Gases30th June 1998.

Since most drains carry some small amounts of sewage in them or storm water there is always the chance of a build-up of methane or carbon dioxide gas. Any gas pockets in drains can kill you! Naked flames and cigarettes in drains is not a good idea, especially in those known to be subject to gas.

So far to my knowledge there have been few gas related injuries in drains. Most drains are well ventilated through gutter boxes, grilles and manholes. Some drains such as Camos and parts of Maze however have persistent natural gas leaks. Drains can also be subject to bad air, mainly low qualities of oxygen but I have never heard of this actually occurring. I have however been almost overcome by bad air/gas in Cougar's drain as a result of an illegal chemical dump.

Carbon dioxide

This gas has no smell and is invisible so the first you'll know of it is when you start getting a headache or dizzy. If this happens get out immediately! Don't wait around or forge ahead. Fortunately humans can and regularly do breath in considerable amounts of carbon dioxide. When levels reach in excess of 5000 ppm danger occurs.

Carbon Monoxide

Produced mainly by cars is also odorless, you CAN'T smell it! You may think you can smell it because it smells of car exhaust but not so! According to an up to date 1998 booklet from Work-Cover 'Confined Spaces, shafts, tunnels & trenches' just 30 parts per million of carbon monoxide can effect your health. As carbon dioxide is odorless symptoms of inhaling it include, headaches, heart palpations, loss of balance, confusion and death. (death would be pretty bad symptom!)

Methane

Is very flammable, and surprisingly it is also odorless. So don't take candles into drains, use a battery powered flashlight. And never, never take gas powered lanterns etc into drains. We have heard of an incident in the US where some kids took a camp stove into a drain to cook some coffee to keep warm. The stove didn't ignite any methane but it set off some natural gas which had leaked into the drain. It's best to explore only well ventilated storm water drains although most railway tunnels are safe.

Hydrogen Sulphide

Is a dangerous gas sometimes caused by sludge. It destroys your sense of smell so you may think it has gone away. Initially it smells of rotten eggs. You may notice that your eyes begin to water and your nose gets blocked up, this is a symptom of Hydrogen Sulphide! We noticed this in Glass Creek and Camos even on a windy day! Even at this low level Hydrogen Sulphide can cause permanent respiratory tract injuries after prolonged exposure. This is a heavier than air gas and collects in depressions in tunnels.

Headaches, feeling dizzy, tingling fingers and toes, increased respiratory effort... all these point to oxygen deprivation. Note well and live by it... if you think anything awry with the atmosphere, then leave. The sooner the better, back the way you came. If one of your party needs help, provide it. Something to look for along the drain route is small feeders from gutter boxes and grills, these often take air from the outside by the Venturi effect and can be a useful source of clean air for a brief time.