Diving hazards and precautions
Additional recommended knowledge
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Divers face specific physical and health risks when they go underwater (e.g. with scuba or other diving equipment) 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.
The ordinary features of diving
Click on the boldface links for more information about each topic.
| Need to:
| Remedy
| Comments
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| Breathe underwater
| Open-circuit scuba set
| Easy to refill. Safer to use than a rebreather.
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| Rebreather
| Longer duration per weight of set, but needs more training to be safe.
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| Surface supplied diving
| Mostly for work diving
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| Standard diving dress
| Mostly for work diving. Mostly merely of historical interest now.
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| Liquid breathing system
| (In the real world this is at the early experiment stage.
It should allow very deep diving when it is developed.)
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See underwater.
Protect the eyes.
(The human eye cannot focus accurately when directly submerged.)
| Eyes-and-nose diving mask
| Easy to clear if flooded. Easily knocked off.
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| Full face mask
| Allows talking if no mouthpiece inside.
Difficult or impossible to go to snorkel on running out of air.
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| Diving helmet
| As fullface mask. Protects the head well.
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| Special contact lenses
| Occasionally used by commando frogmen instead,
to avoid searchlight beams reflecting off a mask window.
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Move faster than
with unequipped swimming
| Fins on feet
| Cheap, easy to use. Even without a diving suit, wetsuit bootees let the diver wear bigger fins.
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| Diver Propulsion Vehicles
| Faster but expensive, and heavy and bulky to carry about on land.
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Avoid hypothermia (losing
body heat to the water)
| In cool or cold water, wear an adequately warm diving suit for the conditions.
| Much heat can be lost from a head without a hood.
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| Control buoyancy
| Diving weighting systems
| Usually a weight belt. Some breathing sets have built-in weight pouches.
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| Diving suits
| The buoyancy of most drysuits can be changed during the dive.
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| Buoyancy compensators
| These make diver's buoyancy control much easier.
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| Protect the skin from cuts and stings and grazes
| Diving suits and diving gloves and diving suit bootees serve this purpose.
| In very warm water try diving in a boiler suit, or other strong clothes with long sleeves and legs.
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| Breathe from atmosphere to save air when on surface
| Snorkel
| Advisable, despite some naval divers' opinions.
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Effects of 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 the boldface links to find symptoms and more information for each topic.
Types of this sort of diving disorder, and how to avoid them
| Type
| Cause
| How to avoid it
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| Drowning
| Being unable to inhale anything but water
| See under "anoxia" hereinunder
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| Secondary drowning
| Can occur hours after a near drowning
| Prompt medical treatment after near drowning
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| Oxygen toxicity
| Breathing gas at too high a partial pressure of oxygen; partial pressure depends upon proportion of oxygen and depth
| Proper training before using a rebreather or oxygen enriched gases such as nitrox.
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| Hypoxia or anoxia occurs while having gas to breathe, but where the oxygen partial pressure is too low to sustain normal activity or consciousness.
| A faulty or misused rebreather can provide the diver with hypoxic gas
| Keep rebreathers properly maintained.
Proper training before using a rebreather.
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| Some deep diving breathing gases such as trimix and heliox can be hypoxic
| Don't breathe hypoxic gas in shallow water.
Proper training before using mixed gases.
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| 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.
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| Anoxia due to having no air or gas to breathe
| Equipment failure - particularly in rebreathers that monitor and maintain oxygen content
| Keep equipment routinely checked and in good condition
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| Running out of air due to poor dive discipline
| Better training of divers. More disciplined attitude when underwater.
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| Running out of air due to getting trapped by nets
| Better awareness underwater. Carry a diver's net cutter, or dive tool/knife.
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| Running out of air due to getting trapped or lost in enclosed spaces underwater (e.g. caves and shipwrecks)
| Specific training and leadership for such types of diving. See cave diving and wreck diving.
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| Running out of air due to getting lost in open water
| Better training and leadership, including in using a compass underwater
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| 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
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| Carbon monoxide poisoning
| Air cylinder filled by a compressor which sucked in products of combustion, often its own engine's exhaust
| Proper precautions when filling cylinders
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| Oil getting into the air feed and firing in the air compression cylinder, like in a diesel engine
| Proper servicing of the compressor
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| 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.
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| Carbon dioxide poisoning: hypercapnia
| Re-inhaling carbon dioxide-laden exhaled gas
| Minimise the volume of any enclosed spaces which the diver breathes through. For example, this hazard can happen with diving with a large "bubblehead" helmet.
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| With a rebreather, the diver re-inhales carbon dioxide because the soda lime scrubber cannot absorb the exhaled carbon dioxide as fast as the diver produces it. See Rebreather#Carbon dioxide scrubber.
| British naval divers called it shallow water blackout. Keep rebreathers properly maintained. Proper training before using a rebreather.
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| 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.
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Effects of barotrauma or pressure damage
See barotrauma and pressure for more information.
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 the boldface links to find symptoms and more information for each topic.
Types of this sort of diving disorder, and how to avoid them
| Type
| Cause
| How to avoid it
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| 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.
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| 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; never wear earplugs.
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| 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
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| Squeeze damage to blood vessels around the eyes
| Caused by suction from the air space inside a mask ("mask squeeze") which is not a fullface mask
| Let air into the mask through the nose. Do not dive with eyes-only goggles.
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| 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
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| Lung squeeze: blood in lungs
| Extreme depth when snorkelling
| Use an underwater breathing set
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| 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.
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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 the boldface links to find symptoms and more information for each topic.
Types of this sort of diving disorder, and how to avoid them
| Type
| Cause
| How to avoid it
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| Pulmonary barotrauma: "burst lung"
| Holding the breath while ascending
| Never hold your
breath while diving
with breathing
apparatus
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| This can cause:
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| Pneumothorax
| Collapsed lung, air loose in the pleural cavity
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| Interstitial emphysema
| Gas trapped in the chest after burst lung
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| Subcutaneous emphysema
| Gas loose under the skin.
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| Gas embolism
| Air or other gas in the blood stream.
Its effects can be very similar to decompression sickness.
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| Pain in a sinus
| Blockage of the sinus's duct
| Do not dive with nasal congestion,
e.g. the common cold.
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| Eardrum bursting outwards
| Blocked Eustachian tube
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Effects of breathing gas at high pressure
Click on the boldface links to find symptoms and more information for each topic.
Types of this sort of diving disorder, and how to avoid them
| Type
| Cause
| How to avoid it
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| Decompression sickness ("the bends")
| Gas dissolves in blood under pressure according to Henry's Law over time. After dive, ascending too quickly will cause gas to supersaturate and form bubbles in tissues according to time and depth of the dive.
| Plan your dive. Know how long you can stay at the planned depth and still make a normal ascent. If stops are necessary, do not miss or cut short decompression stops. Training in using diving tables and a dive computer. See decompression sickness for a detailed list of the symptoms. Provide something for the diver to hold onto while decompressing.
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| Bends in snorkellers. Uncommon but known.
| Many deep dives in succession. See taravana.
| Use an underwater breathing set
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| Nitrogen narcosis
| Breathing a high partial pressure of nitrogen (or other inert gas, to varying degrees)
| Do not dive too deep on ordinary air. With mixture diving, use the correct breathing gas.
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| Oxygen toxicity
| Breathing a high partial pressure of oxygen
| This hazard is well known with rebreathers.
This can happen in very deep diving with open-circuit scuba.
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| HPNS: High Pressure Nervous Syndrome or Helium Tremors
| Breathing a high partial pressure of helium
| Use another diving technique, such as an ROV; or add a little nitrogen as described at HPNS.
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The term dysbarism describes Decompression sickness, arterial gas embolism, and barotrauma.
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.
Other risks encountered by people in water
Types of this class of diving disorder, and how to avoid them. Click on the boldface links to find symptoms and more information for each topic.
Where it says "Avoid diving with bare skin", a boilersuit could be worn in very warm water.
| Type
| Cause
| How to avoid it
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| 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.
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| Cuts, sometimes with coral tissue left in them
| Coral
| Do not get too close to coral.
Avoid diving with bare skin.
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| Cuts
| Rock, metal, etc
| Avoid diving in bare skin, particularly in caves or shipwrecks.
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| Stings
| Fire coral
| It is yellow. Learn to identify it.
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| Stings, some dangerous
| Some jellyfish
| Learn about the dangerous species.
Avoid diving with bare skin.
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| A deep cut which leaves poison in the wound
| sting ray (its self-defence reaction)
| Do not poke about in sand where they live.
Care when wading.
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| Reef rash
| This includes sunburn, jellyfish stings, sea lice bites, fire coral inflammation and other skin injuries that a diver may gain from using a shorty wetsuit or no diving suit.
| A generic catch-all term that refers to the various cuts, scrapes, bruises and various skin conditions that result from diving in tropical waters with exposed skin.
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| Poison-injecting spines
| lionfish, stonefish, crown of thorns starfish, some sea urchins in warm seas
| Learn to identify them. Keep away from them.
Care when wading.
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| Poison injection
| Blue ringed octopus, in parts of the Pacific Ocean
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| Shark bites
| Sharks, likelihood of risk is location dependent
| Consult location-specific information to determine risk; never molest even seemingly-tame sharks underwater.
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| Crocodile attack
| Crocodiles, in some tropical waters
| Get proper information on them
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| Attack by an unusually large grouper.
| Epinephelus lanceolatus can grow very big in tropical waters, where protected from attack by sharks.
| Get proper information on them. A throat inlet that can expand to 2 feet square can swallow a scuba diver.
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| Electrocution
| Electric eel, in some South American fresh water
| Get proper information on them
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| Electric ray, in some warm seas
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| It is said that some naval anti-frogman defences use electric shock
| Keep out of armed forces areas
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| 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.
See Underwater Port Security System.
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| Exposure to disease carried by in-water organisms
| Weil's disease (in rat's urine)
Bilharzia (in some warm fresh water)
Various bacteria found in sewage
| In affected water, dive in watertight drysuit and full face diving mask
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| Exposure to harmful chemicals in the water
| May be found in water polluted by industrial waste outfalls or by natural sources. For example hydrogen sulfide in some lakes and caves can be absorbed through the skin.
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| 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 surfacing position and aid searchers. Plan a safe exit point and check weather and tidal conditions.
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| Diver lost at sea after a boat dive
| Separated from boat cover due to poor visibility at surface or strong underwater currents.
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| Diver lost at sea after a shore dive
| Big waves made it unsafe to leave the water; currents moved the diver away from a safe exit; surface weather on the shore make the sea too rough to safely exit.
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See also
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