Diving Accidents

Diving accidents may be divided into 3 groups:

• Accidents that occur whilst entering the water.
• Accidents associated with snorkel or SCUBA diving.
• Accidents associated with deep sea diving.

The first group will be mentioned just briefly. Accidents may occur due to hyperextension of the spine, especially the neck. If it is necessary to enter the water from a great height, as when abandoning a sinking ship whilst being unable to be lowered in a lifeboat, it is much safer to enter the water feet first than head first. When people commit suicide by jumping from a very high bridge, it is often the force of the impact with the water that is fatal. However, a great many accidents related to entering the water occur when diving into shallow water. Nocturnal swimming and, particularly, the consumption of alcohol are major risk factors. The problem of alcohol and injudicious entry to water are discussed in accidents and their prevention. Acute spinal cord compression is also discussed elsewhere.

Anyone who wishes to engage in diving needs to be adequately physically fit and appropriately trained. Deep sea diving is almost invariably conducted by professionals. They may be in the Royal Navy or working for the gas and oil industry. There are strict regulations regarding fitness, training and behaviour but it is a high risk occupation and accidents are not uncommon.¹

SCUBA stands for self-contained underwater breathing apparatus. It first became available for civilian use in the late 1940s. It enables the diver to take a supply of air with him so as to prolong time under water and to reach greater depths. It is generally regarded as suitable for depths of up to 40 metres. That represents 4 atmospheres of pressure and is not to be taken lightly. The British Sub Aqua Club (BSAC) website shows that the organisation is very keen on safety issues.² Diving is a wonderful sport but it must be treated with respect.

The BSAC also covers snorkel diving and their website has a section for this.³ Basically, a snorkel is a J-shaped tube from the mouth that enables the swimmer to breathe whilst face down in water. In normal breathing there is a dead space that ventilates the airways and does not reach the gas exchanging tissues of the alveoli. This represents about 1ml for every 1cm of the person's height. A snorkel effectively increases this dead space by its own volume. If the swimmer goes deeper so that the snorkel tip is below the surface he can prevent water from entering by blowing against it and when he reaches the surface he can blow out the water. An extra piece that may be present is like a table tennis ball in a cage and if the swimmer dives, the ball floats up and blocks the snorkel so that water will not enter.

For depths down to 60 to 70 metres, a proper diving suit is required. There are heavy boots to help take the diver down feet first. Rather than a SCUBA apparatus, air is pumped through a line and the diver does not swim freely but is raised and lowered from above.

For greater depths, special high pressure suits are necessary and for very great depths a bathysphere is required.

Whether diving is a hobby or an occupation, it carries significant risks. This applies to both shallow or deep water diving. These may be simple matters such as becoming entangled in something. A skin diver will carry a knife to help in any necessary disentanglement. However, what is essential in any diving at any level is a buddy. This means not being alone. The pair look after each other and they must be able to communicate by sign language as verbal communication is impossible. Some well known signs are thumbs up to show intended ascent, thumbs down for intended descent and index finger and thumb tips in apposition to indicate that all is well.

Fitness to dive will be considered later. Training is essential before embarking on a proper dive. Some will be classroom learning and some will be basic training in a swimming pool.

Diving as a sport has become much more popular in the past 30 years and it is estimated that 100,000 people partake in the sport in the UK.⁴ Exploitation of underwater sources of gas and oil have also increased the need for professional divers.

• A study from the Orkneys was unusual in that it was possible to make a reasonably accurate estimate of the number of dives that took place. The target was usually marine wrecks. The estimate was of 1 accident per 178 dives in 1999 and 1 in 102 in 2000. They stated that some of these accidents appear to have been predictable and could be avoided by better education and preparation of visiting divers.⁵
• This lack of preparation and avoidable accidents is echoed elsewhere. The BSAC safety report of 2005 noted² "As has been stated many times before, most of the incidents reported within this document could have been avoided had those involved followed a few basic principles of safe diving practice. Remember you can never have too much practice and the further you stay away from the limits of your own personal capabilities the more likely you are to continue to enjoy your diving."
• The Health and Safety Executive reported,⁶ "Diving is considered to be a high hazard activity. In the 8 year period from 1996/97 to 2003/04 there were 24 fatal accidents. Many of these were members of the public undergoing recreational diving training with paid instructors. However, the risks can be significantly reduced by adhering to regulations and adopting established good practice." Presumably this figure of 24 fatalities in 7 years refers to diving in the waters around the British Isles and excludes British divers abroad.
• About 90 deaths a year are reported worldwide.⁷
• There is a British Diving Safety Group⁸ that includes many organisations including the Health and Safety Executive, the Royal Navy and the Institute of Naval Medicine.
• Diving requires the individual to be in peak physical and mental condition and even small amounts of alcohol must be avoided. In addition, there may be problems of narcosis from gases at high pressure as will be discussed below, and this is enhanced by any alcohol.

Under normal conditions, there are many facets to the drive to breathe but the main one is pCO₂. If pCO₂ rises and pO₂ falls, the two may be synergistic but generally pO₂ in unimportant in the respiratory drive except in some people with COPD who should not be diving. Breathing gases at pressures of several atmospheres may totally distort the picture of partial pressures. Even with snorkel diving, gas pressures can be a problem. One way to delay the irresistible urge to breathe, and hence to prolong time under water for snorkeling, is to hyperventilate before diving. This can drop the pCO₂ markedly but it does little to the pO₂. Hence pO₂ may fall to dangerous levels before pCO₂ rises and unconsciousness from hypoxia can be very swift. The practice is to be discouraged.⁹

Breathing gases at high pressure can cause many problems and gases that are thought of as inert become toxic and produce narcosis.¹⁰ Obvious mental deterioration occurs at depths below 50m, and divers behave in a manner that is clearly inappropriate.¹¹ This is caused by nitrogen dissolving in parts of nerve membranes, thickening them. Effects develop within minutes and can be reversed in the same time by ascent. Replacing nitrogen with helium allows divers to go deeper. An oxygen-helium mixture instead of air, allow a diver to reach 700m depth without narcosis.

At great depths, neurological disturbance occurs in divers breathing oxygen-helium mixtures. This is caused by partial thinning of the neurone membranes from compression of nerve tissues so that nerve impulses travel more quickly causing convulsions. Addition of nitrogen to the mix thickens the tissues and prevents this.

There are a number of people who get a toxic response to a high pO₂. This appears to be an idiosyncratic response that affects only a minority of people but it is possible to screen for it as it may have serious consequences in anyone undertaking deep sea diving.¹² Nausea is the commonest feature, followed by muscle twitching. Predisposing factors are the use of closed circuit SCUBA and body cooling.¹³

This is not likely to be a problem when SCUBA diving in shallow water in a warm environment such as the Mediterranean or the Caribbean, but even here, the temperature of the water falls rapidly on descent and deep water is at 4°C. Hypothermia is a significant problem when working on North Sea rigs and it limits the time underwater. As well as being very uncomfortable, hypothermia impairs intellect and judgement and so is potentially very dangerous under such conditions. The provision of hot water suits to North Sea saturation divers appears to be adequate to prevent a dangerous fall in core temperature.¹⁴

If serious hypothermia does occur, re-warming should be slow, especially if the core temperature falls below 32°C.¹⁵

Ascent is much more dangerous than descent as there is considerable risk with decompression if it is too fast. "The bends" are by no means the only danger. If the diver is having trouble there is a natural urge to get him out of the water as soon as possible and to have access to him but a slower ascent, or even a temporary descent to a greater depth, may be what is required.

• Expansion of gas in sinuses may be very painful and eventually burst them. Rarely, the ethmoid sinus ruptures with risk of cerebral infection.
• Gas trapped in the middle ear can cause problems in that attempts to clear the ears can cause a situation where one ear clears before the other causing disorientation due to uneven stimulation (alternobaric vertigo).
• With the external auditory canals unequally blocked before diving, cold water entering one canal leads to caloric vertigo.
• As a diver ascends, compressed air in the lung expands and divers are taught to exhale continuously and ascend at a rate no faster than the bubbles they are exhaling. With these measures, lungs have time to empty adequately and there is a low risk of rupture. Lung rupture usually occurs in divers holding their breath on ascent or ascending too fast. Mediastinal emphysema is caused by a central tear. Peripheral tears lead to pneumothorax.
• Air emboli may occur and they expand as the ascent continues.
• The diver may either lose consciousness immediately or present with signs such as dyspnoea, cough or haemoptysis.
• There may also be voice change with discomfort in the throat or behind sternum. Surgical emphysema of the neck and upper chest may be apparent and signs of pneumothorax.
• With air embolism there will also be neurological signs.
• Treatment with oxygen can be given but avoid positive-pressure ventilation.
• Tension pneumothorax requires immediate needle thoracocentesis with emergency chest drain and the presence of neurological signs requires recompression immediately.

Decompression Sickness

Decompression sickness or "the bends", so called because of the severe pain that may occur, is well known and justifiably feared by divers. Those that dive deep are at highest risk but it can even occur in breath-holding divers.¹³

• This occurs because nitrogen or helium dissolves in the tissues and then comes out of solution on ascent, forming bubbles within the circulation and tissues.
• They continue to increase in size and number as ascent continues.
• They block blood vessels and distort or rupture cells.
• With sufficiently slow ascent the gas diffuses into the blood stream and is removed from the lungs without formation of significant number of bubbles.

It is imperative to control ascent and decompression schedules can be obtained from diving clubs. They take into account both the depth reached and the time at any given depth. Even when these schedules are followed, around 1% of dives result in decompression sickness with a rather higher figure when they are not followed. Symptoms are:

• In military and commercial diving there is often limb pain, usually in the shoulders or elbows.
• It may appear a few minutes after the dive or up to 24 hours later.
• Is often dull, poorly localised, gradual onset and not exacerbated by movement of the joint. Untreated pain will reduce and disappear over 2 or 3 days with rapid improvement on recompression.
• Sports divers tend to show neurological symptoms although limb pain may occur.
• Usually sensory disturbance is seen with numbness and paraesthesia but no clear dermatomal or peripheral nerve distribution.
• In severe form, it starts with girdle pain with loss of sensation and movement in lower limbs.
• Cerebral involvement is often found but it may be subtle. It frequently involves denial with higher functions affected, such as short-term memory, mood and vision.
• There may be loss of consciousness.
• Any patient who shows signs of decompression illness within 24 hours of diving should be treated as if they have the illness. This involves first aid with oxygen at 100% and rehydration.
• The risk is increased by flying soon after diving.¹⁶

Obtain expert opinion from either the British Hyperbaric Association on 0831 151523 or the Institute of Naval Medicine on 02392 768026.

The foramen ovale is the link between the atria in the fetal circulation. It usually closes soon after birth. This is not invariable and failure to close is usually asymptomatic as the higher pressure in the left heart tends to push it shut. It can sometimes be a problem if right sided pressure rises, as may happen with pulmonary embolism and then paradoxical embolism occurs into the systemic circulation. The other time of risk is with the considerable pressure and physiological changes of diving when a right to left shunt may occur. Hence, gas emboli that should be discharged to the lungs reach the systemic circulation. A patent foramen ovale is said to occur in 30% of the population, being large in 6%. Its presence increases the risk of decompression sickness around 2.5 times.¹⁷ The implications for screening all potential divers is uncertain.¹⁸ It may be responsible for as many as two thirds of "unexpected" cases of decompression sickness.¹⁹

Prospective divers have to undergo a medical examination. The following are regarded as exclusion criteria:

• Epilepsy
• Asthma
• History of Obstructive Lung Disease or signs of condition
• Ear Surgery
• Poorly controlled diabetes
• Addiction to alcohol or drugs
• Ruptured eardrums
• Mental instability
• Obesity

Routine chest x-ray is not required but spirometry should be undertaken. Forced expiratory volume in 1 second (FEV₁), forced vital capacity (FVC), and peak expiratory flow rate (PEF) should be measured. FEV₁ and PEF should normally be greater than 80% of predicted and the FEV1/FVC ratio greater than 70%. There is much more detail on the British Thoracic Society website on the list of further reading below.