A number of years ago, mid-2000s, I had just gone through immigration at LGW. there is a large room just after the passport check (I guess where people regather before getting on the escalators to claim their luggage...there is also a currency exchange in there). anyway, the fire alarm went off and a number of gates came down. We were trapped with no place to go. Couldn't go back toward passport control and couldn't go upstairs to the luggage carousels. I think we were in there for about 20-30 minutes.