Issued: 12 April 2005
To alert employers, self employed persons, persons in control of workplaces, designers, importers, manufacturers, installers and suppliers of plant, and workers in the diving industry to the hazards caused by inappropriate construction, positioning and inspection of air intake hoses on surface supplied breathing air systems, primarily of the 'hookah' style, powered by combustion motors.
There have been a number of incidents where divers have been poisoned or killed by breathing in toxic doses of carbon monoxide due to the incorrect construction, positioning and inspection, or inadequate safeguards, in relation to setting up a 'hookah type' compressed air delivery system.
Figure 1: An example of a hookah style compressor showing an appropriately constructed air intake pipe.
What is carbon monoxide?
Carbon monoxide (CO) gas is an odourless, colourless and tasteless gas and is found in the exhaust of petrol and diesel motors, such as those used with diving compressors for filling diving air tanks or for supplying divers air at depth through surface-supplied air systems.
Carbon monoxide has an affinity for haemoglobin over 200 times greater than oxygen. This means that it displaces oxygen from the blood and leads to the formation of carboxyhaemoglobin. This lack of oxygen going to the brain, heart and other tissues can lead to death.
Diving at depth increases the toxic effect of carbon monoxide.
What are the symptoms of carbon monoxide poisoning?
The symptoms of carbon monoxide are listed in Table 1 below. Note that smokers have a carboxyhaemoglobin level (HbCO) of up to 10%. Levels higher than this, especially at depth, put divers at risk as they become rapidly confused and don't realise they are in trouble.
Table 1 - Percentage carboxyhaemoglobin produced in the blood as a result of breathing various amounts of carbon monoxide in air at 1 ATA
Carbon monoxide concentration
Breathless with exertion
Collapse on exertion
The next two cases illustrate what can happen to divers who inadvertently breathe in carbon monoxide. Following a dive at 10 metres for one hour, a 42-year-old diver noticed headache, fatigue, uncoordination and confusion immediately after surfacing. He recovered and went diving two days later with friends. After 10 minutes at 10 metres he surfaced and was noticed to be acting strangely. Shortly after returning to the bottom he swam rapidly to the surface and then slowly sank back down.
When his friends hauled him to the surface he was unconscious, not breathing and without a pulse. Cardio pulmonary resuscitation (CPR) was initiated and he regained consciousness and had frothy pink phlegm. He was confused and uncoordinated, requiring treatment in an intensive care unit.
In another case, a 25-year-old diver was working in a dock using an airline from a surface compressor. Having dived 10 meters for 30 minutes he had difficulty returning to the quayside and was seen by his co-workers to be confused and needing help to remove his equipment. He was coughing, disoriented and weak with a rapid pulse. There has been a recent death of a Queensland diver where CO was a significant contributing factor.
Other deaths of divers in other states show that the most common source of CO poisoning is via contamination from the exhaust gases of the motors powering their compressors.
- Always ensure that the air intake of the compressor is fitted with an extension pipe or hose so that the inlet is located away from any source of contamination such as engine or motor exhaust. The compressor's manufacturer should determine the length and cross sectional area of any hose or pipe. See Figure 1.
- The compressor intake and hose or pipe should be positioned to take advantage of available ventilation. Where possible compressors and hoses should be located off decks and out of wells or holds. As a guide, when operated from an open dory, the inlet should be at least 1.5m above the exhaust outlet.
- An inspection should be made of the intake hose prior to use and monitored during use to identify any defects in hoses or couplings and eliminating kinks. Particular attention should be given to the wear and loosening effects caused by engine vibration.
- Make sure that the intake hose is routed, positioned and secured to ensure that there is no possibility of contact with hot, moving or vibrating parts. Where any section of the pipe or hose can be melted, crushed or otherwise damaged whilst in use, the section should be constructed of a suitable metal pipe or tube. This is to avoid damage that may allow fumes and combustion gases to enter the diver's air intake.
- Ensure divers, standby persons and attendants are trained to recognize the symptoms of carbon monoxide poisoning and what actions to take should CO poisoning be suspected. Divers who surface for no apparent reason, bob up and down near the surface and bottom again, or show other erratic or unusual behaviour, may be confused.
- Standby persons or attendants should have current training in CPR. Oxygen resuscitation and therapy equipment, suitable for non-breathing and breathing persons should be immediately available at the dive site with person(s) currently trained in its use.
- Each diver should carry an emergency gas supply (commonly known as a bailout bottle) on their person, to be used in the event of a diver suspecting CO poisoning, or in case of other failures of the air supply. This gas supply will be of sufficient capacity to enable a diver to safely return to the surface. The bailout bottle is filled with air from a high pressure compressor.
- Each diver should also be equipped with a weight system that has a quick release mechanism. A quick release system is a readily operated mechanism that allows the immediate release of the weight system from the secured position by the single operation of one hand. It is designed to minimize the risk of accidental release such that sufficient weight can be released to make the diver positively buoyant. Should a diver become disorientated, or in the event of other diving incidents, the quick release mechanism can be readily released.
- Where the diver's air hose is also the diver's lifeline, the air hose must be attached to the diver in such a way that allows the weight system to be discarded independently of the air hose attachment. The minimum breaking strain of any potentially load bearing sections, including the attachment to the diver, surface attachment points, the air hose and any fittings, shall be at least 6kN.
Contact Workplace Health and Safety on 1300 362 128.
- Allen, H. Carbon monoxide poisoning in a diver. Archives of Emergency Medicine, 9: 65-66, 1992.
- Mark, P. Carbon monoxide poisoning: a review. SPUMS Journal, Vol 22(3): 127-135, 1992
- Edmonds C, Lowry C, Pennefather J. Diving and Subaquatic medicine. Third edition. Butterworth Heinemann, Oxford 1992.
- Furgang, F A. Carbon monoxide intoxication presenting as air embolism in a diver: A case report. Clinical Aviation and Aerospace Medicine, pp 785-786, July 1972.
- Gold, D; Geater, A; Aiyarak, S; Juengpraert, W. The Indigenous Sea Gypsy Divers of Thailand's West Coast: measurement of carbon monoxide in the breathing air. Applied Occupational and Environmental Hygiene, 14: 488-495, 1995.
- Standards Australia. AS/NZS 2299.1:1999: Occupational Diving Operations, Part 1 Standard Operational Practice. Sydney 1999.
- WHO/IPCS. Environmental Health Criteria 213: Carbon monoxide, 2nd edition. WHO, Geneva, 1999, p307.