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Glossary of Common Safety and Chemical Terms
Appendix XV (adapted from NMSU Lab Guide - dls)


(Scroll down or select a link to first letter of the word)



 ACGIH - ACGIH stands for American Conference of Governmental Industrial Hygienists.  The ACGIH is an association of occupational health professional employed by the government and educational institutions.   The Threshold Limit Value (TLV) Committee and Ventilation Committee of the ACGIH publish guidelines which are used worldwide.

Active Ingredient - An active ingredient is the part of a product which actually does what the product is designed to do.  It is not necessarily the largest part of the product.  For example, an insecticidal spray may contain less than 1% pyrethrin, the ingredient which actively kills insects.  The remaining ingredients are often called inert ingredients.

Acute - Acute means sudden or brief.  Acute can be used to describe either an exposure or a health effect.  An acute exposure is a short-term exposure.  Short-term means lasting for minutes, hours or days.  An acute health effect is an effect that develops either immediately or a short time after an exposure.  (Also see Chronic).
 Aerosol - An aerosol is a collection of very small particle suspended in air.   The particles can be liquid (mist) or solid (dust or fume).  The term aerosol is also commonly used for a pressurized container (aerosol spray) which is designed to release a fine spray of material such as paint.  Inhalation of aerosol is a common route of exposure to many chemicals.  As well, aerosols may be fire hazards.
Temperature  - The auto-ignition temperature is the lowest temperature at which materials begin to burn in air in the absence of a spark or flame.  Many chemicals will decompose (break down) when heated.  The auto-ignition temperature is the temperature at which the chemicals formed by decomposition begin to burn.   Auto-ignition temperatures for a specific material can vary by one-hundred degrees Celsius or more depending on the test method used.  Therefore values listed on the MSDS may be rough estimates.  To avoid the risk of fire or explosion, materials must be stored and handled at temperatures well below the auto-ignition temperature.

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Biological Hazard,
Biohazard Materials - Under the Occupational Safety and Health Administration, a biohazard means those infective agents presenting a risk of death, injury or illness to employees.  For example, a person exposed to a blood sample from someone with Hepatitis B may contract the disease.
Boiling Point - The boiling point is the temperature at which the material changes from a liquid to a gas.  Below the boiling point, the liquid can evaporate to form a vapor.  As the material approaches the boiling point, the change from liquid to vapor is rapid and vapor concentration in the air can be extremely high.  Airborne gases and vapors may pose fire, explosion and health hazards.  Sometimes, the boiling point is given as a range of temperatures.  This is because different ingredients in a mixture can boil at different temperatures.  If the material decomposes (breaks down) without boiling, the temperature at which it decomposes may be given with the abbreviation, "dec."  

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Carcinogenicity - A carcinogen is a substance which can cause cancer.   Carcinogenic means able to cause cancer.  Carcinogenicity is the ability of a substance to cause cancer.  Under the Controlled Products regulation, materials are identified as carcinogenic if they are recognized as carcinogens by the American Conference of Governmental Industrial Hygienist (ACGIH), or the International Agency for Research on Cancer (IARC).  MSDS's from the United Stated also identify carcinogens recognized by the US National Toxicology Program (NTP).  The lists of carcinogens prepared by these organizations include known human carcinogens and some materials which cause cancer in animal experiments.  Certain chemicals may be listed as suspect or possible carcinogens if the evidence is limited or so variable that a definite conclusion cannot be made.
CAS Registry Number - The CAS Registry Number is a number assigned to a material by the Chemical Abstract Service (CAS) to provide a single unique identifier.  A unique identifier is necessary because the material can have many different names.  For example, the name given to a specific chemical may vary from one language or country to another.  The CAS Registry Number has no significance in terms of the chemical nature or hazards of the material.  The CAS Registry Number can be used to locate additional information on the material, for example, when searching in books or chemical data bases.
Ceiling (C) - See Exposure Limits for a general explanation.
Chemical Name - The chemical name is a proper scientific name for the principle or active ingredient of the product.  For example, the chemical name for the herbicide 2,4-D is 2,4-dichlorophenoxyacetic acid.  The chemical name can be used to obtain additional information.
Chronic - Chronic means long-term or prolonged.  It can describe either an exposure or a health effect.  A chronic exposure is a long-term exposure.   Long-term means lasting for months or years.  A chronic health effect is an effect that appears months or years after an exposure.  The Controlled Products Regulations describes technical criteria for identifying materials which cause chronic health effects.  (See also Acute).
Coefficient of
Oil/Water Distribution -  The coefficient of oil/water distribution, also called the partition coefficient, abbreviated as P, is the ratio of the solubility of a chemical in an oil to its solubility in water.  The P value is typically represented as a logarithm of P (log P).  It indicates how easily the chemical can be absorbed or stored in the body.  The P value is also used to help determine the effects of the chemical on the environment.
Combustible - Combustible means able to burn.  Broadly speaking, a material is combustible if it can catch fire and burn.  (See Combustible Liquid).  The terms combustible and flammable both describe the ability of material to burn.  Commonly, combustible materials are less easily ignited than flammable materials.

Combustible Liquid - Under 29 CFR 1910.106(a)(18), a combustible liquid has a flash point at or above 37.8?C.  This flash point is well above normal room temperature.  Combustible liquids are, therefore, less of a fire hazard than flammable liquids.  If there is a possibility that a combustible liquid will be heated to a temperature near its flash point, appropriate precautions must be taken to prevent a fire.

Compressed Gas - Under 29 CFR 1910.1200(c), a compressed gas is a gas or mixture of gases having, in a container, an absolute pressure exceeding 40 psi at 70?F (21.1?C); a gas or mixture of gases having, in a container, an absolute pressure exceeding 104 psi at 130?F (54.4?C) regardless of the pressure at 70?F; or, a liquid having a vapor pressure exceeding 40 psi at 100?F (37.8?C) as determined by ASTM D-323-72.  Regardless of whether a compressed gas is packaged in an aerosol can, a pressurized cylinder or a refrigerated container, it must be stored and handled very carefully.  Puncturing or damaging the container or allowing the container to become hot may result in an explosion.
Corrosive Material - A corrosive material can attack (corrode) metals or human tissue such as the skin or eyes.  Corrosive material can cause metal containers or structural to become weak and eventually to leak or collapse.  Corrosive materials can burn or destroy human tissues on contact and can cause effects such as permanent scarring or blindness.  

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Dangerously Reactive
Material                         - A dangerously reactive material that can react vigorously:

                                        •   with water to produce a very toxic gas;
                                        •   on its own by polymerization or decomposition; or
                                        •   under conditions of shock, or an increase in pressure or temperature.

A dangerously reactive material may cause a fire, explosion or other hazardous condition.  It is very important to know which conditions (such as shock, heating or contact with water) may set off a dangerous reaction so that appropriate preventative measures can be taken.

Density - The density of a material is its mass for a given volume.  Density is usually given in units of grams per milliliter (g/ml) or grams per cubic centimeters (g/cc).  Density is closely related to specific gravity (relative density).  The volume of a material in a container can be calculated from its density and mass.

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Embryotoxicity  - An embryo is an organism in its early stages of development prior to birth.  In humans, the embryo is the developing child from conception to the end of the second month of pregnancy.  (See also Fetus).  Embryotoxic means harmful to the embryo.  Embryotoxicity is the ability of a substance to cause harm to the embryo.  (See also Fetotoxicity and Reproductive Effects).

Evaporation Rate - The evaporation rate is a measure of how quickly the material becomes a vapor at normal room temperature.   Usually, the evaporation rate is given in caparison to certain chemicals, such as butyl acetate, which evaporates fairly quickly.  For example, the rate might be given as "0.5 grams of material evaporates during the same time that  1 gram of butyl acetate evaporates.  Often, the evaporation rate is given only as greater or less than 1, which means the material evaporates faster or slower than the comparison chemical.  In general, a hazardous material with a higher evaporation rate presents a greater hazard than a similar compound with a lower evaporation rate.

Explosive Limits
 * LEL, LFL  - The Lower Explosive Limit (LEL), or lower flammable limit (LFL), is the lowest concentration of gas or vapor which will burn or explode if ignited.

 * UEL, UFL -  The Upper Explosive Limit (UEL), or the upper flammable limit (UFL), is the highest concentration of gas or vapor which will burn or explode if ignited.
From the LEL to the UEL, the mixture is explosive.  Below the LEL, the mixture is too lean to burn.  Above the UEL, the mixture is too rich to burn.  However, concentrations above the UEL are still very dangerous because, if the concentration is lowered (for example, by introducing fresh air), it will enter the explosive range.   In reality, explosive limits for a material vary since they depend on many factors such as air temperature.  Therefore the values given on an MSDS are approximate.

 Not Flammable:  


Not Flammable:

Too Lean to Burn

Can Burn Explosively

Too Rich to Burn



<--------   -------->



Percent volume of vapor or gas in air

The explosive limits are usually given as the percent by volume of the material in the air.  One percent by volume is 10,000 ppm.  For example, gasoline has a LEL of 1.4% and a UEL of 7.6%.  This means that gasoline vapors at concentrations of 1.4% to 7.6% (14,000 to 76000 ppm) are flammable or explosive.

Exposure Limits - An exposure limit is the concentration of a chemical in the workplace to which most people can be exposed without experiencing harmful effects.  Exposure limits should not be taken as sharp dividing lines between safe and unsafe exposures.  It is possible for a chemical to cause health effects, in some people, at concentrations lower than the exposure limits.   Exposure limits have different names and different meaning depending on who developed them and whether or not they are legal limits. 

Threshold Limit Values (TLV's) are exposure guidelines developed by the American Conference of Governmental Industrial Hygienists (ACGIH).  They have been adopted by several governments as their legal limits. 

Permissible Exposure  Limits (PEL's) are legal exposure limits in the United States.  Sometimes, a manufacturer will recommend an exposure limit for a material.  Exposure limits have not been set for many chemicals, for many different reasons.  For example, there may not be enough information available to set an exposure limit.  Therefore, the absence of an exposure limit does not necessarily mean the material is not harmful. 

There are three types of exposure limits in common use:

TWA  -     Time-Weighted Average exposure limit is the average concentration of a chemical in air for a normal 8-hour workday and 40-hour workweek to which nearly all workers may be exposed day after day without harmful effects.  Time-weighted average means that the average concentration has been calculated using the duration of exposure to different concentrations of the chemical during a specific time period.  In this way, higher and lower exposures are averaged over the day or week.

STEL          -     Short-Term Exposure Limit is the average concentration to which workers can be exposed to for a short period (usually 15 minutes) without experiencing irritation, long-term or irreversible tissue damage or reduced alertness.  The number of times the concentration reaches the STEL and the amount of time between these occurrences can also be restricted.

Ceiling (C)
-       Ceiling (C) exposure limit is the concentration which should not be exceeded at any time.

        -        "SKIN" notation (SKIN) means that contact with the skin, eyes and moist tissues (for example, the mouth) can contribute to the overall exposure.  The purpose of this notation is to suggest that measures be used to prevent absorption occurs through the skin, then the airborne exposure limits are not relevant.

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Fetus                 -  Fetotoxic means the substance is harmful to the fetus.  Fetotoxicity describes the ability of a substance to harm the fetus.  (See also Embryotoxicity, Teratogenicity, and Reproductive Effects).  A fetus is an organism in the later stages of development prior to birth.  In human, it is the unborn child from the end of the second month of pregnancy to birth.

Flammability    -    Flammable means able to ignite and burn readily.  Flammability is the ability of a material to ignite and burn readily.  (See Combustible, Flammable Aerosol, Flammable Gas, Flammable Liquid, Flammable Solid, and Reactive Flammable Material).  Local, state and national fire codes also classify and regulate the use of flammable materials in the workplace.

Flammable Aerosol   -    Flammable Aerosol means an aerosol that, when tested by the method described in 16 CFR 1500.45, yields a flame projection exceeding 18 inches at full valve opening, or a flash back at any degree of valve opening (29 CFR 1910.1200(c)).  A flammable aerosol is hazardous because it may form a torch (explosive ignition of the spray) or because a fire fuelled by the flammable aerosol may flash back.

Flammable Gas - A flammable gas is a gas which can ignite readily and burn rapidly or explosively.  Under 29 CFR 1910.1200(c), it is a gas that, at ambient temperature and pressure, forms a flammable mixture with air at a concentration of thirteen (13) percent by volume or less; or, a gas that at ambient temperature and pressure forms a range of flammable mixtures with air wider than twelve (12) percent by volume, regardless of the lower limit.  Flammable gases can be extremely hazardous in the workplace; for example:
     * If the gas accumulates so that its lower explosive limit (LEL) is reached and  if there is a source of ignition, an explosion will occur.
     * If there is inadequate ventilation, flammable gases can travel considerable distances to a source of ignition and flash back to the source of the gas.
Flammable Limits - See Explosive Limits.

Flammable Liquids - A flammable liquid gives off a vapor which can be easily ignited at normal working temperatures.  Under the 29 CFR 1910.106(a)(19), a flammable liquid is a liquid with a flash point (using a closed cup test) below 37.8?C (100F).  Flammable liquids can be extremely hazardous in the workplace; for example:
  * If there is inadequate ventilation, flammable gases can travel considerable  distances to a source of ignition and flash back to the flammable liquid.
    * It may be difficult to extinguish a burning flammable liquid with water because  water may not be able to cool the liquid below its flash point.

Flammable Solid - A flammable solid is a solid material that is liable to cause fire through friction, absorption of moisture, spontaneous chemical change, or retained heat from manufacturing or processing or which can ignite readily and when ignited burns vigorously and persistently as to create a serious hazard (29 CFR 1910.1200(c)).  Flammable solids in the form of dust or powder may be particularly hazardous because they may explode if ignited.

Flash Back - Flash back occurs when a trail of flammable gas, vapor or aerosol is ignited by a distant spark, flame or other source of ignition.  The flame then travels back along the trail of gas, vapor or aerosol to its source.  A serious fire or explosion could result.

Flash Point - The Flash Point is the lowest temperature at which a liquid or a solid gives off enough vapor to form flammable air-vapor mixture near its surface.  The lower the flash point, the greater the fire hazard.  The flash point is an approximate value and should not be taken as a sharp dividing line between safe and hazardous conditions.  The flash point is determined by a variety of test methods which give different results.  Two of these methods are abbreviated as OC (open cup) and CC (closed cup).

Freezing Point - The temperature at which a material freezes.  (See also Melting Point).

Fumes - Impervious Fumes are very small, airborne, solid particles formed by the cooling of a hot vapor.  For example, a hot zinc vapor may form when zinc-coated steel is welded.  The vapor then condenses to form fine zinc fumes as soon as it contacts the cool surrounding air.  Fumes are smaller than dusts and are more easily breathed into the lungs.

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Hazardous - Hazard is the potential for harmful effects.  Hazardous means potentially harmful.  The hazards of a material are evaluated by examining the properties of the material, toxicity, flammability and chemical reactivity, as well as how the material is used.  How a material is used can vary greatly from workplace to workplace and, therefore, so can the hazard.

Hazardous Combustion
Products                           -   Hazard Combustion Products are chemicals which may be form products when a material burns.  These chemicals may be toxic, flammable or have other hazards.  The chemicals released and their amounts vary depending upon conditions such as the temperature and the amount of air (or more specifically, oxygen) available.  The combustion chemicals may be quite different from those formed by heating the same material during processing (thermal decomposition products).  It is important to know which chemicals are formed during combustion in order to plan the response to a fire involving the material.

Products                  -    Hazardous Decomposition Products are formed when a material decomposes (breaks down) because it is unstable or reacts with common materials such as water or oxygen (in air).  This information should be considered when planning storage and handling procedures.

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IARC - IARC stands for International Agency for Research on Cancer.  IARC evaluates information on carcinogenicity of chemicals, groups of chemicals and chemicals associated with certain industrial processes.  IARC has published lists of chemicals which are generally recognized as human carcinogens, probable human carcinogens or carcinogens in animal tests.

IDLH - IDLH stands for Immediately Dangerous to Life or Health.  For the purpose of respirator selection, NIOSH defines the IDLH concentration as the maximum concentration which would not cause any escape-impairing symptoms or irreversible health effects to a person exposed for thirty minutes, if the respirator failed.

  -  Impervious is a term used to describe protective gloves and other protective clothing.  If a material is impervious to a chemical, then that chemical cannot readily penetrate through the material or damage the material.  Different materials are impervious (resistant) to different chemicals.  No single material is impervious to all chemicals.  If an MSDS recommends wearing impervious gloves, you need to know the type of material from which the gloves should be made.  For example, neoprene gloves are impervious to butyl alcohol but not the ethyl alcohol.
Incompatible Materials - Incompatible materials can react with the product or with components of the product and may:
        * destroy the structure or function of a product;
        * cause a fire, explosion or violent reaction; or,
        * cause the release of hazardous chemicals.

Inert Ingredient - An inert ingredient is anything other than the active ingredient of a product.  It may be a solvent, colorant, filter or dispersing agent.  In some cases, inert ingredients may be hazardous.

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

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

Irritation   - Irritancy is the ability of a material to irritate the skin, eyes, nose, throat, or any other part of the body that it contacts.  Signs and symptoms of irritation include tearing in the eyes and reddening, swelling, itching and pain or the affected part of the body.  Irritancy is often described as mild, moderate or severe, depending on the degree of irritation caused by a specific amount of the material.  Irritancy may also be described by a number on a scale of 0 to 4, where 0 indicated no irritation and 4 means severe irritation.  Irritancy is usually determined in animal experiments.  The Controlled Products Regulations, describe technical criteria for identifying materials which are skin or eye irritants.

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LC50 - LC stands for lethal concentration.   LC50 is the concentration of material in the air which causes the death of 50% (one half) of a group of test animals.  The material is inhaled over a set period of time, usually 1 to 4 hours.  The LC50 helps determine the short-term poisoning potential of a material.  (See also LD50).  The MSDS must indicate the species of animal tested and the route by which the hazardous substance was administered.  Note: if the LC50 is known for a mixture, this should be listed for the mixture and not the separate ingredients.

LD50 - LD stands for lethal dose.  LD50 is the amount of a material, given all at once, which causes death of 50% (one half) of a group of test animals.  The LD50 can be determined by any route of entry, but dermal (applied to skin) and oral (given by mouth) are the most common.  The LD50 is one measure of the short-term poisoning potential of a material.  (See also LC50).   The MSDS must indicate the species of animal tested and the route by which the hazardous substance was administered.  Note: if the LD50 is known for a mixture, this should be listed for the mixture and not the separate ingredients.

Lower Explosion(ive) Limit (LEL) - See Explosive Limits.

Lower Flammable Limit (LFL) - See Explosive Limits.

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Melting Point  -  The melting point is the temperature at which a solid material becomes a liquid.  The freezing point is the temperature at which a liquid material becomes a solid.  Usually one value or the other is given on an MSDS.  It is important to know the melting or freezing point for storage or handling purposes.  For example, a melted or frozen material may burst a container.  As well, a change of physical state could alter the hazards of the material.

mg/m3 - The abbreviation mg/m3 stands for milligrams (mg) of material per cubic meter (m3) of air.  It is a unit of metric measurement for concentration (mass/volume).  The concentration of any airborne chemical can be measured in mg/m3, whether it is a solid, liquid, gas or vapor.

Mist - A mist is a collection of liquid droplets suspended in air.  A mist can be formed when spraying or splashing a liquid.  It can also be formed when a vapor condenses into liquid droplets in the air.  (See also Aerosol).

Mutagenicity - A mutagen is a substance which can cause changes in the DNA of cells (mutations).  Mutagenic means able to cause mutations.  Mutagenicity is the ability of a substance to cause mutations.  A number of mutagenicity tests are used to screen chemicals for possible carcinogenicity or reproductive effects.  This is because there is some evidence that mutations can increase the Risk of cancer and reproductive problems such as infertility or birth defects.  However, mutagenicity test results are not very reliable predictors of these effects.  One reason for this is that the human body can repair mutations while most mutagenicity tests cannot.   Mutagenicity is indicated on MSDS's because it is an early indicator of potential hazard, and often there is very little evidence available on possible carcinogenic or reproductive effects.  The Controlled Products Regulations describe technical criteria for identifying materials which are mutagenic.

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NA Number - See UN Number.

NIOSH - NIOSH stands for National Institute for Occupational Safety and Health.  NIOSH is a branch of the Department of Health and Human Services which undertakes research and develops occupational health and safety standards.

NTP - NTP stands for National Toxicology Program.  This program is part of the Department of Health and Human Services.   The NTP has a large program for testing the potential carcinogenicity of chemicals.   It also does many other types of studies on short-term and long-term health effects.

Nuisance Dust,
Nuisance Particulate  -  Nuisance particle is a term used by the ACGIH to describe airborne materials (solids and liquids) which have little harmful effects on the lungs and do not produce significant disease or harmful effects when exposures are kept under reasonable control.  Nuisance particulates may also be called nuisance dusts.   High levels of nuisance particulates may reduce visibility and can get into the eyes, ears and nose.

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Odor Threshold - The Odor Threshold is the lowest concentration, in ppm, of a chemical in the air that is detectable by smell.   The odor threshold should only be regarded as an estimate.  This is because odor thresholds are commonly determined under controlled laboratory conditions using people trained in odor recognition.  As well, in the workplace, the ability to detect the odor of a chemical varies form person to person and depends on conditions such as the presence of other odorous materials.  Odors cannot be used as a warning of unsafe conditions since workers may become used to the smell (adaptation), or the chemical may numb the sense of smell, a process called olfactory fatigue.  However, if the odor threshold for a chemical is well below its exposure limit, odor can be used to warn of a problem with your respirator.

OECD - OECD stands for Organization for Economic Cooperation and Development.  The OECD is an international agency which supports programs designed to facilitate trade and development.  The OECD has published Guidelines for Testing Chemicals.  These guidelines contain recommended procedures for testing chemicals for toxic and environmental effects and for determining physical and chemical properties.

OEL - OEL stands for Occupational Exposure Limit.  (See Exposure Limit for a general explanation).

OSHA - OSHA stands for Occupational Safety and Health Administration.  It is the branch of the US government which sets and enforces occupational health and safety regulations.  For example, OSHA sets the legal exposure limits in the United States, which are called Permissible Exposure Limits (PEL's).  OSHA also specifies what information must be given on labels and Material Safety Data Sheets (MSDS) for materials in the US that have been classified are hazardous using their criteria.

Oxidizing Agent,
Oxidizing Material  - An oxidizing agent or material gives up oxygen easily or can readily oxidize other materials.  Examples of oxidizing agents are chlorine and peroxide compounds.  These chemicals will support a fire and are highly reactive.

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Partition Coefficient - See Coefficient of Oil/Water Distribution.

PEL - PEL stands for Permissible Exposure Limit.  PEL's are legal limits in the United States set by the Occupational Safety and Health Administration (OSHA).  (See Exposure Limits for a general explanation).

Personal Protective Equipment (PPE)  - Personal Protective Equipment (PPE) is clothing or devices worn to help isolate a person from direct exposure to a hazardous material or situation.  On a MSDS, personal protective equipment which protects from chemical exposure is listed.  This can include protective clothing, respiratory protection and eye protection.  The use of protective equipment is the least preferred method of protection from hazardous exposures.   It can be unreliable and, it if fails, the person can be left completely unprotected.  This is why engineering controls are preferred.  Sometimes, personal protective equipment may be needed along with engineering controls.  For example, a ventilation system (an engineering control) reduces the inhalation hazard of a chemical, while gloves and labcoat (personal protective equipment) reduce skin contact.   In addition, personal protective equipment can be an important means of protection when engineering controls are not practical; for example, during an emergency or other temporary conditions such as maintenance operations.

pH - The pH is a measure of the acidity or basicity (alkalinity) of a material when dissolved in water.  It is expressed on a scale from 0 to 14.  Roughly, pH can be divided into the following ranges:

     pH  0 -  2 Strongly acidic
     pH  3 -  5 Weakly acidic
     pH  6 -  8 Neutral
     pH  9 - 11 Weakly basic
     pH 12 - 14 Strongly basic

ppm - The abbreviation stands for parts per million.  It is a common unit of concentration of gases or vapor in air.  For example, 1 ppm of a gas means that 1 unit of gas is present for every 1 million units of air.

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Relative Density  - See Specific Gravity.

Reproductive Effects,
Reproductive Toxicity  - Reproductive effects are problems in the reproductive process which may be caused by a substance.  Possible reproductive effects include reduced fertility in the male or female, menstrual changes, miscarriage, embryotoxicity, fetotoxicity, teratogenicity, or harmful effects to the nursing infant form chemicals in breast milk.  Most chemicals can cause reproductive effects if there is an extremely high exposure.  In these cases, the exposed person would experience other noticeable signs and symptoms caused by the exposure.  These signs and symptoms act as a warning of toxicity.  Chemicals which cause reproductive effects in the absence of other significant harmful effects are regarded as true reproductive hazards.  Very few workplace chemicals are known to be true reproductive hazards.  The Controlled Products Regulations describe technical criteria for identifying materials which have reproductive toxicity.  These criteria refer to adverse effects on fertility.

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Sensitization - Sensitization is the development, over time, of an allergic reaction to a chemical.  The chemical may cause a mild response on the first few exposures but, as the allergy develops, the response becomes worse with subsequent exposures.  Eventually, even short exposures to low concentration can cause very severe reaction.  There are two different types of occupational sensitization: skin and respiratory.  Typical symptoms of skin sensitivity are swelling, redness, itching , pain and blistering.  Sensitization of the respiratory system may result in symptoms similar to a severe asthma attack.   These symptoms include wheezing, difficulty in breathing, chest tightness, coughing and shortness of breath.

"Skin" Notation - See Exposure Limits for a general explanation.

Specific Gravity - Specific Gravity is the ratio of the density of a material to the density of water.  The density of water is about 1 gram per cubic centimeter (g/cc).  Materials which are lighter than water (specific gravity less than 1.0) will float.  Most materials have specific gravities exceeding 1.0, which means they are heavier than water and will sink.  Knowing the specific gravity is important for planning spill clean-up and fire fighting procedures.  For example, a light flammable liquid such as gasoline may spread and if ignited burn on top of a water surface.

Stability - Stability is the ability of a material to remain unchanged in the presence of heat, moisture or air.  An unstable material may decompose, polymerize, burn or explode under normal environmental conditions.   Any indication that the material is unstable gives warning that special handling and storage precautions may be necessary.

STEL - STEL stands for Short-Term Exposure Limit.  (See Exposure Limits for a general explanation).

Synergistic - As used on MSDS, synergism means that exposure to more than one chemical can result in health effects greater than when expected when the effects of exposure to each chemical are added together.  Very simply, it is like saying 1 + 1 = 3.  When chemicals are synergistic, the potential hazards of the chemicals should be reevaluated, taking their synergistic properties into consideration.

Synonyms - Synonyms are other names for the same chemical.  For example, methanol and methyl hydrate are synonyms for methyl alcohol.   Synonyms may help in locating additional information on a chemical.

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TDG - The transportation of potentially hazardous materials is regulated under the HM-181 regulations which are administered by the Department of Transportation (DOT).  These regulations set out criteria for the classification of materials as dangerous goods and state how these materials must be packaged and shipped.

Teratogenicity - A teratogen is a substance which can cause birth defects.   Teratogenic means able to cause birth defects.  Teratogenicity is the ability of a chemical to cause birth defects.  Teratogenicity results from a harmful effect to the embryo or fetus.  (See also Reproductive Effects).

Thermal Decomposition Products - Thermal Decomposition Products are chemicals which may be formed when the material is heated but does not burn.  These chemicals may be toxic, flammable, or have other hazards.   The chemicals released and their amounts vary depending upon conditions such as temperature.  The thermal decomposition products may be quite different from the chemicals formed by burning the same material (hazardous combustion products).  It is important to know which chemicals are formed by thermal decomposition because this information is used to plan ventilation requirements for processes where a material may be heated.

TLV - TLV stands for Threshold Limit Value.  It is the occupational exposure limit established by the American Conference of Governmental Industrial Hygienist (ACGIH).   TLV is a registered trademark of ACGIH.  (See Exposure Limits for a general explanation).

Toxicity - Toxic mean able to cause harmful health effects.  Toxicity is the ability of a substance to cause harmful health effects.  Description of toxicity (e.g., low, moderate, severe, etc.) depend on the amount needed to cause an effect or the severity of the effect.

Trade Name - A trade name is the name under which a product is commercially known.  Some materials are sold under common names, such as Stoddard solvent or degreaser, or internationally recognized trade name, like Varsol.  Trade names are sometimes identified by symbols such as 'TM' for an 'R' with a circle around it.

TWA - TWA stands for Timed-Weighted Average.   (See Exposure Limits for a general explanation).

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UN Number - UN Number stands for United Nations number.  The UN number is a four-digit number assigned to potentially hazardous material (such as gasoline, UN 1203) or class of material (such as corrosive liquids, UN 1760).  These numbers are used by fire fighters and other emergency response personnel for identification of material during transportation emergencies.  UN numbers are internationally recognized.  NA (North America) numbers are used only for shipments with Canada and the United States.  UN, NA and PIN numbers have the same use.

Upper Explosion(ive) Limit (UEL)             -    See Explosion Limits.

Upper Flammable Limit   -  See Explosion Limits

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Vapor  -  A Vapor is the gaseous form of a material which is normally solid or liquid at room temperature and pressure.   Evaporation is the process by which a liquid is changed into a vapor.   Sublimation is the process by which a solid is changed directly into the vapor state.

 Vapor Density - Vapor Density is the mass per unit volume of a pure gas or vapor.  On an MSDS, the vapor density is commonly given as a ration of the density of the gas or vapor to the density of air.  The density of air is given a value of 1.  Light gases (density less than 1) such as helium rise in air.  If there is inadequate ventilation, heavy gases and vapors (density greater than 1) can accumulate in low lying areas such as pits and along floors.

Vapor Pressure -  Vapor Pressure is the pressure of a vapor when in equilibrium with its liquid or solid form.  It is a measure of the tendency of a material to form a vapor.  The higher the vapor pressure, the higher the potential vapor concentration.  In general, a material with a high vapor pressure is more likely to be an inhalation or fire hazard than a similar material with a lower vapor pressure.

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Lab Safety Guide

Table of Contents

Chapter- 1 2 3 4 5 6 7 8 9 10




Contact Information 
 Environmental Health& Safety: MSC-3578, P.O. Box 30001, Academic Research Bldg. C, Rm. 109
    Street delivery address: NMSU, 1620 Standley Dr., Academic Research Bldg. C, Las Cruces, NM 88003
    Training Office: Academic Research Unit C, rm110 (see map ), 
    Telephone: 575-646-3327; FAX: 575-646-7898. Website - http://www.nmsu.edu/safety
    Send email to David Shearer, EH&S (click here) with questions or comments about this web site. 
    This page was last updated on 09/21/2014