Glossary of Technical Terms

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Acute exposure: A single exposure to a toxic substance which may result in severe biological harm or death. Acute exposures are usually characterized as lasting no longer than a day. The toxic effect may be temporary and reversible, or may be permanent (disability or death).
Action Levels: Indicator of the level of a toxic or harmful substance and/or activity which requires medical surveillance, industrial hygiene monitoring, or biological monitoring. Action levels are used by OSHA and NIOSH to express a health or physical hazard.
Administrative Controls: Work procedures, written safety policies, rules, supervision, laboratory testing, schedules, and training that are implemented to reduce or remove the duration, frequency, and severity of exposure to hazardous chemicals or situations.
Backdraft: A backdraft is an explosion caused by the inrush of air from any source or cause, into a burning enclosure, where combustion has been taking place in a shortage of air. A fire needs oxygen, or an oxidizer, in order to burn. Generally, this is not a problem since the atmosphere contains sufficient oxygen to allow a fire to burn. However, if the fire is burning in a closed confined area or space, the fire will consume the available oxygen and generate large amounts of carbon monoxide along with an assortment of other fire gases. These products of incomplete combustion accumulate in the compartment and create an extremely hazardous condition. A backdraft event generally occurs when a fire is smoldering. As oxygen levels drop, visible flames start to diminish because the fire is being starved of oxygen. The confined space can become charged with superheated gases and smoke. The temperature increases, the gases expand and the pressure builds within the confined space. If oxygen is reintroduced into this confined environment, the hot vaporized fuel bursts into flames and the pressurized gases will ignite with explosive force. The explosive force at which the backdraft occurs is a result of the amount of superheated gas in the space and the amount of oxygen introduced. A backdraft is an air-driven event.
Biological Oxygen Demand (BOD): Refers to the amount of oxygen that would be consumed if all the organic materials in a 1-liter water sample were oxidized by bacteria and protozoa. It is generally a good measure of the organic contamination level of a water supply.
Boiling point: The boiling point is the temperature at which the vapor pressure of a liquid equals the external pressure surrounding the liquid. Therefore, the boiling point of a liquid depends on atmospheric pressure. The boiling point becomes lower as the external pressure is reduced.
Chemical sensitization: Sensitization to chemicals can be defined as changes in the organism, usually the immunochemical system, by exposure to a chemical such that further chemical exposure leads to recognition by the organism. Such recognition will lead to a response that is marked by a greater reaction at lower doses than what would be observed in non-sensitized individuals.
Code of Federal Regulations (CFR): A compilation of the general and permanent rules published in the Federal Register by the Executive departments and agencies of the Federal Government of the United States of America.
Combustion: A combustion reaction involves a substance combining with an oxidizer, releasing a large amount of heat (exothermic) and produces a flame. The heat produced can make combustion self-sustaining. An oxidizer is a compound that takes electrons in a reaction and can promote or initiate combustion. Oxygen and chlorine are examples of oxidizers. When oxygen is available in sufficient amounts, complete combustion occurs. If a hydrocarbon undergoes complete combustion, carbon dioxide and water vapor are produced. Combustion reactions can be oxygen starved or can involve excess oxygen. In an oxygen starved combustion reaction, a combustion reaction has a limited oxygen supply and incomplete combustion occurs. In an environment of combustion in excess air, the amount of oxygen supplied to the combustion reaction is more than is needed for complete combustion and can lead to a hotter, faster burning fire.
The products of incomplete combustion (PICs) are different than the products of pyrolysis. Some of the products of incomplete combustion (PIC) of a hydrocarbon are gasses such as carbon monoxide, methane and polyaromatics because there is not enough oxygen to completely oxidize the hydrocarbon. Carbon in the form of soot or ash can also be a a product of incomplete combustion. Typically, a mixture of unreacted carbon char and ash remains in the products of pyrolysis. Char is a porous carbon structure that remains after the bonds are broken in the pyrolytic reaction and all the hydrogen and oxygen, along with some carbon is removed as a gas. Char is often defined as the solid residue after pyrolysis. Pyrolytic carbon is a material similar to graphite which is produced by the pyrolysis of carbon containing compounds at very high temperatures.
Chronic exposure: continuous or repeated contact with a chemical and/or toxic substance over a long period of time (months or years). Over time, the exposure of some chemicals can build up in the body and/or cause long-term health effects. The toxic effect may be temporary and reversible, or may be permanent (disability or death).
Daubert Challenge: A Daubert Challenge is a particular type of motion made to the judge either before or during litigation, in an effort to exclude the introduction of unqualified expert witness testimony to the judge or jury during trial.
Dermal exposure: - Many chemicals can cause direct effects at the point of contact with the skin. Some chemicals can be absorbed into the body through the skin. Dermal exposure to hazardous agents can result in a variety of occupational diseases and disorders, including occupational skin diseases (OSD) and systemic toxicity. Chemicals can also come in contact with the eyes as dusts, mists, gases, vapors or splashed liquids. Some chemicals can be absorbed through the eyes causing harmful effects elsewhere in the body. Certain acids and other chemicals can be adsorbed through the skin and damage both the nervous and/or the lymph system.
Ember: A particle of solid material that emits radiant energy due either to its temperature or the process of oxidation on its surface.
Emergency Decontamination: The physical process of immediately reducing contamination of individuals in potentially life-threatening situations.
Emissivity: The ratio of radiation emitted by a surface to the radiation emitted by a blackbody at the same temperature.
Equivalence Ratio: For a particular fuel-oxidant mixture, the fuel oxidant ratio of a particular mixture divided by the fuel oxidant ratio of the stoichiometric mixture.
Explosion: The sudden conversion of potential energy (chemical, mechanical, or nuclear) into kinetic energy that produces and violently releases gas.
Flammable limit: Applies generally to vapors are defined as the concentration range in which a flammable substance can produce a fire or explosion when an ignition source (such as a spark or open flame) is present. The concentration is generally expressed as percent fuel by volume.
Flashover: Flashover, in contrast with backdraft, is a temperature driven event. A flashover is the rapid transition to a state of total surface involvement in a fire of combustible materials within an enclosure, the point between the growth phase and the fully developed phase of a fire. It requires that the fire’s energy is radiated back to the contents to produce a rapid rise in temperature and simultaneous ignition. A flashover occurs when there is a good supply of air that allows the accumulated unburned fuel to heat up to its auto ignition temperature.
Heartcut: The various components of a mixture have different molecular sizes, molecular weights and boiling temperatures.  Because they have different boiling temperatures, they can be separated by a process called fractionation and heart cutting.
Hazardous: As defined by OSHA Standard 1910.1200, a hazardous chemical is one which is a physical hazard or a health hazard.
Ingestion exposure: Chemicals can be ingested through the mouth (swallowed). Ingestion can result from consuming contaminated food or drinks, hand-to-mouth contact, or smoking cigarettes that have come into contact with a chemical. Ingested materials can be absorbed anywhere along the gastrointestinal tract; the major absorption site is the small intestine. Once absorbed, they eventually enter the blood stream by one of several means, and circulate throughout the body.
Inhalation exposure: For most chemicals in the form of vapors, gases, mists or fine particulates, inhalation (breathing) is the major route of entry. Contaminants that enter the respiratory system through inhalation may harm the tissues of the respiratory tract or lungs. Once inhaled into the body, chemicals can enter the bloodstream and circulate throughout the body, causing harm. Inhalation exposure can be either chronic exposure or acute exposure.
Lower explosive limit (LEL): The minimum concentration of a particular combustible gas or vapor necessary to support its combustion in air. Below this level, the mixture is too “lean” to burn.
NIOSH: The National Institute for Occupational Safety and Health, NIOSH, is part of the U.S. federal government's Centers for Disease Control and Prevention (CDC). NIOSH is the only federal Institute responsible for conducting research and making recommendations for the prevention of work-related illnesses and injuries.
OSHA: : The U.S. Occupational Safety and Health Administration, OSHA, is a federal government agency in the U.S. Department of Labor. OSHA was created by the Occupational Safety and Health (OSH) Act of 1970. The primary goals of OSHA are to save lives, prevent injuries and protect the health of America's workers.
Permissible Exposure Limit (PEL): Permissible exposure limits are set by OSHA to protect workers against the adverse effects of exposure to chemical substances. PELs are legal limits and OSHA can enforce their use and any non-compliance in the United States.
Pyrolysis: Pyrolysis is the process of heating organic material at high temperatures in the absence of oxygen or any other oxidizer. The term pyrolyze is used when subjecting a substance to pyrolysis. Pyrolysis involves the simultaneous change of chemical composition and physical phase, and is irreversible. Pyrolysis is not combustion and the compounds produced by pyrolysis are generally different than those produced by combustion or incomplete combustion. Pyrolysis has been used since ancient times for turning wood into charcoal. Charcoal is obtained by heating wood in the absence of air until its complete pyrolysis (carbonization) occurs, leaving only carbon and inorganic ash.
pH: pH stands for percentage of hydrogen and is a measure of acidity or alkalinity of water soluble substances. pH tells you whether a solution is acidic, basic or neutral. Acidic solutions are present when the values for pH are between zero and 7. A solution is basic (or alkaline) when the values for the pH are between 7 and 14. A solution is considered neutral when the pH is 7.
Percent by Volume: Defined as the volume of the solute divided by the sum of the volumes of the other components multiplied by 100%. This is typically used for mixtures of liquids.
Recommended Exposure Limits (RELs): The REL is a level that National Institute for Occupational Safety and Health (NIOSH) believes would be protective of worker safety and health over a working lifetime if used in combination with engineering and work practice controls, exposure and medical monitoring, posting and labeling of hazards, worker training and personal protective equipment. RELs are not legally enforceable.
Rubber - Factice vs. Synthetic: Factice is vulcanized vegetable oil and is typically a springy type solid of friable consistency. Vulcanizing from the manufacturers point of view is applying heat at a given temperature for a given time to cure the product so it takes up its shape. Curing involves the chemical reactions which occur in the rubber mixture to produce the crosslinking. Heating can be done in the mold using steam, or in autoclaves, ovens, typically using hot gases. One of the uses of factice is an additive as a processing aid in the manufacture of synthetic rubber. As a processing aid factice reduces tackiness of compounds during roll operations, improves processability and shortens mixing time, gives dimensional stability and smooth surface to compounds and can reduce die swell and shrinkage. As a softener and a dry plasticizer, factice can be useful to make low-hardness rubber products, absorbs liquid plasticizers and oils, prevents blooming, improves oil and solvent resistance. The two types of rubber in common use today are natural and synthetic. Natural rubber comes from the rubber tree (Hevea brasiliensis). Synthetic rubber is made by man from petrochemical feedstocks. Crude oil is the principal raw material. Polybutadiene synthetic rubber is widely employed in tire treads. Polybutadiene rubber generally consists of polybutadiene, and an elastomer (elastic polymer) built up by chemically linking multiple molecules of butadiene to form giant molecules, or polymers. 1,3-butadiene is a an industrial chemical with the formula C4H6. 1,3-Butadiene is typically a reactive colorless gas produced by the dehydrogenation of butane or butene or by the cracking of petroleum distillates. The gas is dissolved in hydrocarbon solvents and polymerized to polybutadiene. Polybutadiene rubber is sometimes notated as PBR.
Route of exposure: The way a chemical comes into contact with an organism (such as a person). Possible routes of exposure include inhalation, ingestion, and dermal contact.
Soot: The term 'soot' refers specifically to the fine, black, carbonaceous (carbon-containing) particles produced by incomplete combustion of an organic material.
Spontaneously Combustible: Materials that can undergo combustion and burn without the addition of heat or a flame.
Threshold Limit Value (TLV): Threshold Limit Values are the maximum average airborne concentration of a hazardous material to which healthy adult workers can be exposed during an 8-hour workday and 40-hour workweek—over a working lifetime—without experiencing significant adverse health effects. Threshold limit values are recommendations set by the American Conference of Governmental Industrial Hygienists.
Upper explosive limit (UEL): The maximum concentration of a gas or vapor that will burn in air. Above this level, the mixture is too “rich” to burn.
Vaporization: The process in which a substance changes from a solid or liquid into a gas.
Weight Percent or Percent by Mass: Defined as the mass of the solute divided by the total mass of the solution and multiplied by 100%.