Outer limits scifi show episode help?

I recall seeing this episode only one time and it was when I was really young. The few things I can remember from it that there are some people who seem to be living in an isolated room but there able to communicate with one another through a video or something. There appears to be some sort of alarm that goes off and if I recall they had a certain amount of time to get to it and shut it off or something would happen. One by one people start to die I believe one person ( a female I think) dies when a fire breaks out in the room she is in. Finally one guy remains and he lets the alarm expire but there is a safety feature that gives him another sixty seconds or something and this army guy comes on and tells him not to give up and to keep pushing the on as the scene cuts to the office of the army guy he falls over pulling the blinds down with him. you see Washington D.C. in flames and the Washington monument being attacked or something.