The explosion followed a build-up of gas in an underground space beneath the Clarkston Toll shopping centre, caused by a gas main leak later ruled to have been accidental. Customers and shop staff had on 20 October complained of a strong smell of gas in the centre and Scottish Gas engineers had attended to investigate, but had identified no source for the smell.^[1][2] The engineers were still in attendance at around 2:50pm on the 21st when the gas ignited and exploded, killing at least 21 people and injuring around 100.^[3] The victims included many female shop staff and housewives on shopping trips, and the passengers of a bus that had been passing the scene.^[2] The explosion destroyed several shops and a terraced car park.

• http://en.wikipedia.org/wiki/Clarkston explosion