Some fire stations may close under changes being considered by Devon and Somerset Fire and Rescue Service.
The brigade is due to reveal options for change later on Wednesday.
Bosses said it was to bring an outdated service into the 21st Century.
Unions said closing any fire stations would be a mistake and they were concerned about a potential "lack of fire cover and increased response times".
Talking about a service delivery public consultation on its website, the brigade said it was originally designed over 50 years ago and that "since then, the make-up of our communities and the way in which people live their lives has changed significantly".
It added: "The majority of our existing 85 fire stations have been in place for well over 30 years and the firefighter duty systems have not changed since the 1970s."