In the "article" the recommendation was to go to paper or cloth cartridges. I guess they'd never heard of the much safer foil cartridges, which is kind of amazing.
Blank firing is the most dangerous kind. Why? Internal pressures, thus to some extent, temperatures are lower and much more debris will remain unburned in the gun compared to firing a round with a normal-weight metal projectile.
Since blanks are often fired with crowds present, the showmanship mentality takes over and safety can suffer. Rapid fire with a muzzle-loader should never be permitted, and wait time between shots should be strictly enforced by a separate observer with no gun crew duties.