Glossary of SCUBA Diving - F

F

faceplate

Viewport of a full face mask or helmet

farmer john

Wet suit that covers the torso and legs only; it resembles a bib overall or salopettes.

fatigue cracking

Cracking in a material resulting from multiple stress cycles below the ultimate or yield strength. Usually refers to large number of cycles.

feather breathing

Technique for emergency breathing from a free-flowing demabd valve where the diver manually controls air flow by opening and closing the cylinder valve.

four-wire system

Voice communications using separate wire pairs for each direction.

filtration

Process for removing impurities from a fluid. Particulates are commonly removed by passing the fluid through porous material with pore size small enough to trap the particles (e.g. micron filters). Liquids and gases are commonly absorbed or adsorbed by the surface of the filter medium (Activated carbon, Molecular sieve, Silica gel), or may be chemically combined with the medium (Sodalime) or catalytically converted (Hopcalite) into a less objectionable substance.

fogging

Condensation of water vapour on the inside surface of a mask or helmet faceplate, reducing visibility.

frame

Tramsportable assemblies of gas cylinders connected by a manifold and securely mounted to a structural framework.

free-diving

Underwater diving that does not involve the use of external breathing apparatus, but relies on a diver's ability to hold his or her breath until resurfacing. also Breath-hold diving, and apnea (q.v.).

free flow

1. Constant flow rate air supply

2. Malfunction of a demand regulator where the valve sticks in the open position, allowing a constant rate of flow.

free flow helmet

A helmet where the breathing air supply is supplied at an approximately constant rate regardless of the diver's instantaneous breathing rate.

free gas volume

Equivalent volume of compressed gas if expanded to atmospheric pressure at constant temperature.

Frenzel maneuver

Technique for equalising the middle ear by pinching the nose closed and moving the back of the tongue upwards.

frogman

A scuba diver, particularly a military diver on an undercover mission.

fsw

feet sea water: Unit of pressure equal to 1/33 atm. Not a linear measure of depth.

full duplex

Voice communication system where both users can transmit and receive at the same time.

full-face mask

Diving mask covering the eyes, nose and mouth, and provides the diver with breathing gas