A B C D E F G H I J K L M
N O P Q R S T U V W X Y Z
vaccine
dead or partial or modified antigen used to induce immunity to certain infectious diseases.
vacuum degasifier
a tower to which a vacuum is applied and through which water droplets descend to remove dissolved gases.
valence
is measured by the number of atoms or ions of hydrogen it takes to combine with or be replaced by an element or radical. In short, the number of positive or negative charges of an ion.
vapor
the gaseous phase of substances that are liquid or solid at atmospheric temperature and pressure -- such as steam.
vapor capture system
any combination of hoods and ventilation system that captures or contains organic vapors in order that they may be directed to an abatement or recovery device.
vapor density
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. The mw of gas/29 = vapor density. Materials lighter than air have vapor densities of less than 1.0. Materials heavier than air have vapor densities greater than 1.0. All vapors and gases mix with air, but the lighter materials tend to rise and dissipate (unless confined). Heavier vapors and gases are likely to concentrate in low or enclosed places (along or under floors; in sumps, sewers, manholes, trenches, and ditches) creating fire, explosion, or health hazards. A factor in still, enclosed air.
vapor dispersion
the movement of vapor clouds in air due to wind, gravity spreading, and mixing.
vapor plumes
flue gases that are visible because they contain water droplets.
vapor pressure
the pressure exerted by a saturated vapor above its own liquid in a closed container. Vapor pressures reported on MSDSs are in millimeters of mercury (mm Hg) at 68 degrees F (20 degrees C), unless stated otherwise. Three facts are important to remember: (1) vapor pressure of a substance at 100 degrees F (38 degrees C) is always higher than the vapor pressure of the substance at 68 degrees F (20 degrees C). (2) Vapor pressures reported on MSDSs in mm Hg are usually very low pressures; 760 mm Hg is equivalent to 14.7 pounds per square inch. (3) the lower the boiling point of a substance, the higher its vapor pressure. Vapor pressures are useful (with evaporation rates) in learning how quickly a material becomes airborne within the workplace and thus how quickly a worker is exposed to it.
vaporization
the change of a substance from a liquid to a gas.
variance
Government permission for a delay or exception in the application of a given law, ordinance, or regulation.
VE
Visual Emissions.
vector
a carrier, usually an insect, which is capable of transmitting disease from one organism to another.
ventilation/suction
the act of admitting fresh air into a space in order to replace stale or contaminated air; achieved by blowing air into the space. Similarly, suction represents the admission of fresh air into an interior space by lowering the pressure outside of the space, thereby drawing the contaminated air outward.
venturi
a device for measuring fluid flow, including a short converging cone succeeded on the same axis by a long diverging cone. This device is also used in gas scrubbing.
VEO
Visible Emissions Observation.
vertigo
a feeling of revolving in space; dizziness, giddiness.
VES
Vertical Electric Sounding.
vessel
as defined by section 101(28) of CERCLA, means every description of watercraft or other artificial contrivance used, or capable of being used, as a means of transportation on water; and, as defined by section 311(a)(3) of the CWA, means every description of watercraft or other artificial contrivance used, or capable of being used, as a means of transportation on water other than a public vessel.
VHS
Vertical and Horizontal Spread Model.
VHT
Vehicle-Hours of Travel.
vinyl chloride
a chemical compound used in producing some plastics. Excessive exposure to this substance may cause cancer.
virus
the smallest form of microorganisms capable of causing disease.
viscosity
Measurement of the flow properties of a material expressed as its resistance to flow. Unit of measurement and temperature are included.
VMT
Vehicle Miles Traveled.
VOC
volatile organic compound; family of highly evaporative organic materials used in a variety of industrial applications, such as paints and solvents; VOC emissions are a component in the formation of ground-level ozone (smog).
void volume
the space between particles of ion exchange resins in a settled bed; also called interstitial volume.
volatile
any substance that evaporates at a low temperature.
volatility
measure of a material's tendency to vaporize or evaporate at ambient routine conditions.
volatile organic compound (VOC)
any organic compound which participates in atmospheric photochemical reactions except for those designated by the EPA Administrator as having negligible photochemical reactivity.
volatile substances
material that is readily vaporizable at a relatively low temperature.
volatile synthetic organic chemicals
chemicals that tend to volatilize or evaporate from water.
volume solids
solids content based on volume.
volunteer
means any individual accepted to perform services by the lead agency which has authority to accept volunteer services (examples: See 16 U.S.C. 742f(c)). A volunteer is subject to the provisions of the authorizing statute and the NCP.The Act, CERCLA, or Superfund means the Comprehensive Environmental Response, Compensation, and Liability Act of 1980 (Pub. L. 96-510);
VOS
Vehicle Operating Survey.
VP
See Vapor Pressure
VSI
Visual Site Inspection.
VSS
Volatile Suspended Solids.
vulnerability analysis
assessment of elements in the community that are susceptible to damage should a release of hazardous materials occur.
vulnerable zone
an area over which the airborne concentration of a chemical involved in an accidental release could reach the level of concern.
