Never mind the spin, what do we know for sure about the controversial process of fracking?

What is fracking?

The process of hydraulic fracturing – or "fracking" – involves drilling a hole deep into the dense shale rocks that contain natural gas, then pumping in at very high pressure vast quantities of water mixed with sand and chemicals. This opens up tiny fissures in the rock, through which the trapped gas can then escape. It bubbles out and is captured in well that brings it to the surface, where it can be piped off.

Why is it controversial?

Many shale deposits are buried under aquifers, and if the cement casing around the wellhole is not adequate, then the process of drilling and fracking can release the chemicals into the aquifer. Leaks of methane can occur, leading potentially to fires or explosions.

The water-chemical mixture pumped in gradually returns to the surface, where it can contaminate land and water. It can also be highly saline and contain solids, such as flakes of rock. Some companies have been accused of poor disposal of the sludge waste that results from fracking. In addition, the vast quantities of water used can lead to problems by depleting local ecosystems. There is also concern about the seismic activity involved in fracking.

These issues have prompted an outcry around the world, and some places are considering a ban – such as Pittsburgh, in the US, while New York called a halt to it pending a review. A bill to ban fracking in France has widespread popular support.

In the US, legal loopholes mean the fracking industry is poorly regulated, as large parts of it were taken out of the control of the Environmental Protection Agency (EPA) by President Bush, and companies do not have to disclose what chemicals they use.

So what chemicals are used?

Reports in the US have found hundreds of chemicals in use, some of them potentially toxic, including methanol, naphthalene, benzene and lead. In the UK, shale gas company Cuadrilla Resources uses only three, including a lubricant commonly found in cosmetics, hydrochloric acid, and a biocide commonly used to purify drinking water.

Should we be worried?

Owing to the legal situation in the US, where fracking has been pioneered, and the secrecy of the fracking industry, it has been hard to gauge how dangerous fracking is and whether the processes can be controlled in such a way as to make them safe. But the US the EPA is currently undertaking a massive study of the industry, so there may be answers from the preliminary report by the end of next year, though the full report will not be available until 2014.