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Reference
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Glossary
A
- Absolute - in the case of pressure calculations,
add one for absolute.
- Absorbent - Material that removes CO2, commonly a
mixture of calcium and sodium hydroxide.
- AC - Alternating current.
- AODC - See IMCA.
- ATM - Atmospheres, unit of pressure measurement
equal to the pressure the atmosphere exerts at sea level
i.e. 14.7psi or 760mm of mercury or 33fsw.
- ATA - measurement of atmospheres absolute.
- Axial Flow Scrubber -
Direction of flow across the absorbant bed will be
either end to end or side to side in this type of
scrubber
B
- BAR - unit of pressure measurement equating to
approximately 1 atmosphere (0.9869), ten metres of
sea-water.
- BARA - Bar Absolute
- BARG - Bar Gauge
- BIBS - Built In Breathing System
- BOB - Bailout Bottle
- Breathing Bag - See Counter
Lung
- Breathing loop - The breathing loop in a
rebreather is composed of all the internal areas within
which the diver's breathing gases flow. This includes,
the counter-lung, scrubber, breathing hoses and the
divers lungs.
- Breathing Resistance - The frictional component
imposed on the breathing cycle by the equipment itself
- BS - British Standard
- By-pass Valve - Manual means of adding oxygen,
Nitrox or dilutent (also an MOV (Manual Override Valve))
C
- CNS - Central Nervous System
- CO - Carbon Monoxide
- CO2 - Carbon Dioxide
- Calibration - To check or correct units of
measurement. This can be done using a specific known
value. For calibrating gas analyzers this can be done
with air or cal/span gas depending on the analyzer.
- Canister - Container that
holds the absorbent (See Scrubber)
- Carbon Dioxide - waste product from metabolic
consumption.
- Caustic Cocktail - Absorbant and water.
- CCR - Closed Circuit Rebreather
- Channeling - Term for a carbon dioxide rich
pathway through the absorbent bed. If absorbent loosens
it will allow a more direct route with minimal chemical
action resulting in increased levels of 002 in the
inhalation bag
- Closed Circuit - No gas loss other than during
ascent (due to expansion). Mechanically or
electronically metered oxygen addition to make up what
is used by the diver
- CNS Toxicity - Central Nervous System Toxicity.
- CNS Oxygen Toxicity - Oxygen toxicity is a
combination of oxygen pressure and time.
- Counter-lung - (abbr.-
CL) - The counter lung is the sealed flexible bag which
inflates as the diver exhales and deflates as the diver
inhales. It acts as a storage area for the diver's
breathing gases. The positioning of this bag within the
breathing loop can greatly affect the breathing effort.
D
- DC - Direct Current
- DCS - Decompression Sickness
- DDC - Deck Decompression Chamber
- Deep Diving - Diving in excess of 180 MSW (in
Norway)
- DESIGN - Diving Equipment Systems Inspection
Guidance Note
- Dilutent - This is the gas used in a closed
circuit rebreather to make up volume in the breathing
loop as the diver proceeds to deeper depths and the
gases in the breathing loop are compressed. Depending on
the rebreather, and the type of diving, the gas used for
diluent could be air, Nitrox, trimix or even heliox.
- Dirty Gas - Exhaled breath that is high in C02
and moisture content
- DMAC - Diving Medical Advisory Committee
- DP - Dynamically Positioned/Dynamic Positioning
- DPV - Dynamically Positioned Vessel
- DPV - Diver Propulsion Vehicle (Scooter)
- DPVOA - DP Vessel Operators Association
- Drowned Lime - Lime with water covering the
active surface. This can happen by flooding the canister
or, as result of a poor rebreather-design, by
condensation water.
- DSV - Diving Support Vessel
- Dyspnea - Shortness of breath through elevated
levels of retained C02
E
- EAD - Equivalent Air Depth (used on Nitrox-Dives
to look into a Decompression-Table that was printed for
Air-Dives.)
- EAN(x) - [Enriched Air Nitrox (percent of
Oxygen)] - Compressed air used to make Nitrox mixes by
adding oxygen to raise the oxygen percentage of the mix,
hence enriched air. Typical percentage figures 32%, 40%,
50% O2 etc.
- ECT - Emergency Control Team
- ECU - Environmental Control Unit
- EL - Entrance Lock
- END - Equivalent Nitrogen Depth (compares the
narcotic potential of a gas with that of air).
- ET - Electrical Technician
- ETA - Estimated Time of Arrival
- Exhalation bag - Receptacle for dirty gas and
water vapour to collect. Often the site of the vent
valve (See Counter Lung)
F
- FP - Final Pressure
- Fraction of gas (f[x]) - The percent of a
particular gas in a gas mix. Air contains, 21 percent O2
and 79 percent N2. In Air the f02 = .21 (21 percent) and
the fN2 = .79 (79 percent).
- FSW - Feet of Sea Water
- Fuel Cell - See Galvanic
cell
- Fully-closed circuit rebreather - This type of
rebreather does not release any gases from the unit
except under the conditions of ascending from depth as
the counter-lung expands with the reduction in ambient
pressure. The advantage is the greatest possible use of
the onboard Oxygen and the maximum Physiological
benefits. The disadvantage is the added complexity of
electronics and mechanics to monitor the ppO2 and to
inject the proper amounts of diluent and O2 into the
breathing loop.
- FV - Floodable Volume
G
- Galvanic cell - An
electrochemical fuel cell that reacts to oxygen and
produces an electrical current.
H
- HAZID - Hazard Identification
- HCU - Habitat Conditioning Unit
- Heliox - A gas mix of helium and oxygen.
- HLB - Hyperbaric Lifeboat
- HP - High Pressure
- HPNS (High Pressure Nervous Syndrome) - HPNS is a
condition which results from breathing Helium under high
pressures. Early symptoms of HPNS are sometimes seen as
shallow as 300FSW but more commonly over 600FSW. The
severity also depends on the mix of breathing gases,
Nitrogen can often moderate the affects of HPNS. The
early symptoms include muscle tremors, followed by
changes in electroencephalogram (EEG) readings, impaired
motor and problem solving skills. Other symptoms can
include euphoria, nausea, vomiting, lack of appetite and
drowsiness. Symptoms sometimes moderate or entirely
disappear with continued exposure.
- HRL - Hyperbaric Rescue Lifeboat
- HSE - Health & Safety Executive
- HUD - Head up display.
- Hypercapnia - Hypercapnia is the physiological
condition that results from too much C02 (carbon
dioxide). In rebreather diving this is usually the
product of a poorly functioning scrubber. However, the
condition is not limited to rebreather users. Typical
symptoms are a shortness of breath and a headache. In
extreme cases the final result is unconsciousness and
eventual death from lack of Oxygen. Skip breathing, hard
work at depth, dead air spaces in the breathing loop and
other problems can lead to hypercapnia.
- Hyperoxic and Hyperoxia - In general, these terms
relate to a more than a normal amount of Oxygen.
Hyperoxic refers to a mixture of gases with higher than
normal Oxygen content (above 21%). Hyperoxia is the
physiological condition associated with breathing too
high of a partial pressure of Oxygen. The human body has
a limit on both the partial pressure of Oxygen it can
tolerate and the long term dosage of Oxygen. The partial
pressure upper limit is generally considered to be
approximately 1.6 ppO2 but most divers leave some margin
for error and a more typical upper limit is 1.4 ppO2.
When high partial pressures of Oxygen are inspired,
convulsions may occur with little or no warning. The
long term dosage of oxygen is measured in units called
OTU's.
- Hypoxic and Hypoxia - In general, both of these
terms relate to a less than normal amount of Oxygen.
Hypoxic refers to a mixture of gases with a lower than
normal fraction of oxygen (less than 21%). Hypoxia is
the physiological condition associated with breathing
too low of a partial pressure of Oxygen. When the ppO2
of oxygen falls below about .12, there is often not
enough Oxygen to maintain consciousness.
I
- IHP - Intermediate hose pressure
- IMCA - International Marine
Contractors Association, was AODC (Association of
Offshore Diving Contractors)
- IP - Initial Pressure
- ISO - International Standards Organisation
J
K
L
- LBC - Lifeboat Chamber
- Loop - The loop refers to the ambient breathing
gas circuit in a rebreather and the divers lungs, from
the mouthpiece through a corrugated hose to the
exhalation bag through the scrubber and into the
inhalation bag and finally back to the diver.
- Loraine Smith Effect - (see Oxygen
Toxicity)
- LP - Low Pressure
- LSP - Life Support Package
- LSS - Life Support Supervisor
- LST - Life Support Technician
- LTA - Lost Time Accident
M
- Mass flow - A delivered
fixed and measured volume of gas.
- MEL - Maximum Exposure Limit
- Membrane - A material with pores of molecular
size.
- Metabolic
Consumption - The amount of O2 consumed by the body,
is directly linked to how hard the work loading is and
is also reflected in a raised RMV.
- Micro-fuel cell - See Galvanic
cell
- ML - Main Lock
- ML - Maximum Lift
- MOD (Maximum Operating Depth) - The maximum
operating depth of a breathing gas before reaching a
predetermined maximum partial pressure of Oxygen,
usually 1.4 or higher.
- MSV - Multi-role Support Vessel
- MSW - Metres of Sea Water
- MT - Mechanical Technician
- Mushroom Valve - Mushroom valve on rebreathers
are one-way valves either side of the mouthpiece. These
control the direction of flow within the breathing loop.
N
- NCR - Non Conformance Report
- NDH - Norwegian Directorate of Health (Offshore)
- NDT - Non Destructive testing
- Nitrogen Narcosis - A narcotic effect produced by
high partial pressures of Nitrogen. This can affect the
divers judgment and for most divers starts to be
noticeable at a PPN2 over 3.00 this corresponds to
approximately 100 FSW when breathing air.
- Nitrox - Any mixture of Oxygen and Nitrogen which
has more or less Oxygen than air. However, It is usually
used to describe those mixtures with a more than normal
fraction of Oxygen. The standard Nitrox mixtures are
EAN32, EAN36 and EAN50. Most basic Nitrox courses assume
a mixture of EAN32 or EAN36.
- NJRH - National Institute of Radiation Hygiene
- NLTA - Non Lost Time Accident
- NMID - Norwegian Maritime Directorate
- Normoxic - This is the term used to describe the
normal mixture of gases found in the atmosphere. More
specifically it refers to the percentage of Oxygen in a
mix. Since the atmosphere has 21% Oxygen, a mixture of
gas with 21% Oxygen would be called normoxic. This is
contrasted with hyperoxic and hypoxic.
- NPCA - Norwegian Pollution Control Authority
- NPD - Norwegian Petroleum Directorate
- NS - Norwegian Standard
O
- OBG - Onboard Gas
- OES - Occupational Exposure Standard
- OTU's (Oxygen Toxicity Units) -
Also called UPTD (Unit Pulmonary Toxic Dose) OTU's are a
rough measurement of long term low ppO2 oxygen exposure.
The units are only viewed as guidelines to help gauge
whole body oxygen toxicity. They are based on the
exposure to 1 ATA of oxygen for 1 minute. 1ATA for 1
minute = 1 OTU.
- Oxygen sensor - See Galvanic
cell
- Oxygen Toxicity -
Physiological damage resulting from higher than normal
partial pressures of Oxygen. There are two primary types
of Oxygen toxicity. One results from long exposures of
elevated ppO2's and is called "The Loraine Smith
Effect" or "Pulmonary Oxygen Toxicity" as
the primary damage is to the lungs and airways. The
other type of Oxygen toxicity results from short high
ppO2 exposures and is called "The Paul Bert
effect" or "CNS Toxicity" (Central
Nervous System Toxicity) and is characterized by
convulsions with little or no warning signs. CNS
toxicity usually occurs with ppO2's above 1.6
P
- Paul Bert Effect - (see Oxygen
Toxicity) Partial Pressure
- Partial Pressure - The fraction of the absolute
pressure that the individual constituent of the gas mix
exerts.
- PPM - Parts Per Million
- PSIA - Pounds Per Square Inch Absolute
- PSIG - Pounds Per Square Inch Gauge
- PPCO2 - Partial Pressure of Carbon Dioxide
- PPN2 - The partial pressure of Nitrogen in a gas
mix.
- PPO2 - Partial Pressure of Oxygen
- Primary display - The main monitoring and display
module
- PTFE - Teflon Thread Tape
- PVC - Poly Vinyl Chloride
Q
- QA - Quality Assurance
- QC - Quality Control
R
- Radial flow scrubber - In a
radial flow scrubber the gas flow path across the
scrubber bed either radiates out from or towards a
central chamber to or from an outer chamber.
- RCC - Rescue Co-ordination Centre
- Rebreather - A device for recirculating the
divers exhaled breath to increase endurance of the gas
supply.
- RMV (Respiratory Minute Volume) - The amount of
gas breathed in and out in one minute.
- ROV - Remotely Operated Vehicle
- RV - Residual Volume
S
- SCR - Semi closed rebreather
- Scrubber - The housing for
absorbent to remove CO2 from the breathing loop. See Axial,
Radial and Canister.
- SCUBA - Self Contained Underwater Breathing
Apparatus
- SDC - Submersible Decompression Chamber
- SDV - Shut Down Valve
- SE - Surface Equivalent
- Secondary display - Backup to primary display
- Set Point - A PPO2 value set in closed circuit
rebreathers.
- Skip breathing - The practice of inhaling,
holding the inhalation for a period of time and then
exhaling in order to attempt to extend the time
underwater by using less air. This practice can lead to
a buildup of CO2 and symptoms of hypercapnia.
- SLS - Secondary Life Support (Rebreather bail
out)
- SPHL - Self Propelled Hyperbaric Lifeboat
- Static lung loading - Used with reference to
position of lungs and breathing bags in the water
column. In various positions underwater the loading upon
the lung can be increased or decreased on inhalation or
exhalation
- SWL - Safe Working Load
T
- TC - Transfer Chamber
- Trimix - A breathing mixture of gases most often
composed of Oxygen, Nitrogen and Helium. This
proportions of each are changed according to the needs
of the particular dive plan to help limit Oxygen
toxicity and Nitrogen narcosis.
- TUP - Transfer Under Pressure
- TV - Tidal Volume
U
- UI-IF - Ultra High Frequency
- UPTD - Unit Pulmonary Toxicity Dose, see OTU's
- UT - Ultrasonic
V
- Ventilation Independent Control - See Mass
Flow
- Ventilation Linked Control - Oxygen injection
dependant on ventilation of the diver
- VHF - Very High Frequency
- VO2 - Volume of oxygen consumed measured in
litres per minute, see metabolic
consumption.
W
- Water Trap - Areas within a loop, usually on the
exhaust side, that allow moisture to drop out of the
breathing path and collect out of harms way
- WC - Water Capacity, the volume a
container/pressure vessel would hold if filled with
water.
- WOB - Work of breathing, the phrase "Work of
breathing" relates to the amount of effort required
by the diaphragm to move the breathing gases in and out
of the lungs. Work of breathing is affected by many
things on a rebreather including the hose diameters,
mushroom valves, scrubber design, counter-lung placement
and design, and more. The work of breathing is also
affected by depth. As depth increases the breathing
gases become more dense which increases the work of
breathing.
X
Y
Z
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