Blow and go is a free ascent where the diver exhales at the bottom before starting the ascent. The breath may be held during part of the ascent, as the lungs are emptied before starting. This procedure is considered unnecessarily hazardous by many recreational training agencies. [3] Divers should be taught to agree on emergency procedures before the dive when intending to dive together. Free ascent is the procedure used in US Navy submarine escape training. However the term is also used for other emergency diver ascent procedures where breathing gas is not available to the diver during the ascent. [3] If the diver is not carrying a bailout cylinder, and another diver is in the immediate vicinity, the diver may request gas from the other diver.

An ascent where the diver is pulled to the surface by the line tender, either as a response to an emergency signal from the diver, or a failure to respond to signals from the surface. A diver may also be assisted in the ascent by the line tender in a normal ascent, particularly divers in standard dress, where it was often the normal operating procedure. Vann, RD; Lang, MA, eds. (2011). Recreational Diving Fatalities (PDF). ISBN 978-0-615-54812-8. Archived from the original (PDF) on 8 October 2016 . Retrieved 29 September 2016. {{ cite book}}: |first2= has generic name ( help); |work= ignored ( help) CS1 maint: multiple names: authors list ( link) The agreement requires scuba instructors to make students aware of the variables and how they affect the choice of an appropriate response.Transcript of Evidence in Fatal Accident Inquiry into the deaths of Gerard Anthony Prangley and Lothar Michael Ward". November 1979: 374. {{ cite journal}}: Cite journal requires |journal= ( help)

A first stage regulator which is to be used with an octopus demand valve should be able to supply the required flow rate without freezing up if the water is cold. [3] a b Brown, Charles V. (1979). Samson, R. L.; Miller, J. W. (eds.). "Emergency Ascent Training". 15th Undersea and Hyperbaric Medical Society Workshop. UHMS Publication Number 32WS(EAT)10-31-79: 42. Archived from the original on October 7, 2008 . Retrieved 2008-08-07. {{ cite journal}}: CS1 maint: unfit URL ( link) An ascent to the surface by a diver in an emergency Alabama National Guard divers performing a controlled ascent during a training exercise Lost buoyancy ascent – where the diver loses the ability to establish neutral or positive buoyancy without resorting to ditching weights. This can be due to a major buoyancy compensator failure or a major dry-suit flood. Drowning is the most likely consequence of a failure to reach the surface during an independent emergency ascent, and is a significant risk even if the diver reaches the surface if he or she loses consciousness on the way.

Egstrom, GH (1978). "Ascents". South Pacific Underwater Medicine Society Journal. 8 (2). ISSN 0813-1988. OCLC 16986801. Archived from the original on April 15, 2013 . Retrieved 2008-08-07. {{ cite journal}}: CS1 maint: unfit URL ( link)

The most direct and well publicised hazard is lung overpressure due to either a failure on the part of the diver to allow the expanding air in the lungs to escape harmlessly, or entrapment of air due to circumstances beyond the control of the diver. Lung overpressure can lead to fatal or disabling injury, and can occur during training exercises, even when reasonable precautions have been taken. There is some evidence [12] that a full exhalation at the start of the ascent in the "blow and go" scenario, can lead to partial collapse of some of the smaller air passages, and that these can then trap air during the ascent sufficiently to cause tissue rupture and air embolism. The procedure of slowly letting the air escape during ascent can also be taken too far, and not allow the air to escape fast enough, [12] with similar consequences. Attempting to breathe off the empty cylinder is one way of potentially avoiding these problems, as this has the double advantage of keeping the airways open more reliably, and in most cases allowing the diver several more breaths during the ascent as the reduced ambient pressure allows more of the residual cylinder air to pass through the regulator and become available to the diver. A 10-litre cylinder ascending 10 metres will produce an extra 10 litres of free air (reduced to atmospheric pressure). At a tidal volume of about 1 litre this would give several breaths during ascent, with increased effectiveness nearer the surface. Of course this air is not available in some cases, such as a rolled off cylinder valve, burst hose, blown o-ring, or lost second stage, where the failure is not simply breathing all the air down to the pressure where the regulator stops delivering, but if it is possible, the demand valve can be kept in the mouth and the diver can continue to attempt to breathe from it during a free ascent. [ citation needed] Loss of consciousness due to hypoxia [ edit ] The diver should not waste time while making the choice of which emergency ascent procedure to use. A controlled swimming ascent is the most recommended default for recreational diving. Divers who venture beyond the safe zone for controlled swimming ascent should be prepared for their most appropriate option at all times. [3] Curtis, ASG (1978). "Free Ascents: A view from the Scottish Sub-Aqua Club". South Pacific Underwater Medicine Society Journal. 8 (2). ISSN 0813-1988. OCLC 16986801. Archived from the original on July 1, 2012 . Retrieved 2012-03-03. {{ cite journal}}: CS1 maint: unfit URL ( link) Clean sections of natural hair are sandwiched between two pieces of tape hair, spaced out in a special section pattern around the head – no heat, glue or rings required. The most generally effective method is for each diver to carry an independent bailout set sufficient to safely reach the surface, after completing all required decompression for the planned dive profile. [6] This is relatively expensive and many recreational divers have never been trained in this skill, so there may be unacceptable additional task loading to carry and use the equipment.Emergency ascents may be broadly categorised as independent ascents, where the diver is alone and manages the ascent by themself, and dependent ascents, where the diver is assisted by another diver, who generally provides breathing gas, but may also provide transportation or other assistance. The extreme case of a dependent ascent is underwater rescue or recovery of an unconscious or unresponsive diver, but this is more usually referred to as diver rescue, and emergency ascent is usually used for cases where the distressed diver is at least partially able to contribute to the management of the ascent. Buddy breathing by two divers on a single second stage is specified as the least desirable of the dependent options.

The Scottish Sub-Aqua Club holds that training is primarily to deal with potential emergencies and that it should be practical rather than purely theoretical. This implies that it is better to have some practical experience of ability to cope with a simulated emergency situation as this gives greater insight and confidence, as well as proven ability, provided that the risk in training is appreciably smaller than the risk in not being trained. If the other diver has the gas available and is both willing and competent to provide it, the donor provides emergency gas and the two divers make an assisted emergency ascent while sharing gas using a single demand valve or octopus demand valve, or supplying the receiver from the donor's bailout set. No other procedures are recommended in this agreement, though the use of a bailout cylinder may be considered effectively equivalent to either octopus assisted ascent, when gas is supplied by a donor, or not actually running out of gas if it is the diver's own bailout set. [3] SSAC [ edit ] Ascent during which the diver is provided with breathing gas from the same demand valve (second stage regulator) as the donor, and they breathe alternately. The out-of air diver must attract the attention of a nearby diver and request to share air. If the chosen donor has sufficient gas, and is competent to share by this method, an emergency ascent may be accomplished safely. Accurate buoyancy control is still required, and the stress of controlling the ascent rate and maintaining the breathing procedure can be more than some divers can handle. There have been occurrences of uncontrolled ascent and panic, in some cases with fatal consequences to both divers. This procedure is best suited to divers who are well acquainted with each other, well practiced in the procedure, and highly competent in buoyancy control and ascent rate control. [ citation needed] In most circumstances analysis of the risk would indicate that the divers should have an alternative breathing gas source in preference to relying on buddy breathing. Failure to provide alternative breathing gas without good reason would probably be considered negligent in professional diving.On a type 2 bell, the divers' umbilicals are connected to the gas panel in the bell, and the procedure used should minimise the risk of the umbilical snagging during the ascent and forcing the diver to descend again to free it. If the diver excursion umbilical is not long enough to allow the diver to reach the surface, the standby diver will have to disconnect the bell diver's umbilical, and the rest of the ascent may be done on bailout, pneumo supply from the standby diver, or the standby diver can connect a replacement umbilical. The controlled buoyant lift is an underwater diver rescue technique used by scuba divers to safely raise an incapacitated diver to the surface from depth. It is the primary technique for rescuing an unconscious diver from the bottom. It can also be used where the distressed diver has lost or damaged their diving mask and cannot safely ascend without help, though in this case the assisted diver would normally be able to control their own buoyancy. [ citation needed] If it is possible, the demand valve can be kept in the mouth and the diver can continue to attempt to breathe from it during a free ascent. [3] The final option is a buoyant ascent, where buoyancy is gained by inflation of the buoyancy compensator (not always possible in an out-of-air emergency), and dropping of weights. This is recommended as a last resort where the diver is unsure of making it to the surface by swimming, as it will ensure that an unconscious diver will rise to the surface rather than sink. Curtis, ASG (1978). "Free Ascents: A view from the Scottish Sub-Aqua Club". South Pacific Underwater Medicine Society Journal. 8 (2). ISSN 0813-1988. OCLC 16986801. Archived from the original on July 1, 2012 . Retrieved 2008-08-07. {{ cite journal}}: CS1 maint: unfit URL ( link)