Three crews from Worthing were called to a house fire in Orchard Avenue, Lancing, at 3.11am.
Ten 999 calls were made and when firefighters arrived the first floor bedroom was well alight with flames pouring out of the first floor window.
There were two occupants, one sleeping on the first floor who managed to escape from the first floor window and the other who got out of the front of the house.
Four fire crews used four breathing apparatus, two hose reels and a jet to contain and extinguish the fire, which took around two hours.
The cause of the fire is thought to have been a faulty electric blanket, which had been left on.
The property had no working smoke alarms in it so the occupants were completely unaware of the incident until the fire was well developed.
Firefighters described them as very lucky and urged people to check their smoke alarms.