The diver has a very limited ability to survive without a supply of breathing gas. Any interruption to that supply must be considered a life-threatening emergency, and the diver should be prepared to deal effectively with any reasonably foreseeable loss of breathing gas. Temporary interruptions due to flooding or dislodging the demand valve are recoverable by recovery and clearing of the demand valve. More permanent interruptions require other strategies. An obvious response which is appropriate in some circumstances is to ascend to the surface. This response is appropriate when the consequences are acceptable. When the surface is near enough to easily be reached, and the diver has no significant risk of decompression sickness as a consequence of a direct ascent, an emergency free ascent may be a suitable response. If the surface is too far to reach with confidence, or if the risk of decompression sickness is unacceptable, other responses would be preferable. These involve getting an alternative supply of breathing gas, either from an alternative source carried by the diver, or from another diver.

Emergency ascents

An emergency ascent usually refers to any of several procedures for getting to the surface in the event of an out-of-air emergency, generally while scuba diving.

Emergency ascents may be broadly categorized as independent ascents, where the diver is alone and manages the ascent alone, and dependent ascents, where the diver is assisted by another diver, who generally provides breathing gas, but may also provide transportation or other assistance. Emergency ascent usually refers to cases where the distressed diver is at least partially able to contribute to the management of the ascent.

An emergency ascent implies that the diver initiated the ascent intentionally, and made the choice of the procedure. Ascents that are involuntary or get out of control unintentionally are more accurately classed as accidents.

Emergency ascents may be classified as independent action, where no assistance required from another diver, and dependent action, where assistance is provided by another diver.

Buoyant ascent is an ascent where the diver is propelled towards the surface by positive buoyancy.
Controlled emergency swimming ascent (CESA) is an emergency swimming ascent which remains under control and which is performed at a safe ascent rate, with continuous exhalation at a rate unlikely to cause injury to the diver by lung over-expansion.
Emergency swimming ascent (ESA) is a free ascent where the diver propels him/herself to the surface by swimming at either negative or approximately neutral buoyancy.
Another form of ascent which may be considered an emergency ascent is a tethered-ascent – where the diver has unintentionally lost full control of buoyancy due to a loss of ballast weight, and controls ascent rate by use of a ratchet dive reel with the end of the reel line secured to the bottom.

Emergency ascent training policy differs considerably among the certification agencies, and has been the subject of some controversy regarding risk-benefit.

Emergency air sharing
Emergency sharing of breathing gas may be done by sharing a single demand valve, or by the donor providing a demand valve to the receiver, and another for their own use. The gas supply for the second demand valve may be from the same scuba set or from a separate cylinder. The preferred technique of air sharing is donation of a demand valve that is not needed by the donor.

The procedure of sharing a demand valve is known as buddy breathing. It is no longer considered the default method of sharing breathing gas as the use of a separate “octopus” demand valve is considered to reduce the risks involved sufficiently to justify it being rated the standard practice by most, if not all, diving certification agencies. As a consequence, buddy breathing is no longer taught as extensively as it was in the past, but some agencies and schools still teach buddy breathing as an entry-level or advanced skill, as the ability to perform the skill successfully is not only considered a potentially life-saving skill in special circumstances, but also demonstrates the self-control and rational behavior that are desirable in an emergency. The standard technique for buddy breathing is for the divers to alternately breathe from the demand valve, usually each taking two breaths before exchanging the DV, but it is common for the receiver to be out of breath at the start of the procedure, and they may need a few more breaths to stabilize. Once a rhythm has been established, it is usual to terminate the dive and start the ascent, so buddy breathing training will usually include assisted ascents. Assisted ascents using a secondary demand valve are simpler than buddy breathing ascents, and this skill is quicker to learn.

The conventional technique, known as octopus donation, is to donate a secondary demand valve supplied from the donor’s primary gas supply, known as an octopus DV, which is mounted ready for use in an easily accessible position in the donor’s chest area, and is often yellow for easy recognition.

The alternative is to donate the primary demand valve that the donor is currently breathing from, on the principle that it is known to be working and is immediately recognizable and accessible. The donor, who should be less stressed, will then switch to the secondary demand valve, which in this arrangement is generally mounted on a loop of bungee cord which hangs on the neck, and keeps the secondary demand valve tucked up under the diver’s chin, where it can often be reached without the use of the hands, by bending the head forward and gripping the mouthpiece with the teeth.

Bailout to alternative gas supply
An alternative to relying on a dive buddy to supply breathing gas in an emergency, is to carry an independent supply of emergency breathing gas in a separate cylinder, known variously as an independent alternative air source, bailout cylinder or pony cylinder. This is necessarily the option used by solo divers, as they may not be anywhere near another diver in an emergency, but it is also the choice of many professional diving organisations and conventional recreational divers, who prefer not to rely on an unfamiliar buddy. The details of the technique vary depending on how the bailout cylinder is carried. This skill is generally not taught to entry level recreational divers, but may be part of the basic required skill set for professional divers.

Standardised emergency procedures used with manifolded twins
One of the standardised configurations used with manifolded twins is that developed by the DIR movement for cave exploration. The procedures listed are those developed for this configuration, and are in general use by a large number of technical divers. The diver breathes from the primary second-stage regulator supplied from the right side first stage by a long (2-meter/7-foot) hose. A secondary second-stage regulator is carried just beneath the chin, suspended by a breakaway elastic loop around the neck, supplied from the left side first stage cylinder by a shorter (0.5-meter/2-foot) hose. The cylinder valves and manifold isolation valve are normally open:

If another diver experiences an out-of-air emergency, the donor diver hands over the primary regulator, which they both know is functioning properly. The donor then switches to the secondary regulator. The entire gas supply is available to both divers for the remainder of the dive and they are able to separate by a sufficient distance to pass through tight restrictions with the donor behind the recipient.

If the primary regulator malfunctions, the diver closes the right-shoulder cylinder valve and switches to the secondary regulator. The entire gas supply is available for the remainder of the dive.

If the secondary regulator malfunctions, the diver closes the left-shoulder cylinder valve, continuing to breathe through the primary regulator. The entire gas supply is available for the remainder of the dive.

Cylinder to manifold connection malfunction, though rare, can result in an extremely violent gas loss. In case of the right side manifold connection leak, the diver closes the isolating valve to secure the gas in the left cylinder, and continues to use the gas from the right cylinder until it runs out, and then switches to the secondary regulator. At least half of the remaining gas volume is available for the remainder of the dive once the isolation valve has been closed.
In case of the left side manifold connection leak, the diver closes the isolating valve switches to the secondary regulator to use as much of the gas in the left cylinder as practicable before it runs out, then switches back to the primary regulator. At least half of the remaining gas volume is available for the remainder of the dive once the isolation valve has been closed.

Mitigation
It is not usually possible to entirely eliminate risk to a diver, and where there is sufficient residual risk it is necessary to provide mitigation for the foreseeable consequences of an incident occurring.

Emergency planning
Professional divers may be legally obliged to make plans and provide equipment and personnel to manage reasonably foreseeable accidents. This can include a requirement for the contractor’s operations manual to include instructions for the members of a dive team in the event of any of several classes of emergency, which may include managing an injured or unconscious diver underwater or at the surface, recovery of such diver from the water, provision of first aid, provision of recompression therapy in the case of decompression illness, communication with emergency services and the contracted diving medical practitioner on standby, decontaminating divers and emergency evacuation of the worksite. Specific checklists or flowcharts may be provided with emergency plans where they may be useful to ensure correct sequencing and that no critical stage is omitted.

Recreational dive leaders such as divemasters and instructors may also be required to produce emergency plans for a dive site or area The contents may vary depending on location and access to assistance, and would contain the information necessary to handle reasonably foreseeable emergencies. Content may include contact details for local emergency medical care, a casualty evacuation plan, how to arrange emergency recompression and other diving specific emergencies, and what assistance can be expected from the local emergency services.

Recreational, and particularly technical divers are recommended by certification agencies to have some form of emergency plan in case something goes wrong. The international organisation Divers Alert Network provides a hotline service giving advice on diving emergencies, and in the case of members, authorising and arranging emergency medical assistance and evacuation.

Training to manage foreseeable incidents
A large part of diver training is in the emergency procedures known to be effective at managing the most common incidents which could be life-threatening if not manages promptly and appropriately. The amount of overlearning and the level of skill required for certification varies considerably with the training standard for different certifications, but minimum standards for recreational diver and instructors have been established by the International Standards Organisation (ISO), and national and international standards for professional divers have been published by various controlling bodies. All of these standards include management of the most frequent diving emergencies by application of well established techniques, though not always by identical procedures.

Emergency and rescue: procedures, personnel and equipment
The diver should be able to manage a reasonably foreseeable and immediately life-threatening emergency unaided as there can be no guarantee that someone else will be near enough to help, will notice and will respond appropriately in time. Lower priority threats can be managed by teamwork and resource sharing. Since most of the critical safety skills for diving are not intuitive, nor associated with activities the diver is likely to have learned for other purposes, diver safety is enhanced by comprehensive training and frequent exercise of safety critical skills.

One of the standard ways to help the diver to manage an emergency is to provide another diver ready to assist. In professional diving this is known as the stand-by diver, and in the case of bell diving, the bellman. In recreational diving, buddy diving and team diving procedures are intended to provide similar benefits, where each diver in a pair or team is stand-by diver to the other or others. This system can be effective when the divers are all adequately skilled, fit and dedicated to the task, as has been shown in many deep dives and cave penetrations. The buddy diver is less effective when insufficiently skilled, inattentive, or unfit. Buddy and team diving procedures impose a significant additional task loading on the divers, particularly in adverse conditions, such as darkness, low visibility, confined spaces, strong currents, cold water and unfamiliarity with each other’s equipment and habits. Nevertheless, many recreational training agencies maintain that buddy diving is intrinsically safer than solo diving.

Stand-by diver
The stand by diver’s job is to wait until something goes wrong, and then be sent in to sort it out. For this reason a stand by diver should be one of the best divers on the team regarding diving skills and strength, but does not have to be expert at the work skills for the specific job. The standby diver is usually required to remain ready for deployment at very short notice during the entire working dive, and will usually be fully dressed ready to deploy, except for helmet or mask. When deployed, the standby diver will normally follow the umbilical of the diver who is in trouble, as unless it has been severed, it will reliably lead to the correct diver. The standby diver must maintain communications with the supervisor throughout the dive and is expected to give a running commentary of progress so that the supervisor and surface crew know as much as possible what is happening and can plan accordingly, and must take the necessary steps to resolve incidents, which may involve supply of emergency air or locating and rescuing an injured or unconscious diver. In bell diving, the bellman is the standby diver, and may have to recover a distressed diver to the bell and give first aid if necessary and possible. The standby diver and working diver are generally interchangeable, unless specialised skills are required for the task of the specific dive, and professional divers are trained in rescue procedures appropriate to the equipment they are qualified to use. Rescue skills are not included in the minimum training standards for entry level recreational divers according to RSTC and ISO publications.

Buddy or team divers
A buddy or team diver is simultaneously the diver and the standby diver for the buddy or other members of the team. Since it is increasingly difficult to keep track of a larger number of divers, and the benefits of larger groups are small, teams are usually of three divers. Larger groups are generally split up into three diver teams and pairs.

When using the buddy system, members of the group dive together and co-operate with each other, so that they can help or rescue each other in the event of an emergency. This is most effective if the divers are both competent in all the relevant skills and are sufficiently aware of the situation to be able to respond in time, which is a matter of both attitude and competence.

In recreational diving, a pair of divers is usually the best combination in buddy diving; with threesomes, one of the divers can easily lose the attention of the other two. The system is likely to be effective in mitigating out-of-air emergencies, non-diving medical emergencies and entrapment in ropes or nets. When used with the buddy check it can help avoid the omission, misuse and failure of diving equipment.

In technical diving activities such as cave diving, threesomes are considered an acceptable practice. This is usually referred to as team diving to distinguish it from buddy diving in pairs.

When professional divers dive as buddy pairs their responsibility to each other is specified as part of the standard operating procedures, code of practice or governing legislation.

Stay safe
The obvious safety concern with diving is that you must rely on your equipment to deliver you air. For this reason, scuba equipment is subject to rigorous testing according to various standards at the design and production stages. Your part of ensuring your own safety is making sure that you are adequately trained and prepared for any dive you do, and that your equipment is suitable for the dive and functioning correctly. Do not assume that rental equipment is in good order: test it yourself.

The other side of this is to ensure that the air you breathe is safe. Most popular diving destinations will provide air fills from a suitable compressor in good condition and adequately filtered. Other places may be more haphazard and compressors that are in bad condition, dirty filters, poor installations, external sources of contamination and careless or unscrupulous operators may provide you with contaminated air. Contamination at levels which may be imperceptible or merely give you a headache or mild nausea on the surface can cause loss of consciousness underwater, often leading to drowning.

Being familiar with symptoms of equipment failure and recovery techniques obviously improves your safety. Your training will include information about performing basic safety checks on your equipment and about other guidelines. Further training is available in specialty courses.

If you’re diving regularly you will probably want to take courses in emergency diving procedures and in first aid including CPR.

Basic safety precautions
The basic precautions you should take for safe diving are:

Have an agreed plan for every dive, including where you expect to go, how you will manage your air supply and what you and others will do if something unexpected happens (common problems are getting low on air, getting lost or losing your buddy)

Unless specially trained and equipped, do not dive alone, always dive with a partner (a “buddy”) who will stay close to you. Typically regulators have a second mouthpiece you can lend a buddy if they are out of air. Remember that a buddy who is not in reach in an emergency or who is not competent or willing to assist is no buddy at all, and that a buddy has no legal obligation to assist if it may endanger him or herself to do so. Do not allow the dive operator to pair you with someone whom you could not assist or who would not be able to assist you.

Solo diving is not illegal in most parts of the world, however some operators will refuse to allow you to dive without a buddy, even if you are trained, experienced and equipped to do so. As solo diving may be less hazardous than diving with an unsuitable buddy, there are divers who prefer it, and take additional precautions to mitigate the risks related to not having a buddy. If you are one of these, check with the operator when booking whether they will be amenable.

Do not dive in unfamiliar conditions without an orientation from a suitably competent person, or you may find your skills are not adequate to the task. This is a common problem for divers who are accustomed to warm, calm water and find themselves under stess the first time they dive in cold rough water, or in a current.

Do not dive in unfamiliar areas without a guide or appropriate orientation. Do some introductory dives or a dive orientation with a divemaster or diver with local experience.

Do not dive outside your training and experience, for example, diving deeper than you trained for, or diving in confined spaces when you’re only certified for open water.

Try on rental equipment in the shop. This is particularly important for wet and dry suits. Don’t assume that if the trousers fit the jacket will too, or any other variation on this assumption. Try drysuits on over the undergarments you plan to wear with them, or there may be an unpleasant surprise when you can’t reach your feet to put on your fins.

Do not dive with unfamiliar equipment except in very easy conditions, where any problems can be sorted out without major inconvenience or risk. Get your weights sorted out in shallow water, make sure the regulator has no leaks, and that the harness fits properly before going on a deep dive. Many divers have no idea of how much weight they will need with an unfamiliar exposure suit, and almost none will get it right the first time.

Weight belts or other weight systems are primarily built to compensate for the buoyancy of your suit. Being able to dive with 2 kg in skins in the tropics does not mean you need the same with a 7mm suit if you go somewhere where the water is cold. On the other hand all the other items of your equipment affect buoyancy, including the size and type of cylinder, and the salinity of the water. There is no substitute for trying all the equipment out together to ensure correct weighting. A little extra weight is better than not enough, but too much can be deadly.

Do not dive when impaired, e.g. by fatigue or alcohol.

If diving in a group led by a guide, do not neglect your own planning and air management and if necessary plan to ascend early without the guide. Divemasters vary in skill, but even the best will not substitute for taking responsibility for yourself.

If you feel overly anxious about the dive, or feel you may not be fully qualified for the conditions, you have the absolute, unconditional right to end the dive without having to justify your decision. Ultimately, you are responsible for deciding if any particular dive is right for you.

Check the air you will be breathing. It should have no smell or taste and should leave no mark when passed through a white cloth. These tests, if passed, do not guarantee that there are no contaminants, but if failed, don’t breathe it. If you have any doubt, ask the shop to show you the latest air quality test results. Some places may not require this to be available, in which case a look at the compressor installation can tell you a lot. If the operator refuses to give this information, decide for yourself whether it is a good idea to stake your life on their product. Some countries have legal standards for minimum breathing air quality. These include the USA, Canada, EU countries, South Africa, Australia and New Zealand. Some other countries do not. Portable testing equipment is available for the most important contaminants, but it is quite expensive. It is a matter of what your life is worth to you, and what risks you accept. When booking, ask about air testing and quality control.

Dive with reputable and competent operators. Find out beforehand what the qualifications are of their skippers and divemasters, and what emergency facilities are available. You can still choose to dive with a less than ideal operation, but it is then an informed choice. Litigation after the accident is a waste of time and money in some parts of the world.

Checklist on potential dive operators
A few questions you could ask the dive operator before booking when planning a dive vacation to an unfamiliar region.

What are the qualifications of the skipper and divemaster?
Is a member of the crew qualified in basic first aid and oxygen administration.
Do they have emergency oxygen administration equipment on site and on the boat?
What is the local air quality standard, and how is it enforced?
How are seaworthiness of the dive boat and competence of the crew enforced?
What emergency facilities are available in case of an accident?
Search and recovery.
Medical evacuation.
Recompression.
First aid.
Medical treatment facilities.
Does your shop have a Automated External Defibrillator (AED).
How do they monitor the time that a diver has been off the boat and whether all the correct divers are back on board before leaving the site?
Standards for these items vary enormously. Do not assume that they will be much the same as at home. Oxygen is unavailable in some places, and some countries do not have any recompression facilities at all. The last item may look a little trivial, but even in countries where safety standards are taken seriously, divers are occasionally left behind by accident, and it has happened that the right number of divers were on the boat, but some of them had dived from another boat, so a simple head count is not always sufficient.

Some operators are affiliated to the Divers Alert Network as DAN Diving Safety Partners. This implies compliance with a fairly good standard of preparedness for emergencies, including provision of oxygen and first aid equipment, personnel trained and certified in the use of this equipment, and emergency assistance and lost diver prevention and retrieval plans. Non-affiliated operators may or may not meet these standards.

Autonomous and Solo diving
Many divers expect to be guided on a Scuba dive at a travel destination. This is partly because this can be a good way to get to see the best of the site, as the dive leader can reasonably be expected to know the site better than a first time visitor, and partly because it has become customary to deal with the customers en masse — it is usually more convenient for the operator to handle a compact group. This is not always to the advantage of either or both parties.

The attitude towards divers who do not habitually dive in buddy pairs, and in some areas, those who do, but do not follow a dive-master around the site in a relatively tight group, varies from place to place, and between operators.

In some places all the divers are obliged to dive in pairs and to stay with the dive leader. This can be for good practical reasons, such as fairly strong currents, limited visibility, or a site which is difficult for an unescorted diver to navigate. In other places it can be more arbitrary, and the reasons range from simple bias on the part of the dive operators and dive leaders, who prefer it for their own convenience, to legal obligations in conservation areas, where the local authorities impose the restrictions as a condition of allowing you to dive. In theory this is probably to make it possible for the dive leader to enforce ecologically sound diving practices on what is usually a motley collection of divers of widely varied skills, experience and interests.

Most diver training agencies encourage the practice of diving in pairs, generally known as the buddy system, on the premise that each diver can be of assistance to his or her buddy in case of an emergency that the diver can not deal with on their own. This functions with a varying degree of success, and can range from critically important and the difference between life and death for the distressed diver, to a complete waste of effort, if the buddy is not physically competent or adequately skilled and equipped to deal with the problem, through to a double fatality where the buddy goes beyond their competence in a futile effort to assist, and ends up getting into trouble as well.

The buddy system, or taken further, the three diver team is a valuable safety advantage if the buddies are familiar with each other’s equipment, abilities and diving style, but a liability if they are not. Many recreational divers have been brainwashed into the false sense of security of assuming that their buddy will be able to get them out of trouble if something goes wrong, but this is often not the case. Unfortunately statistics are very sporadic, as fatal accidents tend to be reported, but less serious accidents are often never made public, and near misses are often not even recognised as such by the divers involved.

For one’s own safety, it is better never to assume that someone else will get you out of trouble unless you know they can, and this generally means having dived together several times, and actually practiced the relevant skills with that person, in conditions similar to those you will be diving in when you put your life in their hands. Dive leaders may or may not have a duty of care to rescue their customers, but if they are leading a large group, they may have more on their hands than they can deal with if things go pear shaped, and you may not be at the top of their priority list.

Instructors definitely do have a duty of care to assist and rescue their learners, and to try to prevent them from getting into trouble in the first place. That, after all, is what you are paying them to do. This duty only applies when they are contracted as instructors to the specific client. Do not presume on the same duty of care if an instructor is acting as a dive-master for your group or just diving with you.

This can become a problem for inexperienced and infrequent divers if they visit an area where the conditions are more severe than they are accustomed to. There is a general tendency among dive charter organisations to arbitrarily appoint buddy pairs, and if you accept this arrangement you may find yourself in a position where you are expected to assist an incompetent person through a dive you have paid good money for, during your once-in-a-lifetime visit to an exotic location. Furthermore, just because a highly competent diver has been assigned to you as a buddy, that does not oblige that person to endanger themselves to get you out of trouble.

There is also an incompatibility issue between underwater photographers and group dives, as the dive leaders and other divers are not always tolerant of the photographers’ requirements for slow speed and minimal silt stirring. In places where there is no legal constraint to diving without the immediate attention of a dive-master, it may suit many divers to dive apart from the guided group, either in compatible buddy pairs, or solo. If you plan to go this route, check ahead of time with the operator to ensure that they will allow this procedure. In many cases you will be expected to produce evidence that you can deal with the dive. Generally a buddy pair will be assumed competent in the absence of evidence to the contrary, providing they both have nominally suitable certification.

Providing convincing evidence that you will be able to safely dive solo can be difficult, particularly as there is a general bias against the practice in the recreational diving industry. There are certifications provided by a few certification agencies for Solo Diver (SDI), but information on the training is not easily available to the general diving public.

Source from Wikipedia