• Asphyxia by drowning.


• 
  Near drowning is the survival of a drowning event involving unconsciousness or water inhalation and can lead to serious secondary complications, including death, after the event.^[4][5]
  

• Avoid out of air emergencies underwater.


• Provide appropriate buoyancy.


• Avoid or prevent accidents resulting in unconsciousness.


• Use of a full face mask.


• Use of helmet.


• Use of surface supplied diving equipment with voice communications.


• Adequate swimming skills and fitness for the circumstances.


• Use of snorkel when appropriate.


• Lifejackets that hold the wearer's face above the water may be worn when appropriate.

• Exudation of liquid into the lungs (pulmonary edema) over the hours following aspiration of liquid, which reduces the ability to exchange air and can lead to a person "drowning in their own body fluid".


• Aspiration of vomit can have a similar effect.

• Correct maintenance, preparation and pre-use procedures and checks.

• Correct use of recommended procedures and checklists when preparing for use.

• Adequate and redundant instrumentation for monitoring gas quality during use.


• Constant vigilance during use.


• Adequate bailout facilities in case of failure.


• Adequate training in the use of rebreathers in general and the specific model.

• Gas requirements planned to suit the intended dive profile.


• Use of a travel mix for descent and a decompression mix for ascent through the depth range where the bottom gas is hypoxic.


• Safe procedures used for gas changes.^[7]
  

• Gas switches planned and executed at appropriate depths.^[6]
  


• Depth and ascent rate accurately monitored and controlled.


• Clear and unambiguous identification of cylinder gases.

• Adequate training in the use of mixed gases.

• Routine periodical inspection and testing of cylinders.


• Analysis of oxygen fraction of gas before use, particularly if cylinder has been stored for a long time.

• Closing and jamming of the cylinder valve by rolloff on something overhead (rotation of the knob to close the valve by friction when dragged along in contact with a surface), or by kelp when pushing through dense kelp.


• Rupture of a bursting disc overpressure protection on a cylinder valve (a thin metal membrane calibrated to fail if the pressure exceeds a safe value for the cylinder).


• Rupture of a regulator hose or loss of the end component, leaving an open hose end.


• Unrecoverable free flow of a second stage (valve jammed open, allowing gas to escape even when not needed by the diver).


• Freezing of a first stage regulator, locking the valve mechanism open, and consequent free flow of the demand valve due to excessive interstage pressure.


• O-ring failure at the connection of a regulator to a cylinder valve.

• Appropriate maintenance and servicing of equipment.


• Inspection of the external condition, and testing of the function of equipment before use.


• Use only of equipment in good working condition.


• Connection and mounting of equipment to minimise risk of damage.


• Avoidance of damage to equipment during dives.


• Use of two fully independent breathing gas supplies.^[10]
  


• Use of bailout gas supply.


• The buddy system, when correctly followed, allows the diver's buddy to supply breathing gas in an emergency.


• 
  "H" or "Y" type cylinder valves or manifolded twin cylinders with two cylinder valves allow the dysfunctional supply to be closed to prevent total loss, and the other regulator to be used for the remaining gas supply.


• Dual independent cylinders ensure that if one cylinder supply fails there is another available.


• Use of DIN connections can reduce the risk of catastrophic O-ring failure.^[11]
  


• 
  Emergency free ascent may be possible, and is generally more survivable than drowning.

• Adequate training of divers.


• Disciplined attitude and situational awareness during dives.


• Use of reserve valve.


• Use of surface supplied diving equipment.


• Use of bailout gas supply.


• The buddy system, when correctly followed, allows the diver's buddy to supply breathing gas in an emergency.

• Situational awareness underwater.


• Use of a diver's net cutter, or dive tool/knife to cut free of entanglement.


• Carrying sufficient gas in reserve to allow a reasonable amount of time to deal with emergencies.

• Appropriate safety equipment and procedures to avoid getting lost (cave lines).


• Specific training for overhead diving. See cave diving and wreck diving.


• Assess stability of underwater structures and avoid entry if a structure is unstable.

• Post-dive cough, with or without sputum, usually suppressed during the dive.


• In serious cases the sputum may be bloodstained, frothy and copious.


• Over time further symptoms may develop, including:

• rigors, tremors or shivering;


• nausea or vomiting;


• hot or cold sensations;


• dyspnoea; cough; sputum;


• headaches; malaise; and generalised aches.

• Appropriate maintenance and servicing of equipment.


• Inspect external condition and test function before use.(specifically test the seal of exhaust valves and possible leaks in the second stage casing and mouthpiece before opening the cylinder valve).


• Use equipment only if it is in good working condition.


• Use of alternative air source if DV breathes wet during dive.


• The technique of inhaling slowly and using the tongue to deflect spray particles may be effective as a temporary mitigation.

• Initial symptoms include: headache, nausea, malaise, and fatigue.^[14]
  

• Headache is the most common symptom; it is often described as dull, frontal, and continuous.^[15]
  

• Increasing exposure produces cardiac abnormalities including fast heart rate, low blood pressure, and cardiac arrhythmia;^[16][17]central nervous system symptoms include delirium, hallucinations, dizziness, unsteady gait, confusion, seizures, central nervous system depression, unconsciousness, respiratory arrest, and death.^[18][19]
  

• Adequate precautions to ensure that intake is in uncontaminated air when operating breathing air compressors.^[20]
  


• Periodical air quality testing of compressors.


• Use of compressor output filter containing "Hopcalite" catalyst to convert possible carbon monoxide contamination to less hazardous carbon dioxide.


• Test air quality before use (portable carbon monoxide analysers are available and may be worth using in places where air quality is questionable).


• Air contaminated with carbon monoxide is often contaminated by substances having a smell or taste. Air smelling or tasting of exhaust fumes should not be breathed.

• Adequate maintenance of the compressor.


• Use of correct oil rated for breathing air compressor lubrication.^[20]
  


• Ensure compressor running temperature is within manufacturer's specifications.


• Ensure adequate supply of cooling air to compressor.


• Compressor should not be run when ambient temperatures exceed manufacturer's limits.

• Use of a suitable separators and air filter after compression.^[20]
  

• Monitor and drain separators and change filters as necessary.

• Periodic testing of delivered air quality.

• Smell and taste can distinguish oil contamination in many cases.


• Passing a metered quantity of the air through an absorbent filter paper may show up an oil deposit.


• Directing air flow onto a clean mirror surface or glass sheet may show gross contamination.

• Symptoms and signs of early hypercapnia include: flushed skin, full pulse, increased breathing rate, shortness of breath, muscle twitches, hand flaps, reduced neural activity, headache, confusion, lethargy, increased cardiac output, an elevation in arterial blood pressure, and a tendency for cardiac arrhythmias.^[24][25]
  


• In severe hypercapnia (generally partial pressure of CO₂ greater than 10 kPa), symptoms progress to disorientation, panic, hyperventilation, convulsions, unconsciousness, and eventually death.^[26][27]
  

• Re-inhaling carbon dioxide-laden exhaled gas due to excessive dead space in breathing apparatus.


• Shallow breathing—not exchanging sufficient air during a breathing cycle.

• Minimise the volume of any enclosed spaces through which the diver breathes. For example, this can happen with diving with a large "bubblehead" helmet.


• Avoiding breathing shallow (low volume) breaths.

• Adequate maintenance of rebreathers.


• Correct packing and assembly of scrubber canisters.^[28]
  


• Pre-use inspection and testing of rebreathers using an appropriate checklist.


• Use of correct scrubber absorbent material.


• Use of absorbent that is of good working quality.


• Discard absorbent after use.


• Use of carbon dioxide monitoring instruments.


• Adequate training in the recognition of hypercapnia before using a rebreather.


• Bail-out to open circuit if carbon dioxide levels get too high.

• Siting the compressor air intake in an area of fresh air and ducting it to the compressor.


• Passing intake air through a carbon dioxide scrubber element before compression.


• Periodical air quality testing of compressors.

• The wrong gas was put in a cylinder.


• A cylinder was marked or labelled incorrectly.


• A correctly labelled cylinder was mistaken by the user.


• The diver unintentionally switches to the wrong gas during a dive.

• Cylinders should be filled by competent people.


• Clear instructions, preferably written, for the composition of the gas to be mixed will reduce the risk of filling with the wrong gas.


• Clear, unambiguous and legible labels indicating maximum operating depth and cylinder contents, applied in a way that the user will be able to positively identify the gas at the time when it is to be used can prevent confusion and inadvertent use of the wrong gas.


• Analysing gas after filling, before accepting delivery, and before use (before the dive) may detect errors in labelling or composition in time to take corrective action.


• Procedures designed to positively identify the gas may be used when switching mixes.


• Valves that change gas mixes may be fitted with a positive interlock preventing accidental or inadvertent switching, and may include a method of confirming the gas connected by feel.

• Unconscious diver releases grip on mouthpiece.^[29]
  


• DV is forcibly knocked or pulled from the diver's mouth by impact with surroundings or another diver.

• Use of full face mask reduces risk of loss of DV as it is strapped to the head and can not be dropped if the diver loses consciousness.


• Adequate training and practice of DV recovery skills.


• Use of an alternative air source such as octopus DV or bailout cylinder, which can be used if the primary DV is not immediately accessible.


• Mounting the alternative air source and DV so that it is easily accessible in an emergency and protected from damage when not in use.

• Disruption of breathing by watery suspension/solution containing scrubber absorbent medium.


• Aspiration of water contaminated by scrubber medium.

• Prevent ingress of water to rebreather by:
  
  
  
  • checking before use that the unit does not leak,
  
  
  • closing the dive/surface valve when the mouthpiece is not in the diver's mouth.
  
  
  
  


• Prevent creation of caustic cocktail by:
  
  
  
  • use of less soluble and less alkaline scubber media,
  
  
  • design using water traps and drainage arrangements (on some rebreather designs),
  
  
  • introducing a semi-permeable membrane to block water from the scrubber.
  
  
  
  


• Avoid aspiration of water from loop by recognising the characteristic gurgling sounds and increased breathing resistance, and taking appropriate action by bailing out or draining the set if possible.


• In the event of caustic cocktail reaching the mouth, bail out to alternative gas supply and rinse mouth with ambient water.

• The hood should not make an airtight seal over the outside ear opening.


• Sealed earplugs should never be worn while diving.^[31]
  

• Mask squeeze can be avoided by allowing air into the mask through the nose whenever the pressure difference is noticeable.


• A fullface mask will automatically equalise through the demand valve.


• Air filled eyes-only goggles can not be equalised and are not suitable for diving.

• Loss of buoyancy.


• Suit squeeze injury (usually restricted to bruising and minor abrasion) to skin.^[33][33]
  

• Volume of air in a drysuit reduces as pressure increases with depth.


• Skin may be pinched by folds in a drysuit as the air inside is compressed.

• The squeeze due to depth changes was more likely when the air supply was powered by men. Motorised compressors are usually able to supply air much faster, so an adequate air reservoir on the compressor should prevent this problem.


• The diver may be prevented from sinking too deep by minimizing slack in the lifeline or umbilical.


• The diver may work at neutral buoyancy when there is a risk of falling off a structure, or may clip on to the structure, but this presents a hazard of entrapment.

• Uncontrolled descent.


• Inability to achieve neutral buoyancy.


• Inability to surface due to insufficient buoyancy.


• Difficulty in controlling depth and ascent rate. This can be critical when decompression is required, and oxygen rich breathing gases are used.

• Use of buoyancy compensator with volume appropriate to expected buoyancy variation during dive.


• Use of appropriate ballast weight for dive profile and equipment in use.


• Use of inflation system for replacing lost volume in drysuits.


• Excessive weighting makes buoyancy control more difficult and loss of control more likely.


• Adequate training and practice of buoyancy control skills.

• 
  Pneumothorax: Free air in the pleural cavity, leading to collapsed lung.


• Interstitial emphysema: Gas trapped in the spaces between tissues.

• Mediastinal emphysema: Gas trapped around the heart.

• Subcutaneous emphysema: Free gas under the skin.


• Arterial Gas embolism: Air or other breathing gas in the blood stream, causing blockage of small blood vessels.

• The best option is to breathe normally while ascending when possible, and exhale during free ascent.^[37]
  


• Forced exhalation before starting an emergency free ascent may increase risk of lung overpressure injury.^[37]
  

• Not diving with nasal congestion, e.g. Hay fever, or the common cold.


• Checking before a dive to ensure that sinuses and middle ears will equalise without undue effort.


• Systemic decongestants have been used successfully, but may have undesirable side-effects, and there is a risk that they will wear off before surfacing. Topical decongestants do not usually have sufficient lasting effect.

• Tooth pain, loss of fillings, cracking of teeth.

• Automatic dump valves in dry suits.


• Monitoring of buoyancy on a continuous basis when in mid-water, and manually adjusting volume of buoyancy compensator when necessary.


• Appropriate training and practice to develop good buoyancy control skills to suit the equipment in use.


• Ability to recover from inversion in dry suit.


• Maintaining the minimum air volume for adequate liner bulk maintenance in a dry suit, as this prevents excessive buoyancy shifts. This implies use of BC for buoyancy control, not the suit.


• Minimizing weighting to what is actually necessary, so compensatory air volume is minimized. This reduces the magnitude and rate of buoyancy change with pressure change.

• Decompress to suit the dive profile and gas mixtures used.


• Use appropriate ascent rates and decompression stops.


• Oxygen-rich gas mixtures may be used to accelerate decompression.


• Use depth control aids to maintain correct decompression depth.


• Avoid dehydration and hypothermia.


• Maintain cardiovascular fitness.

• A reversible alteration in consciousness that occurs while diving at depth.


• A state similar to alcohol intoxication or nitrous oxide inhalation.


• The most dangerous aspects of narcosis are the loss of decision-making ability and focus, and impaired judgement, multi-tasking and coordination.


• Other effects include vertigo, and visual or auditory disturbances, exhilaration, giddiness, extreme anxiety, depression, or paranoia, depending on the individual diver.

• Related to the increased solubility of gases in body tissues at elevated pressure.^[39]
  


• Inert gases dissolving in the lipid bilayer of cell membranes may cause narcosis.^[40]
  


• Other possibilities include neurotransmitter receptor protein mechanisms.^[41]
  

• Use of less narcotic gases to dilute the breathing gas, or


• Limit the partial pressure of narcotic gases at maximum depth by limiting the depth of the dive.

• 
  Convulsions similar to epileptic seizure. Loss of consciousness may occur with no warning, or may be preceded by any of the following symptoms:

• Muscle twitching,


• 
  Tinnitus,


• Blurred or tunnel vision,


• Disorientation,


• 
  Aphasia,


• 
  Nystagmus,


• Incoordination.

• Appropriate training before using a rebreather or oxygen enriched gases such as nitrox.


• Correct labeling of cylinders containing mixed breathing gases, specifying oxygen fraction and maximum operating depth.


• Accurate monitoring of dive depth to ensure that gases are not used below the appropriate maximum operating depth for the mixture.

• Signs of pulmonary toxicity begin with inflammation of the upper airways.


• Temporarily reduced lung capacity.


• Acute respiratory distress syndrome.

• Not normally a risk for recreational divers due to short exposures.


• Limit use of rich nitrox mixtures and pure oxygen for accelerated decompression.


• Limit exposure by calculating Oxygen Toxicity Units for pre-existing and planned exposures and keeping below recommended limits.


• Most likely to be encountered in recompression treatment for decompression illness.

Symptoms include:^[42][43]

• 
  visual disturbance


• nausea


• dizziness


• decreased mental performance


• tremors


• myoclonic jerking


• somnolence


• 
  EEG changes

• The compression effects may occur when descending below 500 feet (150 m) at rates greater than a few metres per minute, but reduce within a few hours once the pressure has stabilised.


• The effects from depth become significant at depths exceeding 1,000 feet (300 m) and remain regardless of the time spent at that depth.^[43]
  

• The susceptibility of divers to HPNS varies over a wide range depending on the individual, but has little variation between different dives by the same diver.^[43]
  


• Use another diving technique, such as an atmospheric diving suit, submersible or ROV.


• Including other gases in the mix, such as nitrogen (creating trimix) or hydrogen to make (hydreliox) suppresses the neurological effects.^[44][45][46]
  

• 
  Diving suits are available that are suited to a wide range of water temperature down to freezing.^[47] The appropriate level of insulation for the conditions will reduce heat loss.


• In extreme conditions and when helium based mixtures are in use as breathing gas, heated suits may be necessary.^{[citation needed]}
  


• On the surface, wind chill can be avoided by staying out of the wind, staying dry, and suitable protective clothing.


• Some parts of the body, particularly the head,^[47] are more prone to heat loss and insulation of these areas is correspondingly important.

• Fully Functional 18 °C (64.4 °F) Non Freezing Cold Injury Threshold < Week.


• 12 °C (54 °F) approximately 3 hours.


• 8 °C (46.4 °F) for maximum of 30 min.


• 6 °C (42.8 °F) immediate rewarming required.

Protection in order of effectiveness:

• Dry gloves attached to drysuit without wrist seal.^[48]
  


• Dry gloves with wrist seal.


• Wet suit (neoprene) gloves.


• Rubberised cloth or leather gloves.

• Adequate insulation of the diving suit, particularly the gloves and boots.


• Prevention of wind chill by use of shelters and additional layers of clothing when out of the water.

• Inadequate insulation.


• Reduced perfusion to the legs and feet (occasionally hands).

• Coral cuts may be prevented by avoiding contact of unprotected skin with coral.


• Protective clothing such as wet-suit, dry suit, skin/lycra suit or overalls are effective.

• Most cuts may be avoided by wearing protective clothing such as wet-suit, dry suit, skin/lycra suit or overalls.


• Avoiding high risk areas such as shipwrecks during strong water movements such as surge or currents is also effective.


• Strength and skill in avoiding contact with sharp edges will help, but does not eliminate the risk when water movement is strong.

• Avoid contact with benthic organisms.


• Protective clothing such as exposure suits, lycra skins, or overalls are effective.

• Avoid contact with jellyfish tentacles.


• Protective clothing such as exposure suits, lycra skins, or overalls is effective.

• Stingrays can usually be avoided by not poking about on the bottom where they may be hiding, partly or completely buried under a thin layer of sand.


• The risk is usually greater when wading, when the wader may inadvertently step on a buried ray.


• Rays are usually very shy and will usually swim away when approached. Risk of injury may be avoided by not molesting or threatening the animals when seen, and by staying a safe distance from the tail.

• Most of these animals are sedentary and non-aggressive and may be avoided if seen and recognised in time.


• The risk is often greater when wading. Some protection is provided by rubber soled neoprene diving boots, but hard soled boots are more effective.

• Found only in parts of the Pacific Ocean from Japan to Australia.


• The octopus is unlikely to be aggressive, and is not likely to bite unless handled. However it can be well camouflaged against the reef and difficult to see, so not contacting the reef is the most reliable way to avoid contact.

• Consult location-specific information to determine risk.


• Never molest even apparently docile sharks underwater.

• Found worldwide in tropical seas and fresh water.


• Consult local information on risk.


• Stay out of waters and surroundings known to be inhabited by crocodiles.

• Get local information on risk.


• Stay clear of very large specimens.


• Do not attempt to feed the fish, they may take more than is offered.

• Get local information on risk.


• Do not touch the animals if seen.

• Do not touch the animal.

• Keep out of armed forces areas.

• Keep out of armed forces areas.


• Avoid large naval ships' anti-submarine warfare sonar.


• See Underwater Port Security System.

• Avoid diving in contaminated water.


• Analyse water before diving if presence of contaminants is suspected, but type and concentration is not known.


• If it is necessary, and depending on risk:

• A watertight drysuit with dry gloves and integral dry hood, and positive pressure full face diving mask will provide acceptable protection in some circumstances.^[57]
  


• Surface supplied equipment with heavy duty full environmentally sealed dry suit with integral boots and gloves, and helmet sealed to suit, with either free flow air supply or series exhaust valve system will provide more protection.


• Gas reclaim systems can provide the greatest security to ingress of contaminants.^[58] The gas need not actually be reclaimed if it is not economically desirable, the systems are used so that there are no potential leaks though underwater exhaust openings.

• Protective overalls may be worn over the drysuit to protect it from puncture damage.


• Appropriate decontamination procedures may be used after the dive.


• The diver should breathe from the diving air supply when surfaced in environments where air quality is uncertain.

• Consequences variable depending on:

• Identity of pollutant


• Concentration of pollutant


• Exposure to pollutant

• Refer to Materials Safety Data Sheet (MSDS) for identified pollutants.

• (Concentrations are listed at normal atmospheric pressure. 1000 ppm at 1 bar is equivalent to a partial pressure of 1 mbar)


• 0.0047 ppm is the recognition threshold, the concentration at which 50% of humans can detect the characteristic odor of hydrogen sulfide,^[59] normally described as resembling "a rotten egg".


• Less than 10 ppm has an exposure limit of 8 hours per day.


• At 100–150 ppm the olfactory nerve is paralyzed after a few inhalations, and the sense of smell disappears, often together with awareness of danger.^[60][61]
  


• 320–530 ppm leads to pulmonary edema with the possibility of death.


• 530–1000 ppm causes strong stimulation of the central nervous system and rapid breathing, leading to loss of breathing.


• 800 ppm is the lethal concentration for 50% of humans for 5 minutes exposure (LC50).


• Concentrations over 1000 ppm cause immediate collapse with loss of breathing, even after inhalation of a single breath.

• Colliding with a boat or its propeller.


• 
  Wave action on rocky shore.

• Use of Surface detection aids or a diving shot to locate and mark surfacing position and warn vessels of the presence of divers.


• A safe exit point and alternatives may be planned for taking into account forecasts for weather and tidal conditions.

• Diver separated from boat cover due to poor visibility at surface or strong underwater currents.


• Diver left behind due to inaccurate check by boat crew.


• Diver unable to return to unattended boat.

• Boat crew may use a positive check system to identify that each diver is on board after a dive.


• Divers may carry a yellow flag or surface marker buoy to attract attention.


• Divers may carry a personal submersible EPIRB or vhf radio.


• Divers may carry a signalling mirror and/or sound signalling device.


• Diving from unattended boats only when a safe shore exit is feasible.

• Big breaking waves make it unsafe to approach the shore.


• Currents move the diver away from a safe exit.


• Weather conditions make the sea too rough to safely exit.

• Local knowledge, good weather forecasts, plan alternative exits.


• EPIRB, marker buoy, flares, die markers, signalling light, mirror, whistle or other means of signalling distress and indicating position to rescuers.


• Good buoyancy aids and exposure suit to provide protection while rescue is awaited.


• Notification before the dive of someone on shore of the expected time of return, so they can notify the rescue orgabisations if the divers do not return within a reasonable time.

• Appropriate trim, buoyancy and propulsion techniques.


• Training and skills for diving in zero visibility and silting risk areas.


• Use of distance line when it is possible to end up under an overhead.

• Entrapment by collapse of terrain or structure, either directly or by obstructing the exit route.

• Carrying at least one effective line cutting implement, more in high risk areas.


• Diving with a buddy who is capable of helping to free the trapped diver and will stay close enough to notice.


• Training in wreck diving and cave diving techniques.


• Use of low snag equipment configurations (avoid dangling gear and snap hooks that can snag on lines).

• Diver may get lost and be unable to identify the way out, and may run out of breathing gas and drown.


• Inappropriate response due to panic is possible.

• Appropriate training and dive planning.


• Correct use of reels, lines and directional markers.


• Backup lights.

• Diver may get drawn into moving machinery or trapped against an intake opening, and may be directly injured or unable to escape and may run out of breathing gas and drown.


• Inappropriate response due to panic is possible.

• Appropriate training and dive planning.


• Correct use of lockout-tagout and permit to work systems


• Restricted length of lifeline or umbilical


• Use of temporary or permanent safety barrier

• Impact against the bottom terrain or underwater structures, which can dislodge equipment such as mask or DV, roll off a cylinder valve, snag and damage equipment or cause impact trauma to the diver. Severity can vary from annoyance to fatal.


• It is also possible to get wedged into a small gap and trapped, or caught up on nets or lines in the water.


• In an overhead environment the diver may be unable to get back against a strong current.

• Strong water movement carrying the diver along and into contact with rigid objects fixed in place.


• Strong water movement creating so much drag on the diver that progress upcurrent is severely restricted.

• Strong currents and surge may often be avoided by planning the time of the dive.


• Divers may stay a safe distance from the bottom terrain during drift dives.


• Drift divers may tow a surface marker buoy to identify their positions to the boat.

• Impact injury and damage to equipment.


• Disorientation.


• Loss of equipment, temporary loss of breathing gas.

• Uncontrolled transportation by surf surge onto rocks or other hard obstacles.


• Tumbling in breaking wave causing vertigo.


• Strong turbulence in breaking wave may pull equipment from diver, particularly mask and demand valve, occasionally fins.

• Avoidance of strong surf transits.


• Minimising time in surf zone.


• Secure attachment of equipment.


• Protection of mask and demand valve security by holding them in place in high turbulence.

• A dive light can provide light if the visibility is sufficient.


• In zero visibility special precautions must be taken.

• It is usually preferable to use surface supplied equipment with voice communications, as the diver can not get lost, and the surface team can monitor depth, time, breathing gas and decompression obligations.


• Navigation and work must be done by feel.

• Acclimatisation at altitude before diving.


• Use of decompression schedules designed for altitude diving.^[62]
  

• Flying in pressurised aircraft.


• Flying in unpressurised aircraft.


• Ascent by road or rail to significantly higher altitude.^[62]
  

• Heart attack, with high risk of death as direct consequence, or by drowning as indirect consequence.


• 
  Angina with severe pain and severely reduced physical strength and endurance, and reduced situational awareness, which increase the risk of further deterioration of the incident

• Periodical medical examination for diving fitness, and discussion of medical history with provider.^{[clarification needed]}
  


• Stress ECG when indicated by medical examination.


• Maintaining good cardio-vascular fitness.


• Use of Nitrox may decrease risk.^{[citation needed]}
  

• Screening for PFO for high risk divers


• Conservative decompression and ascent


• Avoidance of exercise which is likely to induce shunting during ascent

• Overlearning of critical skills.^{[citation needed]}
  


• Avoidance of high stress dive plans.

• Increased risk of decompression sickness


• Muscular cramps
  

• Overheating and sweating before dive.


• Drinking diuretic beverages before diving.


• Immersion effects of diving.

• Ensure adequate hydration before diving.


• Rehydrate during dives if they are several hours long.


• Rehydrate after dives.

• Reduced ability to respond effectively to emergencies


• Muscular cramps

• Inadequate demonstration and assessment of skills by instructor.


• Ineffective skills taught, due to inappropriate training standard, or misinterpretation of training standard.


• Insufficient correct repetition of skills during training.

• Quality assurance by training agency

• Insufficient practice of skills during training.


• Insufficient practice of skills after training.

• Clear standards for competence in assessment criteria of training programme.


• Quality assurance by training agency.


• Post training practice of vital skills by the diver.


• Periodical re-assessment of skills by a competent assessor.

• Over-optimistic self-assessment of personal competence by the diver.


• Insufficient information due to inadequate training.

• Objective assessment and accurate feedback during training.


• Realistic training standards and competence level descriptions.

• Inability to compensate for difficult conditions even though well versed at the required skills.


• Over-exertion, overtiredness, stress injuries or exhaustion.

• Underestimating severity of conditions.


• Overestimating fitness and strength.


• Conditions deteriorate during the dive.


• Excessive task loading.


• Use of equipment that requires greater exertion than the diver can produce.

• Experience and familiarity with local conditions.


• Use of weather and tide forecasts when planning dives.


• Maintaining fitness to dive by adequate exercise.


• Use of equipment and techniques that reduce physical exertion required.


• Gradual buildup of task-loading to develop appropriate skills and fitness.


• Training with equipment in benign conditions before using in severe conditions.

• Divers may be pressurised into undertaking dives beyond their competence or fitness.


• Divers may be pressurised into diving with unsuitable buddies, often by dive professionals who should know better.

• Objective and accurate knowledge of the diver's capabilities.


• Recognising and accepting responsibility for possible consequences of exerting or submitting to peer pressure.

• The buddy may get into difficulty due to inattention or incompetence, and require a rescue that is hazardous to the rescuer.


• The buddy may get into difficulty and mishandle the situation or panic, creating an incident that is hazardous to both divers.

• Diving with a buddy is known to be competent and who can be trusted to behave responsibly.^[64]
  


• Training to deal with emergencies and rescue.


• Carrying equipment to be independent of the buddy in most emergencies.


• In some circumstances it may be safer to dive without a buddy.^[65]
  

• Uncontrolled descent.


• Inability to establish neutral buoyancy.

• Inefficient swimming.


• High gas consumption.


• Poor trim.


• Kicking up silt.

• Difficulty in ascent


• Inability to control depth accurately for decompression

• Density of water (sea or fresh).


• Buoyancy of equipment (mainly exposure suit).


• Buoyancy change of cylinders as gas is used up.


• Tasks of the dive.


• Capacity of buoyancy compensator to neutralise buoyancy at depth and provide positive buoyancy at the surface.


• Use surface supply equipment or a lifeline if it is necessary to dive heavy.

• Inability to achieve neutral buoyancy, particularly at decompression stops.

• Inappropriate or delayed response to contingencies.^[66]
  

• reduced ability to deal timeously with problems, leading to greater risk of developing into an accident.

• Increased risk of hypothermia.


• Increased risk of decompression sickness.

• Exercise to develop skills and fitness appropriate to the fins chosen


• Use softer or smaller bladed fins (this may compromise speed and/or maneuverability)

• Use of integrated weight systems, which support the weights directly by the buoyancy compensator


• Different distribution of weights - some weight transferred to the harness, BCD, cylinder or backplate


• Avoiding excessive weighting

• Inspection of weight belt buckle or weight pocket clips for good condition and correct function before dive.


• Use of correct length weight belt.


• Use weight harness or integrated weight system if weight belts tend to slide over hips and fall off.


• Carry weights in secure method, which can not easily be accidentally released.


• Carry the amount of weight appropriate for regaining neutral buoyancy on a releasable system, and the rest securely attached to the harness.

• Insulation loss, accelerated loss of body heat, potentially leading to hypothermia.


• Buoyancy loss - potential inability to establish neutral or positive buoyancy, and difficulty or inability to ascend.

• Zipper bursting.


• Tear of latex neck seal.

• Maintenance and pre-use inspection of dry suit zip and seals.


• Use of a dry suit undergarment that retains moderate insulation properties when flooded (e.g. Thinsulate B).^[67][68]
  


• Use of a drysuit material having significant inherent insulation properties (e.g. foam neoprene).


• Training and practice of skills for recovery from this situation.


• Use of a buoyancy compensator with sufficient volume to compensate for the suit buoyancy loss.


• Use of a lifeline with a surface tender.


• Sufficient ballast weight ditchable to recover neutral buoyancy at depth.


• Use of a DSMB or surfave marker buoy with sufficient volume to compensate for loss of buoyancy.

• Use of low flow rate inflator hose connections.


• Training and competence at emergency procedures for inflation valve failure.

• Inability to swim against current.


• Inability to exit overhead environment before running out of gas.

• Pre-use inspection of straps and strap connectors.


• Practice skill of finning with one fin.


• Spare fin strap in emergency spares for team.


• Replace original straps with more reliable type.^[69]
  

• High level of stress.


• Inability to read instruments

• Broken lens/faceplate due to impact with hard object.


• Mask knocked off and lost

• Inspection of the mask and strap before use.^[10]
  


• Hold mask in place with hand.


• Practice diving with no mask.^[10]
  


• Spare mask in emergency spares for team.^[10]
  


• Use of full face mask that is more securely attached to the head and tethered by the hose.

• Inspection and testing of inflator mechanism before use.


• Appropriate maintenance after use.


• Training and practice of skills to control situation.


• Use of buoyancy compensator with moderate volume.

• Loss of manifold fitting.


• Corrugated hose failure.


• Torn bladder.

• Maintenance and inspection of BC before use.


• Use of drysuit as emergency buoyancy control device


• Use of reel and DSMB of sufficient volume as shotline and buoyancy aid for ascent.


• Use of lifeline and surface tender.


• Use of double bladder buoyancy compensator.


• Ditching of sufficient weights to allow ascent.

• Inspect and test cutting edge periodically


• Sharpen or replace tool when blunt

• Increased risk of drowning.


• difficulty in controlling ascent rate.


• Risk of losing tools if they must be abandoned.

• Tools may be lifted and lowered to the worksite using a rope.


• Tools may be returned to the surface using a lift bag and a surface marker buoy in case the bag sinks.


• Surface supplied divers may be pulled up by the tender or lifted on the diving stage or bell.

• Use of an independent air cylinder dedicated to bag filling, rather than filling from the breathing gas cylinder(s).


• Use of surface supplied air to fill bags.

• Impact of falling objects.


• Loss of lift bag and cargo.


• Damage to lift bag, cargo or other equipment.

• Lift bag broaching at surface or leaking, losing gas and sinking on top of divers.


• Lift bag broaching at surface or leaking and sinking at unknown position.


• Lift bag surfacing under vessel or structure and snagging on projection that punctures bag, or fouling propeller or rudder etc.


• Poor rigging causing damage to bag or cargo.

• Marking lift bag or load with a surface marker buoy before lifting.


• Ensuring that lift takes place when surface vessels and structures are clear of the area.


• Buoyant assisted lifting, where the lift bag is insufficient volume to lift the load without assistance from a crane or winch.


• Staged lifting, where the load is lifted in stages, a short distance at a time.


• Adequate training and use of suitable rigging equipment and lift bag size and style. Attachment to suitable lift points, taking trim and stability into account.