Glossary of SCUBA Diving - M

M

manufacturing standard

also manufacturing code

Set of design and manufacturing rules intended to produce uniform and safe products by several manufacturers in an industry.

Marsh Marine connector

One of the popular underwater plug connector systems for diver communications cables..

MCCR

Manual Closed Circuit Rebreather: A closed cirduit rebreather which relies on the diver to control the gas mixture in the loop.

medical lock

Small lock on a decompression chamber used for transfer of medical equipment and other supplies into and out of the chamber while the chamber remains under pressure.

mixed gas

Breathing gas for diving other than air, but usually implies a helium based mixture.

MOD

Maximum operating depth: Limiting depth for safety based on partial pressure of oxygen of a breathing gas mixture.

MODU

Mobile offshore drilling unit - a generic term for several classes of self-contained floatable or floating drilling rigs such as drilling vessels, semisubmersibles, submersibles, jack-ups, and similar facilities that can be moved without substantial effort. These facilities may have self-propulsion equipment on board and may require dynamic positioning equipment or mooring systems to maintain their position.

monofin

A type of swimfin typically used in finswimming and free-diving. It consists of a single surface attached to footpockets for both of the diver's feet.

molecular sieve

Material containing tiny pores of a precise and uniform size that is used as an adsorbent for gases and liquids. Molecules small enough to pass through the pores are absorbed while larger molecules are not. It is different from a common filter in that it operates on a molecular level.

monkey diving

Further information: Sidemount#Terminology

The use of sidemount configuration and procedures with a single cylinder.

moonpool

An opening in the floor or base of the hull, platform, or chamber giving access to the water below.

msw

metres sea water: Unit of pressure equal to 1/10 bar. Not a linear measure of depth.

multiple stage compressor

Further information: Gas compressor#Reciprocating compressors

Compressor in which gases are compressed more than once, often with cooling between stages. Used to improve efficiency and reduce temperatures.

mushroom valve

A rubber non-return valve flap which is circular or oval, with a stem in the middle to attach it to the holder in the centre of the grating over the orifice.

M-values

Further information: Decompression (diving)#M-values

At a given ambient pressure, the M-value is the maximum theoretical value of absolute inert gas pressure that a tissue compartment can take without presenting symptoms of decompression sickness.