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Glossary V-SERIES NERVE AGENTS Chemical agents of the moderate to high toxicity developed in the 1950's. They are generally persistent. VACCINE A preparation of killed or weakened microorganism products used to artificially induce immunity against a disease. VACUUM A condition in which normal atmospheric pressure is reduced in a pump chamber during priming operations; space completely devoid of matter or pressure. In fire service terms, it is more commonly used to describe a pressure that is somewhat less than atmospheric pressure; a vacuum is needed to facilitate drafting of water from a static source. VALVE Mechanical device with a passageway that controls the flow of a liquid or gas. Movable parts that control the flow of a liquid or gas through a pipe or out of an enclosed space by opening or closing the passage. VAPOR An air dispersion of molecules of a substance that is normally a liquid or solid at standard temperature and pressure. VAPOR AGENT A gaseous form of a chemical agent. If heavier than air, the cloud will be dose to the ground, if lighter than air; the cloud will rise and disperse more quickly. VAPOR DENSITY The relative density or weight of a vapor, compared to air. A comparison of any gas or vapor to the weight of an equal amount of air. The weight of a vapor or gas compared to the weight of an equal volume of air; an expression of the density of the vapor or gas calculated as the ratio of the molecular weight of the gas to the average molecular weight of air, which is 29. Materials lighter than air have vapor densities of less than 1.0. VAPOR DISPERSION Use of water spray to disperse or move vapors away from certain areas or materials. Note that reducing the concentration of a material through the use of a water spray may bring the material into its flammable range. VAPOR LINE The system of piping in a tank container used to collect or introduce a vapor into the system, as opposed to a liquid line. VAPOR PRESSURE The pressure exerted by a saturated vapor above its own liquid in a closed container. Vapor pressures reported on MSDS’s are in millimeters of mercury at 68•F (20•C), unless stated otherwise. VAPOR RECOVERY A system, which removes the vapors coming off liquids and draws them back into the feed tank (as seen at a gasoline pump). VAPOR VALVE Valves used to remove vapor from the tank or to the pressurized tank. On the pressure cars, it is called the vapor valve, but on nonpressure tank cars, it is called the air inlet or air valve. VAPORIZATION The passing from a liquid state to a gaseous state. Rate of vaporization is dependent upon the substance involved, heat, and pressure. VAPORIZING LIQUID AGENT Any liquid that evaporates at elevated temperatures; one of several vaporizing liquid agents used on Class B or Class C fires; an extinguishing agent that produces vapors heavier than air; a smothering vapor agent. See Extinguishing Agents. VAPORS The gaseous form of a substance, which is solid or liquid under ordinary conditions. VELOCITY Speed; the rate of motion in a given direction. It is measured in feet per second (meters per second), miles per hour (kilometers per hour), and so on. VELOCITY OF WATER The speed of water. VENT AND BURN The use of shaped explosive charges to vent the high pressure at the top of a pressurized container and then, with additional explosive charges, release and burn the remaining liquid in the container in a controlled fashion. This is a highly sophisticated technique that is only used under very controlled conditions. VENT PIPE An opening leading out of or into some enclosed space, especially made for the passage of air or liquid; an escape outlet. VENTILATION A technique of permitting or forcing the heated smoke and gases of a fire to escape to the atmosphere and replacing with cooler fresh air. VENTING The controlled release of a liquid or compressed gas to reduce the pressure and diminish the probability of an explosion. The method of venting will depend upon the nature of the hazmat. VENTURI PRINCIPLE When a fluid is forced under pressure through a restricted orifice, there is a decrease in the pressure exerted against the side of the constriction and a corresponding increase in the velocity of the fluid. Because the surrounding air is under greater pressure, it rushes into the area of lower pressure. VESICANT AGENT An agent that acts on the eyes and lungs and blisters the skin. VESICLES Blisters on the skin. VESSEL Any watercraft used or capable of being used as a means of transportation by water. Also, a container such as a drum. VHF Very high frequencies in the range from 54 MHz to 216 MHz, NTSC TV channels 2 through 13. VIDEO MONITOR A television that accepts un-modulated baseband signals (audio and video) to reproduce a broadcast. VIOLENT REACTION The action whereby a chemical changes its composition near or exceeding the speed of sound, often releasing heat and gases. VIOLENT RUPTURE Associated with chemical reactions having a release rate of less than one second (i.e., deflagration). There is no time to react in this scenario. This behavior is commonly associated with runaway cracking and overpressure of closed containers. VIRAL PENETRATION The penetration of a material by a virus. VIRAL RESISTANT Referring to materials that impede viral penetration under specified laboratory test conditions and detection methods. VIRUS An infectious microorganism that exists as a particle rather than as a complete cell. Particle sizes range from 200 to 400 nanometers (one-billionth of a meter). Viruses are not capable of reproducing outside of a host cell; a minute infectious agent, which lacks independent metabolism and is only able to replicate within a living host cell. VISCOSITY The degree to which a fluid resists flow. The measurement of the flow properties of a material expressed as its resistance to flow. VISIBILITY When evaluating garment colors for safety applications, visibility refers to the color of a garment fabric in brightly lit and dimly lit situations, as well as the difference in color between the fabric and the background; refers to the ability to see through a faceplate in an encapsulated suit. VITON Trademark of a fluoroelastomer copolymer Used in chemical protective clothing and container materials such as gaskets and linings. VOLATILE Material that has a tendency to vaporize and evaporate rapidly. VOLATILITY A measure of how readily a substance will vaporize. 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. VOLTMETER A device used for measuring the voltage existing on an electrical system. VOLUME OPERATION See Parallel Operation. VOLUTE Spiral, divergent chamber of a centrifugal pump in which the velocity energy given to water by the impeller blades is converted in to pressure. VOMITING AGENTS Produce nausea and vomiting effects, can also cause coughing, sneezing, pain in the nose and throat, nasal discharge, and tears. |
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