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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. |
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Valley |
The "V"
shaped area of a roof where two sloping roofs meet. Water drains off the
roof at the valleys. |
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Valley flashing
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Sheet metal
that lays in the "V" area of a roof valley. |
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Valley jacks |
Rafters that
run from a ridgeboard to a valley rafter. |
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Valley rafter |
Diagonal
rafter at the intersection of two intersecting sloping roofs. Valley The
internal angle formed by two slopes of a roof. |
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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. |
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Vapor |
The gas
phase of a substance; particularly of those that are normally liquids or
solids at ordinary temperatures. (See also Gas.) |
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Vapor agent |
A gaseous form of a chemical agent. If
heavier than air, the cloud will be close to the ground, if lighter than
air; the cloud will rise and disperse more quickly. |
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Vapor barrier
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A building product installed on exterior
walls and ceilings under the drywall and on the warm side of the insulation.
It is used to retard the movement of water vapor into walls and prevent
condensation within them. Normally, polyethylene plastic sheeting is used.
Watertight material used to prevent the passage of moisture or water vapor
into and through walls and under concrete slabs. |
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Vapor density |
The weight of a given volume of pure vapor
compared to the weight of an equal volume of dry air at the same temperature
and pressure. |
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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. |
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Vapor pressure [VP] |
The pressure, usually expressed in
millimeters of mercury, characteristic at any given temperature of a vapor
in equilibrium with its liquid or solid form; the pressure exerted by a
vapor. Vapor pressures reported on MSDS's are in millimeters of mercury at
68 degrees Fahrenheit (20 degrees Celsius), unless stated otherwise. If a
vapor is kept in confinement over its liquid so that the vapor can
accumulate above the liquid, the temperature being held constant, the vapor
pressure approaches a fixed limit referred lo as the saturated vapor
pressure, which is dependent only on the temperature and the liquid, |
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Vaporization |
The passing from a liquid state to a gaseous
state. Rate of vaporization is dependent upon the substance involved, heat,
and pressure. |
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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. |
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Vaulted ceiling
|
A ceiling that slopes up to a peak. |
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Vector |
An arrow used in a fire scene drawing to show
the direction of heat, smoke, or flame flow. |
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Vegetation |
Type A standardized description of the
vegetation in which a fire is burning. The type is based on the dominant
plant species and the age of the forest and indicates how moist a site may
be and how much fuel is likely to be present. |
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Velocity of water |
The speed of water; 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. |
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Veneer |
Extremely thin sheets of wood. Also a thin
slice of wood or brick or stone covering a framed wall. |
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Veneer construction
|
Type of wall construction in which frame or
masonry walls are faced with other exterior surfacing materials.
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Vent |
a) A pipe or duct which allows the flow of
air and gasses to the outside. b) Also, another word for the moving glass
part of a window sash, i.e. window vent. c) An opening for the passage of,
or dissipation of, fluids, such as gases, fumes, smoke, and the like. d) An
intentional opening for the escape of gasses to the outside. This is a
function carried out by truck company operations at a structure fire. |
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Vent pipe |
An opening
leading out of or into some enclosed space, especially made for the passage
of air or liquid; an escape outlet. |
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Vent stack |
Vertical soil pipe connected to the drainage
system to allow ventilation and pressure equalization. |
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Ventilation |
Ventilation is the systematic
removal of smoke from a building. The operation of opening windows, doors
and cutting holes in a building in the highest points of the structure and
removing windows and doors. Heat and fire gases are replaced with cooler
fresh air. This action facilitates an improved working environment for
firefighters to permit advancement of hose lines into effective positions
for fire extinguishment, as well as reducing smoke and fire damage to the
contents of the building, and to prevent explosive concentrations. Active
Ventilation is usually accomplished with one of three methods: positive and
negative pressure or mechanical ventilation. Positive pressure ventilation
increases the atmospheric pressure in the building until it is greater than
the pressure outside the building. With negative pressure ventilation, the
pressure inside the building is reduced until its less than the pressure
outside the building. Passive Ventilation does not use any mechanical means
to move air and relies on convection of air currents. Mechanical ventilation
is done with a flowing fog nozzle put in the opening of an exterior window,
door or hole in the roof. This uses a venturi principle effect to create a
negative pressure inside the structure. |
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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. |
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Vergeboard |
The
board that serves as the eaves finish on the gable end of a building.
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Vestibule |
A small lobby or entrance room.
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VHF |
Very high frequencies in the range from 54
MHz to 216 MHz, NTSC TV channels 2 through 13. |
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Violent reaction |
The action whereby a chemical changes its
composition near or exceeding the speed of sound, often releasing heat and
gases. |
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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. |
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Viscosity |
The degree to which a fluid resists flow. The
measurement of the flow properties of a material expressed as its resistance
to flow. |
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Visqueen |
A 4 mil or 6 mil plastic sheeting. |
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Volatile |
Material that has a tendency to vaporize and
evaporate rapidly. |
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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. |
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Voltage |
Electric pressure; the force which causes
current to flow through an electrical conductor. Most homes are wired with
110 and 220 volt lines. The 110 volt power is used for lighting and most of
the other circuits. The 220 volt power is usually used for the kitchen
range, hot water heater and dryer. |
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Voltage Regulation |
For a transformer, the change in secondary
voltage which occurs when the load is reduced from rated value to zero, with
the values of all other quantities remaining unchanged. The regulation may
be expressed in percent (or per unit) on the basis of the rated secondary
voltage at full load. |
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Volt-Amperes (VA)
|
The current flowing in a circuit multiplied
by the voltage of that circuit. An expression of the output rating of a
transformer. |
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Voltmeter |
A
device used for measuring the voltage existing on an electrical system. |
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Volume ceiling |
Any ceiling higher than the standard 8 feet.
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Volume operation |
See Parallel Operation. |
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Volunteer |
For purposes of the NIMS, a
volunteer is any individual accepted to perform services by the lead agency,
which has authority to accept volunteer services, when the individual
performs services without promise, expectation, or receipt of compensation
for services performed. |
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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. |
