Glossary of Terms: F

Fail safe
Description of a detector that has no unseen failure modes.
Fan rating
data describing the volumetric output of a fan at different static pressures
Federal Register
Publication of US government documents officially promulgated under the law, documents whose validity depends upon such publication. It is published on each day following a government working day. It is, in effect, the daily supplement to the Code of Federal Regulations, CFR.
Fieldbus
Digital communication standard.
Fire point
The lowest temperature at which a material can evolve vapors fast enough to support continuous combustion.
Firedamp
A mixture of methane and other Hydrocarbon gases that forms in coalmines.
First aid
Emergency measures to be taken when a person is suffering from overexposure to a hazardous material, before regular medical help can be obtained.
Fixed point system
Gas detection system using individual fixed point gas sensors and/or transmitters. Not mobile or transportable.
Flame arrestor
A structure that allows gas to diffuse through it into a detector but prevents propagation of any flame back out.
Flameproof
A name for Ex d apparatus design.
Flammable limits
Flammables have a minimum concentration below which propagation of flame does not occur on contact with a source of ignition. This is known as the lower flammable explosive limit (LEL). There is also a maximum concentration of vapor or gas in air above which propagation of flame does not occur. This is known as the upper flammable explosive limit (UEL). These units are expressed in percent of gas or vapor in air by volume.
Flammable liquid
Any liquid having a flash point below 37.8°C (100°F), except any mixture having components with flashpoints of 100°F or higher, the total of which make up 99 percent or more of the total volume of the mixture.
Flammable range
The difference between the lower and upper flammable limits, expressed in terms of percentage of vapor or gas in air by volume, and is also often referred to as the "explosive range."
Flammable
Capable of easily catching fire and of burning, usually a material that has a flash point below 37.8°C. See also combustible.
Flash point
The minimum temperature at which a liquid gives off vapor within a vessel in sufficient concentration to form an explosive or ignitable mixture with air near the surface of the liquid. Two tests are used: open cup and closed cup. The lower the flash point, the higher the risk of fire.
FM approval
Factory Mutual. USA Safety Certification.
Fog
Suspended droplets of a liquid that are produced by condensation or by the breaking up of a liquid (for example, by splashing or foaming).
Free field setting
Measurements made in an area without sound reflections, diffractions and absorptions caused by nearby objects (including the operator). Sound waves are free to spread out continuously, like ripples on a pond, without reflection. When making free field measurements with a dosimeter set up for use as a sound level meter, the microphone is typically pointed directly at the sound source.
Friction loss
pressure losses in a duct system due to friction
Fugitive emission
A gas, liquid, solid, vapor, fume, mist, fog or dust that escapes from process equipment, emission control equipment or a product.
Fume
Finely divided solid particles that are formed when a hot metal vapor cools and condenses. Fumes are usually associated with molten metals (for example, copper, lead or zinc and are often accompanied by a chemical reaction such as oxidation. Usually less than one micron in diameter.