A smaller air burst occurred over a populated area on 15 February 2013, at Chelyabinsk in the Ural district of Russia. The exploding meteoroid was determined to have been an asteroid that measured about 17–20 metres (56–66 ft) across. It had an estimated initial mass of 11,000 tonnes and exploded with an energy release of approximately 500 kilotons. The air burst inflicted over 1,200 injuries, mainly from broken glass falling from windows shattered by its shock wave.