BSAC Technical Publications - Safe Diving Practices D-H LEARNING TO DIVE MEMBER SERVICES TECHNICAL SERVICES FORUMS BSAC WORLD SNORKELLING MAIL SHOP NEWS TECHNICAL SERVICESSearch the BSAC Site: sitemap BSAC TECHNICAL PUBLICATIONS SAFE DIVING PRACTICES D-H A-C | I-P | Q-Z | Code of Conduct | Rebreathers Decompression 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 for a simple rectangular profile they should give dive times as conservative as the BSAC 88 Decompression Tables. 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 (DCI). 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 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 01224 681 818 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 Decompression Tables/Oxygen) Decompression Stops The NDC considers the BSAC 88 Decompression Tables to be the safest sports diving tables available in the world and recommends their use. In areas of the world where other tables are being used, members should check the correct application of these tables and if in doubt use the BSAC 88 tables. 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, as is an appropriate means of controlling the depth of the stops, such as a shotline. 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 Decompression Tables/Decompression/Oxygen) Delayed SMB A Delayed SMB is no subtitute 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. Depth 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 and Qualification Record Logbook. There is a statistical 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 involvement. When diving deeper than 35 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. 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 dives in excess of 50 metres mixed gas or Trimix should be used and the BSAC recommends a maximum depth of 70 metres. All divers using mixed gas should be suitably qualified in its use. 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 (DCS), a DCS alert should be activated on Channel 70 followed by a voice call on Channel 16. For non-DCS 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 Discipline It is a rule of the BSAC that the Dive Marshal 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, also Dive Planning and Organisation. Dive Planning and Organisation When boat dives are taking place, make sure that a responsible person on shore has details of your 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 in order to sink before you need to use them. Endeavour to allow divers to 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 two main types of drysuit in common use, the membrane type (which requires adequate 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 (BCD) is 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. They should also advise their buddy on whether their suit is capable of being used as the main source of buoyancy during a Controlled Buoyant Lift, or whether their BCD will have to be used. The NDC recommends that drysuited divers adjust their buoyancy underwater by introducing air into their drysuits, rather than into their buoyancy compensators. Explosives It is extremely dangerous to attempt to recover or retain live explosive devices. Immersion in water could render them very unstable, especially if they are consequently dried out, so keep well clear of any such devices you find. If you consider that they are in a dangerous location, inform the Maritime and Coastguard Agency (MCA). Never: (i) attempt to bring them to the surface and on no account abandon them in shallow water, or on the beach; (ii) undertake the use of underwater explosives for carrying out underwater work without a recognised course of training; (iii) dive near sites where underwater explosives are being used since the shock waves can be fatal. Fitness to Dive Diving uses as much energy as moderate to heavy work. Before resuming diving, after a lay off, you are advised to regain physical fitness, practice basic underwater skills in the pool or sheltered water training area and complete a series of 'work up' dives before diving to depth. Ensure all divers are both physically and psychologically fit for the dives they plan to undertake. Flares Orange smoke and red handheld/parachute flares should be carried by all dive boats in order to attract attention when in difficulties at sea. Similar flares, in waterproof containers, are available for divers to carry in the event of them becoming lost at sea. Flares should not be used for signalling purposes in a non-emergency situation. Gun type flare launches require a Firearms Certificate for use within the UK. Divers are cautioned against taking such devices abroad, particularly when flying. Flying and Diving Flying or travelling to altitude after diving can give rise to decompression illness. Flying or travelling to altitude before diving, may increase the risk of decompression illness on a subsequent dive. It is therefore recommended that divers use the BSAC 88 Decompression Tables (Levels 1-4) to determine whether the proposed dive/journey combination is acceptable. (See BSAC 88 Decompression Tables/Altitude) Hyperventilation Hyperventilation, before a snorkel dive, should be avoided at all costs, as it has the effect of flushing out carbon dioxide from the respiratory system. Build up of carbon dioxide, rather than lack of oxygen, creates the desire to breathe and, by getting rid of carbon dioxide in this way, snorkellers are more likely to suffer a 'blackout' through hypoxia (shortage of oxygen). A-C | D-H | I-P | Q-Z OTHER BSAC TECHNICAL PUBLICATIONS ©2003 BSAC | Home Page | Member Services | Technical Services | News