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Divers face specific physical and health risks when they go underwater (e.g. with scuba) or use high pressure breathing gases. Some of these conditions also affect people who work in raised pressure environments out of water, e.g. in caissons.
Relying on breathing equipment while underwater
Being unable to breathe fresh air naturally whilst submerged and relying on limited breathing gas supplies and fallible breathing equipment can have these effects. Click on each type to find its symptoms. Types of this sort of diving disorder, and how to avoid them | Type | Cause | How to avoid it | | Drowning | Being unable to inhale anything but water | See under "anoxia" | | Secondary drowning | Can occur hours after a near drowning | Prompt medical treatment after near drowning | | Oxygen poisoning | Breathing gas with too much oxygen in | Proper training before using a rebreather. | | Hypoxia or anoxia while having gas to breathe, but with too little oxygen to support normal activities or consciousness. | This is a risk when using a rebreather | Keep rebreathers properly maintained.
Proper training before using a rebreather. | | A full cylinder standing for a long time while the inside of the cylinder rusts, using up oxygen in the contained air, before the diver uses the cylinder | Keep cylinders routinely checked and tested. If a cylinder has stood full for months, empty it and refill it. | | Anoxia due to having no gas to breathe | Equipment failure | Keep equipment routinely checked and in good condition | | Running out of air due to poor dive discipline | Better training of divers. More disciplined attitude when underwater. | | Running out of air due to getting trapped by nets | Better awareness underwater. Carry a diver's net cutter. | | Running out of air due to getting trapped or lost in enclosed spaces underwater (e.g. caves and shipwrecks) | Better training and leadership for such types of diving. See cave diving and wreck diving. | | Running out of air due to getting lost in open water | Better training and leadership, including in using a compass underwater | | Salt water aspiration syndrome | Inhaling a mist of sea water from a faulty demand valve causing a reaction in the lungs | Keep equipment routinely checked and in good condition | | Carbon monoxide poisoning | Air cylinder filled by a compressor which sucked in its engine's (or another engine's) exhaust | Proper precautions when filling cylinders | | Oil getting into the air feed and firing in the air compression cylinder, like in a diesel engine | Proper servicing of the compressor | | Emphysema caused by inhaling oil mist | This happens gradually over a long time. This is a particular risk with a pumped surface air feed. | Use proper filters in the air pump or air compressor. | | Carbon dioxide poisoning | The diver producing carbon dioxide faster than his rebreather's soda lime can absorb it | Keep rebreathers properly maintained.
Proper training before using a rebreather. | | Various effects of breathing a wrong gas | A wrong gas was put in a cylinder | Check conditions where you have your cylinders refilled. Put the proper gas identification markings on cylinders. |
On descent Air spaces within the body provide no support against greater outside pressure. This can happen from losing control of buoyancy causing excessive vertical speed during descent. Click on each type to find its symptoms. Types of this sort of diving disorder, and how to avoid them | Type | Cause | How to avoid it | | Eardrum damage. Cold water in the middle ear chills the inner ear, causing dizziness and disorientation etc. | Failing to equalize the pressure in the middle ear with surrounding pressure. | Do not dive if the eustachian tube is congested, e.g. with the common cold.
Proper diver training in clearing the ears. | | The pressure in the outer ear not equalizing with surrounding pressure | Make sure that your hood does not make an airtight seal over the outside ear hole. | | Damage to other body air spaces, such as the paranasal sinuses. | Obstruction to the sinus ducts | Do not dive with conditions such as the common cold | | Squeeze damage to bood vessels around the eyes | Caused by suction from the air space inside a mask which is not a fullface mask | Let air into the mask through the nose. Do not dive with eyes-only goggles. | | Squeeze damage to skin under folds in a drysuit | Suction into the space inside the fold | Modern drysuits have a tube connection to inflate the drysuit from the cylinder | | Lung squeeze: blood in lungs | Extreme depth when snorkelling | Use an underwater breathing set | | Helmet squeeze, with the old standard diving dress. This does not happen with scuba where there is no solid pressure-tight helmet | A valve in the helmet failing. In severe cases much of the diver's body could be mangled and compacted inside the helmet | Keep equipment in good order and inspected. Proper training in its use. |
On ascent Air spaces within the body expand when the outside pressure decreases. This can happen from holding the breath on ascent, or from losing control of buoyancy causing excessive vertical speed during ascent. Click on each type to find its symptoms. Types of this sort of diving disorder, and how to avoid them | Type | Cause | How to avoid it | | Pulmonary barotrauma: "burst lung" | Holding the breath while ascending | Never hold the
breath while diving
with breathing
apparatus | | This can cause: | | Pneumothorax | Collapsed lung, air loose in the pleural cavity | | Interstitial emphysema | Gas trapped in the chest after burst lung | | Subcutaneous emphysema | Gas loose under the skin. | | Gas embolism | Air or other gas in the blood stream.
Its effects can be very similar to decompression sickness. | | Pain in a sinus | Blockage of the sinus's duct | Do not dive with nasal congestion | | Eardrum bursting outwards | Blocked Eustachian tube | Do not dive with nasal congestion |
Breathing gas at high pressure Click on each type to find its symptoms.
The term dysbarism describes Decompression sickness, arterial gas embolism, and barotrauma.
Other risks encountered by people in water Types of this class of diving disorder, and how to avoid them. Click on each type to find its symptoms. | Type | Cause | How to avoid it | | Hypothermia | Losing body heat to the water. Water carries heat away far better than air. | In cool or cold water, wear an adequately warm diving suit for the conditions. Also, much heat can be lost from a head without a hood. | | Cuts, sometimes with coral tissue left in them | Coral | Do not get too close to coral. Avoid diving with bare skin. | | Cuts | Rock, metal, etc | Avoid diving in bare skin, particularly in caves or shipwrecks. | | Stings | Fire coral | It is yellow. Learn to identify it. | | Stings, some dangerous | Some jellyfish | Learn about the dangerous species. Avoid diving with bare skin. | | A deep cut which leaves poison in the wound | sting ray (its self-defence reaction) | Do not poke about in sand where they live | | Poison-injecting spines | lionfish, stonefish, crown of thorns starfish, some sea urchins in warm seas | Learn to identify them. Keep away from them. | | Poison injection | Blue ringed octopus, in parts of the Pacific Ocean | Learn to identify them. Keep away from them. | | Shark bites | Sharks, in warm seas | Get proper information on them | | Crocodile attack | Crocodiles, in some tropical waters | Get proper information on them | | Electrocution | Electric eel, in some South American fresh water | Get proper information on them | | It is said that some naval anti-frogman defences use electric shock | Keep out of armed forces areas | | Powerful ultrasound | It is said that some naval anti-frogman defences use powerful ultrasound. Also used for long-range communication with submarines | Keep out of armed forces areas. Avoid large ships' ordinary sonar. | | Exposure to disease carried by in-water organisms | Weil's disease (in rat's urine)
Bilharzia (in some warm fresh water) | In affected water, dive in watertight drysuit and full face diving mask | | Broken bones, bleeding wounds and other trauma | Colliding with a boat or its propellor. Wave action on the shore. | Use Surface detection aids or a diving shot to mark position. Plan a safe exit point and check weather and tidal conditions. | |
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