Safety, safety, and more safety. If one is standing close to the muzzle of a cannon when it goes off, they can fell the concussion, and it can really effect them. This is why we have safety rules. This is why we use the best of materials when building a Cannon or Mortar. Don't ever cut corner's, build it right!
I have heard stories where people are luckly to be alive. Some I have forgotten, some I remember. I'll start a post on this subject some time soon.