Safe Diving Practices R

Rebreathers - Ascent

A rebreather diver should ascend slowly to allow proper venting of the breathing loop and to avoid becoming positively buoyant.

Rebreathers - Boats
Increased care must be taken when manoeuvring a boat in the vicinity of rebreather divers as they may produce no, or very few, obvious bubbles. Boathandlers should be aware that a rebreather diver may surface unexpectedly, especially just after the initial descent. The boathandler should therefore patrol the dive site at a safe distance to enable an unplanned ascent by the rebreather diver.

The rebreather diver should deploy a delayed SMB before surfacing unless they are returning up a fixed datum.

The suitability of a boat as a diving platform and also the stowage possibilities for the rebreather to ensure adequate protection of rebreather units (e.g. hoses and cylinder valves) should be considered.

Rebreathers - Breathing

It is recommended that rebreather divers make a conscious effort to breathe freely and normally. Many open circuit divers skip breathe, whether consciously or unconsciously. This practice will lead to carbon dioxide retention and is highly dangerous when applied to rebreathers.

Pre-dive breathing checks should be conducted prior to entering the water.

Rebreathers - Bubble check

As early in the descent as possible, but preferably no deeper than 6m, a bubble check should be performed to identify potential leakage.

Rebreathers - Buddy diving

It is important to ensure the rebreather diver is partnered with a buddy who can assist them in the event of a problem. Therefore, the BSAC recommends that, in order of preference, the buddy of a rebreather diver should be:

To 40 m maximum:-

·         Another rebreather diver using the same type of rebreather (i.e., CCR with CCR or SCR with SCR)

·         Another rebreather diver using a different type of rebreather (i.e., SCR / CCR mix)

·         An open circuit diver.

From 40 m to 80 m:-

Within this depth range rebreather dives will involve the use of gas mixes including helium and hence the above order of preference is modified to:-

·         Another rebreather diver with an appropriate mixed gas qualification using the same type of rebreather.

·         Another rebreather diver with an appropriate mixed gas qualification using a different type of rebreather.

·         An open circuit diver. Note: If diving below 50m the open circuit diver will also require an appropriate mixed gas qualification.

If the buddy is not to be a rebreather qualified diver then:-

·         The buddy of a rebreather diver (whether SCR or CCR) should be, as a minimum, a qualified Sports Diver with their DO's consent.

·         For dives to greater than 35m, the buddy should be either a minimum of Dive Leader or a qualified Sport Diver holding an appropriate deep diving certification from a recognise training agency,

·         For dives to greater than 50m the buddy should hold an appropriate mixed gas qualification from a recognised training agency.

·         The DO (or DM acting on behalf of DO) should ensure that the diver who will buddy a rebreather diver is:-

o        Experienced under the current diving conditions (i.e. depth, site and weather).

o        Capable of recognising the conditions of hyperoxia, hypoxia and hypercapnia.

o        Capable of performing a rescue (CBL and surface support) on the rebreather diver in the case of an emergency.

o        The buddy of a rebreather diver should be diving using a gas mix appropriate to the intended depth and be suitably equipped.

·         The buddy of any rebreather diver should carry an independent bale out (i.e. redundant) breathing system. The capacity of this independent system (e.g. pony or twin set) should suit the dive profile of the dive being undertaken.

·         The buddy should carry a DSMB (or SMB as appropriate) and at least one other surface detection aid.

·         The buddy check procedure should be modified to accommodate the rebreather layout and any controls the buddy may need to operate.

Rebreathers - CO₂ absorbent material

It is imperative that for all rebreather diving the manufacturer's recommendations regarding both the type of absorbent material(s) and its effective duration are followed.

Absorbent material should be stored and disposed of according to the manufacturer's instructions.

It’s important to note that long car journeys, bumpy boats trips, airplane flights and anywhere where there is vibration can have an effect on the packing of the absorbent material, possibly causing settling or ‘channelling’. Both of these effects can adversely affect the performance of the absorbent material. This impact can be minimised by packing of the absorbent material as late as is practicable before the dive commences.

Rebreathers - Decompression

The available entry-level training for rebreather diving incorporates limited decompression using nitrox as the breathing gas in rebreathers. Normoxic and full mixed gas rebreather training courses, available from recognized training agencies, provide qualifications involving more extended decompression diving.

The BSAC recommends that when using a rebreather for dives involving decompression, the maximum planned decompression requirement should not exceed that permitted by the unit manufacturer and / or the training agency certification held by the rebreather diver.

For the decompression phase of the dive, the maximum pO₂ should be limited to a set-point of 1.4 bar; actual pO₂ must not exceed 1.4 bar below 6m, and 1.6 bar between 6m and the surface.

Rebreathers - Equipment standard

Each model of rebreather is designed by its manufacturer to operate under a specific set of conditions and using specific gas mixes. These conditions may differ, not just from manufacturer to manufacturer, but also from model to model. Rebreather divers should ensure that they fully understand and observe the performance limits of their particular equipment. There is a growing range of independently produced modifications for rebreathers. Before applying any such modifications to their rebreathers, divers should understand that any such modification extends the equipment beyond the design parameters envisioned by the manufacturer. Any such modification is therefore entirely at the risk of the user who needs to satisfy themself that the modification is not detrimental to the performance of the equipment.

As part of the buddy check, the buddy of the rebreather diver should clearly understand the implications of the particular configuration of rebreather being used.

Rebreathers - Hygiene

Rebreather divers should always disinfect the breathing loop in accordance with the manufacturer's recommendations.

Rebreathers - Maintaining breathing loop volume

The BSAC firmly believes that all rebreathers should be designed and manufactured as standard with an automatic means of maintaining an adequate breathing loop volume during the descent, to minimise the task loading to the rebreather diver.

The manual addition of gas to maintain the breathing loop volume is required when an automatic diluent addition valve is not fitted, is isolated or fails. Under such circumstances a slow descent is recommended so that gas addition and buoyancy control can be managed without excessive task loading. The pO₂ in the breathing loop should be monitored to avoid excessive values during descent.

Rebreathers – Oxygen monitoring

The BSAC firmly believes that all rebreathers should be designed and manufactured with a facility for monitoring the oxygen within the breathing loop as standard. Furthermore, the BSAC strongly recommends that rebreathers should not be used without an effective and efficient, real time pO₂ and / or FO₂ monitoring system that enables the diver to know their precise content of oxygen in the loop at all times. Where such a system is fitted to a rebreather, the reading should be checked regularly and appropriate action taken if it is not at the expected value.

Closed circuit rebreather divers should always use a diluent gas that has a pO₂ equal to or lower than their maximum selected set-point to facilitate effective diluent flushes.

Rebreathers - Oxygen cells

Oxygen cells fitted to rebreathers should be changed at the interval recommended by the manufacturer.

Rebreathers - Pre-dive checks

Pre-dive checks should be conducted in accordance with unit specific training, including pre-breathing the unit prior to entering the water.

Rebreathers - Rebreather diver rescue

Rebreather divers should ensure that their buddy understands the operation of their rebreather. The provision of adequate buoyancy to recover the casualty to / support the casualty at the surface, in the event of a rescue, should be emphasised. This may involve the need to close off the rebreather mouthpiece to counter the negative buoyancy incurred by loss of gas from the breathing loop.

Rebreathers - Rebreather training

Divers wishing to use rebreathers should complete a training course provided by a recognised training agency. BSAC has introduced training courses for both SCR and CCR rebreathers. The training course should be specific to the particular rebreather that they wish to use and should be recognised by the manufacturer of that equipment.

Divers wishing to extend their use of rebreathers to include gas mixes other than nitrox should complete a further unit specific training course, provided by a recognised training agency, covering the use of such gas mixes. BSAC has introduced mixed gas rebreather courses.

For diving within the BSAC, qualified rebreather divers should register a copy of their highest rebreather qualification (entry level initially and, if subsequently upgraded, for mixed gas also) with BSAC headquarters.

Recognition will be sent in the form of a BSAC qualification record book certificate.

Semi-closed rebreathers (SCR)

SCR - Ascent

A slow controlled ascent is important to avoid a drop in the partial pressure of oxygen (pO₂) in the breathing loop to hypoxic levels. It is therefore recommended that, whenever possible, ascents are made via a shot line or some other fixed datum.

A SCR diver should flush the breathing loop before commencing an ascent, to ensure that the FO₂ is at a maximum and try to maintain this FO₂ during the ascent profile.

SCR - Flow rate

When using an SCR the flow rate and gas mix recommended by the manufacturer for the planned dive should always be used.

The flow rate should be tested prior to every dive to ensure it is within the manufacturer’s prescribed limits.

SCR - Surface swims

If a semi-closed circuit rebreather diver has to make a surface swim, the BSAC strongly recommends that, in order to avoid the potential of hypoxia, the swim is completed using an open circuit regulator. If the gas within the bale out cylinder is planned to be used for a surface swim, then the pre-dive gas planning should take this into account when selecting the bale out cylinder.

Closed circuit rebreathers (CCR)

CCR - Batteries

Any batteries in a rebreather should be changed or charged at the recommended intervals.

Where batteries are rotated the new or fully charged battery should be powering the slave monitor wherever there is redundancy of control systems incorporated in the rebreather. This means that if the master battery fails there will always be an effective battery to power the control system.

CCR - Partial pressure of oxygen (pO₂) / Set-Point

The BSAC recommends the following maximum partial pressures of oxygen / set-points for the breathing mix for CCR diving:

1.3 bar set-point during the dive

1.4 bar set-point during decompression.

When diving using gas mixes other than nitrox, the depth exposure and decompression obligations can result in significant exposure to high partial pressures of oxygen and its attendant CNS toxicity. For such diving use of a partial pressure / set-point lower than 1.4 bar / 1.3 bar should be considered.

Rebreathers in BSAC training

A BSAC publication titled "Rebreathers in BSAC Training" outlines the recommendations for the use of rebreathers in branch diver training and for BSAC events such as Skill Development Courses and Instructor Training Events. This publication is available from BSAC HQ or can be downloaded from the BSAC web site http://www.bsac.org/page/441/rebreathers-in-training.htm

Re-entry decompression

If a diver misses planned decompression stops, no attempt should be made to enter the water again in order to complete them. In this situation the diver is increasing the risk of decompression illness and merely placing a possible casualty in a hostile environment.

Repeat dives

An appropriate planning tool should be used whenever planning and performing repeat dives. Where two or more dives are being made the same day, it is good practice to carry out the deepest dive first. You should also take care if you are involved in several days of diving deeper than 30m. It is probable that excess nitrogen will be accumulated over this period, and apparently 'innocent' dives, carried out near the end of the period of diving, can cause decompression illness. It is therefore recommended that any dive series involving consecutive days diving to 30m+ is limited to three days, after which a 24 hour break should be taken.

(See BSAC 88 deco tables (Air and nitrox diving))

Rescue breathing and cardiac compression

When rescue breathing on land, the rate of ventilations should be judged by monitoring the rise and fall of the casualty's chest and the sound of the casualty's exhalations. To give a rescue breath take 1 second to inflate, and then watch for the chest to deflate.

When in water, the rate should be a minimum of 2 breaths/15 sec.

When demonstrating or practising rescue breathing in the water, a proper seal (usually nose), should be made. A simulated seal is not sufficient to give the sense of realism required, and does not guarantee a successful acquisition of technique. The use of a manikin is strongly recommended when practising rescue breathing on land.

Cardiac compressions should never be practised on a conscious breathing subject; a manikin should always be used. Cardiac compressions should be at a rate of 100 compressions/min.

When both techniques are being used a sequence of 30 cardiac compressions followed by 2 rescue breaths should be used.

Ropes

Divers should take great care with the use of ropes underwater, especially using reels as distance lines from shot lines. Reels for SMB use should have a quick release system such as a bayonet fitting snap lock and divers should be taught how to use them. When divers do get into difficulties on ascent it is often the best course of action to ditch the reel so that both hands are free to deal with the situation. When using a reel and line as a bottom distance line, we recommend that a reel and line which sinks is used and that when deploying line, hold the reel and line away from the body and especially the legs. It should also be recovered from in front of you. Never let a bight of line develop in front of you; slow down and wind in.

Divers should always carry an adequate knife, especially when dealing with ropes.

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Page last modified: 18th Dec 2006 - 10:53:08