Have an allweather access road to your barn for the local fire engine. In some rural areas, you need to be a member of the local fire company. Develop an evacuation plan. Stall your most valuable horses so they can be removed first from the barn. Have adequate holding pens or an area where horses can be properly confined when removed from the barn.
Loose horses are dangerous and often charge back into a burning barn.
Consider having your local fire department inspect your barn and make recommendations.