Bert P. Krages Attorney at Law Photographer's Rights Page
I carry one of these card with me so that I can show an officer that I know specifically what my rights are. Generally if you're standing in a place where the public is allowed to be then you are allowed to take pictures of whatever is in plain view. You are not allowed to take pictures where people have a reasonable expectation of privacy; e.g., someone entering their pin number into an ATM machine.
In your case, taken pictures at a fire, as long as you are standing in a place where the police (or fire department) have allowed the public to be then you should be allowed to take pictures.
With all this said, the main reason that I carry one of these cards is that there are still a lot of officials, police, private security, building management, etc and even some judges that still have a misunderstanding of what peoples rights are in regards to taking photographs.