I’ve seen shootouts in Guthrie Oklahoma and Branson Missouri.
When one of the “lawmen” passed me I glanced down and saw his pistol was an old black powder front loader with the nipple areas ground down so nothing could be fired in it.
When the “shootout” happened, different guns were used and I noticed, during a reload, the blanks casings were black, not brass. I was not able to get close enough to see what they really were.
Blanks should be marked. There is no way you can mistake a real cartridge for a blank.
To chase off stray dogs, I use plastic cases with primers and wax “bullets”. No powder. They WILL STING.
Last time I watched this particular show, the reenactors told the audience that even though blanks were being used, they were still dangerous. Then proved it, by firing a blank at a sheet of cardboard 10’ away. The plug/wad left a hole in the ‘target’ as it passed through.
But another poster up-thread made the money comment - the shooter arrived late and managed to bypass the safety check.
Tombstone’s mayor Dusty Escapule released a statement within a couple of hours of the incident stopping all gunfights in Tombstone until more stringent safety procedures are drawn up and put in place.