I thought the same - wonder whether the first couple were inside (copper in our stand may have been guessing). The riot police were about to go down the stairwell but after the first couple of bangs they moved away from it, and a couple of staff came up the stairs into the stand covering their faces…….the later ones were def outside, heard them when we were going down the stairs to the buses.I was in the lower tier concourse when it went off and the air was thick with it. I can still taste it this morning. I can’t believe that just blew in from outside, they must have fired it in the concourse somewhere.