The majority of spray foam using your house would have a fireproofing additive and would have trouble Catching Fire but in this example is if you have a type without the additive such as the great stuff. A vapor barrier is very important in a wall so just the rockwool batt insulation it's more commonly used for an attic floor not a wall. Fiberglass proved to be pretty safe in the test but if you're worried they make fiberglass with a aluminum radiant / vapor barrier. They do make fire retardant spray foam but it's usually for commercial application but I don't see why you couldn't pay that company to put it in your house but you're going to pay. They make fire retardant paint especially for spray foam which I personally can't see it working very well since the heat of the fire will cause the foam to melt behind it leading to the collapse of the paint exposing it to Fire and on the other hand it's most likely the firewood start behind the Paint as a slow smolder first in the wall