A strange time to set one off if set to kill. That's what makes me think it's a gas explosion, unless the hypothetical terrorists were too worried about being rumbled before using it as in the Bristol case.
Hope it isn't severe, and isn't terrorists. I worked in Leeds for four years, including filling in work in Burley library around the time the London bombers would have frequented it. I'd hate for any race violence to kick off over there over this.
Don't you just hate that cold-gut-stomach thrill of a breaking news? (Unless it's 'Breaking News!: Obscure Commons Motion defeated' - that mischevious BBC.)