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Flashcards in NFPA 472 Definitions Deck (40):


Compounds that forms hydrogen ions in water. These compounds have a pH less than 7, and acidic aqueous solution will turn litmus paper red. Materials with a pH less than 2 are considered strong acid.



The percentage of an acid or a base dissolved in water concentration is not the same strength.



Chemical combination of two or more elements, either the same elements or different ones, that is electrically neutral. Compounds have a tendency to break down hinto their component parts, sometimes explosively.


Air Reactivity

A substance that ignites spontaneously in air at or below 130.19 Fahrenheit. Most pyrophoeic fires should be extinguished with a class D extinguisher for burning metals.


Chemical Change

Chemical changes occur when a substance combines with another to form a new substance, called synthesis or, alternatively, decomposes into two or more difference substances.


Ignition (auto ignition) temperature

Minimum temperature required to ignite gas or vapor without a spark or flame being present. Significant in Evaluating the ease at which a flammable material may ignite.



Auto-refrigeration is a phenomenon common to liquefied compressed gases. This is the process in which Liquefied gases are kept at its boiling point, so that any added heat is countered by energy lost from the boil off.



Added to products to control their chemical reaction with other products. If the inhibitor is not added or escapes during an incident, the material will begin to polymerize, possibly resulting in container failure.


Halogenated Hydrocarbon

A hydrocarbon with halogenated atom (chlorine, Bromine, Fluorine) substituted for a hydrogen atom. They are often more toxic than naturally occurring organic chemicals, and they decompose for a smaller, more harmful elements when exposed to high temperature for a sustain period of time.


Dose Response (relationship)

Basic principle of toxicology. The intensity of a response elicited by a chemical within a biologic mechanism is a function of the administered dose.


Fire Point

Minimum temperature at which a liquid gives off sufficient vapors that will ignite and sustain combustion. It is typically several degrees higher than the flash point. In assessing the risks posed by a flammable liquids release, greater emphasis is placed upon the flash point, since it is a lower temperature and sustain combustion is not necessary for significant injuries or damage to occur.


Flash point

Minimum temperature at which a liquid gives off enough vapors that will ignite and flash over but will not burn without the addition of more heat. Significant in determining the temperature at which the vapors from a flammable liquid are readily available and may ignite.


Caustic (Base, alkaline)

Compound that forms hydroxides ion in water. These compounds have a pH of >7, and caustic solutionsa will turn litmus paper blue. Materials with a pH >12 are considered a strong base. Also known as alkali, alkaline or base.


Critical temperature and pressure

Is the minimum temperature at which a gas can be liquified no matter how much pressure is applied.


Expansion Ratio

The amount of gas produced by the evaporation of one volume of liquid at a given temperature. Significant property when evaluation liquid and vapor release of liquefied gases and cryogenic materials. The greater the expansion ratio, the more gas that is produced and the larger the hazard area.



The concentration or amount of material to which the body is exposed over a specific time period. the amount of a substance ingested, absorbed and/or inhaled during an exposure period.


Blood agents

Chemical agents that consists of a cyanide compound, such as hydrogen cyanide and cyanogen chloride. These agents are identical to their civilian counterparts used in industry.


Half Life

The time it take for the activity of a radioactive material to decreases to one half of its initial value through radioactive decay. The half life of known materials can range from a fraction of a second to millions of years.


Chemical interaction

Reaction cause by mixing two or more chemicals together. Chemical interactions of materials within a container may result in a build up of heat and pressure, leading to container failure.


Boiling Point

The temperature at which a liquid changes it’s phase to a vapor or gas. The temperature where the vapor pressure of the liquid equals atmospheric pressure.


Flammability (Explosive) range (LEL & UEL)

The range of gas or vapor concentration (percentage by volume in air) that will burn or explode if an ignition source is present. Limiting concentrations are commonly called the "lower flammability (explosive) limit and the upper flammability (explosive) limit. Below the lower flammability, the mixture is too lean or rich to burn; above the upper flammability limit, the mixture is too rich to burn. If the gas or vapor is released into oxygen enriched atmosphere, the flammability range will expand. Likewise if the vapor is released into a oxygen deficient atmosphere, the flammability range will contract.


Biological agents and Toxins

Biological threat agents consist of pathogens and toxins. Pathogens are disease producing organisms and include bacteria and virus. Toxins re produced by a biological source and include ricin, botulinum and mycotoxins.


Aromatic Hydrocarbon

A hydrocarbon containing benzene “ring” which is formed by six carbon atoms and contains resonant bonds.


Instability (reactivity)

The ability of a material to undergo a chemical reaction with the release of energy. It could be initiated by mixing or reacting with other materials, application of heat, physical shock, etc.



A material that causes visible destruction of or irreversible altercation to living tissues by chemical actions at the point of contact.



A material that causes visible destruction of or irreversible alterations to living tissue by chemical actions at the point of contact.


Inorganic Materials

Compounds derived from other thanvegetable or animal sources which lack carbon chains , but may contain a carbon atom (Sulfur dioxide & Cyanide)



Used to control the rate of chemical reaction by either speeding up or slowing down. If used improperly, catalyst can speed up a reaction and cause a container failure due to pressure or heat build up.


Inorganic Materials

Compounds derived from other than vegetables and animals sources which lack carbon chains, but may contain a carbon atom



The ability of a material to undergo a chemical reaction with the release of energy. It could be initiated by mixing or reacting with other materials, applications of heat, physical shock, etc.


Ionic and Covalent compounds

The electrostatic attention of oppositely charged particles. Atoms or groups of atoms can form ions or complex ions. Covalent bonding is the force holding together atoms that share electrons


Irritants (riot control agents)

Usually solid materials that are dispersed in a liquid spray and cause pain or burning on exposed mucous membranes and skins. Like pepper spray.


Maximum safe storage Temperature (MSST)

The maximum storage temperature that an organic peroxide may be maintained, above which a reaction and explosion may occur.


Melting Point/ Freezing Point

The temperature at which the a solid changes into a liquid. This temperature is also the freezing depending on direction of the change.



Refers to the tendency or ability of two or more liquids to form a uniform blend or to dissolve in each other. Liquids may be totally miscible, partial or non miscible.h



Substance made up from two or more compounds, physically mixed together. A mixture may also contain elements and compounds mixed together.


Nerve Agents

Nerve agents are a class of phosphorus containing organic chemicals that’s disrupt the mechanism by which nerves transfer messages to organs.


Organic Materials

Material that contain carbon. Organic material are derived from materials that are living or were once living, such as plants or decayed products. Most organic materials are flammable.


Oxidation potential (ability)

The ability of a material to either give up its oxygen molecule to stimulate the oxidation of organic material or receives electrons being transferred from the substance undergoing oxidation.



Refers to the length of time a chemical agent remains as a liquid. A chemical agent is said to be persistent it remains as a liquid for longer than 24 hours and non persistent if it evaporates within that time.