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The five major risks
Whether you are an autonomous or a tackle guide, managing your dive well means controlling the following five essential parameters:
• airautonomy
• decompression (ascent speed, bearings)
• the profile (curve of evolution of the depth as a function of time, maximum depth)
•orientation (position of the tackle in relation to the intended point of return)
• the cohesion of the tackle (relative positions of the divers in relation to the other).
The consequences of mismanagement of one of these parameters can be dramatic:
Mishandled setting | Risks |
Air autonomy |
Air failure in addition to: • ADD (too fast ascent) • Pulmonary overpressure (panic lift) • Drowning
|
decompression |
• ADD (too fast ascent, steps not made or interrupted)
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Profile |
• Exceeding the maximum depth, non-compliance with the decree of 22/06/98 (criminal risk in case of accident) • Narcosis from 30 meters • Profiles favoring the ADD (Yo-Yo, sawtooth, consecutive, successive deeper …)
|
orientation |
Exit far from the planned point of return, which leads to: • dangerous return journey on the surface because of the waves, the current, the other boats (shortness of breath, drowning, shock) • help of the boat postponed in the event of an incident or accident (air failure at the landings, …) • decompression more delicate to achieve in open water (bearing difficult to stabilize, drift in case of current …)
|
Cohesion of the tackle |
• loss of a crew member, resulting in a rise to the surface and consecutive dives • if the maximum depth of a crew member is greater than that of the GP, there is a risk of insufficient decompression of the crew member, and an ADD • disparity of divers, which causes risks of delayed assistance, or even impossible, in the event of a problem of a crew member (air failure …)
|
–
Autonomy in air
Before diving
• check the initial pressure of the block with the pressure gauge
• define the reserve pressure: 50 to 100 bar depending on the profile of the dive and according to individual consumption
• recall the signs of passage on reserve and passage at mid-pressure (100 bar)
During the dive
• regularly check his pressure gauge (autonomous) and that of the team members (for the GP)
• report the mid-pressure passage and the passage on reserve
• start the ascent as soon as a team member passes on reserve.
Decompression
To calculate decompression, diving computers have become common use today. However, their use requires some precautions because the mathematical model they incorporate does not cover certain diving profiles. Computers are particularly suitable for exploration dives that take place in the safety curve. For any other use, and especially for technical dives, tables are preferable.
Recent studies show that the rate of ascent is an essential element for a successful decompression. They tend to reduce it to around 10 meters /minutes (that of most computers) and even to 6 meters / minutes when approaching the surface (30 seconds between the bearings and between the 3 meter bearing and the surface, according to tables MN90)
Studies have also shown that above 7 meters deep, the tissues no longer saturate. As a result, bearings at 3 meters, often difficult to hold because of the waves and swell, can be made at a depth of 4 or 5 meters. In any case, in decompression to the computer, it is better to make the bearings at a slightly higher depth than to take the risk of crossing the level, the computer always taking into account the real depth at which the diver is.
Before diving
• determine the mark-up (or safety curve) of each and adopt the least favorable to set the characteristics of the dive, maximum duration and depth, so as to remain in the safety curve
• for a successive dive, keep the same decompression means (same computer or same table) as the first dive
• for a successive dive, avoid changes of tackle
• adjust its lestage to hold a possible bearing close to the surface
During the dive
• regularly check:
– the maximum duration and depth for a decompression at the tables
– the duration without a bearing for a decompression to the computer
• stay in the safety curve as much as possible
• report the imminence of the passage on bearings (for example, for a period without a bearing = 3 minutes)
• respect the speed of ascent; stall on the crew member at the slowest speed; if decompression at the MN90 tables, integrate the ascent time into the duration of the dive in case of slow ascent (< 15 m/mn) ; contrôler les paramètres de décompression de chaque équipier avant d’entamer la remontée
• respecter les paliers s’il y en a ; se caler sur l’équipier astreint aux paliers les plus importants ; remonter très lentement entre les paliers et entre le dernier palier et la surface (30 secondes tous les 3m)
• aux paliers, respirer normalement sans faire de manœuvre de Valsalva
• ne sortir que lorsque tous les équipiers ont achevé leur procédure de décompression
In the presence of a factor favoring the ADD (fatigue, cold, efforts at the bottom, stress, successive), realize a step of principle (3 minutes at 3/5 meters).
DO NOT carry out a level of principle in case of current (with the risk of not being able to return to the boat then too far).
In case of abnormal ascent, too fast (> 17 m / min), reduced ventilation (CSR, RA2), consequent efforts (rescue fins), or bad profile (Yo-Yo, consecutive dive), make a safety level of 5 minutes at mid-depth, then go up and carry out any other bearings.
In case of interruption of bearing (following an air failure for example), go up to the surface to change block and re-immerse in less than 3 minutes, then resume the decompression procedure at the interrupted bearing which is completely redone.
After diving
• do not make significant efforts for several hours
• do not snorkel for at least 6 hours
• do not fly or climb altitude for at least 12 hours
• drink plenty of still water to combat dehydration
• warn those around you (and in particular the GP and the DP) of any unusual sensation
The profile of the dive
Two important parameters characterize the profile of a dive:
• the maximum depth
• the shape of the depth evolution curve over time
The maximum depth
The maximum depth is fixed by the decree of 22 June 1998 according to the level of prerogatives of divers. It can be reduced by the DP according to the objective of the dive, the particular circumstances (poor visibility, current, …), etc. Itself, can be reduced by the GP to adapt it to the real skills of its teammates. It may be imposed by the nature of the gas breathed. For example, for a nitrox dive, a floor depth must be observed to prevent a hyperoxic crisis.
The evolution curves of the diver
The shape of the curves of evolution of the depth over time have a preponderant role on the decompression of the diver. Some profiles promote the triggering of an ADD.
Before diving
• plan the route to be made according to the description of the site and the exploration proposals made by the dive director and also according to the interests of each one
• set the maximum depth not to be exceeded
During the dive
• regularly check the depth reached (so as not to exceed the maximum depth)
• start diving to the maximum depth and continue always approaching the surface
Consecutive dives not recommended: wait at least 1 hour before diving again
Successive dives
• perform a successive dive to a shallower depth than the previous dive
• do not do more than 2 dives per day and in case of an extended stay, allow yourself a day of rest every 4-5 days
In case of bad profile type Yo-Yo, or consecutive dive: make a safety level of 5 minutes at mid-depth, then go up and realize any other bearings.
Guidance management
Several clues make it possible to orient yourself in diving:
• the depth (and in particular that of the anchor of the vessel)
• the relief (type of bottom, slope, …)
• a characteristic element (rock, anchor, …)
• the orientation of the current
• the orientation of the wrinkles drawn on the sandy bottoms
• the direction of the sun (of the moon or the fires of the boat in night diving)
• particles raised on the way
• the orientation of the waves
• the shadow of the boat
Before diving
• listen carefully to the description of the site and the exploration proposals made by the dive director
• identify the direction of the current, the position of the sun, the position and distance of the site and remarkable underwater reliefs from the boat or the coast
• identify the direction of the journey to be made in relation to the current, the waves, the sun, the boat, the coast
• note the depth of the remarkable points to explore
During the dive
• for a round trip, record the time traveled in one direction. On the way back, travel the same time in the other direction, the boat will not be far.
• memorize the landscape of the return trip by turning around at regular intervals
The management of the tackle
Before diving
• plan the route to be made according to the description of the site and the exploration proposals made by the dive director and also according to the interests of each one
During the dive
• stay grouped in all circumstances: at the launching (regroup on the surface before immersion, at anchoring for example) at the descent (waiting for the crew members who have problems with ears or sinuses), during the dive and at the ascent (to carry out the decompression phase)
• introduce monitoring in pairs (without, however, excluding general monitoring of the tackle)
• the clamp, when there is one, closes the walk by having an eye on the whole of the tackle
• the cohesion of the tackle is the responsibility of all divers
Special case of the loss of a crew member
• go up a little by performing a 360 ° to spot its bubbles (and make signs with a lamp), then slowly go up to the surface in case of failure. The lost teammate, having followed the same procedure, must wait for you on the surface.
Take into account the specificities of diving
Reduced visibility
Visibility may be reduced by the presence of suspended particles (natural turbidity or caused by divers by palming near a sandy or muddy bottom) or by the low light of the moment (night diving in particular).
Potential risks:
• risk of losing his tackle
Precautions to take
• be equipped with a lamp (per diver)
• descend slowly preferably at anchor, and go up there as far as possible
• in open water, slowly descend in seal all together
• stay grouped on the descent, during the dive, at the ascent
• limit the number of divers per tackle
• control its buoyancy so as not to palmer near the bottom (no overlestage)
The current
In diving, you can encounter only a surface current, or only a bottom current, or both. A distinction is made between general currents (those that cross the oceans) and that are due to differences in temperature or salinity between nearby water bodies, and local currents (observed near the coasts) that are due to the wind (drift currents), or to the simple fact that the sea is not flat (slope currents), or , the phenomenon of tides (tidal currents). In fact, the current observed is the result of currents of various origins.
Potential risks
• risk of losing his tackle
• risk of running out of breath by absolutely wanting to fight it
• risk of injury by clinging to falls or rocks to fight the current
• risk of destroying the fixed fauna (gorgonians, corals, …) clinging to falls and rocks
• risk of moving thoughtlessly away from the boat and no longer being visible from it
• risk of not being able to return to the boat
Precautions to take
• do not fight against the current so as not to run out of breath, progress possibly by clinging to the bottom (where the current is weaker) or to the rocks (taking care to look carefully where you put your hands)
• mandatory presence of an annex with the boat to recover lost divers
• be equipped with a bearing parachute to signal its position to the boat in case of drift
• go down to anchor, and go up as far as possible
• install trail lines (long ends lined with floats attached to the boat allowing divers to haul to the ladder)
• limit the number of divers per tackle
• stay grouped on the surface and for the duration of the dive
• perform a dive without landing
• in tidal regions, dive at the stall (period when the sea neither rises nor falls)
The waves & the swell
Potential risks
• risk of falling when launching (due to the movements of the boat)
• risk of taking the ladder in the gums or shins when boarding the boat
• risk of drinking the cup on the surface
• risk of getting seasy by staying at shallow depths
• risk of losing its tackle, on the surface
•risk of being drossed on the rocks of the coast or on the coral reef if one approaches it too close
Precautions to take
• always keep your regulator in the mouth whether before immersion or after diving until you return to the boat
• do not stay below the ladder when a diver occupies it
• stay together
• when diving, descending enough or moving far enough from the coast or reef to be protected from the grip of the waves
The cold
Potential risks
• the cold is a source of accidents, in particular shortness of breath
Precautions to take
• be equipped with a suit of sufficient thickness, or even a waterproof garment in very cold waters
• adopt a diet rich in carbohydrates
• do not hesitate to warn your tackle guide or, independently, your teammates (sign "I'm cold") and to interrupt the dive
Cave diving
Potential risks
• risk of losing its tackle (because of the reduced brightness, or even zero)
• risk of reducing visibility by lifting a cloud of particles
• risk of not finding the exit (orientation problem or strong contrary currents)
Precautions to take
The exploration of underwater caves is a specialty in its own right: underground diving. It calls for special training accessible only to experienced divers. It requires specific evolution techniques and equipment adapted to this environment (double block, regulator, helmet, headlights, breadcrumbs …)
Diving in narrow passages (arches, tunnels…)
Potential risks
• risk of reducing visibility by lifting a cloud of particles
• risk of getting stuck in the passage
• risk of destroying the fixed fauna (gorgonians, corals, …) by forcing the passage
Precautions to take
• do not palmer near the bottom
• do not touch the walls
• pass in indian line, without haste, one diver at a time
Navigate to the surface
Potential risks
• risk of hitting the head on the hull of the dive boat
• risk of being hit by a vessel on the move (motorboat or sailing boat, jetski, …)
• risk of being caught by a propeller
Precautions to take
• do not dive too close to the surface
• at the ascent, listen (the sound moves 5 times better in the water than in the air) and when approaching the surface, make a tour of horizon to check that the emersion area is clear
• do not park near a propeller
Diving on a wreck
Wrecks represent all that man's hand has left behind, voluntarily or involuntarily, in the seas. These are the boats and planes that have come to join, in spite of themselves, the kingdom of Neptune, the nets of our poor fishermen, the rubbish rejected every year by boaters and by everyone (bottles, tires, chairs, newspapers, what do I know?). These objects, gnawed by rust, are often a danger because of their amazing ability to cut. As for wrecks of respectable size of the kind that can be visited from the inside, there is no shortage of dangers.
Potential risks
• risk of being trapped in a fishing net
• risk of injury to sharp and rusty structures
• risk of getting stuck in a narrow passage
• risk of losing its tackle (because of the reduced brightness, or even zero)
• risk of reducing visibility by lifting the silt
• risk of not finding the exit (orientation problem)
• risk of taking a heavy and blupping element on the head, an element that was waiting for you to fall
Precautions to take
• do not palmer near the bottom
• do not touch the structures
• be equipped with a lamp and a cutting tool (wire cutter, dagger, …)
• stay together
• do not venture inside a wreck
Diving with at-risk wildlife
Potential risks (not exhaustive)
• risk of bite: conger, moray eel, barracuda, shark (deadly), Australian blue-ringed octopus (deadly)…
• risk of sting (venomous stinger): stingrays (especially stingrays), live, redfish, flying scorpionfish (lion fish), scorpion fish, stone fish (deadly), cone (deadly), sea snake (Caledonian striped knitting, mortal)
• risk of sting (mechanical): sea urchin, acanthaster
•risk of electric shock: torpedo line
• risk of cut: surgeon fish
• stinging reactions by contact: fireworm, fire coral, jellyfish, physalia, sea anemone, soft coral
Precautions to take
• learn to recognize fauna and flora and in particular species presenting a particular danger
• do not touch in case of doubt