Poisonous Air — It’s Very Serious When It Happens

Twelve pupils were treated for carbon monoxide poisoning after becoming ill during a school scuba diving lesson on June 26 at Manchester Grammar School in the UK. They were taken to the hospital, and eleven were later discharged following treatment, while one, aged 14, was released after several days. Greater Manchester Police were investigating the incident.

The air was supplied by Aqualogistics Dive Center, which has since recalled all tanks recently filled. Geoff Shearn, the proprietor, was not able to comment as to the probable cause of the contamination of the air supplied while the matter is under investigation by the government's Health & Safety Executive, or even if the contamination was actually by carbon monoxide. The company is well established and has been supplying divers with gas for more than 16 years.

Carbon monoxide (CO) is a colorless, flavorless gas that is a bi-product of burning fossil fuels such as gasoline. It binds more readily with the hemoglobin in the blood than oxygen. Consequently, those suffering from carbon-monoxide poisoning can appear to look very pink and healthy, but in fact, their tissues are being starved of oxygen. Hypoxia (severe oxygen deficiency) due to acute carbon-monoxide poisoning may result in reversible neurological effects, or it may result in long-term (and possibly delayed) irreversible neurological (brain damage) or cardiological (heart damage) effects.

As such, CO is a very dangerous contaminant of a scuba tank, since the small amounts are more apparent when breathed at the increased pressure of depth. The first symptoms are a serious headache and possible vomiting.

We divers have to trust that the gas we are supplied is safe to breathe. While the risk of contaminated air might be especially true when diving in far-off countries where standards may be lower than we are used to, as events in the UK have proved, contamination can happen anywhere. The investigation into that particular cause continues.

There was a case in the Maldives in May 2008 where a compressor, driven by a gasoline engine, suffered a punctured air-intake hose so that the prime mover's exhaust gases were drawn back into the air supply. One diver from MV Baani Adventurer was killed,and nine others, including two dive guides, severely injured. A survivor surfaced to discover most of his group semi-conscious or unconscious. https://goo.gl/M9LejF

Undercurrent reported the death of a scuba diver at Cabo San Lucas, Mexico, in 2012. https://goo.gl/p5pvLX

The treatment for (CO) poisoning is immediate inhalation of 100 percent oxygen for a period to load any surviving hemoglobin in the blood with oxy-hemoglobin. Severe cases require hyperbaric oxygen treatment in a recompression chamber.

The only way to detect contamination of the gas in a scuba tank is by chemical analysis. Compressor installations should be tested during set periods of use, using, for example, Dräger test kits. The allowable limit for CO contaminant in scuba gas supplies is less than one part per million when diving to a maximum of 165 feet (50m). The Analox CO Clear monitor is designed to be installed inline with a compressor feed to warn the operator of a problem. Portable gas analyzers such as the Analox ACG+, which include CO testing, are available, but relatively expensive for individual divers to buy.

If you are unsure of the integrity of a compressed gas supply, it's always worth checking the filling installation and the position of a compressor's air intake, being sure it is far from any engine exhaust and that the supply pipe is not punctured in any way.