I realize this is an old thread, but it was referenced in another, similar post so I wanted to share a few thoughts.
1) Barn fires are incredibly COMMON. A 100+ yo barn in a controlled burn used for training a fire department was completely involved in less than 4:30. That was empty; add in hay (proven to be more flammable & burn faster than a puddle of gasoline) + shavings, and your horses are SOL.
You might also explain how horses think and let them try leading one in a controlled area (round pen, indoor arena) so they understand that horses are not big dogs (after they sign the appropriate liability releases) and are likely to find the scents and sounds of a suited up firefighter more than a little unnerving. You will be grateful you took the time later.
(I assist in training first responders on emergency horse handling techniques, and have taken TLAER training with the author of the Horse911: What's Your Emergency blog on TheHorse.com, Dr. Rebecca Gimenez, who also happens to be a firefighter -- and sits on the National Fire Protection Association committee that just rewrote NFPA 150: Standard on Fire and Life Safety in Animal Housing Facilities.)
2) Horses under the care, custody and control of a BM are the BM's responsibility. BM can be arrested and charged with failure of owner's duties or cruelty, regardless of monies owed or circumstances.
I have a case that was successfully prosecuted in 2011 (from a 2010 arrest - yay for speedy justice!) where the defendant made a practice of finding small, private, self-care board places, then would stop paying board = locked off property (horses not locked in stalls, the front gates locked); defendant would load up horses when no one was around and move onto the next self-board place with a sob story about big ole meany BMs. Nailed in the 4th place, but if any of the subsequent property owners had called animal control on the previous BMs based on defendant's pathological lies, until the investigation raised the truth, they could have been considered responsible for the horses' condition.