Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B63—SHIPS OR OTHER WATERBORNE VESSELS; RELATED EQUIPMENT
  • B63C—LAUNCHING, HAULING-OUT, OR DRY-DOCKING OF VESSELS; LIFE-SAVING IN WATER; EQUIPMENT FOR DWELLING OR WORKING UNDER WATER; MEANS FOR SALVAGING OR SEARCHING FOR UNDERWATER OBJECTS
  • B63C11/00—Equipment for dwelling or working underwater; Means for searching for underwater objects
  • B63C11/02—Divers' equipment
  • B63C11/18—Air supply
  • B63C11/22—Air supply carried by diver
  • B63C11/24—Air supply carried by diver in closed circulation

Definitions

• the present invention relates to a secondary life support [SLS] system designed specifically for use in bail-out by divers, particularly bail-out during deep diving operations.
• SLS secondary life support
• Conventional bail-out equipment comprises compressed breathing gas in a bottle with a connecting hose or hoses and demand regulator valving allowing a diver to breath down the gas from the bottle. This is an open circuit system and the breathed gas is expelled from the divers helmet or mask.
• the quantity of breathing gas which can be carried [e.g. 4 litres at 300 bar] is sufficient only for a short period of time [e.g. bout 20 to 90 seconds] depending on breathing rate.
• the present invention has as one aspect a divers secondary life Gupport system comprising a rebreather set connected via one or more hoses to an isolating valve and a helmet- or mask-in erf ce, the rebreather set in a standby mode during normal diving operations being maintained at a pressure in excess of ambient external pressure.
• a further aspect of the invention is a rebreather set for a divers secondary life support system, the set being attachable by one or more hoses to an isolating valve and helmet- or mask- interface, the set comprising at least, one counterlung, a moisture absorber, a carbon dioxide scrubber, and a restrictor which is attachable to a pressurised gas bottle so that when the set is actuated gas can bleed into the set at a substantially constant rate. It is a particularly advantageous feature of such a set that it may be maintained at a pressure in excess of ambient external pressure when in a standby mode.
• the over-pressure may be, for example, about 4 bar but a preferred over-pressure of about 0.1 to 0.2 bar is considered sufficient.
• Particular advantages of an SLS system described above include :
• the operation of the set in the standby mode can be controlled so there is neither variation in buoyancy nor in gas over-pressure when the diver changes depth.
• FIGURE 1 is a schematic representation of a bail-out rebreather set according to the invention.
• FIGURE 2 shows the predicted work of breathing of a bail-out rebreather set at various breathing rates at 450 MSW and 250 MSW depth;
• FIGURE 3 is a schematic representation of a further bail-out rebreather set according to the invention.
• a divers secondary life support system includes a semi-closed circuit bail-out rebreather set having a counterlung 1 connected via a single hose 2 to a helmet 3, with an isolating valve 4 mounted on the helmet.
• prior art rebreather sets for use in standard diving operations e.g. closed circuit oxygen rebreathers
• a conventional bottle 5 of approximately 4 litres water volume is used for make-up gas storage at a pressure of e.g.
• the outlet pressure of this make-up gas is regulated to a pressure in excess of the ambient external pressure and when the set is in the actuated mode for bail ⁇ out the gas is allowed to bleed via a restrictor 6 into the counterlung at a fixed rate of e.g. 1 to 2 litres per minute.
• the make-up gas preferably has a physiologically high oxygen content of up to about 2.5 bar partial pressure.
• the set In the standby mode the set may be maintained at a predetermined pressure relative to the external ambient pressure; it is particularly preferable to have an over-pressure in the set in the standby mode of up to approximately 4 bar, e.g. generally about 0.1 to 0.2 bar.
• a back pack 7 the hose 2 splits into separate inhale and exhale hoses 8 and 9, which pass through a water trap 10 and a CO2 scrubber 11 on the exhale/cycle.
• the major system components, including the CO- scrubber 11 are heated in normal operation by a bleed 12 taken from the normal diver hot water supply.
• the back pack 7 is preferably insulated against external cold. Heating of the CO scrubber 11 in the standby mode maintains the chemical absorbent [e.g. silica gel] at a temperature at which it will operate efficiently if the set is put into the actuated mode for bail-out.
• a thermal regenerator consisting of layers of fine wire mesh may be placed upstream of the counterlung to prevent heat loss via the large surface area of the counterlung.
• the helmet valve When bail-out is required, the helmet valve is opened and the counterlung will immediately vent any over-pressure into the helmet. Depending on the nature of the emergency, this immediate supply of " gas may be of value in purging the helmet. The helmet mushroom valve will vent any excess quantity of gas introduced in this way, avoiding any over-pressurisation of the helmet.
• exhaled gas which consists mainly of a diluent
• some residual oxygen and carbon dioxide passes via one or more hoses to a chemical absorbent [i.e. silica gel] to remove carbon dioxide and to the counterlung where the gas is mixed with make-up gas containing a physiologically high oxygen content.
• a chemical absorbent i.e. silica gel
• the endurance of the set is governed to a large extent by the bleed rate of make-up gas into- the counterlung. As is shown later a bleed rate of 1-2 /min is adequate for respiration rates of up to 75 /min RMV [Respiratory Minute Volume]. Since each breath removes only a fraction of the total oxygen content, given a high initial oxygen partial pressure, the same gas can be rebreathed many times over providing that effective CO2 scrubbing is provided. In order to maximise the reliability of the set and avoid maintenance problems offshore, electronic devices for controlling oxygen injection have been avoided. Because of the relatively wide range of oxygen levels which can be breathed satisfactorily, a fixed bleed of mixed gas having an oxygen partial pressure of up to about 2.5 bar can be shown to give acceptable oxygen levels at all breathing rates.
• the minimum desirable oxygen level is 0.4 bar, although levels down to 0.2 bar are tolerable.
• the design target for a bail-out set be 20 millibar average inspired CO2 level and 7 millibar end tidal inspired C0 2 level at the end of the scrubber canister duration.
• Table 1 shows the results obtained for 4 breathing rates at depths from 100 metres to 450 metres.
• the oxygen level falls from the initial value to reach a plateau, depending on breathing rate.
• the maximum oxygen level was around 2.5 bar, at the start of the run.
• Plateau levels varied from around 2 bar at the lowest breathing rate down to 0.4 - 0.8 bar at the highest breathing rates.
• the endurance of the set is determined principally by the rate at which the gas bleed depletes the storage volume. However, some additional time is gained by "breathing down" the gas in the counterlung. In general, the endurance of the set diminishes with depth because of the greater quantity of gas consumed at depth.
• the shortest endurance calculated was approximately 16 minutes, at a depth of 450 metres, breathing continually at a rate of 75 A/min KMV. At lower breathing rates, at the same depth, this endurance extends to 24 minutes. At shallower depths, the endurance of the set will generally exceed 25 minutes.
• the oxygen profiles for a more realistic breathing sequence with a variable SMV show that the oxygen level in the set to vary according to the work rate, with overall endurance figures slightly in excess of that obtained at the maximum RMV. On this basis, the set can achieve a minimum endurance of 15 minutes at 450 MSW and considerably longer at shallower depths. Although no electronic oxygen partial pressure control is provided it may be shown that the upstream level stays at all times within a band which is acceptable, at least for the short durations required of a bail ⁇ out set.
• the rebreather hose calculation is based on conventional pipe friction theory.
• the (X>2 scrubber calculations are based on tests carried out on a survival kit scrubber, charged with MPUD 797 Grade Sodalime. Results have been scaled to 450 MSW and the higher work rates associated with the present equipment. The hydrodynamic losses in the counterlung have been based on plausible assumptions having regard to its geometry.
• Figure 2 summarises the results of this calculation.
• the open and closed circles on the Figure ' represent results for. a set at 450 and 250 MSW depth respectively.
• the dashed line represents a recommended limit for work of breathing and the upper full line represents an upper limit.
• No data has been presented for peak inhale/exhale resistance since this will depend on the biasing applied to the set.
• the predicted values are modest at low work rates and acceptable at the highest work rate of 75.c/min RMV. It is reasonable to suppose that it is easier to obtain satisfactory work of breathing values in a bail-out rebreather rather than a conventional rebreather because of the lower quantities of CO2 absorbent involved.
• FIG.3 A second embodiment of a secondary life support system is shown in Fig.3.
• the semi-closed circuit bail-out rebreather set when in a standby mode for diving operations, is maintained at a pressure 0.2 bar in excess of the ambient external pressure.
• Counterlungs 1 which are physically restrained to prevent inflation by the over ⁇ pressure whilst in the standby mode are mounted on the divers shoulders. This minimises hydrostatic effects on the breathing circuit when the set is in the actuated mode. On actuation, the counterlungs 1 are released and are inflated [or partially inflated] by the over-pressure within the set. In the event of emergency the diver is required to actuate the rebreather set by two non ⁇ sequential actions;
• the diver When the set is actuated the diver will accept the mouthpiece 16 and breath naturally on it.
• the expired gas will pass through the mouthpiece 16, helmet interface 17 and be directed by the exhale valve 18 into the exhale hose 9.
• the expired gas Within the back pack 7, the expired gas will flow to the plenum below the scrubber canister 11 where even distribution is achieved.
• the gas then passes through the CO2 scrubber canister 11 which is charged with sodalime granules for removal of CO2 from the expired breath. From here the gas passes through a thermal regenerator 19, consisting of a number of layers of fine wire mesh which, due to their large surface area, absorb heat allowing relatively cold gas to pass via the hoses 20 to the shoulder mounted counterlungs 1.
• hot water is fed to the rebreather set and directed into a hot water jacket 21 around the scrubber/thermal regenerator to preheat and hold the temperature within the scrubber/thermal regenerator at an acceptable level. Heat will be transferred to the breathing gas from the thermal regenerator/scrubber after the actuated mode has been selected even in the worst case situation where the hot water supply to the rebreather set is terminated.
• a moisture separator is incorporated within the backpack 7 primarily to collect suspended moisture from the divers expired breath.
• a further refinement to the SLS system may be the inclusion of a bladder which is inflated by the predetermined over-pressure in the standby mode and positioned so that in normal diving attitudes it is below the packaged co.unterlungs so that when the set is actuated the hydrostatic pressure differential between this bladder and the now open counterlungs causes the gas contained in the bladder to be transferred, via a non-return valve, into the set allowing the counterlungs to fully expand.
• An alternative method is to use a small high pressure bottle which dumps gas into the set on actuation allowing the counterlungs to fully expand.
• a pressure gauge 22 a filter 23; a blow-out plug 24; a dip tube 25; a charging connection 26; a primary life support system exhaust valve 28; and an oral nasal mask 29.

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• Health & Medical Sciences (AREA)
• General Health & Medical Sciences (AREA)
• Pulmonology (AREA)
• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Ocean & Marine Engineering (AREA)
• Respiratory Apparatuses And Protective Means (AREA)
• Molding Of Porous Articles (AREA)
• Vehicle Body Suspensions (AREA)
• Indicating And Signalling Devices For Elevators (AREA)

Priority Applications (1)

Applications Claiming Priority (2)

Publications (2)

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• 1984
  • 1984-11-23 GB GB08429706A patent/GB2169209B/en not_active Expired
• 1985
  • 1985-11-22 EP EP85905862A patent/EP0203133B1/de not_active Expired - Lifetime
  • 1985-11-22 BR BR8507074A patent/BR8507074A/pt not_active IP Right Cessation
  • 1985-11-22 WO PCT/GB1985/000540 patent/WO1986003171A1/en active IP Right Grant
  • 1985-11-22 CN CN85109648A patent/CN1009816B/zh not_active Expired
  • 1985-11-22 ZA ZA858960A patent/ZA858960B/xx unknown
  • 1985-11-22 JP JP60505325A patent/JPS62501280A/ja active Pending
  • 1985-11-22 DE DE8585905862T patent/DE3577074D1/de not_active Expired - Fee Related
  • 1985-11-22 AU AU52001/86A patent/AU580829B2/en not_active Ceased
• 1986
  • 1986-07-21 NO NO862931A patent/NO162063C/no unknown
  • 1986-07-23 SU SU864027986A patent/SU1722222A3/ru active

Non-Patent Citations (1)

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