The fire that put itself out saved a terraced house from serious damage.
And today firefighters welcomed the intervention of an impromptu sprinkler system for making their job easier.
Crews were called to the property in Bridge Road, Lancaster just before midnight after the occupants returned to find the upstairs of their house full of acrid smoke.
When they called 999 firefighters with breathing apparatus went in to discover the blaze had started in an electric shower unit - and then extinguished itself.
“Neighbours said they had heard a smoke alaram going off, but then it stopped and they assumed the people were in the house and had sorted it out,” said watch manager Warren Topp at Lancaster fire station.
“But they weren’t in and, when they returned, they found it was full of smoke.
“It turned out the shower unit had started the fire and then extingusied itself. The plastic unit had melted and released the water - in effect its own in-built sprinkler system.
“We sent two firefighters in with breathing apparatus because the smoke from plastic and PVC can be very nasty stuff. You get a few lungfuls of that and your legs can go from unnder you.
“The shower unit was severely damaged and there was smoke damage elsewhere in the property. But it could have been a lot worse had the shower not put itself out.
“We would advise people not to leave electric showers switched on when not in use. Always turn them off at the pull switch to isolate them from the electricity supply.
“When the people got back they did the right thing, which was to shut the bathroom off, get out and get us out.”