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Access/egress (entries and exits)

  • Before diving, ensure that you will be able to get into the water and climb out again safely with your diving equipment. 
  • Remember that weather and tides can change while you are underwater, potentially affecting your planned exit point and possibly making it harder to exit the water.
  • Ensure you can successfully regain contact with, and recover, your boat.



  • You should always breathe normally throughout your dive. 
  • Never hold your breath, especially when ascending. If you do so, you might suffer damage to your lungs.
  • You should not “skip breathe”. Skip breathing is when you inhale, then hold the breath in for a while, before exhaling. Skip breathing can lead to a build-up of carbon dioxide in your lungs. 
  • If you are breathing quickly, it could be a sign that something is wrong. You should try to regain control of the dive and your breathing. If possible stop (after signalling your buddy) and take a moment or two to regain control. 
  • If, after stopping, you cannot regain control of your breathing, it could be a sign that you are suffering from a serious problem such as a carbon dioxide toxicity incident/problem or immersion pulmonary oedema. If you cannot regain control you should abort the dive.

Buddy checks

  • A buddy check is an equipment check that you perform with your buddy immediately before entering the water. These checks help ensure that you understand your buddy’s equipment configuration and they understand yours, and that both sets of kit are functioning correctly. BSAC recommends that all divers conduct a buddy check before every dive.
  • As well as checking your kit you should check that you have enough gas for the dive, and that any cylinders are switched on as appropriate.
  • You should also confirm with your buddy what you expect them to do in an out of gas situation. If you are diving a rebreather or a primary donate configuration, a dry run before the buddy check is advisable as a buddy check is not the time to be explaining the out of gas response for the first time. 
  • It’s also a good idea to tell your buddy whether you plan on using your buoyancy compensator (BC) or drysuit for buoyancy, in case they need to lift you to the surface.

Buddy diving

  • BSAC trains divers to be self-reliant. This means that you are trained to manage all parts of the dive yourself, and to resolve the problems that might occur.
  • BSAC recommends that you dive with a buddy. Buddy diving means that divers operate as a unit, with each diver taking some responsibility for the safety of the other(s).
  • Before every dive everyone should be clear who is going to lead the dive, and how you will be positioned underwater. 
  • Trainees without a diving qualification should be led by an Instructor (or an Assistant Instructor under supervision) on training dives. They can be led by a Dive Leader or above on non-training dives.
  • When snorkelling, you should take turns to dive so that one snorkelling buddy is on the surface at all times.
  • BSAC does not provide training for, or support, solo diving, but does train and encourage divers to be self-reliant.
  • There are occasions, for example, in nil visibility or when working underwater, when the ‘buddy’ system is ineffective. On these occasions a solo dive may be required, with the diver being securely roped and in constant rope communication with a surface ‘tender’, who should be a diver themselves. The rope must be securely fastened to a suitable object on the surface. Communication signals must be fully understood and a fully kitted, roped, ‘stand-by’ diver must be immediately available to dive in the event of an emergency.

Building experience

  • As well as formal lessons, building experience is an important part of the Diver Training Programme.
  • The learning process does not stop once you have gained your qualification. You will continue to develop and consolidate your skills through regular use and practice.
  • BSAC recommends that after gaining a new qualification, you build up your experience progressively by practising those skills with more experienced divers, or your peers. 

Build-up dives

  • If you have not dived for a while, BSAC recommends you do some build-up dives to help make sure you’re “dived up”.
  • Similarly if you have not dived to a particular depth for a while, then you should do a series of build-up dives to prepare you for diving at depth again.
  • Any skills not regularly used will deteriorate over time. Due to the good safety record of diving rescue skills are rarely required to be performed for real. If you have not practised rescue skills for a while, then you should think about practising these skills in a controlled environment.
  • Similarly if you dive a rebreather, you should periodically practise bailout ascents to make sure your skills don’t degrade over time.
  • It can take time to get used to changes in your kit configuration, and sometimes they can be a bit unsettling. Therefore, if you change a piece of your equipment, or add something new, or rearrange your existing configuration, BSAC suggests you try it out in a controlled environment before using it on a more challenging dive. Try to limit changes to one at a time. 

Buoyancy and trim

  • Good buoyancy control makes your diving more efficient with the benefit that it is both safer and more enjoyable.
  • You should be able to maintain neutral buoyancy at all points during the dive.
  • During decompression stops, you should aim not to vary your depth by more than +/- 0.5m (for example, a 6m stop should be within 5.5m and 6.5m).
  • You should be competent and confident at managing emergencies, including faulty inflation valves, drysuit inversions and controlled buoyant lifts.
  • During a dive, you will need to adjust your buoyancy to compensate for buoyancy changes due to changes in pressure. This can be done either through adjusting the amount of gas in your drysuit or in your BC.
  • When underwater, BSAC recommends that you should use either the drysuit or your BC for primary control of your buoyancy, but not both at the same time.
  • A drysuit is not a good method for providing positive buoyancy on the surface, and so BSAC recommends that you wear a BC on every dive. 
  • Make sure that you choose the correct size BC. This means that not only does the harness fit you well, but that the buoyancy cell is neither too large nor too small for the rest of your kit. If you use a wing-style BC and it is too large, it can wrap around your cylinder(s) and make it very hard to vent all the gas, potentially causing an uncontrolled ascent.
  • Practice makes perfect. 

Cave diving

  • Requires specialist training and is not covered within BSAC training.
  • BSAC recommends that if you want to go cave diving, you do formal training beforehand. The Cave Diving Group can advise on cave diving in the UK.

Deeper diving

  • If you are planning a deeper dive you should carefully consider the potential hazards and whether the level of risk is acceptable to you and your buddy. In particular you should consider the following risks (many of which are covered in greater detail elsewhere in Safe Diving):

As you dive deeper, the effects of narcosis increase, becoming increasingly noticeable beyond 30m when diving on air. You can reduce this risk by using trimix when diving deep. 

Decompression obligations
Deeper dives often require decompression stops. You should make sure that you are well-prepared (both mentally and with the right equipment) for these stops.

Oxygen toxicity
Deeper dives increase the partial pressure of oxygen within a breathing gas mix towards toxic levels. Deeper dives should be carefully planned to account for this increased risk (see Oxygen toxicity)

Gas density
As you dive deeper, the density of the gas you are breathing increases. This has implications for how much physical effort it takes to breathe (see Work of breathing). You can reduce this risk by using trimix when diving deep, and by avoiding situations that cause you to breathe heavily (such as swimming into a current).

The surface (and help) is further away
This means that it will take longer to reach the surface and you will need more gas. Consideration must be given to the need to resolve problems underwater while accounting for the time to ascend and the implication of any required decompression stops.

More complex equipment
Often you will need more complex equipment to dive deep, including a fully redundant gas supply. This can mean that there are more things to go wrong and diving with unfamiliar equipment can cause problems itself. You can reduce this risk by making sure you are familiar with any new equipment before the dive and practising regularly.

Longer dives
As you dive deeper, you may choose to do dives that require lengthy decompression stops. The increased time in the water can bring on physiological stresses. For example you may need to think about how you will stay warm and hydrated.

Psychological stress
You may find that deeper dives are more stressful mentally, especially if you are not used to diving to a particular depth. This stress can be exacerbated by cold water, complex equipment, poor visibility, and other factors.

Depth limits

  • Divers should adhere to the depth limits set by their qualifications. Extending such depth limits should only be undertaken after gaining further relevant qualifications.
  • Different breathing gases may impose different depth limitations due to the risks associated with the component gases and these must be adhered to.
  • BSAC recommends a maximum depth limit for diving using air of 50m.
  • In an emergency, before carrying out a rescue consideration should be given to personal safety of the rescuer/s as well as their ability to do the rescue. 
  • BSAC recommends a maximum depth of 100m when using helium-based mixed gases by suitably trained and qualified divers.

Depth progression

Except where it is part of the course, such as AOD and technical, depth progression must only take place after the award of the qualification.

  • Depth progression must be conducted by a minimum of Dive Leader (or equivalent) under the on-site supervision of a BSAC Open Water Instructor, or higher.
  • The diver leading the depth progression must have previously dived to the maximum depth of the dive
  • If the divers haven’t dived to their previous maximum depth recently it may be appropriate to complete progressive build up dive(s) to reach this depth.
  • Progression beyond the previous maximum depth should be in increments of no more than 5m.
  • Multiple depth progression increments must not be completed within a single dive, i.e it is not permissible to depth progress from 20m to 25m and then complete a further depth progression from 25m to 30m within the same dive.

The dive planning and buddy drills for depth progression dives need to be of the highest standard.   The diver completing the depth progression is likely to have high gas consumption and may experience nitrogen narcosis so these should be monitored closely.  If there is any doubt the dive should be aborted.

Diving in a three (or more)

  • Diving in buddy pairs is preferable to diving in a three or more. 
  • A key issue in diving with three people or more is the distraction factor, which can affect either the identification of a developing problem or its subsequent resolution. The task loading when diving in threes is increased and requires that all three divers are capable of coping. 
  • Trio diving is not for the inexperienced or those unfamiliar with each other. 
  • Trio diving requires serious consideration by the Dive Manager to ensure that divers with the appropriate level of skill and reliability are grouped together. 
  • A dive plan understood and agreed by all divers prior to entering the water is essential. 
  • It should also be understood and agreed beforehand that the Dive Leader’s decisions and directions will be adhered to. 
  • All three divers should consciously and conscientiously monitor both of their buddies.
  • You should think carefully about how you will position yourself relative to each other.
  • It is recommended that all divers should be equipped to be as self-sufficient as possible; each should have an adequate, completely independent bail-out gas supply; each should carry, and be able to deploy unassisted, a delayed surface marker buoy (DSMB). 
  • Training dives can involve groups larger than buddy pairs and for teaching some skills, for example controlled buoyant, lift this may even be necessary and requires separate consideration. Where appropriate it may be prudent for instructors to be assisted by an experienced diver whose role is to act as safety monitor for both students and instructor. 

Diving with an unfamiliar buddy

  • Sometimes, for example on holiday, you might find yourself diving with a diver whom you have never met before. There are many excellent divers out there, however there is a risk you may find yourself paired with a buddy who has poor buddy skills, dreadful buoyancy or poor gas consumption. There is a lot you can do to reduce the risk of an accident. 
  • Before the dive you should talk to your new buddy about their diving experience.
    - What qualification do they hold?
    - How many dives have they done? 
    - When was their last dive?
  • Observe your new buddy.
    - The way someone puts their kit together tells you a lot about how comfortable and competent they may be as a diver.
    - Does your new buddy seem nervous?

  • Talk through the dive beforehand.
    - Start with the descent; what will you do when you get to the bottom (for example some people like to pause for a couple of minutes to get their breath back). 
    - Then move on to the dive itself. How will you position yourselves? What sort of things do you enjoy when diving? How will you communicate?
    - Talk through the ascent, including whether you will be ascending up a reef, DSMB, or shotline. How quickly do you like to ascend? Does your computer ask you for deep stops? How long a safety stop will you do? Is it at 6m or 5m or 3m?
    - Don’t forget to explain how you will respond in an out of gas situation.


  • When snorkelling or surface diving, BSAC recommends that you shouldn’t hyperventilate before the dive. This is because hyperventilation lowers carbon dioxide levels in your blood, reducing the stimulus to breathe. This means that you could pass out from hypoxia (lack of oxygen) before the urge to surface becomes too great to ignore.

Lines, ropes and nets

  • When diving you should be alert for entanglement hazards such as nets, ropes and lines underwater. This may include lost fishing gear or part of the equipment of a wreck. Other lines might have been laid intentionally by divers. BSAC recommends that you always carry a cutting device such as a knife or shears, and ideally two.
  • Dedicated line cutters can be easier to use than a knife, especially for cutting thin line or a net. Whatever type of cutting device you carry, you should make sure it is sharp enough, and practice beforehand on dry land so that you know what it can do.
  • If you are caught in lines or nets then you should stop and remain calm. Do not twist about or try to turn around as this can make the tangle worse. Instead, you should signal to your buddy. It will often be easier for them to cut you out of the line. 
  • If your buddy does not respond to your distress signal, then keep calm. Think about inflating your BC slightly so that the line is taut and easier to cut. 
  • Try to avoid cutting line that looks like it might have been laid intentionally by other divers; they might be relying on it to (for example) get back to the shot.
  • If you are laying line yourself, then make sure the line is kept taut at all times. You should secure it at regular intervals and at every change in direction. Make sure your line is secured close to the bottom, so that it’s not a hazard to other divers.
  • When laying line, don’t let a loop of line form and float in the water where it might entangle you or others. 

Low visibility

  • You may need to swim more slowly and much closer to your buddy, or even hold hands or use touch to remain in contact.
  • A good torch not only helps you see, but also helps your buddy see you. Consider carrying a spare.
  • If the visibility is so bad that there is no ambient light (you cannot see the “green glow” above), then the risk of swimming into an overhead environment without realising is higher. On sites where this is a possibility you can dive using a distance line, if you are competent to do so, anchored at your point of descent, to provide a route back to a known clear overhead.

Night diving

  • You need to plan your dive carefully when night diving, especially in tidal waters.
  • Being familiar with the site can help with navigation. Where possible explore the site during daylight before night diving.
  • You and your buddy should have a minimum of one working torch each at all times. If your torch breaks, and you don’t have a spare, you should terminate the dive.
  • You should plan how you will exit the dive and how you will be seen on the surface.
  • Avoid shining your torch in your buddy’s eyes.
  • Agree the signals you intend to use. Complex hand signals don’t work as well in the dark, so think about whether torch signals are more appropriate.

No clear surface

  • A no clear surface dive is one where you cannot make a direct return to the surface. Examples include cavern, ice and wreck dives, requiring mandatory decompression stops.
  • Some diving with no clear surface requires different equipment, certain skills and techniques. You should make sure that you have appropriate formal training and equipment for the diving environment you are in. 
  • Lay a line, to provide a route back to the exit.
  • Carry enough gas to get back to the exit point in an emergency situation.
  • Diving under ice should only be undertaken with a surface party of at least two. This allows one to act as tender and one to manage any emergency. One of the divers should be securely roped to the surface and contact between the divers should be by means of a buddy line.
  • Whether to go inside an overhead environment is ultimately a judgement call for you based on your own assessment of the hazards and your own assessment of your abilities, training, and experience. 
  • Similarly your buddy is responsible for making their own decision on whether to go inside an overhead environment. You should not pressure them to do something they are not comfortable doing. Nor should you be pressured yourself.


  • The best solution to feeling panic is to prevent it from occurring in the first place. It is easier to resolve a small problem early on, before it has time to turn into a major issue. 
  • Before the dive you should talk with your buddy, and explain if there are particular things, such as going inside a wreck, which make you nervous, and find out if there is anything they are apprehensive about. Be prepared to abort the dive any time you are not happy about it.
  • Once on the dive, you should try to be self aware. If you are becoming nervous, understand the reasons why, and let your buddy know. 
  • Similarly, you should monitor your breathing rate. If you find yourself breathing hard, it could be a symptom that something is wrong. Stop (after signalling your buddy) and regain control of your breathing. 
  • As part of normal buddy diving, you should also be alert for signs of discomfort in your buddy.


  • When divers need to be recalled to the surface there are several means available.
  • A pre-arranged signal on the line of an surface market buoy (SMB) or DSMB may be sufficient. This can be achieved either by pulling on the line (four pulls is a widely recognised signal for the diver(s) to return to the surface) or by clipping a small karabiner to the line and allowing it to slide down the line to the diver; this karabiner could have a message or coloured tab attached.
  • Thunderflashes can be purchased for use as diver recall signals. 

    - 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.
    - Thunderflashes, like all pyrotechnic devices such as flares should be: stored, transported and operated in accordance with the manufacturer’s instructions; not be used after their expiry date; and should be disposed of properly.
    - Divers are cautioned against taking explosive devices abroad, as they are certain to cause major concerns with travel security personnel. 


  • You should agree with your buddy what you will do if you become separated underwater.
  • If you lose sight of your buddy remember that divers have a blind spot directly behind and above them, so look behind and above you first. 
  • If separated underwater, make a brief attempt (approx. 30 seconds) to re-locate your buddy, after which the divers should surface. Continue to look around during the ascent. 
  • If you re-join your buddy either during the ascent or on the surface consider carefully your decompression requirements before you decide to re-descend. You will almost certainly be increasing your risk of Decompression Illness (DCI).


  • As well as marking a dive site, a shotline provides a good visual reference, making descents and ascents easier and safer to monitor and control.
  • You should not need to hang onto the shotline. Your buoyancy should be good enough that you can hold on with a couple of fingers. However, sometimes the current will be too strong and you will need to hold on more tightly. 
  • Avoid pulling yourself down on a line in a current as you could pull the shot away from the planned dive site. 
  • If you encounter other divers on a shotline, you should be courteous and polite, especially if they are inexperienced. 


  • Divers should be completely familiar with the standard code of visual signals and should give them accurately and clearly.
  • If you are diving with an unfamiliar buddy, check you use the same signals or understand any differences.
  • All signals should be acknowledged.
  • If using rope signals, all divers should have a clear understanding and be practiced in using them.
  • If you need to communicate very complex information, you can always use a slate or underwater notebook.

Technical diving (definition)

  • BSAC uses the term technical diving to encompass mixed gas diving involving the use of helium-based gas mixes and the use of rebreather systems.

Wreck diving

(also see Legislation and The Diver’s Code of Conduct)

  • In poor visibility it is possible to go inside wrecks without realising. If this is the case you should think about laying a line (see No clear surface).
  • Many wrecks are old and decaying, and full of silt, debris, and dangling cables. If you are not careful, you might cause a loose piece of metal to become dislodged or even collapse. 
  • Many wrecks have very sharp edges. You should be careful that you don’t cut yourself or your equipment.
  • Avoid excessive finning inside a wreck as sediment stirred up can be slow to settle, due to lack of tidal flow.

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