Sulphur hexafluoride (SF₆) is an extremely effective electrical insulant and has very significant advantages over alternative materials. It is non-flammable, a critical requirement in the high-voltage applications for which we use it, and because of its effectiveness, takes up less volume than an equivalent insulating volume of an oil alternative. Equipment filled with SF₆ can leak and requires replacement.

SF₆ is a greenhouse gas and one tonne is equivalent to approximately 23,900 tonnes of carbon dioxide.

Reported gas loss, as an absolute amount and (percentage of inventory) was14.7 tonnes (2.6%) in 2008/09 compared with 18.8 tonnes (3.5%) in 2007/08.

There has been no increase in our inventory due to the acquisition of KeySpan, so direct comparison with previous years is possible.