acfm - actual cubic feet per minute (see also cfm). The flow of a gas under pressure, measured in actual volume at pressure per minute. For example 1 acfm at 3 ATA is 3 cfm.

AGE - arterial gas embolism; a blockage of blood supply to organs caused by bubbles in an artery.

ATA – atmospheres absolute, a measure of pressure above absolute vacuum or zero pressure. 1 ATA, or sea level, is 14.7 psi, 101,325 Pa or 1.01325 bar.

atm - atmosphere, a measure of pressure at sea level.

bar - barometric pressure about the same as atmospheric pressure, and is commonly used in countries using the Metric Units System. 1 bar is 0.987 atm. It refers to a relative pressure, not an absolute pressure.

BIBS - Built In Breathing System. Breathing gases delivery system for patients and attendants inside the chamber during treatment.

Blow-up - An uncontrolled ascent to the surface at greater than 60 feet per minute.

Bottom time (BT) - Total time elapsed from leaving the surface to the time of beginning the ascent (rounded up to the next whole minute).

Caisson gauge – Used to measure chamber depth and installed inside the chamber. It measures pressure relative to outside, not an absolute pressure.

°C - degrees Celsius, a metric measure of temperature

cf or ft³ - cubic feet, a measure of volume. (1 cfm = 28.3 LPM)

cfm or ft³/min - cubic feet per minute (an indication of flow rate) determined at sea level (1 ATA). Also referred to as scfm.

CGA - Compressed Gas Association which includes valuable information on breathing and inert gases, and the equipment used to manage them

Chamber - the pressure vessel, including the inner and outer lock

CNS - central nervous system, used in the context of breathing elevated levels of oxygen and pressure, as experienced in a recompression chamber.

CO - carbon-monoxide – toxic product of combustion. It easily binds with hemoglobin in the blood and competes with oxygen with 200 times the binding strength of oxygen.

CO2 - carbon-dioxide

DAN - Divers Alert Network

dB(A) - A-weighted decibel (a measure of the relative loudness in air as perceived by the human ear)

DCI - decompression illness. Includes both AGE and DCS but is less specific to the exact nature of the gas bubble injury.

DCS - decompression sickness. Similar term to DCI and used to describe a variety of muscular, neurological or cerebral symptoms related to the presences of nitrogen gas bubbles in the diver. DCS Type 1 is pain; generally limited to extremity joint pain. DCS Type 2 is anything of a neurological presentation, such as numbness, tingling sensation, weakness, extreme fatigue, paralysis, confusion and disorientation after diving or pain occurring anywhere in the trunk of the body. Symptoms can begin within minutes of surfacing but generally begin anywhere from 20 or 30 minutes post dive and may take up to 24 hours after diving to show up.

Decompression stop or Deco – A required stop for a diver or inside attendant in a recompression chamber to allow for off-gassing of inert gas (e.g., nitrogen, helium), or during the dive, in order to prevent decompression sickness.

Descent time (DT) - The total elapsed time from leaving surface to the time of reaching the bottom or intended depth of a dive (rounded up to the next whole minute).

Dive – In the context of recompression therapy, refers to a treatment in the hyperbaric chamber

DMO - diving medical officer, a term used to describe a physician, trained in diving (and hyperbaric) medicine, and responsible for all aspects of the treatment of an injured diver.

EANx - enriched air nitrox

EAP - emergency action plan

ET - endotracheal tube, placed between the vocal cords through the trachea, that allows oxygen (or other breathing gases) to enter the lungs using some form of forced ventilation device.

Exhaust valves – Devices used to control the ascent of a chamber, as well as ventilation. BIBS or treatment gas exhaust valves control exhaled breathing gas from inside the chamber.

°F - degrees Fahrenheit, an imperial measure of temperature

Fire Triangle – Describes the three primary components of any fire and that must be controlled, namely, fuel (materials that burn), oxygen (including the chamber atmosphere with more than 23.5% oxygen), and a source of ignition (heat, sparking, adiabatic heating).

FiO₂ – Fraction of inspired oxygen – measured as a fraction but commonly expressed in percentage. Room or ambient air has an FiO₂ of 0.21 or 21%. Pure oxygen (100%) at sea level would be FiO₂ of 1 or 100%.

fsw - feet of sea water

GFI - ground fault interrupter (also ground fault circuit interrupter; detects current leakage to ground)

gpm - gallons per minute, a measure of flow usually associated with a liquid. (1 gpm = 3.8 LPM)

HBOT – hyperbaric oxygen therapy

Heliox - A mixture of helium and oxygen, supplied as a treatment gas. Commonly a 50/50 mixture is used to treat at 100 fsw (±30 msw).

HP - In context of hyperbaric facilities, assumed as > 1.5 MPa/225 psi for air and inert gases; > 0.86 MPa/125 psi for O2.

Hypoxia – Insufficient oxygen levels in tissue to ensure proper body function.

Hypoxic - A gas mix with less than 21% oxygen, generally 16% or lower.

Hypobaric - An environment with a pressure which is below atmospheric pressure (1 ATA), such as an environment at altitude.

Inlet valves – The inlet valve controls the flow of compressed gas entering the chamber. Compressed gas includes air (for pressurization and ventilation), and oxygen or any other treatment gas. Compression and treatment gas controls must be separate, clearly labeled, and directional arrows must be used.

LP - In the context of hyperbaric facilities, assumed as < 1.5 MPa/225 psi for air and inert gases; < 0.86 MPa/125 psi for O2.

LPM - liters per minute, a measure of flow.

Mixed gas – Any gas mixture made up of any combination of gases other than air. See also Nitrox and Heliox.

MPa - A metric measure of pressure where 1 MPa = ±10 bar, 1000 kPa or 145 psi

msw – meters of sea water, where 1 msw is 0.1 bar

m³ - cubic meter (an indication of volume where 1 m3 = 1,000 liters)

NLPM - normal liters per minute (see LPM). The volume flow of gas measured at sea level, taken as 1 ATA (101.325 kPa absolute) and 21°C.

N₂ - nitrogen gas – a naturally occurring inert gas and the primary component of compressed air (±79%)

Nitrox or EANx - A mixture of nitrogen and oxygen with a greater percentage of oxygen than in normal air. In the context of recompression therapy, supplied as a treatment gas to allow for treatment at deeper depths. Commonly a 50/50 mixture is used to treat at 100 fsw (30 msw).

Needle valve – Slow opening controlling valve typically used in oxygen lines to reduce speed of the gas in order to reduce the risk of ignition (resulting from a rapid rise in pressure, and thereby in significantly elevated temperatures). Also used for fine or measured control of any gas.

NFPA - National Fire Protection Association; NFPA 99 Chapter 14 contains guidance in the safe use of recompression chambers.

NOAA - National Oceanic and Atmospheric Administration (USA)

Normobaric - When used as normobaric oxygen therapy, this implies oxygen administered at one atmosphere.

OTU - oxygen toxicity unit, used to determine the degree of pulmonary oxygen toxicity produced by breathing 100% oxygen. This is not the same as CNS. See also UPTD.

O₂ – oxygen, a treatment gas used in recompression and other hyperbaric oxygen therapies. Oxygen exists at 21% of normal air. 100% 02 is used in most HBOT applications. Oxygen at 23.5% or higher inside a hyperbaric environment introduces a significant risk of fire.

Oxygen clean – Material or equipment that has been suitably cleaned for use with oxygen or any other gas mixture with more than 25% oxygen. The term oxygen clean implies that all hydrocarbons and other combustible materials have been removed.

partial pressure or pp – The portion of any specific gas in a mixture, usually expressed as a pressure in ATA. Air at 2 ATA has an O₂ pp of 0.42. Oxygen in an O₂ - N₂ 50/50 mixture at 4 ATA (100 fsw or 30 msw) is 2 ATA.

ppm - parts per million; a measure of the concentration of a substance in a total volume. ppm relates to percentage, with there being 10,000 ppm in 1%.

psi or psig - pounds per square inch, an indication of relative pressure above ambient (1 ATA). The g stands for “gauge”. 14.7 psig equates to 1 atm or 2 ATA.

psia – psi absolute, an indication of total pressure, meaning above absolute vacuum or zero pressure. This measure is especially useful in altitude corrections.

Pt - patient

PVHO - Pressure Vessel for Human Occupancy, a safety standard for the design, construction, testing and certification of any PVHO with a differential pressure of more than 2 psi (±0.14 bar).

scfm - standard cubic feet per minute (see cfm). The volume flow of gas measured at sea level, taken as 1 ATA and 70°F. Equivalent measure to NLPM.

SEV - surface equivalent value (expressed in percentage or %)

SS – Safety Stop, a safety measure used by recreational scuba divers to stop the diver’s ascent to the surface before exiting the water. This is done to assist in the off-gassing of nitrogen and prepare the diver to exit the water safely.

SOP - standard operating procedure

TT - Treatment Table see also below.

Tx – treatment, followed by the name or the designated number for the type of treatment used

Treatment Tables - Usually described by an abbreviation followed by a number. E.g., USN TT 6, the most commonly used treatment table in the initial treatment of a diving injury.

Table extensions - Time that may be added onto a treatment table, if the patient is not symptom free upon reaching the scheduled treatment time. Table extensions must be prescribed by the attending DMO.

UPTD - unit pulmonary toxicity dose. This expresses any pulmonary oxygen toxicity in terms of an equivalent exposure from breathing 100% O2 continuously at 1 ATA. This predicts pulmonary toxicity as a function of ppO2 and time, based on decreased vital capacity (the greatest volume of air that can be expelled from the lungs after taking the deepest possible breath). The diving industry uses the term OTU interchangeably with UPTD.

USN – United States Navy

UV - ultraviolet light (light spectrum immediately below visible light; wavelength range 10 – 400 nm)

Venting – Process where the chamber environment is gradually replaced by venting. This is done to remove stale air and odor, reduce oxygen to 21%, reduce CO₂ to normal levels, and to cool the chamber. This is achieved through adding fresh compressed air using the inlet valve, while exhausting an equal amount of chamber air, keeping chamber pressure constant at all times.

WOG – water, oil or gas valve, an industry term used for pressure control instruments installed on typical recompression chambers.