Safe Diving Practices D

All dives involve some decompression, which normally takes place during the ascent and subsequent period on the surface. It follows that it is as important to correctly perform

these stages as it is to monitor the dive itself. Decompression computers can assist in this if they are correctly used and are programmed to an appropriate algorithm. This means that for a simple rectangular profile they should give dive times at least as conservative as the BSAC 88 decompression tables.

All dives must be planned using a decompression tool the diver has been trained to use. These could include hard copy tables, PC generated tables or a dive computer. Whatever primary decompression plan is being used the diver must also have a back up plan.

It is important to realise that both tables and computers are unable to make allowance for factors such as age, fitness, exertion, obesity and injuries, which may all significantly affect susceptibility to decompression illness. Divers should therefore be aware of these factors and avoid diving beyond their limits. Take particular care when planning repeat dives. Where two or more dives are being made the same day it is good practice to carry out the deepest dive first. It is also good practice to achieve maximum depth as early in the dive as possible and to avoid redescending once any ascent has commenced.

Decompression illness

Decompression illness (DCI) symptoms vary between those so sudden that immediate air evacuation to a chamber is vital, to those which may not become apparent for some hours. Some of these less dramatic symptoms, such as tingling and numbness, may well be delayed but can be more serious and produce greater disability than the excruciating pain often associated with DCI in a joint. Tingling and numbness are included in this category.

Severe DCI symptoms, occurring at sea, require rapid transfer of the subject to a recompression chamber, laid flat on their back and if possible, the administration of 100% oxygen and fluids. Being bounced, repeatedly, in a small boat is almost certainly going to worsen the symptoms rather than help the situation.

For assistance with decompression illness, advice in the UK can be obtained from the National Decompression Illness Helpline.

When at sea, contact should be made via the Coastguard on VHF Channel 16. When on shore, contact can be made via the following 24-hour telephone numbers:

If calling in England, Northern Ireland or Wales call 07831 151 523 to be connected to the BHA / RN Diver Helpline.

If calling in Scotland call 0845 408 6008 to be connected with the Aberdeen Royal Infirmary.

For other emergency assistance, when ashore in the UK, use 999 or 112, as usual.

When diving outside of the UK, ensure that you know the local emergency contact procedures.

(See BSAC 88 deco tables / Oxygen)

Decompression stops

Dives requiring decompression stops should be well planned beforehand and executed according to recommended techniques. Avoid deciding upon decompression stops once in the water.

An accurate means of measuring depth and time is essential and all decompression stops should be carried out using a suitable decompression system, static line, decompression trapeze or a minimum of a delayed SMB. For the longer decompression schedules the use of a decompression station is recommended as spare gas can be attached to the system and the entire dive team are together. It also assists the surface team, who only have to monitor one decompression station.

Any diver who has missed planned decompression stops could be suffering from decompression illness and should be returned to the shore as quickly as possible. No attempt should be made to carry out any form of re-entry decompression as this inevitably worsens the situation. The diver should be treated as a potential casualty, kept quiet and administered oxygen and oral fluids. Emergency advice should be sought and their recommended actions followed - see the section on Decompression for contact information.

(See BSAC 88 deco tables / Decompression / Oxygen)

Delayed surface marker buoy

A delayed SMB (DSMB) is no substitute for a fixed shot-line and, wherever practical, a shotline should be used for the ascent and descent phases of the dive. However there are situations where the use of a shot line or a conventional SMB may not be appropriate, and in these circumstances consider the use of a delayed SMB. Ensure that you practice deployment and usage of the delayed SMB in safe, simulated conditions before using one in earnest, and when deploying the delayed SMB do not attach the free end of the line or reel to yourself, or to other personal equipment. Ideally the reel should be attached to some feature on the bottom (such as a wreck), during deployment, to avoid the risk of being pulled towards the surface.

Many divers now carry two DSMBs, often one yellow and one red. The purpose here is to have the red one for general use when making a normal ascent. When a problem arises and divers wish to notify the surface cover that they need assistance, the yellow and red ones will be sent up together and on the same line. For dives where a direct ascent to the surface is inadvisable (e.g. dives involving planned decompression stops), the BSAC recommends this as a good practice.

Depth limits (Air diving)

A depth of 50 metres is recommended as the limit for normal recreational air diving. Within this limit BSAC divers have additional restrictions upon the maximum depth to which they should dive, dependent upon their diving grade. The specific depth limitations for each grade are contained within the current Diver Training Programme, Qualification Record Logbook and on the BSAC website http://www.bsac.org/page/278/syllabus--sequencing.htm

There is evidence that decompression illness is more likely to occur on dives deeper than 50 metres, even though decompression tables may be strictly adhered to, and such occurrences are usually serious, with central nervous system (CNS) involvement. When diving deeper than 30 metres, special care with planning is vital, and recommended deep diving practices should be adhered to. The NDC strongly recommends that dives in excess of the recommended maximum depth limits should not be undertaken by recreational divers.

Depth limits (Technical Diving)

The BSAC recommends: -

For oxygen / nitrogen gas mixes, a maximum depth the lesser of 50 metres or the depth at which the partial pressure of oxygen in the mix reaches 1.4bar. When diving with oxygen enriched mixtures it is essential that the maximum operating depth for the mixture is adhered to. Failure to do so may have fatal consequences due to the onset of oxygen toxicity.

For oxygen / nitrogen / helium or oxygen / helium gas mixes a maximum of 80 metres. The use of helium mixtures is recommended for depths deeper than 40 metres. (See also Equivalent narcotic depth)

All divers using mixed gas should be suitably qualified in its use.

Divers planning an expedition may conduct dives to depths beyond those currently recognised by the BSAC provided that they have recognised qualifications gained outside the BSAC. Dives in excess of 80 metres demand very serious dive planning and logistical requirements including support diver teams, etc. There is also the added potential risk for these deeper dives.

Specific details of depth limits and the implications of exceeding them for divers and those responsible for Dive Management are covered in the document “Dive Definitions‿ which can be found on the BSAC website at http://www.bsac.org/page/674/branch-dives.htm

Distress at sea

Distress at sea can range from an extreme form of decompression illness, where life is threatened, to divers being lost on the surface having been swept away by the tide. Procedures to deal with such a range of emergencies are as follows:-

Any dive boat at sea requiring Search or Rescue assistance for a missing or overdue diver should use a 'MAYDAY' call if life is in danger. Less serious, but nonetheless urgent requests (e.g. a boat drifting with no engine), may warrant a 'PAN PAN' (Urgency) call. For vessels with Digital Selective Calling (DSC), a DSC alert should be activated on Channel 70 followed by a voice call on Channel 16. For non-DSC equipped vessels the call should be made on Channel 16. If your boat does not carry VHF radio it is sometimes possible to attract the attention of passing vessels who may radio on your behalf.

Flares can be used to attract attention, either from the shore or from other vessels in the area. It is important that flares are not wasted, so only fire them if there is someone likely to see your signal. Several Maritime and Coastguard Agency reports, each year, indicate that some divers leave it too long before raising the alarm. Do not delay too long if you are convinced problems are arising which you cannot control.

For distress at sea, where decompression illness is involved, see Decompression.

Dive computers

Dive computers offer accurate and automatic recording of depth and time and continuously calculate the diver's decompression requirements according to the depth and duration of the dive. Computers are also available with advanced features such as the ability to calculate decompression requirements for a variety of nitrox mixes and mixed gases, and also to monitor available air and air consumption rates. The use of a dive computer is no substitute for proper dive planning, including proper attention to air requirements and dive time.

It is recommended that divers choose a computer which is at least as conservative as the BSAC 88 decompression tables on a rectangular dive profile. Individual susceptibility to decompression illness varies and can be affected by a number of factors, for which no computer or decompression table is able to allow. Divers should be aware of this and avoid pushing computers beyond their limits. The advice on safer diving attached to use of the BSAC 88 tables applies equally to computer users and should be followed.

(See BSAC 88 deco tables)

Dive discipline

It is a rule of the BSAC that the Dive Manager has the authority of the Branch Diving Officer to suspend a member from diving if instructions are not obeyed.

(See Authorised branch dives).

Dive leadership

See Authorised branch dives / Buddy diving / Dive planning and organisation.

Dive management (Used to be dive marshalling)

The Dive Manager should be appropriately qualified or have an assistant who is qualified for the dive(s) to be undertaken.

The Dive Manager must know and document:-

Divers’ names and pairing
Divers’ cylinder size and contents
Divers’ planned decompression schedule
Divers’ planned decompression technique
Divers’ back up plan in case of an emergency
Dive start and finish times

The Dive Manager should complete a full dive log.

Additionally for mixed gas diving the Dive Manager must know and document:-

Divers’ gas mixes for bottom, travel and decompression
Divers’ maximum operating depth (MOD)
Divers’ cylinder sizes and contents for all gases
Rebreather divers’ absorbent material life and primary set-points

Dive planning and organisation

When planning any dive the following factors should be considered:-

The divers’ experience and qualifications
The divers’ current fitness to dive
The divers’ depth limitations
A suitable dive platform and experienced skipper (for boat diving)
A safety backup plan for all aspects of the dive in case of an emergency

Additionally, technical diving involves planning for the various combinations of gas mixtures to be used at different depths and also accounting for loss of gas mix scenarios. This requires a very disciplined diver to both plan and then execute the dive as planned.

The technical dive plan should consider:

The 80 metre depth limit
Manufacturers’ equipment specific depth limit recommendations
The MOD (maximum operating depth) of the gases being used
END (Equivalent narcotic depth)

When boat dives are taking place, divers should make sure that a responsible person on shore has details of the dive plan and estimated time of return. The Maritime and Coastguard Agency (MCA) is always grateful for a phone / radio call to brief them of your intentions, and confirmation that you have returned to shore safely.

Accurate records of diver training, dives and expeditions should be kept at all times.

Diving flag

The international code flag 'A' should always be flown when divers are in the water. For small boats it should be at least 1/2 metre square and should have the means to fully extend it in calm conditions. It should not be flown when travelling to or from a dive site.

Diver propulsion vehicles

A diver propulsion vehicle (DPV) is a very effective and effortless way for the diver to cover a large underwater area. By riding, or being dragged along by the DPV, the diver is provided with greater mobility and range for the dive, as well as breathing a reduced amount of the appropriate breathing mixture due to the reduced effort required for motion. Such a reduction in gas consumption may therefore also allow the diver to spend a longer period of time underwater, subject to the personal decompression requirements.

The major risks related to DPVs are listed as follows:-

Difficulty looking at, and therefore properly monitoring, pressure, depth and other gauges whilst holding on to the DPV. However the diver can pause from time to time to review these instruments.
Loss of equipment due to the speed of the DPV. The diver will need to ensure that all ancillary equipment such as torches etc. is securely strapped to the person, and, in addition, do not dangle from the body where they could fall into the propeller guard.
Barotrauma and other pressure related injuries could occur as a consequence of a rapid descent, and particularly on the ascent. Due to the potential speed that the diver may travel using a DPV, these vehicles should be very carefully used for the descent and ascent phases of the dive.
Diver separation from the buddy could occur, unless the buddy also has a DPV. It is important that both members of the buddy pair use DPVs, since if only one member of the pair has such a vehicle then it is quite possible that the pair may become separated due to their obvious different speeds of movement through the water.
Collision in poor visibility; always a potential risk, but unlikely.

Diver recall systems

When divers need to be recalled to the surface there are several means available. If they are using SMB's a pre-arranged signal on the line is sufficient. Thunderflashes can be purchased, but ensure they are of large enough size and that they are weighted, before you need them, so that they will sink before they explode. Endeavour to allow divers to safely experience a thunderflash going off as a training drill so that they will recognise the sound when they experience it in a real situation.

There is also a diver recall system available using a .38 'blank' cartridge. This allows several signals to be fired. Divers are cautioned against taking such devices abroad, particularly when flying.

Drugs

If you are taking prescribed medication of any kind, do not dive unless clearance has been given by an approved UK Sports Diving Medical Committee referee.

Drysuits

There are three main types of drysuit in common use, the membrane type (which requires adequate undersuit thermal protection), compressed or crushed neoprene (which requires some undersuit thermal protection) and foam neoprene drysuits. Each type has different weighting requirements. The buoyancy a drysuit provides cannot be guaranteed to support a diver on the surface safely - the air in the suit is too easily vented when swimming or in rescue situations. For this reason, plus the common sense of having a 'redundant' method of obtaining controlled buoyancy, a buoyancy compensator (BC) should be worn.

Drysuit training can be undertaken by branches during initial training or at any time in later training. Sheltered water / pool training, is essential before progressing to open water. Do not wear excess weight when using a drysuit, wear just sufficient to be neutrally buoyant at 6 metres with a nearly empty cylinder. Divers have experienced problems on ascents because they have used both buoyancy compensator and drysuit to compensate for buoyancy loss, and have not enough hands to operate all the controls plus coping with whatever else they might be carrying.

Drysuited divers should include their method of achieving neutral buoyancy as part of the buddy check and dive brief. Dry suits are generally not capable of supporting a controlled buoyant lift (CBL) since gas can escape through the neck seal and render the diver negatively buoyant.

The NDC recommends that drysuited divers adjust their buoyancy underwater by introducing air into their drysuits, rather than into their buoyancy compensators.

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Page last modified: 1st Jun 2007 - 09:26:21