I was employed as a fire engineer in the fire service and stayed there for three years untill I left last year. It became obvious that I was there to do the job of a fire safety officer at a much lower rate of pay than a watch manager that I was doing the same job as, and I was working longer hours. There was also nothing in the way of promotion as all of the slots open in any kind of management role was under grey book conditions (operational employment). I enjoyed the job, but there was no future in it as I could seen myself doing the same job forever. When a similar job in another office was advertised with the same qualifications as I had, they couldn't find anyone, so the job went the admin manager. This was my cue to leave. On the positive side, the training for fire safety was pretty good, the flexi time was great and the pension is better than what most companies can provide.
If you're after a fire engineering job, you'd be better off finding a graduate program with an engineering company - there is simply not enough people around for the work that is out there. We're always looking for new starters, particularly in London, so feel free to PM me if you want more info.