Many of the blankets were too old or worn with some found to be more than 20-years-old.
A total of 256 of the 655 tested across West Sussex were found to be potentially unsafe.
Jackie Boyle, WSFRS Community Fire Safety Officer, said: “People assume if they have been using their blankets for many years without a problem that they are safe.
“However, many very old blankets have no over-heat protection and industry guidelines advise people to replace their electric blankets at least every 10 years.
“Some of the blankets we checked were over 20 years old!”
The free checks took place in ten venues across the county from October 21 to November 1.
The night before Horsham’s testing event, a Southwater bedroom fire was caused by an electric blanket.
For the County Times report of the incident and testing event, click here.
Lionel Barnard, West Sussex County Council cabinet member for Resident Services, added: “If you did not get an opportunity to come to one of the testing days, don’t take any chances and follow the safety advice of our Fire & Rescue Service.”
Advice on the safe use of electric blankets can be found by visiting this website or by calling the Community Safety Team on 01243 642878.