The nature of an emergency requires action to be taken to prevent or avoid death, injury, or serious damage to property or the environment.
The diver survives in an inherently hostile environment by competence, suitable equipment, vigilance, and attention to detail at a level appropriate to the specific situation.
This can happen either by the diver being unable to ascend in time to avoid the problem, or by using up or losing gas supply due to circumstances or inattention.
The bailout gas carried by the diver may not be sufficient for long decompression, and if this is expected a diving stage or wet bell will be used which carries a larger supply of emergency breathing gas, as well as providing a relatively secure platform for decompression stops.
The transparent faceplates of most helmets in current use are highly impact resistant and not easily damaged to the extent that they leak dangerously.
If this does occur, the free-flow valve can be opened to increase internal pressure to reduce leak flow and purge the helmet of water.
[14] In the event of a suit heating water supply failure that cannot be resolved promptly, the diver will abort the dive.
This is a serious problem for divers using helium based breathing gas as heat loss is rapid and the risk of hypothermia is high.
If the leak starts at the surface, the supervisor would attempt to maintain internal pressure while the bell would be reconnected to the trunking.
[15] A lost guide line under an overhead where the exit cannot be seen is a life-threatening emergency, as the diver will die if they cannot find the way out before they run out of breathing gas.
The guideline is usually the only sure way of finding the exit in a cave or wreck penetration, and if not found, the probable consequence is that the diver will not get out before their breathing gas runs out, and they drown.
[17][18] An aggravated version is when one or more divers enter an overhead knowingly or unknowingly without laying a guide line, and cannot find the way out.
Severe symptomatic decompression sickness can develop during ascent for a variety of reasons, some poorly understood and therefore not entirely reliably avoided.
[10] Underwater diving is an activity with a high exposure to inherent hazards, which can be conducted at acceptably safe levels when divers participate within the scope of their technical competence, range of experience, physical, and psychological limits.
Raised levels of physical and psychological stress can develop rapidly due to unexpected events and situations.
In many of these situations it is not practicable to treat the problem in the water, so it is urgent for the diver to surface and get appropriate first aid as soon as possible without causing more serious injury through haste.
Excessive work of breathing (WoB), when extreme, can exceed the capacity of the diver to eliminate carbon dioxide and eventually cause a hypocapnic blackout, which is likely to be followed by asphyxia or drowning.
Several mechanisms may cause high work of breathing WoB, such as high gas density, regulator malfunction, loop flood in a rebreather, or excessive exertion with hypercapnia and the cause must be identified before effective action can be taken, but bailout to open circuit and an immediate termination of the dive is generally an appropriate response where possible.
[26] A buddy or standby diver with lower work of breathing may be able to carry out a rescue, depending on the cause of the high WoB.
In this case the diver is likely to be aware of the problem, and the dive team is likely to be prepared for emergency decontamination procedures.
This is accomplished by restricting diving activities to contexts that are reasonably safe given the diver's training and experience, using suitable equipment, and by following procedures developed, tested and otherwise determined to be as effective in those circumstances.
When an unforeseen emergency occurs, a diver or diving team must make the best of the situation using the skills, knowledge, intelligence and facilities they have available.
[4] Where a hazard cannot be avoided, and the risk is significant, procedures and the relevant skills are developed to manage the problems as they occur, usually at the earliest practicable stage.
However the service provider is usually required to have some level of emergency plan in place for events which are outside the scope of a buddy diver.
[39] A significant proportion of divers experience relatively long term psychological consequences, such as post traumatic stress disorder after a diving accident.