"Holmes," John Watson said, "Why are the lights flickering?"
Sherlock Holmes looked up at him from where he was bent over his chemistry set, his look half annoyed and half confused. "Because we have gas lamps, Watson," he drawled. "The lights always flicker slightly."
"Look around you," Watson replied.
Holmes did, realizing that one in particular was, in fact, flickering. "Watson…"
The bulb exploded in a magnificent display of glass and fire. Holmes watched, frozen, as everything seemed to happen slowly. The glass shards spread out in every direction, and there was a moment of awe before the sparks caught and a ball of fire flared and died, reaching the ceiling at its height.
Holmes was moving before he was quite aware of it. He quickly turned off the gas and moved to Watson who had retreated, collapsing behind the couch and covering his head. He was brushing himself off as Holmes crouched next to him.
"Alright, old man?"
Watson was slightly stunned and moderately singed, but smiled nevertheless. "I told you something was wrong," he murmured.
"Yes," Holmes replied, pulling out his handkerchief and dabbing a spot of blood away from Watson's ear. "I apologize, Watson. I was not looking for danger for we have no case on, but, after all this time, I suppose I should have known better."
A 221B, for the prompt from: trustingHim17: Why are the lights flickering?
(The snarky response, of course, would be just the first two lines)... I have read that gas lamps could explode, but it wasn't common.