Blanks typically contain wadding to hold the powder in place; this wadding is ejected from the gun and can, at short range, kill people. This has famously happened on several film sets before: https://en.wikipedia.org/wiki/Blank_(cartridge)#Safety
yes, but that is not the case here. Even if the gun was right next to the target when it went off, a blank would not penetrate the body, go through it, and enter another person like it did here. 2 people were stuck with this single "blank." Only something with the mass of a bullet can do that (unless there was a serious manufacturing defect, which is highly unlikely). I believe that is also where the term "point blank range" came from. A blank is generally not lethal unless it is fired at extremely close range, such as holding it to your head, like in the examples in that wikipedia article if you research the individual incidents.
Depending on the mode of shooting blanks, there is still a significant amount of pressure generated due to the gunpowder in the round. Therefore, anything in the barrel, including a weak blank-firing adaptor (which Hollywood appears not to use) could be ejected at a high velocity. This could eject through the blank firing adaptor also, breaking it off and turning it likewise into a projectile.
Military rifles fitted with blank adaptors are known unsafe at close distances.
Any cleaning component left inside a firearm such as a cleaning rod, or metal bore brush, or debris from a previous round, could be ejected as a projectile from a blank fire. Additionally, gunpowder is really an explosive, so parts of the weapon can break and be ejected. I think this is more likely to happen with an older weapon, or a weapon firing high power rounds [1]
Suspect that Hollywood doesn't use blank firing adaptors like the US military which leads to a much more dangerous situation. Believe they do this for realism.
In the US military we'd take a number of steps to avoid these kind of mishaps.
safe weapon clearing procedures & intentional firing of weapon into sandbagged areas for hazardous conditions
Lots of Training about weapon safety
Team Leaders inspect fire teams
Squad Leaders inspect Squads
Platoon sergeants & LTs inspect platoons
Range Safety controls the whole show and may conduct their own inspections
Inspections include both weapons, magazines, and ammo pouches.
Our exercises never mix blanks with MILES gear, and actual live-fire exercises.
We don't fire weapons towards people at close range unless during warfare.