Ted Jarboe, M.S., C.E.M.
Montgomery County, MD Fire and Rescue Service
Number: 6
Definitions: Chemical Agent-Related
This list is provided to help first responders learn new terms or to refresh terms related to chemical agents. Readers are encouraged to add other terms to this list. Moreover, I suggest that first responders include these definitions in a notebook (using document protectors) as a convenient reference. Building a good vocabulary facilitates understanding by first responders, promotes information sharing and builds confidence.
ABSORPTION: The process of an agent being taken in by a surface (clothing, fabrics, wood, etc.), much like a sponge and water.
ACTUAL BREAKTHROUGH TIME: The average time elapsed between initial contact of the chemical with the outside surface of the fabric and the detection time.
ACETYLCHOLINE: A chemical compound formed from an acid and an alcohol, which causes muscles to contract (neurotransmitter). It is found in various organs and tissues of the body. It is rapidly broken down by an enzyme, cholinesterase.
ACETYLCHOLINESTERASE: An enzyme (a protein produced in the cells) which stops (inactivates) the action of acetylcholine by separating the acetylcholine into its components of acetic and choline. This occurs as soon as acetylcholine has produced a muscle contraction. Nerve agents combine with acetylcholinesterase to prevent it from performing its inactivation of acetylcholine.
ADSORPTION: The process of an agent sticking to or becoming chemically attached to a surface.
AEROSOLS: A suspension or dispersion of small particles (solids or liquids) in a gaseous medium.
AGENT DOSAGE: The concentration of a toxic vapor in the air multiplied by the time that the concentration is present or the time that an individual is exposed (mg-min/m3).
ANTICHOLINERGIC: An agent or chemical that blocks or impedes the action of acetylcholine, such as the (also cholinolytic) antidote atropine.
ANTICHOLINESTERASE: A substance that blocks the action of cholinesterase (acetylcholinesterase) such as nerve agents.
ANTIDOTE: A substance that neutralizes toxic agents or their effects.
ARSENICAL: Pertaining to or containing arsenic; a reference to the vesicant lewisite.
ATROPINE: An anticholinergic used as an antidote for nerve agents to counteract excessive amounts of acetylcholine. It also has other medicinal uses.
BLISTER AGENT: A chemical warfare agent which produces local irritation and damage to the skin (vesicant) and mucous membranes, pain and injury to the eyes, reddening and blistering of the skin, and when inhaled, damage to the respiratory tract.
BLOOD AGENT: A chemical warfare agent that is inhaled and absorbed into the blood. The blood (cyanogen) carries the agent to all body tissues where it interferes with the tissue oxygenation process.
CAS REGISTRY NUMBER: A number assigned to a material by the Chemical Abstract Service to provide a single unique identifier.
CEILING EXPOSURE VALUE: The maximum airborne concentration of a biological or chemical agent to which a worker may be exposed at any time.
CHEMICAL AGENT: Any chemical substance which is intended for use in military operations to kill, seriously injure, or incapacitate humans because of its physiological effects.
CHEMICAL AGENT SYMBOL: A code usually consisting of two letters that are used as a designation to identify chemical agents, e.g., GB for the chemical agent sarin.
CHEMICAL CONTAMINATION: The presence of a chemical agent on a person, object, or area.
CHEMICAL WARFARE AGENT: A chemical substance, which, because of its physiological, psychological, or pharmacological effects, is intended for use in military operations to kill, seriously injure, or incapacitate humans (or animals) through its toxicological effects. Excluded are riot control agents, chemical herbicides, and smoke and flame agents.
CHOKING AGENTS: These agents exert their effects solely on the lungs and result in the irritation of the alveoli of the lungs. Agents cause the alveoli to constantly secrete watery fluid into the air sacs, which is called pulmonary edema. When a lethal amount of a choking agent is received, the air sacs become so flooded that the air cannot enter and the victim dies of anoxia (oxygen deficiency); also known as a dry land drowning.
CLASSIFICATION OF CHEMICAL AGENTS: Chemical agents are classified according to their physical state, use and physical action.
CONCENTRATION: The amount of a chemical agent present in a unit volume of air, usually expressed in milligrams per cubic meter (mg/m3).
CONCENTRATION TIME: The amount of a chemical agent present in a unit volume of air multiplied by the time an individual is exposed to that concentration.
CONJUNCTIVITIS: Redness in the eyes.
CONSEQUENCE MANAGEMENT: Measures to alleviate the damage, loss, hardship, or suffering caused by emergencies. It includes measures to restore essential government service, protect public health and safety, and provide emergency relief to affected governments, businesses, and individuals.
CONTAINMENT: The attempt to prevent the spreading of contamination by holding it in, enclosing, encapsulating, or by controlling it.
CRISIS MANAGEMENT: Measures to resolve the hostile situation, investigate, and prepare a criminal case for persecution under Federal law.
CRYOGENICS: Materials, which exist at extremely low temperatures, such as nitrogen.
CUMULATIVE: Additional exposure rather than repeated exposure. For example, a one-hour exposure of HD followed within a few hours by another exposure of one hour, had the same effect as a single exposure lasting for two hours.
DECONTAMINATION: The process of neutralizing or removing contaminants that have accumulated on personnel, clothing, and equipment.
DESORPTION: The reverse process of absorption. The agent will be "removed" from the surface (off gassing or out gassing).
DILUTION FACTOR: Dilution of contaminated air with uncontaminated air in a general area, room or building for the purposes of health hazard or nuisance control, and/or for heating and cooling.
DOSAGE: The concentration of a chemical agent in the atmosphere (C) multiplied by the time (t) the concentration remains, expressed as mg-min/m. The dosage (Ct) received by a person depends upon how long he is exposed to the concentration. That is, the respiratory dosage in mg-min//m3 is equal to the time in minutes as individual is unmasked in an agent cloud multiplied by the concentration of the cloud.
DOWNWIND DISTANCE: The distance a toxic agent vapor cloud will travel from its point of origin, with the wind.
EVAPORATION RATE: The rate at which a liquid changes to vapor at normal room temperature.
HYDRATION: The combining of a substance with water.
HYDROLYSIS: The reaction of any chemical substance with water by which decomposition of the substance occurs and one or more new substances are produced.
HYDROLYSIS PRODUCTS: Those new substances formed when a chemical agent or compound reacts with or is decomposed by water.
IMMEDIATELY DANGEROUS TO LIFE AND HEALTH (IDLH): An atmospheric concentration of any toxic, corrosive or asphyxiant substance that poses an immediate threat to life or would cause irreversible or delayed adverse health effects or would interfere with an individual's ability to escape from a dangerous atmosphere.
IMPERMEABLE PROTECTIVE CLOTHING: Protective clothing that does not allow penetration of gas and liquid, or evaporation of perspiration. Designed primarily for protection of personnel engaged in extremely hazardous decontamination or other special operations involving life threatening danger from liquid or high concentrations of vapor from chemical warfare agents.
IMPROVISED EXPLOSIVE DEVICES (IED): Devices placed or fabricated improvisational incorporating destructive, lethal, noxious, pyrotechnic, or incendiary chemicals, designed to destroy, disfigure, distract, or harass. They may incorporate military stores, but are normally devised from nonmilitary or commercial components.
INCAPACITATING AGENT: An agent that produces physiological or mental effects, or both, that may persist for hours or days after exposure, rendering an individual incapable of performing his or her assigned duties.
INITIAL DOWNWIND VAPOR HAZARD AREA: Areas initially establish to evacuate all unprotected personnel and to prevent other unprotected personnel from entering and thus encountering agent vapors or any other type of contamination.
LATENT PERIOD: Specifically, in the case of mustard, the period between exposure and onset of signs and symptoms; otherwise, an incubation period.
LETHAL CHEMICAL AGENT: An agent that may be used effectively in a field concentration to produce death.
LIQUID DOSAGE: The weight of a liquid agent received by a person on his skin is usually expressed as dosage in milligrams of contaminant per kilogram of body weight (mg/kg). This is equivalent to parts per million (ppm).
MEDIAN INCAPACITATING DOSAGE (ICt50): The volume of a chemical agent vapor or aerosol inhaled that is sufficient to disable 50% of exposed, unprotected people (expressed as mg--min/m3).
MEDIAN LETHAL DOSAGE (LCt50): The dosage of a chemical agent vapor or aerosol inhaled that is lethal to 50% of exposed, unprotected people (expressed as mg-min/m3).
MEDIAN LETHAL DOSAGE (LD50): The amount of liquid chemical agent expected to kill 50 percent of a group of exposed, unprotected individuals.
MEDIAN INCAPACITATING DOSAGE (ID50): The volume of a liquid chemical agent expected to incapacitate 50% of a group of exposed, unprotected individuals.
METHOD OF DISSEMINATION: The way a chemical agent or compound is finally released into the atmosphere.
MIOSIS: A condition where the pupil of the eye becomes contracted (pinpointed) which impairs night-vision.
NERVE AGENTS: Agents that effect the transmission of nerve impulses by reacting with the enzyme cholinesterase, permitting an accumulation of acetylcholine and continuous muscle stimulation. The muscles tire due to over-stimulation and begin to contract.
NON-PERSISTENT AGENT: An agent that remains in the target area(s) for a relatively short period of time. The hazard, predominantly vapor, will exist for minutes or, in exceptional cases, hours after dissemination of the agent. As a general rule, a non-persistent agent duration will be less than 12 hours.
ORGANOPHOSPHATE: A compound with a specific phosphate group which inhibits acetylcholinesterase. Organophosphates are used in chemical warfare and as an insecticide.
PERMEABLE PROTECTIVE CLOTHING: Protective clothing made of materials that absorb or neutralize vapors, aerosols, and small liquid droplets of chemical warfare agents, but allow a degree of evaporation of perspiration.
PERMEATION: The process by which a chemical moves through a protective clothing.
PERMEATION RATE: The rate at which the challenge chemical permeates the fabric.
PERSISTENCY: An expression of the duration of effectiveness of a chemical agent, dependent on physical and chemical properties of the agent, weather, method of dissemination, and terrain conditions.
PERSISTENT AGENT: An agent that remains in the target area for longer periods of time. Hazards from both vapor and liquid may exist for hours, days, or in exceptional cases, weeks or months after dissemination of the agent. As a general rule, persistent agents duration will be greater than 12 hours.
PHYSIOLOGICAL ACTION: Most toxic chemical agents are used for their toxic effects that is to produce a harmful physiological reaction when applied to the human body externally, or when breathed, or taken internally. This reaction of chemical agents, within the body or on the body, is the physiological action.
RATE OF ACTION: The rate at which the body reacts to or is affected by a chemical substance or material.
RATE OF DETOXIFICATION: The rate at which the body can counteract the effects of a poisonous chemical substance.
RATE OF HYDROLYSIS: The rate at which the various chemical agents or compounds are decomposed by water.
RESPIRATORY DOSAGE: This is equal to the time in minutes an individual is unmasked in an agent cloud multiplied by the concentration of the cloud.
RHINORRHEA: A runny nose.
SHORT TERM EXPOSURE LIMIT (STEL): A 15-minute time-weighted average exposure which should not be exceeded at any time during a work day even if the 8-hour time-weighted average (TWA) is within the threshold limit value (TLV). Exposures at the STEL should not be repeated more than four times a day and there should be at least 60 minutes between successive exposures at the STEL.
SKIN DOSAGE: This is equal to the time of exposure in minutes of an individual's unprotected skin multiplied by the concentration of the agent cloud.
SOLUBILITY: The ability of a material to dissolve in water or another liquid.
SOLVENT: A material that is capable of dissolving another chemical.
SPECIFIC GRAVITY: The weight of a liquid compared to the weight of an equal volume of water.
TEAR AGENTS: Compounds that cause a large flow of tears and intense eye pain and irritation of the skin.
TIME-WEIGHTED AVERAGE (TWA): The average concentration for a normal 8-hour workday and a 40-hour workweek, to which nearly all workers may be repeatedly exposed without adverse effect.
TOXICITY: The property a material possesses which enables it to injure the physiological mechanism of an organism by chemical means, with the maximum effect being incapacitation or death.
UPWIND: In or toward the direction from which the wind blows. To be upwind of an item, the wind would be blowing from your position to the item.
URTICANT: A chemical agent that produces irritation at the point of contact, resembling a stinging sensation, such as a bee sting. For example, the initial physiological effects of phosgene oxime (CX) upon contact with a person's skin.
URTICARIA: A skin condition characterized by intensely itching red, raised patches.
VAPOR DENSITY: A comparison of any gas or vapor to the weight of an equal amount of air.
VAPOR PRESSURE: The motion of the escaping molecules of a liquid in an enclosed container is confined to the vapor space above the surface of the liquid. As an increasing number of molecules strike and reenter the liquid, a point of equilibrium is eventually reached when the rate of escape of molecules from the liquid equals the rate of return to the liquid. The pressure exerted by the escaping vapor at the point of equilibrium is called vapor pressure.
VESICANT AGENT: An agent that acts on the eyes and lungs and blisters the skin.
VESICLES: Blisters on the skin.
VISCOSITY: The degree to which a fluid resists flow.
VOLATILITY: With chemical agents, it refers to their ability to change from a liquid state into a gaseous state. (The ability of a material to evaporate.)
VOMITING AGENT: Compounds that cause irritation of the upper respiratory tract and involuntary vomiting.
WHEAL: An acute swelling of the skin. This condition is common to a bee sting.
*Most of these definitions were taken from a 1996 booklet prepared by Jef L. Harris, Geomet Technologies, Inc., titled Chemical Warfare Agents or Chemical Surety Material Properties. Other definitions were from other resources such as the course book provided by the U.S. Army Chemical School, titled Chemical/biological Countermeasures course.
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About the Author - Ted Jarboe, M.S., C.E.M.
Ted Jarboe is a Deputy Chief with the Montgomery County (MD) Fire and Rescue
Service. He is the County’s Fire Marshal and also heads the Bureau of Life
Safety Services.
Jarboe has been a member of many local, state and federal programs involved
with studying and training for weapons weapons of mass destruction (WMD)
incidents. He has tested and trained with a wide range of equipment used in
such incidents.
In January 2000, he designed and created a website titled WMD First
Responders www.wmdfirstresponders.com.
Ted Jarboe has 38 years of career service.
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