In old Coal mines there were a lot of problems, including what they called “black damp” and “fire damp”.  Black damp was carbon dioxide, often mixed with Nitrogen.  This is a colourless, odourless and gas which can lower the percentage of Oxygen to dangerously low levels which have been responsible for many deaths.  Miners used to have a Canary to detect the black damp.  Canaries are much more sensitive black damp than Humans.  When the Canary died, the miners got out.

Fire Damp is Methane.  This is colourless, odourless, inflammable and explosive.  In the old days the naked flame in the helmet of the miners would sometimes set off a methane explosion.

Sir Humphrey Davy invented a “Safety Lamp”.  This lamp had a fine wire mesh screen which acted as a spark arrester.  It would not set off the Methane or other inflammable gasses.  In their presence, the flame changed visibly, giving some warning.  If the Oxygen level dropped below 17 percent, the flame went out; Humans can still survive at this Oxygen level.  This gave warning of black damp.

In the old days, the answer to both black damp and fire damp was to ventilate the mine.  Now people are extracting the Methane from the coal seams and using it.

Problems

Often the water pressure in the coal seam needs to be lowered to get the Methane out.  This water is often saline and contaminated with various things making is quite unsuitable for drinking or irrigating.  Removal of this water can cause very serious environmental problems, including the contamination of rivers and useful underground water, as well as subsidence of the surface. 

Subsidence can make buildings collapse. 

Coal Bed Methane projects need to be very carefully evaluated before they are started.

Sources

Song “Coal Bed Methane Blues”.

http://www.sqwalk.com/media/ToddButler_CoalbedMethaneBlues.mp3

Concerns in New South Wales about coal bed gas extraction.

http://www.ccag.org.au/images/stories/pdfs/doc-41-wyonghydrogeologicalreport_execsumm.pdf

AGL

http://www.agl.com.au/about/EnergySources/indevelopment/Pages/Camden-Gas-Project.aspx