There is a book written by Stewart O'Nan entitled "The Circus Fire - A true Story of an American Tragedy" that I found in an well known book store in San Francisco which specializes in obscure books that tells what appears to be the most correct story of the Hartford fire that exist today. It was published by Anchor Books, a division of Random House Publishing in June of 2001. ISBN 0-385-49684-2
Mr. O'Nan writes on the dedication page: "This book is for everyone who went to the circus that day -- those who came home and those who stayed."
There is a huge list of acknowledgements at the end of the book and if you can find a copy, it might be a good place to try researching for additional sources. You do not include your relatives name so it is difficult for anyone to attempt to assist you. Do you know what his position was with the show? Anything likje that makes searching for such historical information easier. You may also want to contact the Circus World Museum in Baraboo, Wisconsin, for access to their extensive collection of historical data. Likewise, the Ringling Museum ofthe Circus in Sarasota, Florida might be of assistance as well.
Hopes this helps a bit in your search.
Warren