Scuba Diving Safety: Ascent, overexpansion, decompression & treatment

After a dive it is important to remain focused and appreciate the importance of ascending correctly. Many incidents occur as a result of ascending incorrectly as divers can sometimes become complacent about shortly returning to the surface. Dangers of ascending include obstructions overhead, decompression sickness and overexpansion injuries.

Steps for an ascent

1. Signal to your buddy that you intend to ascent with the thumbs up signal. When your partner responds with a thumbs up signal this is your go ahead.
2. Establish neutral buoyancy then very slow fin towards the surface. As you fin, in one hand you will hold up the hose of your BCD while releasing a slow and consistent stream of air from the BCD. This will make you less buoyant so that your ascension is slower, safer and controlled. Your other arm should be raised above and over your head for protection. Also look up to avoid any obstructions and so you can see when you are near the surface.
3. Your rate of ascent should be roughly 18m per minute. If possible, a 3 minute safety stop at 6m from the surface is ideal
4. Ascending slowly is particularly important in the last 3 metres before surfacing. A length of a minute is recommended. During this time revolve so that you are aware of your surroundings, both to your side and upwards. Also listen carefully for sounds such as boats.

Overexpansion injuries

This occurs when a person holds their breath in ascent. As the diver gets closer to the surface, the water pressure on the body decreases and the air in the lungs expand. Because this expanding air is being held inside the lungs, alveoli will burst and oxygen is released into other parts of the body.

There are many side effects that can result from overexpansion, some of them quite scary including the possibility of death itself. Symptoms of overexpansion include numbness, loss of hearing, vision, speech, chest pain, breathing difficulty and unconsciousness. There are 4 main ways this release of oxygen effects the body.

• Arterial gas embolism occurs when air bubbles moves into the bloodstream. An air bubble in the bloodstream can end up in the small brain capillaries, blocking the flow of blood, resulting in a stroke. It is not uncommon for people to suffer paralysis, brain damage and death from such a stroke.
• Mediastinal Emphysema occurs when oxygen makes its way into the space around the heart. This can put pressure on the heart resulting in failure
• Pneumothorax occurs when oxygen makes its way into the pleural cavity, the body cavity that contains the lungs. This will cause chest pain and may lead to collapsed lungs.
• Subcutaneous Emphysema occurs when oxygen makes its way under the skin making it itchy and spongy in texture. It happens most commonly around the neck and shoulder area.

Decompression sickness

Decompression sickness is most likely to occur when a diver does at least one of the following

• Spends too much time at a particular depth
• Ascends too fast
• Decompression stops are skipped on ascent

The deeper you are the more pressure your body is under. When gases are under more pressure they are more soluble in liquids and as a result nitrogen is absorbed into bodily tissues at greater depths. During Ascent, pressure is reduced which allows the nitrogen to be dissolved in the tissue. The nitrogen will try and make its way back out with less pressure and if a diver has been deep for too long too much nitrogen is produced in the tissues to be safely discharged. Ascending too fast will have the same affect, whereby nitrogen is released as bubbles which can build up under the skin, tissues, joints and against the spinal column.

Symptoms from decompression sickness are very similar to those of overexpansion, though it is less dangerous and likely to end in death.

Treatments

Overexpansion and Decompression sickness are treated the same.

• The Victim should breathe in as high a concentration of oxygen as possible, preferably 100%.
• They must be comfortable and if capable, drinking some water or other non-alcoholic fluid.
• Ideally, decompression sickness is treated by recompression in a hyperbaric chamber. This involves a chamber that increases the pressure, making the nitrogen more soluble again, before the pressure is reduced in a controlled manner so that nitrogen is safely released.

Drowning

The main reason that would lead to drowning while diving is if the oxygen supply were exhausted. There are some major aspects of diving that help you to avoid drowning (other then a tank of oxygen)

• Equipment, such as the standard Submersible Pressure Gauge (SPG), tell you how much oxygen you have remaining. It is important to observe periodically your levels of oxygen.
• Unless it is a solo dive, a diver should always have a buddy. When one person runs out of oxygen, one tank can be shared between two divers.
• If solo diving, you will need to have undergone the required training and equipped with the correct gear which will generally include separated oxygen reserves.