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Diver communications are the methods used by divers to communicate with each other or with surface members of the dive team.
There are several distinct forms of diver communications:
- Voice communications – Most professional surface supplied diving equipment uses full face diving masks and diving helmets which include voice communication equipment.
- Video communications – Surface supplied divers often carry a closed circuit video camera on the helmet which allows the surface team to see what the diver is doing and to be involved in inspection tasks. This can be used to transfer signals to the surface if voice comms fails, and is in itself a one way mode of communicating useful data to the surface.
- Text communications – Underwater slates may be used to write text messages which can be shown to other divers, and there are some dive computers which allow a limited number of pre-programmed text messages to be sent through water to other divers or surface personnel with compatible equipment.
- Non-verbal communications:
- Hand signals – Recreational divers do not usually have access to voice communication equipment, and it does not generally work with a standard scuba demand valve, so they use other signals. Hand signals are generally used when visibility allows, and there are a range of commonly used signals, with some variations. These signals are often also used as an alternative by professional divers
- Line signals (rope pulls) – Rope signals can be used if the diver is connected to another diver or tender by a rope or umbilical. There are a few partly standardised codes using "pulls" and "bells" (a pair of short tugs). These are mostly used as backup signals by professional divers in the event that voice communications fails, but can be useful to recreational and particularly technical divers, who can use them on their surface marker buoy lines to signal to the surface support crew.
- Light signals – Made using an underwater torch at night. There are not many standard light signals. Suitably skilled divers can transmit morse code using a light.
- Cave line symbols – these are symbols attached to cave lines, indicating critical information such as the direction to the exit.
- Sign language Divers who are familiar with a sign language such as American sign language and equivalents may find it useful underwater, but there are limitations due to the difficulty of performing some of the gestures intelligibly underwater with gloved hands and often while trying to hold something.
- Tap codes – made by knocking on the walls, are used occasionally to communicate with divers trapped in a sealed bell or the occupants of a submersible during a rescue.
- Rattle – a tube containing ball bearings used by guides of large groups to attract attention.
- Miscellaneous emergency signals – Including the use of mirrors, compressed air sirens, whistles, noisemakers, colour-coded Delayed Surface Marker Buoys etc., to alert the surface support personnel of a problem
- Diver down signals – The dive flags, lights and shape signals used to indicate the presence of divers in the water.
- Underwater communication device Buddy-Watcher - a wearable which can be worn on the arm or wrist and has vibration as a call signal to a buddy. The device is soundless underwater. Because of bidirectional ultrsound technology together with appropriate frequency range, the device does not disturb marine life.
- 1 Voice communications
- 2 Video communications
- 3 Hand signals
- 4 Torch / flashlight signals
- 5 Rope signals
- 6 Cave line markers
- 7 Miscellaneous emergency signals
- 8 Diver down signals
- 9 Ultrasonic wearables
- 10 References
Both hard-wired (cable) and through-water electronic voice communications systems may be used with surface supplied diving. Wired systems are more popular as there is a physical connection to the diver for gas supply in any case, and adding a cable does not make the system any different to handle. Wired communications systems are still more reliable and simpler to maintain than through-water systems. The communications equipment is relatively straightforward and may be of the two-wire or four-wire type. Two wire systems use the same wires for surface to diver and diver to surface messages, whereas four wire systems allow the diver's messages and the surface operator's messages to use separate wire pairs.
A standard arrangement with wired diver communications is to have the diver's side normally on, so that the surface team can hear anything from the diver at all times except when the surface is sending a message. This is considered an important safety feature, as the surface team can monitor the diver's breathing sounds, which can give early warning of problems developing, and confirms that the diver is alive.
Divers breathing helium may need a decoder system which reduces the frequency of the sound to make it more intelligible.
Through water communications systems are more suitable for scuba as the diver is not encumbered by a communications cable, but they can be fitted to surface supplied equipment if desired. Most through water systems have a Push To Talk (PTT) system, so that high power is only used to transmit the signal when the diver has something to say. For commercial diving applications this is a disadvantage, in that the supervisor can not monitor the condition of the divers by hearing them breathe.
Dry bells may have a through water communication system fitted as a backup.
Voice communication protocol
Underwater voice communication protocol is like radio communication protocol. The parties take turns to speak, use clear, short sentences, and indicate when they have finished, and whether a response is expected. Like radio, this is done to ensure that the message has a fair chance of being understood, and the speaker is not interrupted. When more than one recipient is possible, the caller will also identify the desired recipient by a call up message, and will also usually identify him/herself.
The surface caller should also give the diver a chance to temporarily suspend or slow down breathing, as breathing noise is often so loud that the message can not be heard over it.
Closed circuit video is often fitted to the helmets of surface supplied commercial divers to provide information to the surface team of the progress of work done by the diver. This may allow the surface personnel to direct the diver more effectively to facilitate the completion of the task. This is always used with voice communication. The communications cables for these systems are part of the divers umbilical. Video may also be used to monitor the occupants of a closed diving bell.
Hand signals are a form of sign system used by scuba divers to communicate when underwater. Hand signals are available whenever divers can see each other, and some can also be used in poor visibility if in close proximity, when the recipient can feel the shape of the signaller's hand and thereby identify the signal being given. Hand signals are the primary method of underwater communication for recreational scuba divers, and are also in general use by professional divers, usually as a secondary method.
RSTC hand signals
Member agencies of the Recreational Scuba Training Council (RSTC) in the United States have recognised a standardised set of hand signals intended for universal use, which are taught to diving students early in their entry level diving courses.
These hand signals provide the following information:
- I am out of breath! Hands indicate rising and falling chest.
- Go that way: Fist with one hand, thumb extended and pointing in the direction indicated.
- Go under, over or around: With palm down, hand motion used to indicate intended route to go under, over or around an obstacle.
Ascend, or I am going up: A fist is made with one hand, thumb extended upward, and hand is moved upward to emphasize direction of travel.
Descend, or I am going down: A fist is made with one hand, thumb extended downward, and hand is moved downward to emphasize direction of travel.
Something is wrong: An open hand with palm down and fingers apart is rocked back and forth on the axis of the forearm.
Are you OK? or I am OK! A circle is made with thumb and forefinger, extending the remaining fingers if possible.
The OK sign may be also be made without extending the fingers if wearing gloves.
I'm OK: Forming a large circle with both hands above the head: Used at the surface as the OK hand sign can be difficult to see from a distance.
I'm OK: Touching or tapping the top of the head with elbow extended sideways: Used at a distance when the hand sign may be difficult to see. Alternative surface "OK" signal.
Stop! Hand raised vertically with fingers together and palm facing the receiver.
Turn around: A forefinger extended vertically and rotated in a circular motion.
Boat: Hands cupped together.
Buddy reference. Used alone: Get with your buddy: Fists made with both hands, forefingers extended, and hands placed together with forefingers parallel and in contact.
Hold on to each other - Maintain physical contact: Both hands clasped together.
Who will lead, who will follow: One hand pointed at the diver who will lead then positioned in front of the body, pointing forward, then other hand pointed to the diver who will follow and positioned behind the first, direction indicated with forefingers.
Level off at this depth: Flat hand with palm down and fingers spread moved slowly side to side horizontally a few times.
Take it easy, Relax or Slow down: Flat hand with palm down moved slowly up and down a few times.
Give me air now (emergency implied): pointing to the mouth with thumb and fingers together, moving hand back and forth a short distance.
Emergency! Help me now: Waving one or both arms in a wide arc. Used on the surface.
I don't know: Shrugging shoulders, arms bent, hands to each side, palms up. 
Danger in that direction: Clenched fist pushed/pointed in the direction of the perceived hazard.
I am cold: Hugging chest and crossed arms in front of chest, upper arms grabbed by opposite hands.
Look: Point with two fingers to the eyes.
Think. or remember: Forefinger extended from fist, touching the side of the head at the temple.
I can't clear this ear: Pointing at the ear with forefinger.
Other commonly used hand signals and variations
Diving signals sometimes differ between groups of divers. Some variations include:
- The throat cut signal: "general danger" or "emergency".
- Tapping the mouthpiece: "share air".
- Pointing at the ear: "listen!"
- Hand cupped behind ear: "listen!"
- Pointing at someone changes the reference of the next signal from "I" to the diver pointed at.
- Flat hand swept over top of head, palm down: "I have a ceiling". This can indicate the diver has gone into decompression obligation or that there is a solid obstruction overhead. When ascending it means "stop here". (this is my decompression ceiling, or we are ascending too fast, or just generally stop ascending at this depth).
- Moving hand across torso in wave motion: "Current"
Divers sometimes invent local signals for local situations, often to point out local wildlife. For example:
- I see a hammerhead shark: Both fists against sides of head
- I see a lobster: Fist with index and middle finger pointed out horizontally and alternately waggling up and down
- I see an octopus: Back of hand or wrist covering mouth, all fingers pointing outward from mouth and wiggling
- I see a shark: Hand flat, fingers vertical, thumb against forehead or chest
- I see a turtle: Hands flat one on top of each other, palms down, waving thumbs up and down together
- You (all) watch me. (usually before demonstrating a skill): Point at diver(s) with forefinger, point at own eyes with forefinger and middle finger, point at own chest with forefinger.
- You try that now, or do it again: Gesture with open hand palm up towards student after a demonstration of a skill.
Torch / flashlight signals
The focused beam of a torch can be used for basic signalling as well.
- OK signal: Drawing a circle on the ground in front of buddy.
- Attention please! Waving the torch up/down.
- emergency! Rapid horizontal motion
Normally a diver does not shine a torch / flashlight in another diver's eyes but directs the beam to his or her own hand signal.
These are generally used in conditions of low visibility where a diver is connected to another person, either another diver or a tender on the surface, by a rope. These date back to the time of the use of Standard diving dress. Some of these signals, or pre-arranged variants, can be used with a surface marker buoy. The diver pulls down on the buoy line to make the buoy bob in an equivalent pattern to the rope signal.
The British Sub-Aqua Club rope signals are
- 1 pull – are you OK? reply 1 pull – Yes I am OK
- 2 pulls – Stay put reply 2 pulls – I am stationary
- 3 pulls – Go down reply 3 pulls – I am going down
- 4 pulls – Come up reply 4 pulls – I am coming up
- 5 or more pulls – Emergency: bringing you to the surface or Emergency: bring me to the surface (no reply required)
Public Safety Divers
Public safety divers and many recreational divers use the following line signals while conducting circular and arc searches underwater.
Tender to diver
- One pull on the line: okay, okay?
- Two pulls: stop, take out slack, reverse direction
- Three pulls: come to the surface
- Four pulls: stop, don't move (there could be danger ahead or a boat entering the search area)
Diver to tender
- One pull on the line: okay, okay?
- Two pulls: advance line
- Three pulls: object found
- Four or more pulls: assistance needed
Commercial diving rope signals
Rope signals used in the UK and South Africa include the following:
Signals are combinations of pulls and bells, A pull is a relatively long steady tension on the line. Bells are always given in pairs, or pairs followed by the remaining odd bell. They are short tugs, and a pair is separated by a short interval, with a longer interval to the next pair or the single bell. The technique and nomenclature derive from the customary sounding of the ships bell every half-hour during the watches, which is also performed in pairs, with the odd bell last. One bell is not used as a diving signal as it is difficult to distinguish it from a jerk caused by temporarily snagging the line.
Attendant to diver:
- 1 pull – Calling for attention, are you OK
- 2 pulls – I am sending down a rope's end (or other pre-arranged item)
- 3 pulls – You have come up too far, go back down till we stop you
- 4 pulls – Come up
- 4 pulls and 2 bells – Come to the surface immediately (often for surface decompression)
- 4 pulls and 5 bells – Come up your safety float line
- 1 pull – Search where you are
- 2 bells – Go out along the jackstay or distance line, or straight out away from tender
- 3 bells – Facing shot or tender, go right
- 4 bells – Facing shot or tender, go left
- 5 bells – Come back towards shot or tender, or back along jackstay.
Diver to attendant:
- 1 pull – To call attention, or have completed the last instruction.
- 2 pulls – Send down a rope's end or other pre-arranged item
- 3 pulls – I am going down
- 4 pulls – I wish to come up
- 4 pulls and 2 bells – Help me up
- 5 or more pulls – Emergency, pull me up immediately
- succession of 2 bells – I am fouled and need standby diver to assist
- succession of 3 bells – I am fouled but can get clear without assistance
- 4 pulls and 4 bells – I am trying to communicate on voice comms
- 1 pull – Hold on or stop
- 2 bells – Pull up
- 3 bells – lower
- 4 bells – Takeup slack on the lifeline or lifeline is too tight
- 5 bells – I have found, started or completed the work
Cave line markers
Cave arrows, Line arrows or Dorff markers (after Lewis Holtzendorff). These are plastic arrowhead markers which are hooked onto a cave line by wrapping the line around the arrow through the slots. They are used to indicate the direction to the exit, and can be identified by feel. The message is simple, but of critical importance, as if a diver does not know which way to go at a line junction there is a risk of serious trouble. Line arrows are used at a junction on the permanent line, and at a tie-off, so when the diver gets back to the tie-off, he or she can identify which way to turn.
Non-directional personal line markers to indicate the identity of a diver who has passed along the line and has not yet returned to that point. They are attached to the line in the same way as cave arrows, and are deployed on the way into the cave, usually at critical points such as forks or jumps, and are used to indicate to other divers that someone is further in along the line. They are marked to identify the diver, and are recovered by the diver on the way out. Cookies (round markers), Rectangular markers and clothes pegs are used for this purpose. The round and rectangular markers are attached to the line in the same way as arrows, and may be personalised in any way that the users can easily recognise. Colour is often used, but as there are a limited number of standard colours available, and they are often poorly distinguishable in the dark, modifications to shape may be used which can be recognised by touch.
Miscellaneous emergency signals
A diver who has deployed a Delayed Surface Marker Buoy (DSMB) at the end of a dive may use a pre-arranged colour code to indicate if there is a problem. In some circles a yellow DSMB is considered an emergency signal, and red means OK. In most circles a second DSMB deployed on the same line will indicate a problem. A DSMB can also be used to carry up a slate with a message, but this is unlikely to be noticed unless a special arrangement has been made.
Diver down signals
- International code flag "Alpha" (White hoist, blue swallowtail fly)
- Diver down flag (Red with white diagonal)
Light and shape signals
A vessel restricted in her ability to manoeuvre, except a vessel engaged in mine-clearance operations, shall exhibit:
- three all-round lights in a vertical line where they can best be seen. The highest and lowest of these lights shall be red and the middle light shall be white;
- three Day shapes in a vertical line where they can best be seen. The highest and lowest of these shapes shall be balls and the middle one a diamond;
- when making way through the water, a masthead light or lights, sidelights and a sternlight, in addition to the lights prescribed in sub-paragraph 1;
- when at anchor, in addition to the lights or shapes prescribed in sub-paragraphs 1 and 2, the light, lights or shape prescribed in Rule 30.
A vessel engaged in dredging or underwater operations, when restricted in her ability to manoeuvre, shall exhibit the lights and shapes prescribed in sub-paragraphs (1, 2 and 3 above) of this Rule and shall in addition, when an obstruction exists, exhibit:
- two all-round red lights or two balls in a vertical line to indicate the side on which the obstruction exists;
- two all-round green lights or two diamonds in a vertical line to indicate the side on which another vessel may pass;
- when at anchor, the lights or shapes prescribed in this paragraph instead of the lights or shape prescribed in Rule 30.
Whenever the size of a vessel engaged in diving operations makes it impracticable to exhibit all lights and shapes prescribed in paragraph (above) of this Rule, the following shall be exhibited:
- three all-round lights in a vertical line where they can best be seen. The highest and lowest of these lights shall be red and the middle light shall be white;
- a rigid replica of the International Code flag "A" not less than 1 metre (3.3 ft) in height. Measures shall be taken to ensure its all-round visibility.
Surface marker buoys
Permanently buoyant or inflatable surface marker buoys may be used to identify and/or mark the presence of a diver below. These may be moored, as a shotline, and indicate the general area with divers, or tethered to one of the divers by a line, indicating the location of the group to people at the surface. This type of buoy is usually brightly coloured for visibility, and may be fitted with one of the diving flag signals.
A surface marker buoy (SMB) tethered to a diver is usually towed on a thin line attached to a reel, spool or other device which allows the diver to control the line length, so that excessive slack line can be avoided.
A deployable, or delayed surface marker buoy (DSMB) is an inflatable marker which the diver inflates while underwater and sends up at the end of a line to indicate position, and usually either that he or she is ascending, or that there is a problem. The use of a DSMB is common when divers expect to do decompression stops away from a fixed reference, or will be surfacing in an area with boat traffic, or need to indicate their position to the dive boat or surface team.
A group of moored surface marker buoys may be used to demarcate an area in which diving is taking place. This is more likely to be used by commercial, scientific or public service divers to cordon off a work or search area, or an accident or crime scene.
The Buddy-Watcher is a wrist mounted buddy alert device which sends an ultrasonic signal when a key is pressed, for at least 20m through the water to the matching unit on the dive buddy, which will produce a silent vibratory and visual signal alerting the diver that their buddy wants attention. There is no direct indication to the sender whether the signal has been received and no indication of distance or direction to the buddy. The device is waterproof to 40m, therefore is suited for recreational scuba diving use, but not technical diving.
- Agnew, J. (2003): Scuba Diver's Travel Companion, The Globe Pequot Press, Guilford, CT, ISBN 0-7627-2668-7
- "UDI Dive Computer Can Send Underwater Text Messages". Retrieved 2013-08-27
- Liebscher, Caren; Pellegrini, Cristian (October 2015). "Enhancing underwater communication - The Buddy Watcher". Alert Diver. Divers Alert Network Europe. Retrieved 22 July 2016.
- Staff (February 2014). "IMCA International Code of Practice for Offshore Diving" (PDF). IMCA D 014 Rev. 2. International Marine Contractor's Association. Retrieved 22 July 2016.
- The Diving Supervisor’s Manual, First edition, 2000. The International Marine Contractors Association, London. www.imca-int.com ISBN 1-903513-00-6
- "Minimum Course Content for Common Hand Signals for Scuba Diving" (PDF). Recreational Scuba Training Council, Inc. (RSTC) (Jacksonville, FL., USA). 1 December 2005. Retrieved 3 July 2016.
- "Dive Links". Retrieved 2009-04-14.
- "Underwater Signals - UKDivers.net". Retrieved 2009-04-14.
- Larn, R and Whistler, R. (1993): Commercial Diving Manual, David & Charles, Newton Abbott, ISBN 0-7153-0100-4
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