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The breathing performance of regulators is a measure of the ability of a breathing gas regulator to meet the demands placed on it at varying ambient pressures and temperatures, and under varying breathing loads, for the range of breathing gases it may be expected to deliver. Performance is an important factor in design and selection of breathing regulators for any application, but particularly for
underwater diving Underwater diving, as a human activity, is the practice of descending below the water's surface to interact with the environment. It is also often referred to as diving (disambiguation), diving, an ambiguous term with several possible meani ...
, as the range of ambient operating pressures and temperatures, and variety of breathing gases is broader in this application. A
diving regulator A diving regulator or underwater diving regulator is a pressure regulator that controls the pressure of breathing gas for underwater diving. The most commonly recognised application is to reduce pressurized breathing gas to ambient pressure and ...
is a device that reduces the high pressure in a
diving cylinder A diving cylinder or diving gas cylinder is a gas cylinder used to store and transport high pressure gas used in diving operations. This may be breathing gas used with a scuba set, in which case the cylinder may also be referred to as a scub ...
or surface supply hose to the same pressure as the diver's surroundings. It is desirable that breathing from a regulator requires low effort even when supplying large amounts of
breathing gas A breathing gas is a mixture of gaseous chemical elements and compounds used for respiration. Air is the most common and only natural breathing gas, but other mixtures of gases, or pure oxygen, are also used in breathing equipment and enclosed ...
as this is commonly the limiting factor for underwater exertion, and can be critical during diving emergencies. It is also preferable that the gas is delivered smoothly without any sudden changes in resistance while inhaling or exhaling, and that the regulator does not lock up and either fail to supply gas or free-flow. Although these factors may be judged subjectively, it is convenient to have
standards Standard may refer to: Symbols * Colours, standards and guidons, kinds of military signs * Standard (emblem), a type of a large symbol or emblem used for identification Norms, conventions or requirements * Standard (metrology), an object t ...
by which the many different types and manufactures of regulators may be objectively compared. Various breathing machines have been developed and used for assessment of breathing apparatus performance. Ansti Test Systems developed a turnkey system that measures the inhalation and exhalation effort in using a regulator, and produces graphs indicating the
work of breathing Work of breathing (WOB) is the energy expended to inhale and exhale a breathing gas. It is usually expressed as work per unit volume, for example, joules/litre, or as a work rate (power), such as joules/min or equivalent units, as it is not parti ...
at the set depth pressure and respiratory minute volume for the gas mixture used. Publishing results of the performance of regulators in the ANSTI test machine has resulted in performance improvements.


Relevance

Breathing performance of the regulator is relevant in all circumstances where a regulator is used to control the flow of breathing gas in a supply on demand system. In some of these applications, a very basic regulator will perform adequately. In other applications, the performance of the regulator may limit the performance of the user. A high-performance regulator for a given combination of gas mixture and ambient pressure is defined as one which will provide a low work of breathing at high RMV, while supplying a flow of gas only when triggered by inhalation, and allowing an outflow of exhaled gas with minimum resistance. Another aspect of breathing performance is demand regulator performance in cold water, where a high flow rate may cause chilling sufficient to lock up the mechanism with ice, which usually causes a severe free-flow with consequent loss of breathing gas, which can only be stopped by shutting off the cylinder valve. A healthy person at rest at surface atmospheric pressure expends only a small amount of available effort on breathing. This can change considerably as the density of breathing gas increases at higher ambient pressure. When the energy expended to remove carbon dioxide produces more carbon dioxide than it removes the person will suffer from hypercapnia in a positive feedback cycle ending in unconsciousness and eventually death. Work of breathing is affected by breathing rate, breathing pattern, gas density, physiological factors, and the fluid dynamic details of the breathing apparatus, these being the frictional resistance to flow, and pressure differences required to open valves and hold them open to flow. Breathing gas density can be reduced by using helium as the basic component, with sufficient oxygen added to suit the circumstances and retain a
partial pressure In a mixture of gases, each constituent gas has a partial pressure which is the notional pressure of that constituent gas as if it alone occupied the entire volume of the original mixture at the same temperature. The total pressure of an ideal g ...
sufficient to sustain consciousness but not so much as to cause
oxygen toxicity Oxygen toxicity is a condition resulting from the harmful effects of breathing molecular oxygen () at increased partial pressures. Severe cases can result in cell damage and death, with effects most often seen in the central nervous system, lung ...
problems. Frictional resistance to flow is influenced by the shape and size of the gas passages, and the pressure, density, viscosity, and velocity of the gas. Valve cracking pressure is a factor of design and settings of the valve mechanisms. The breathing performance of regulators assumes gas density is specified and measures the resistance to flow during the full breathing cycle with a given volumetric flow rate as a pressure drop between the mouthpiece and the exterior environment.


Measurement


Work of breathing

Work of breathing (WOB) is the energy expended to inhale and
exhale Exhalation (or expiration) is the flow of the breath out of an organism. In animals, it is the movement of air from the lungs out of the airways, to the external environment during breathing. This happens due to elastic properties of the lungs ...
a
breathing Breathing (spiration or ventilation) is the rhythmical process of moving air into ( inhalation) and out of ( exhalation) the lungs to facilitate gas exchange with the internal environment, mostly to flush out carbon dioxide and bring in oxy ...
gas. It is usually expressed as work per unit volume, for example, joules/litre, or as a work rate (power), such as joules/min or equivalent units, as it is not particularly useful without a reference to volume or time. It can be calculated in terms of the pulmonary pressure multiplied by the change in pulmonary volume, or in terms of the oxygen consumption attributable to breathing. The total work of breathing when using a breathing apparatus is the sum of the physiological work of breathing and the mechanical work of breathing of the apparatus. In a normal resting state the physiological work of breathing constitutes about 5% of the total body oxygen consumption. It can increase considerably due to illness or constraints on gas flow imposed by breathing apparatus, ambient pressure, or breathing gas composition. The performance of a regulator refers to the mechanical work of breathing of the regulator and excludes the physiological work of breathing. Mechanical work of breathing is strongly influenced by breathing rate, which is specified in the standards. For a given volume over a given time, work of breathing for the full breath cycle and for the inhalation part of the cycle are calculated from the instantaneous pressures measured between the inside and outside of the regulator casing. The changes in volume are known from the characteristics of the positive displacement breathing cycle simulator. Peak pressures and transient pressure spikes are also measured, and recorded for analysis, as there are limits specified in the standards for these values. Work of breathing is the instantaneous pressure x change in volume integrated over the cycle, and inhalation work of breathing is the work of breathing for the inhalation part of the cycle. The breathing cycle of the test machine may not accurately represent flow in any given human breath. The ANSTI testing machine uses a sinusoidal volume change, which is simple to analyse. A human breath can be very variable.


Cold water function testing

U.S. Navy Experimental Diving Unit's unmanned cold water test procedures (1994) have been used as an unofficial standard for cold water testing by various military users and major equipment manufacturers. European CE open circuit standard EN 250 of 1993 set a higher level for open circuit scuba testing for breathing performance, cold water testing, proof, pressure, mechanical, storage temperatures, and CO2 wash out tests. The standard also set requirements for failure modes and effects analysis, and other issues relating to manufacturing,
quality assurance Quality assurance (QA) is the term used in both manufacturing and service industries to describe the systematic efforts taken to assure that the product(s) delivered to customer(s) meet with the contractual and other agreed upon performance, design ...
and documentation. This standard drew attention to issues with a lot of existing equipment, and led to major improvements in open circuit regulator performance. Early testing done by the US Navy was the origin of underwater breathing apparatus simulation testing in the late 1970s. The breathing simulator systems built by Stephen Reimers were bought by the Ministry of Defence in the UK and by some private equipment manufactures like Kirby Morgan Diving Systems, and helped develop European standards in the early 1990s, but the introduction of a complete breathing simulator system by ANSTI Test Systems Ltd in the UK made possible the accurate breathing simulator testing that is the current practice. The computerized ANSTI breathing simulator systems made faster, easier and more accurate testing possible, and are designed for testing in all realistic water temperatures. The system includes precise humidity and exhalation temperature control as well as environmental water temperature control from , facilities for breath by breath CO2 analysis and closed circuit rebreather set point control and scrubber endurance testing. Neither the EN250 standard nor the US Navy unmanned test procedures use any kind of real world human diving scenario as the basis for testing, including cold water testing. The US Navy procedure has been to test regulators primarily at a depth of 190 fsw (58 msw) in water at a very high breathing rate of 62.5 lpm for a minimum of 30 minutes, with inlet pressure to the first stage of , which results in an average second stage inlet temperature of around , compared to an average of if would be used. The US Navy cold water test criteria and the EU EN250 test criteria are based on whether the regulator meets minimum breathing performance requirements and whether or not a free flow starts. Very few regulators can pass this test because all regulators will form ice in the second stage under the extreme test conditions, though this may not cause the regulator to free flow or go outside the performance criteria. The cold water testing specified in EN250:2000 has scuba regulators tested in water or colder. Regulators are tested in both facing forward and facing down positions. The test starts at (50 msw) 165 fsw and the regulator is breathed at 62.5 lpm for five minutes. To pass, the regulator must remain within the
work of breathing Work of breathing (WOB) is the energy expended to inhale and exhale a breathing gas. It is usually expressed as work per unit volume, for example, joules/litre, or as a work rate (power), such as joules/min or equivalent units, as it is not parti ...
limits and must not free flow. The formation of ice is not considered as long as the ice does not degrade the breathing performance beyond minimum performance requirements, and it does not free-flow. The CE test uses an air supply starting at the highest pressure the regulator is rated for and is breathed for five minutes at 62.5 lpm using an exhalation temperature of 28 ±2°C (82.4 ±3.6°F) and an exhalation relative humidity of no less than 90%.


ANSTI machine

The ANSTI Breathing Simulator is rated to a maximum working pressure of 100 msw. It uses a piston mechanism to provide an accurate and repeatable volume displacement with a sine wave drive mechanism. It has adjustable
tidal volume Tidal is the adjectival form of tide. Tidal may also refer to: * ''Tidal'' (album), a 1996 album by Fiona Apple * Tidal (king), a king involved in the Battle of the Vale of Siddim * TidalCycles TidalCycles (also known as Tidal) is a live coding ...
and
breathing rate The respiratory rate is the rate at which breathing occurs; it is set and controlled by the respiratory center of the brain. A person's respiratory rate is usually measured in breaths per minute. Measurement The respiratory rate in humans is me ...
settings which can provide ventilation rates from 10 to 180 litres per minute.


Applications of breathing gas regulators

*
Scuba diving Scuba diving is a Diving mode, mode of underwater diving whereby divers use Scuba set, breathing equipment that is completely independent of a surface breathing gas supply, and therefore has a limited but variable endurance. The word ''scub ...
– All breathing gas is carried in high-pressure cylinders by the diver. primary pressure reduction in the first stage from storage pressure to an intermediate pressure causes cooling proportional to the pressure drop. **
Recreational scuba diving Recreation is an activity of leisure, leisure being discretionary time. The "need to do something for recreation" is an essential element of human biology and psychology. Recreational activities are often done for enjoyment, amusement, or pleasure ...
– Air and nitrox at ambient pressures up to about 40 msw. **
Technical diving Technical diving (also referred to as tec diving or tech diving) is scuba diving that exceeds the List of diver certification organizations, agency-specified limits of recreational diving for non-Professional diver, professional purposes. Technica ...
– Ambient pressures may significantly exceed 30 msw ***Mixed gas – Breathing gases containing helium to limit narcosis and work of breathing *** Decompression gas – Breathing gases with high oxygen partial pressures, generally not very high ambient pressure *
Surface-supplied diving Surface-supplied diving is a mode of underwater diving using equipment supplied with breathing gas through a diver's umbilical from the surface, either from the shore or from a diving support vessel, sometimes indirectly via a diving bell. ...
– Breathing gas supplied from the surface at a wide range of depths **
Open circuit Open circuit may refer to: * Open circuit breathing apparatus, any type of breathing apparatus where the exhaled gas is discharged to the surroundings without recycling any of it ** Open-circuit scuba, a type of Scuba-diving equipment where the user ...
– Gas is released into the environment and lost on exhalation ** Breathing gas reclaim systems – Helium based breathing gas is returned to the surface for recycling via an exhaust regulator to save expensive gas *
Built-in breathing system A built-in breathing system is a source of breathing gas installed in a confined space where an alternative to the ambient gas may be required for medical treatment, emergency use, or to minimise a hazard. They are found in diving chambers, hype ...
s in hyperbaric environments – High oxygen content gas is vented to the exterior via an exhaust regulator to avoid high fire risk. High performance not generally needed, as the user is normally resting. * Oxygen administration for first aid in diving accidents – High oxygen fraction at surface pressure, fairly low flow rate, but user may be injured and have difficulty breathing. *
Self-contained breathing apparatus A self-contained breathing apparatus (SCBA) is a respirator worn to provide an autonomous supply of breathable gas in an atmosphere that is immediately dangerous to life or health from a gas cylinder. They are typically used in firefighting a ...
(SCBA) for rescue, firefighting, or other work in unbreathable atmospheres. * Submarine emergency gas supply (Submarine BIBS) – Survival conditions, at unpredictable pressures, but higher than normal atmospheric. Exhaled gas is trapped in the submarine, so pressure will gradually build up. * Flight crew breathing apparatus – Oxygen supply for unpressurized aircraft – Low ambient pressure due to high altitude. Air supply enriched by additional oxygen. Flow rate not expected to be very high


Standards


European Union

In the
European Union The European Union (EU) is a supranational union, supranational political union, political and economic union of Member state of the European Union, member states that are Geography of the European Union, located primarily in Europe. The u ...
the standard EN250:2000 ''Respiratory equipment. Open-circuit self-contained compressed air diving apparatus. Requirements, testing, marking'' defines minimum performance standards for "Open-circuit self-contained compressed air diving apparatus", and BS 8547:2016 defines requirements for demand regulators to be used at depths exceeding 50 m. EN 13949: 2003 – ''Respiratory Equipment – Open Circuit Self-Contained Diving Apparatus for use with Compressed Nitrox and Oxygen – Requirements, Testing, Marking'' defines requirements for regulators to be used with raised levels of oxygen. The standard contains limits on inhalation and exhalation pressures and overall work of breathing. It specifies the following, under test conditions of a breathing rate of per minute and an ambient pressure of : *Work of breathing: <3.0 joules per litre *Peak respiratory pressure: ±25 mbar (±2.5 kPa) (inhalation or exhalation) *Inhalation work of breathing: <0.3 joule per litre *Pressure spikes with no measurable positive work of breathing: <10 mbar (1 kPa) *Pressure spikes with measurable positive work of breathing: <5 mbar (0.5 kPa) Although a regulator meeting the above limits will supply sufficient air where the first stage feeds a single second stage, it is not necessarily capable of supplying sufficient air in all circumstances when a single first stage feeds two second stages simultaneously.


Related standards

In Europe, EN 250: 2014 – ''Respiratory Equipment – Open Circuit Self - Contained Compressed Air Diving Apparatus – Requirements, Testing and Marking'' defines the minimum requirements for breathing performance of regulators, and BS 8547:2016 defines requirements for demand regulators to be used at depths exceeding 50 m. EN 13949: 2003 – ''Respiratory Equipment – Open Circuit Self-Contained Diving Apparatus for use with Compressed Nitrox and Oxygen – Requirements, Testing, Marking''. defines requirements for regulators to be used with raised levels of oxygen. EN 15333 – 1: 2008 COR 2009 – ''Respiratory Equipment – Open-Circuit Umbilical Supplied Compressed Gas Diving Apparatus – Part 1: Demand Apparatus''. and EN 15333 – 2: 2009 – ''Respiratory Equipment – Open-Circuit Umbilical Supplied Compressed Gas Diving Apparatus – Part 2: Free Flow Apparatus''. I.S. EN 14143: 2013 – ''Respiratory Equipment – Self-Contained Re-Breathing Diving Apparatus'' defines minimum requirements for rebreathers.


US Military

In the United States Military, the standard for single-hose scuba regulators was MIl-R-24169B, now withdrawn.


See also

* * * * *


References

{{DEFAULTSORT:Breathing Performance Of Regulators Underwater breathing apparatus