Fire crews were called out when a portable heater set on fire at commercial premises on Monday afternoon.
The blaze happened at premises in Carr Road, Nelson, at around 1-45pm on Monday.
Two fire engines from Burnley and one from Nelson attended the scene and firefighters wearing breathing apparatus used a hosereel to extinguish the flames.
They also needed a ventilation unit to clear the premises of smoke.
No-one was injured in the incident.