Decompression management
Persons conducting a business or undertaking should ensure that all dives are planned conservatively and consistently to one set of recognised dive tables to minimise the risks of decompression illness.
Recognised dive tables include:
- DCIEM tables
- Buhlemann tables
- tables approved by a recreational dive training organisation when conducting diving similar to recreational dives
- dive computers used in accordance with the manufacturer's instructions.
Decompression management for occupational diving (high risk diving work), must be undertaken in accordance with the requirements in AS/NZS 2299.1: 2015 Occupational diving operations – Standard operational practice.
Contributing factors
Factors that may predispose a diver to developing decompression illness should be minimised as far as is reasonably practicable. These factors include:
- depth - generally the deeper the dive the greater the risk, although decompression illness has occurred in divers diving to depths of less than 10 metres
- prolonged dive times
- decompression stop diving
- multiple dives over multiple days
- poor physical condition (obesity, age)
- the diver having a patent formane ovale (PFO)
- heavy physical exertion before, during or after a dive
- alcohol or some drugs (taken before or after a dive)
- previous incidences of decompression illness
- multiple ascent diving
- cold conditions
- prolonged hot showers after a dive. previous incidences of decompression illnesses
- carrying out free or buoyant ascent training
- carbon dioxide excess
- increase in altitudes shortly after diving, for example, flying or travelling over mountains.
Decompression illness
Decompression Illness (DCI) includes two conditions, decompression sickness (DCS) and Arterial Gas Embolism (AGE) which results from the expansion of inert gas bubbles (typically nitrogen) due to decreasing environmental pressure (decompression). It’s often difficult to distinguish which condition has caused the injury and the first aid management and treatment are usually the same, so the term Decompression Illness is used to cover both conditions.
What is arterial gas embolism?
Arterial Gas Embolism (AGE) occurs when gas in the lungs is trapped and cannot be released quickly enough due to the speed of ascent. This causes the lungs to rupture (pulmonary barotrauma) and release gas. The escaped gas can get pushed into the blood vessels surrounding the lungs and is carried to the heart where it can directly enter the arterial blood. Bubbles can become trapped and cause significant injuries. While rapid ascents and holding your breath are typically the main causes of AGE, there are instances where medical factors such as asthma, infections, obstructive lung disease or scar tissue from previous surgery has caused AGE.
Sign and symptoms of AGE usually occur within minutes of surfacing and include:
- dizziness
- disorientation
- visual blurring
- chest pain
- bloody froth from the mouth or nose
- paralysis or weakness in the extremities
- convulsions
- cessation of breathing
- loss of consciousness
What is decompression sickness (DCS)?
When a diver breathes gas under pressure, the body absorbs inert gases in proportion to the surrounding pressure. If the diver ascends too quickly without allowing enough time for the inert gas to be released, small bubbles can form in our tissues and venous blood. Different tissues in the body will absorb and release gas at different speeds depending on how well blood moves in and out of these tissues (perfusion). Divers who fail to follow their decompression profile, omit stops and ascend too quickly are at a greater risk of DCS, however it has occurred with divers who were diving conservatively and within decompression limits.
Signs and symptoms of DCS can occur immediately upon surfacing or up to 48 hours later (usually between one to six hours) and include:
- extreme fatigue
- numbness or tingling
- joint pain
- mottled rash
- itchy skin
- muscle weakness
- vertigo
- loss of balance
- confusion
- hearing loss
- headaches
- nausea
- breathing difficulties
- personality change
- loss of bladder/bowel control
- visual disturbances
- impaired responsiveness
The most commonly reported symptoms of decompression sickness are tingling (sometimes called pins and needles), extreme fatigue and joint pain. These symptoms, when mild, are often overlooked and first aid treatment is often delayed as a result. Symptoms can be progressive and what starts as tingling in the feet can progress to weakness or even paralysis in the legs. Any sign or symptom that occurs within 24-48 hours after a dive should be considered to be diving related until demonstrated to be otherwise.
Flying after diving
The longer the period between diving and travelling to altitude, including flying, the less likely it is that decompression illness will occur.
Generally, a 12 hour wait is advisable before any pressurised flights and a 24 hour wait if a diver has done multiple dives over several days or decompression stop diving. Specific advice is usually available from the recognised dive tables selected for the dive.
Travel to altitude, including flying after diving, for high risk diving work must be undertaken in accordance with the requirements in AS/NZS 2299.1: 2015 Occupational diving operations – Standard operational practice.
Maximum diving depths
Selecting the maximum depths for diving activities is important to minimise risks of decompression illness, gas toxicity and rescue of a diver in an emergency. Many dive qualifications, training programs and some medical certificates carry their own depth restrictions.
For recreational diving the dive operator should implement maximum depths for the diving conducted, becoming progressively shallower throughout the day. The operator should ensure that certified divers do not dive deeper than what they have been trained to.
For occupational diving (high risk diving work), the advice regarding maximum depth in AS/NZS 2299.1: 2015 Occupational diving operations – Standard operational practice must be followed.
For occupational diving (general diving work), the recognised dive tables used will specify maximum depths. Divers who are competent under the requirements for incidental diving work and limited scientific diving work must only dive to a maximum depth of 30 metres without decompression stops.
Decompression stop diving
Dive profiles that require mandatory decompression stops create additional risks to divers of decompression illness, hypothermia and 'out of air' situations. In some situations, it is difficult for divers to undertake in-water decompression safely without surface support. Decompression stop diving is considered to be technical diving and has additional requirements. Decompression stop diving should only be undertaken by divers undergoing specific training or who have been trained in decompression stop diving techniques.
For occupational diving (high risk diving work), the advice regarding decompression stop diving, including the provision or recompression chambers, in AS/NZS 2299.1: 2015 Occupational diving operations – Standard operational practice must be followed.
For occupational diving (general diving work), the recognised dive tables used will specify decompression stop requirements. Divers who are competent under the requirements for incidental diving work and limited scientific diving work must not undertake decompression stop diving.