There is no completely safe way to house or contain horses. If you leave them outdoors, there are 101 ways they can hurt or destroy themselves. They can run crazily and fall or smash into things, they can kick each other, they can get loose, they can get caught in the fence, they can rip off shoes, step in holes, get struck by lightning, the list goes on and on.
Barn fires can kill horses that are housed inside, but that`s just one hazard of many. They can get cast, they can stock up, they can get all kinds of respiratory diseases, they are somewhat more prone to colic, I think, than horses that can move around.
Here are just a few of the pros and cons that might help determine one course of action over the other, keeping in mind that there isn`t a clear cut “right” answer, or a definite “wrong.”
Pros of living indoors: Less chance of running and hurting themselves. Less chance of being hit by lightning. Less chance of getting loose, and possibly running out into traffic. Less chance of having to brave the elements, rain, wind, freezing cold, snow, wind, scorching sun. Less chance of tearing off shoes, or getting scratches. Easier to check on, easier to spot colic or other problems, especially at night, because they are right there, not off in the corner of some pasture.
Pros of living outdoors: With all the recent fire tragedies, one big pro is that the outdoor horses don`t get trapped in a burning barn. They have cleaner air to breathe. They live more “naturally”, in that they can move around when they feel like it. If they have a run in shed, they have the choice of staying out in the wind, snow, heat or rain, or coming under shelter. (Most do what humans wouldn`t, I find.) “Outies” can burn off energy when the spirit moves them, and they are less likely to get cast when they roll or lie down.
Many horse owners don`t have the choice to make. Outdoor horses require lots more space than stalled horses, so my guess is that most urban and suburban horses live indoors by necessity. Either way has its plusses and its minuses, and it always seems, thanks to Murphy`s Law, that whichever system we choose will turn out to be the one we might wish to have traded for the other!