devices. It recommends exposure limits to OSHA for substances, investigates incidents, and researches occupational safety. (NIOSH, 4676 Columbia Parkway, Cincinnati, OH 45226; [513] 533-8328.)


National Library of Medicine. A government library in Bethesda, ME containing medical documents (l-888-FINDNLM, Web site:


No Observed Adverse Effect Level.


Not otherwise classified.


No observed effect level.


Incapable of easy ignition. Does not burn, or burns very slowly. Also, a DOT hazard class for any compressed gas other than a flammable one.

Nonionizing Electromagnetic Radiation

Radiation that does not change atom structure (e.g., micro waves, radiowaves, or low-frequency electromagnetic fields.)


Not otherwise regulated.


Not otherwise specified.


National Paint and Coatings Association. The trade association of manufacturers that developed the HMIS labeling system. (1500 Rhode Island Ave., NW, Washington, DC 20005; [202] 462-6272.) See HMIS


National Response Center. A notification center that must be called if a RQ (reportable quantity) released, or an oil or chemical spill or other environmental accident occurs. (800-424-8802).


National Technical Information Service (703-487-4600, Web site:

National Toxicology Program (NTP)

Federal activity overseen by the Dept. of Health and Human Services with resources from the National Institutes of Health the Food and Drug Administration, and the Centers for Disease Control. Its goals are to develop tests useful for public health regulations of toxic chemicals, to develop toxicological profiles of materials, to foster testing of materials, and to communicate the results for use by others. (NTP Information Office, MD B2-04 , Box 12233, Research Triangle Park, NC 27709.)

Nuisance Particulates

Dusts that do not produce significant organic disease or toxic effect from "reasonable" concentrations and exposures. Otherwise known as "Particulates not otherwise classified" (PNOC). The 1992-93 ACGIH TLV is 10 mg/m3. The value is for total dust containing no asbestos and <1% crystalline silica.

Occupational Exposure

See Action Level.

Occupational Safety and Health Act

See OSH Act.

Occupational Safety and Health Administration


Odor Threshold

The lowest concentration detectable by odor; note that published values vary greatly, as does an individual's ability to detect chemical odors; air monitoring is a much more reliable way to detect chemical hazards for many substances.


Occupational Exposure Limit. See Exposure Limits.


Impervious to light rays.


An exposure route "through the mouth."

Organic Materials

Compounds composed of carbon, hydrogen, and other elements with chain or ring structures. Almost all chemical constituents of living matter are of this type, but many compounds of this type are manufactured and do not occur naturally.

Organic Peroxide

A compound containing the bivalent - O - O - structure and which is a structural derivative of hydrogen peroxide (H2O2) where one or both hydrogen atoms are replaced by an organic radical. These compounds tend to be reactive and unstable.


Synthetic organic compound containing phosphorus used as insecticides, plasticizers, flame-retardants, and in fertilizers. Many are highly toxic; insecticides affect the central nervous system by causing cholinesterase inhibition.


Highly toxic, alkyl tin compounds widely used as stabilizers for plastics (rigid vinyl polymers) and some as catalysts.


Other Regulated material. DOT hazard classification of a particular hazardous material to label in transport.


Materials such as consumer commodities that present limited hazards during transportation due to their form, quantity, and packaging.


The Occupational Safety and Health Administration. Pant of the U.S. Dept. of Labor. The regulatory and enforcement agency for safety and health in most U.S. industrial sectors. (Documents are available from the OSHA Technical Data Center Docket Office, Rm N-3670, 200 Constitution Ave., NW, Washington, DC 20210; [202] 219-7500, Web site:


The Occupational Safety and Health Act of 1970. Effective April 28, 1971. Public Law 91-596. Found at 29 CEP 1910, 1915, 1918, 1926. OSHA jurisdiction. The regulatory vehicle to ensure the safety and health of workers in firms larger than 10 employees. Its goal is to set standards of safety that prevent injury and illness among the workers. Regulating employee exposure and informing employees of the dangers of materials are key factors. This act established the Hazard Communication Rule (29 CFP 1910.1200). See Hazard Communication Rule for details.

OSHA Flammable/Combustible Liquid Classification

(29 CFR 1910.106). Flammable/combustible liquid is a standard classification used to identify the risks of fire or explosion associated with a liquid. Flammable, or Class I, liquids (flash point below 38 C [100 F]) are divided into: Class IA -- flash point below 22.8 C (73 F), boiling point below 38 C (100 F); Class IB -- flash point below 22.8 C (73 F), boiling point at or above 38 C (100 F); and Class IC -- flash point at or above 22.8 C (73 F), boiling point below 38 C (100 F). Combustible liquids (flash point at or above 38 C [100 F]) are divided into two classes: Class II, flash point at or above 38 C (100 F) and below 60 C (140 F), except any mixture having components with flash points of 93.3 C (200 F) or higher, the volume of which makes up 99% or more of the mixture's total volume; and Class III, flash point at or above 140 F (60 C). Class III liquids are divided into two subclasses: Class IIIA, flash point at or above 60 C (140 F) and below 93.3 C (200 F), except any mixture having components with flash points of 93.3 C (200 F) or higher, the volume of which makes up 99% or more of the mixture's total volume; and Class IIIB, flash point at or above 93.3 C (200 F).


The passage of a fluid through a semi-permeable membrane to equalize the concentrations on both sides of the membrane.


An abbreviation for oxidizer.

An abbreviation for oxidizer.

A reaction in which a substance combines with oxygen or another oxidizer.

Oxide Pox

Dermatitis caused by contact with metal oxides under poor personal hygienic conditions.


The DOT defines an oxidizer or oxidizing material as a substance that yields oxygen readily to cause or enhance the combustion (oxidation) of other materials. Many oxidizers, such as chlorate (C1O3), permanganate (MnO4), and nitrate (NO3) compounds contain large amounts of oxygen (O). Others, such as chlorine, do not.

Oxidizing Agent

A chemical or substance that brings about an oxidation reaction. The agent may:

Provide the oxygen to the substance being oxidized (in which case the agent has to be oxygen or contain oxygen)

Receive electrons being transferred from the substance undergoing oxidation. (Chlorine is a good oxidizing agent for electron-transfer purposes, even though it contains no oxygen.) See Reducing Agent.

Peak Exposure Limit (DFG)

A short-term exposure level established for a certain duration and frequency per shift.


Permissible Exposure limit. Established by OSHA. This may be expressed as a time-weighted average (TWA) limit, a short-term exposure limit (STEL), or as a ceiling exposure limit. A ceiling limit must never be exceeded instantaneously even if the TWA exposure limit is not violated. OSHA PELs have the force of law. Note that ACGIH TLVs and NIOSH RELs are recommended exposure limits that OSHA may or may not enact into law.


The passage of a chemical through an opening in a protective material. Holes and rips can allow penetration as can space between zipper teeth stitch holes, and open jacket and pant cuffs. See also chemical-protective clothing.

Percent Volatile

Percent volatile by volume. The percentage of a liquid or solid (by volume) that evaporates at an ambient temperature of 70 F (20 C) unless another temperature is stated. E.g., gasoline and paint thinner (mineral spirits) are 100% volatile; their individual evaporation rates vary, but over a period of time each evaporates completely. This physical characteristic reflects the potential for releasing harmful vapor into the air.


Through the skin; often referring to absorption of a chemical.

Peripheral Nervous System (PNS)

Nerves outside of the brain and spinal cord, including motor nerves control the function of muscles, sensory nerves to carry sensations to the brain, and autonomic nerves to control a variety of organ functions.

Peripheral Neuropathy

An abnormal or degenerative state involving the nerves of the extremities (hands, feet, arms, legs).


Allows passage of water through soil or rock or other fluids such as solvents through gloves. Permeation through protective clothing occurs on a molecular level and may occur even if there are no signs of degradation.

Permissible Exposure Limit

See PEL.

Personal Hygiene

Precautionary measures taken maintain good health when exposed to potentially harmful materials. This includes keeping hands, and other parts of the body, work clothing, and equipment free of a material's residue, as well as not eating, drinking, applying makeup, or using toilet facilities where a material is in use.

Personal Protective Equipment

See PPE.


Hydrogen ion exponent, a measure of hydrogen ion concentration of a solution. A scale (0 to 14) representing an aqueous solution's acidity or alkalinity. Low pH values indicate acidity and high values, alkalinity. The scale's mid-point, 7, is neutral. Some substances in aqueous solution ionize to various extents giving different concentrations of H and OH ions. Strong acids have excess H ions and a pH of 1 to 3 (HC1, pH = 1). Strong bases have excess OH ions and a pH of 11 to 13 (NaOH, pH = 12).


Principle Hazardous Constituent.


Aromatic organic compounds with one or more hydroxy groups directly attached to the benzene ring. Toxic; strong tissue irritants.


(U.S.) Public Health Service.

Physical Hazard

Physical Hazard

Physical State

Condition of a material; i.e., solid, liquid, or gas, at room temperature.


Product identification number. A four-digit number, prefaced by UN or NA, used in Canada under the Transportation of Dangerous Goods Regulation for use by emergency personnel to identify a material in the event of an accident. See DOT identification number, the same numbering system used in the U.S.


A diamond-shaped marker required by the DOT on vehicles transporting hazardous materials. It displays DOT identification number and applicable warning symbols (for ex., flammable, corrosive, or explosive).


Man-made materials comprised of large molecules (polymers) and modifying agents such as fillers, colorants, and stabilizers that can be molded or shaped.


Pensky-Martens closed cup. One of several types of apparatus for determining flash points. The Pensky-Martens closed tester (ASTM D93-79) is used for liquids that: have a viscosity of 45 SUS (Saybolt universal seconds) or more at 38 C (100 F), have flash points of 93.6 C (200 F) or higher, contain suspended solids, or form surface films.


An ACGIH term for "particulates not otherwise classified." See Nuisance Particulates.


An OSHA term for "particulates not otherwise regulated." (TWA: 15 mg/m3, total dust; 5 mg/m3, respirable fraction).

Poison Control Center

Provides medical information on a 24-hr basis for accidents involving ingestion of potentially poisonous materials. Call your area's largest hospital to find the one nearest you.

Poisonous Material

A material, other than a gas, which is known (on the basis of animal tests) to be so toxic to humans or causes such extreme irritation as to afford a hazard to health during transportation.

Polycyclic Aromatic Hydrocarbons (PAH)

A family of chemical compounds containing only carbon and hydrogen, in which molecules consist of three or more carbon ring structures fused so that some carbon atoms are common to two or three rings. A large number of this chemical family's members are carcinogens, or are converted to carcinogens when metabolized by animals or humans. PAHs are formed during incomplete combustion of hydrocarbons. They are common in smoke, such as that of vehicle exhaust or tobacco, and are also important industrial contaminants in coal gas or coke manufacture and other processes involving heating of coal tar and pitch.


A natural or synthetic high-polymer substance containing ionic constituents. Major uses include treatment of paper-mill wastewater and flocculation (clumping) of solids in potable water.


A large molecule formed by the union of five or more identical combining units (monomers).


A chemical reaction in which one or more small molecules combine to form larger molecules. Hazardous polymerization takes place at a rate that releases large amounts of energy that can cause fires or explosions or burst containers. Materials that can polymerize usually contain inhibitors that can delay reactions.

Polyvinyl Chloride (PVC)

A tough, environmentally indestructible plastic that when burned releases hydrochloric acid.

Pour Point

The temperature at which a liquid either congeals or ceases to flow.


Parts per billion.


Personal protective equipment. Devices or clothing worn to help isolate a worker from direct exposure to hazardous materials. Examples include gloves, respirators, safety glasses, or ear plugs.


Parts per hundred.


Parts per million. "Parts of vapor or gas per million parts of air by volume at 25 C and 1 atm pressure" (ACGIH). At 25 C, ppm =(mg/m3 x 24.45) divided by molecular weight.


Parts per trillion.


Parts per thousand.


Pounds per square inch absolute.


Pounds per square inch gauge (i.e., above atmospheric pressure).


Chemical decomposition or breaking apart of molecules produced by heating.


Describes materials that ignite spontaneously in air below 54 C (130 F).

Reactive Material

A chemical substance or mixture that vigorously polymerizes, decomposes, condenses, or becomes self-reactive due to shock, pressure, or temperature. Includes materials or mixtures within any of these categories:

Explosive material - a substance or mixture that causes sudden, almost instantaneous release of pressure, gas, and heat when subjected to sudden adverse conditions;

Organic peroxide - an organic compound that contains the bivalent -O-O- structure, which can be considered a structural derivative of hydrogen peroxide, in which one or both of the hydrogen atoms has been replaced by an organic radical

Pressure-generating material - a substance or mixture that spontaneously polymerizes with an increase in pressure unless protected by the addition of an inhibitor or by refrigeration or other thermal control; decomposes to release gas in its container, or comprises the contents of a self-pressurized container

Water-reactive material - a substance or mixture that reacts with water releasing heat or flammable, toxic gas.


A substance's tendency to undergo chemical reaction either by itself or with other materials with the release of energy. Undesirable effects such as pressure buildup; temperature increase; or formation of noxious, toxic, or corrosive by-products may occur because of the substance's reactivity to heating, burning, direct contact with other materials, or other conditions in use or in storage. A solid waste that exhibits a "characteristic of reactivity," as defined by RCRA, may be regulated (by the EPA) as a hazardous waste and assigned the number D003.


Substance used in a chemical reaction to aid in qualitative or quantitative analysis of another substance.

Recommended Exposure Limit

See REL. Reducing Agent. In a reduction reaction (which always occurs simultaneously with an oxidation reaction), the reducing agent is the chemical or substance that 1) combines with oxygen or 2) loses electrons to the reaction. See Oxidation; Oxidizing Agent.


The NIOSH REL (Recommended Exposure Limit) is the highest allowable airborne concentration that is not expected to injure aworker. It may be expressed as a ceiling limit or as a time-weighted average (TWA), usually for 10-hr work shifts.


A variety of devices that limit inhalation of toxic materials. They range from disposable dust masks to self-contained breathing apparatus (SCBA). All have specific uses and limitations. Their use is covered by OSHA, 29 CFR 1910.134. See SCBA,

Chemical Cartridge Respirator.


A term applied to a variety of laws and regulations enacted by local, state, and federal governments to make information on chemical hazards readily available to workers and communities. Also includes the OSHA Hazard Communication Standard and SARA Title III, Community Right-to-Know. See also Hazard Communication. Route of Entry or Route of Exposure. The way a chemical enters the body; inhalation, skin contact, eye contact, and ingestion.


Reportable Quantity. The amount of a material that, when spilled, must be reported to the DOT (Section 311 of the Clean Water Act).


Registry of Toxic Effects of Chemical Substances, published by NIOSH. Presents basic toxicity data on thousands of materials. Its objective is to identify all known toxic substances and to reference the original studies. A substance's identification number on the U.S. Registry of Toxic Effects of Chemical Substances, a database compiled, maintained, and updated by the National Institute for Occupational Safety and Health (NIOSH). More information is available at the RTECS home page at NIOSH. Saint Andrew's Cross. X. Used in packaging for transport; means harmful - stow away from foodstuffs. (IMO, Material Class 6.1, Group III).


A state of immune-response reaction in which exposure to a material elicits an immune or allergic response.


A material that on first exposure causes little or no reaction in humans or test animals, but upon repeated exposure may cause a marked response not necessarily limited to the contact site. Skin sensitization is the most common form. Respiratory sensitization to a few chemicals also occurs. Skin. A notation to exposure limits (TLVs) indicating possible significant contribution to overall exposure to a material by way of absorption through the skin, mucous membranes, and eyes by direct or airborne contact.


A pourable mixture of solid and liquid.


Dry particles and droplets (usually carbon or soot) generated by incomplete combustion of an organic material combined with and suspended in gases from combustion.


See Synthetic Organic Chemicals.

Solubility in Water

A term expressing the percentage of a material (by weight) that dissolves in water at ambient temperature. Solubility information is useful in determining cleanup methods for spills and fire-extinguishing methods for a material. Solubility may be expressed as negligible, less than 0.1%; slight, 0.1 to 1.0%; moderate, 1 to 10%; appreciable, more than 10%; complete, soluble in all proportions. Alternatively, and more usually, it may be expressed as a percentage by weight in a solution, as grams of solute per liter of solution, or as grams of solute dissolved in 100 g of water. Solution, Soln. A uniformly dispersed single-phase mixture of a solvent (water or other fluid) and a dissolved substance, called the solute.


A material that can dissolve other materials to form a uniform single-phase mixture. Water is the most common solvent.


Fine particles, usually black, formed by combustion (complete or incomplete) and consisting chiefly of carbon. Soot gives smoke its color.


Standard Operating Procedure.


Action of soaking up or attracting substances.


Spill Prevention, Control, and Counter-measure plan.

Specific Gravity

The ratio of the density of a substance to the density of a reference substance, at a specified temperature. Specific gravity is a dimensionless number. Water (density 1 kg/1, or 1 g/mL, or 1 g/cm3 at 4 C) is the reference for solids and liquids, while air (density 1.29 g/l at 0 C and 760 mm Hg pressure) is the reference for gases. If a volume of a material weighs 8 g, and an equal volume of water weighs 10 g, the material has a specific gravity of 0.8 (8 divided by 10 = 0.8). Insoluble materials with specific gravity greater than 1.0 will sink (or go to the bottom) in water. Specific gravity is an important fire suppression and spill cleanup consideration since most (but not all) flammable liquids have a specific gravity less than 1.0 and, if insoluble, float on water.

Specific Gravity

The ratio of the mass of a substance to the mass of an equal volume of distilled water at 4 degrees celsius. A unitless quantity. Since the mass of one ml of water at 4 degrees celsius is exactly 1 gram, the specific gravity (unitless) is numerically equivalent to its density (in grams per ml).

Spontaneously Combustible Material

A material which undergoes self-heating to the point of ignition without requiring heat from another source.


The ability of a material to remain unchanged. For MSDS purposes a material is stable if it remains in the same form under expected and reasonable conditions of storage or use. Conditions such as temperatures above 66 C (150 F) or shock from being dropped that may cause instability (dangerous change) are stated on the MSDS. See Unstable.


Prescriptive norms that govern actual limits of airborne contaminants in the workplace and the amount of pollutants or emissions produced by industry.


Short-term exposure limit; ACGIH terminology. See TLV-STEL.


To change from the solid to the vapor phase without passing through the liquid phase. Dry ice exhibits sublimation.


Saybolt Universal Seconds. A unit measure of viscosity determined by the number of seconds required for an oil heated to 54 C (130 F) (lighter oils) and 99 C (210 F) (heavier oils) to flow through a standard orifice and fill a 60-ml flask.


A combined action of two or more toxic substances to give an effect greater than the sum of their activity when each toxic substance is alone. For example, both smoking and exposure to asbestos can cause lung cancer; however, if a smoker is also exposed to asbestos, the danger of lung cancer is far greater than just adding together the separate risks from the two exposures.


Alternative names by which a material may be known.

Synthetic Organic Chemicals (SOCs)

Man-made organic chemicals including products manufactured from coal, crude petroleum, natural gas, and certain natural substances such as fats, protein, carbohydrates, vegetable oils, rosin, grain, and their derivatives.

Systemic Toxicity

Adverse effects induced by a substance which affects the body in a general manner rather than locally. For example, a substance absorbed through the skin of the hands may result in kidney damage.


Toxic concentration low. The lowest concentration of a substance in air to which humans or animals have been exposed for any given period of time that has produced any toxic effect in humans or produced a tumorigenic or reproductive effect in animals or humans.


Toxic Chemical Release Inventory.


The lowest dose of a substance introduced by any route other than inhalation over any given period of time and reported to produce any toxic effect in humans or to produce tumorigenic or reproductive effects in animals or humans.

Threshold Limit Value

See TLV. Threshold Planning Quantity (TPQ). Per 40 CFR 302. The amount of material at a facility that require emergency planning and notification per CERCLA.

Time-Weighted Average

See TLV.


Threshold limit value. A term ACGIH uses to express the maximum airborne concentration of a material to which most workers can be exposed during a normal daily and weekly work schedule without adverse effects. "Workers" means healthy individuals, "healthy" is defined as a 150 lb. male, age 25 to 44. The young, old, ill, or naturally susceptible have lower tolerances and need to take additional precautions. ACGIH expresses TLVs in three ways: TLV-TWA, allowable time-weighted average concentration for a normal 8-hour workday or 40-hour week; TLV-STEL, short-term exposure limit or maximum concentration for a continuous exposure period of 15 minutes (with a maximum of four such periods per day, with at least 60 minutes between exposure periods, and provided that the daily TLV-TWA is not exceeded); and Ceiling (C), concentration not to exceed at any time. TLV-Ceiling Limit. TLV-C. The ceiling exposure limit or concentration not to exceed at any time, even for very brief times. The ACGIH publishes a book annually that explains and lists TLVs called: Threshold Limit Values for Chemical Substances and Physical Agents and Biological Exposure Indices. Copies are available from ACGIH (q.v.).


See Skin.


A unit of pressure, equal to 1 mm Hg. See atm (atmosphere).


A material is defined as toxic if it falls into any of the following four categories:

Has a median lethal dose (LD50) of more than 50 mg/kg, but no more than 500 mg/kg of body weight, when administered orally to albino rats.

Has a median lethal dose (LD50) of more than 200 mg/kg, but no more than 1000 mg/kg of body weight, when administered by continuous contact for 24 hours with the bare skin of albino rabbits.

Has a median lethal concentration (LC50) in air of more than 200 (parts per million (ppm), but no more than 2000 ppm of gas or vapor by volume, or more than 2 milligrams per liter (mg/L), but no more than 20 mg/L, of fume, mist, or dust, when administered by continuous inhalation for 1 hour to albino rats.

Is a liquid having a saturated vapor concentration (ppm) at 68 F (20 C) for more than one-fifth its LC50 (vapor) value (ppm), if the LC50 value is not more than 5000 mL/m3 (ppm) when administered by continuous inhalation for 1 hour to albino rats.


An agent capable of being toxic.

Toxic Chemical Release Reporting Form

A form required to be submitted by facilities that manufacture, process, or use toxic chemicals listed under SARA Title III.


The degree of a chemical substance's ability to produce deleterious effects. See also Acute Toxicity; Chronic Toxicity.


The study of the nature, effects, and detection of poisons in living organisms. Also, substances that are otherwise harmless but prove toxic under particular conditions. The basic assumption of toxicology is that there is a relationship among the dose (amount), the concentration at the affected site, and the resulting effects.

Toxic Substance

Any chemical or material that

Has evidence of an acute or chronic health hazard and

is listed in the NIOSH Registry of Toxic Effects of Chemical Substances (RTECS), provided that the substance causes harm at any dose level causes cancer or reproductive effects in animals at any dose level; has a median lethal dose (LD50) of less than 500 mg/kg of body weight when administered orally to rats; has a median LD50 of less than 1000 mg/kg of body weight when administered by continuous contact to the bare skin of albino rabbits; or has a median lethal concentration (LC50) in air of less than 2000 ppm by volume of gas or vapor, or less than 20 mg/L of mist, fume, or dust when administered to albino rats.

Toxic Substances Control Act



See Threshold Planning Quantity.

Trace Impurities

Small amounts of impure substances present due to natural occurrences or formation or contamination during the derivation process.


A name, usually not the chemical name, given to a product by the manufacturer or supplier and usually protected as a Registered Trademark. The same or similar products can be marketed under different tradenames by different companies.

Trade Secret

Confidential information (formula, process, device, etc.) that gives the owner an advantage over competitors. Manufacturers may choose to withhold proprietary data from an MSDS. Typically these would be ingredients of a formulated product. OSHA permits this provided

The trade secret claim can be substantiated.

The MSDS indicates that data is being withheld, and

The properties and health effects are included. State laws vary on this practice; some states require a trade secret registration number to be assigned to a material. There are procedures to obtain necessary trade secret information in emergency situations.

Trichoroethylene (TCE)

Trichoroethylene (TCE)


Tending toward decomposition or other unwanted chemical change during normal handling or storage. An unstable chemical in its pure state, or as commonly produced or transported, polymerizes vigorously, decomposes, condenses, or becomes self-reactive under conditions of shock, pressure, or temperature. See Stability, Reactive


Upper Explosive Limit, Upper Flammable Limit. UEL, UFL. The highest concentration of a material in air that produces an explosion or fire or that ignites when it contacts an ignition source (high heat, electric arc, spark, or flame). Any concentration above the UEL in air is too rich to be ignited. See Flammable Limits.


Hives caused by a systemic allergic reaction.


United States Department of Agriculture. (202-720-2791, Web site:


United States Public Health Service.


Gases given off by a substance normally encountered as liquid or solid at standard temperature and pressure.

Vapor Density (Definition # 1)

The ratio of the mass of a substance to the mass of an equal volume of air, both at standard temperature and pressure. A unitless quantity.

Vapor Density (Definition #2)

The ratio of the formula mass (FM) of the compound to the average formula mass of the gases in air (29 grams per mole). This formula mass ratio is correct for a pure gas at room temperature. However, this ratio does not accurately express the vapor density of a liquid solvent. A liquid cannot liberate vapors more concentrated than its saturated vapor concentration. The saturated vapor concentration of a liquid is the ratio of its vapor pressure at a given temperature to the atmospheric pressure. Using this ratio, the % of the compound in air and the remaining % of air at saturation (i.e., 19.7% hexane and 80.3% air) can be calculated. The saturated vapor density is then determined by multiplying the % of the compound in air by its FM and the % of air by its FM; adding this air/liquid vapor mixture at saturation; and dividing the sum by 29 and multiplying by the density of pure air (1.2 kg/m3, 0.075lbs/ft3). Saturated air/liquid vapor mixtures may be heavier than air, but not as heavy as formula mass ratios indicate. Temperature differences and turbulence create density differences between volumes of air and often have a greater influence on the movement of contaminated air than the actual saturated vapor density the chemical. Vaporization. The charge of a substance from a liquid to a gas.

Vapor Pressure

The pressure a saturated vapor exerts above its own liquid in a closed container. Vapor pressures reported on MSDSs are usually stated in millimeters of mercury (mm Hg) at 20 C (68 F). The lower a substance's boiling point, the higher its vapor pressure; and the higher the vapor pressure, the greater the material's tendency to evaporate into the atmosphere. Vapor pressures are useful (with evaporation rates) in learning how quickly a material becomes airborne within the workplace and thus how quickly a worker is exposed to it.


Vinyl Chloride Monomer.

Vinyl Chloride

A chemical compound, used in producing some plastics. Toxic, flammable and reactive (polymerizes) material. A human carcinogen.


Measurement of a fluid's thickness or resistance to flow. Unit of measurement, usually centipoise (cP), and temperature are included.


Volatile organic compounds. Used in coatings and paint because they evaporate very rapidly. Regulated by the EPA per the Clean Water Act.


Measure of a material's tendency to vaporize or evaporate at ambient routine conditions.

Workplace Hazardous Materials Information System (WHMIS)

A nationwide Canadian system providing information to workers on hazardous materials in the workplace. This is accomplished through labels, MSDSs, and worker education. It is similar to the United States' OSHA Hazard Communication Standard.


Workplace Environmental Exposure Level. Guides established by the American Industrial Hygiene Association for certain substances which do not have exposure guidelines (such as TLVs) established.

Wilson RISK Scale

An acute hazard rating scale unique to Genium's MSDS Collection. This scale was developed by a certified industrial hygienist for compliance with the OSHA Labeling Standard (29 CFR 1910.1200). This numbering system (of 0-4) & four hazard categories - reactivity (R), inhalation (I), skin contact (S), and kindling (K) - represents a material's degree of hazard based on documented values and/or the best judgments of certified industrial hygienists. The higher numbers indicate an increased hazard.

Water Solubility An indication of the solubility in a substance, sometimes listed in relative terms (very soluble); sometimes listed quantitatively (5mg/ml)