Firefighters were called to Maudland House, a sheltered accommodation complex for pensioners, in Maudland Bank at 4.57pm on July 31.
Fire crews from Preston and Penwortham were mobilised after an automatic fire alarm was activated after smoke was detected in one of the rooms.
More than 30 pensioners were evacuated from the building after the alarm sounded.
On arrival, the fire officer in charge identified a smell of smoke issuing from a resident's flat on the ground floor.
After knocking and and receiving no answer, access was gained to the flat through a nominated key holder.
The resident was not at home, but it was soon discovered that the electric hob had been left on, with a number of combustible items on top.
Penwortham crew manager Peter Blamire said: "Upon inspection of the kitchen area it was identified that the occupier had left a pair of scissors on the hob which was turned on.
"The plastic handle on the scissors had melted severely which in turn had activated the alarm system due to the smoke.
"The room was quickly ventilated utilising a ventilation unit which fire appliances carry.
"In this particular incident the damage was light, however this could have been much worse."
The incident has led Lancashire Fire and Rescue Service (LFRS) to issue a warning, urging people to keep hobs and other ignition sources free from clutter.
The fire chief added: "As a rescue service we actively promote fire safety, in particular houses of multiple occupation and sheltered accommodation with our partner agencies.
"Safety advice can be sought by contacting your local fire station or logging onto LFRS website.
"We also offer a safe and well service where we can assess the risk to individuals and families, again further advice can be caught from the local fire station or our website or other social media sites.
"We advise the community of Lancashire very regular during our proactive work, so please ensure that combustible items are not left on or near ignition sources."