Without a pic it is just a guess, but my guess it is just a normal bristleworm. I have always read about the "dreaded fireworm" but in all my years of working on tanks in my area I have never seen or even heard from anyone else locally or online about anyone actually finding a real fireworm. So just going off 17 years of experience I have to say the chances of actually getting a true fireworm are very slim, although not impossible.
This is what a true fireworm looks like. Very distinctive and after seeing thousands of normal bristleworms in my time it would be very easy to tell the difference if I saw one that looked like this.
Bearded Fireworm
vs.
Normal Bristleworm