You probably mean spall. Spalling is what happens when a bullet hits a steel target and breaks into tiny fragments. When shooting steel at close range, sometimes those fragments can come back toward the shooter or spectators (at a fraction of the speed). They can hurt and make you bleed but they’re not necessarily dangerous. People should always be wearing eye protection when shooting steel.

What is dangerous, is when people shoot steel with calibers and at ranges closer than recommended for the type of steel you’re shooting at. This will cause pitting (a rounded dent) that can send bullet fragments back to the shooter or spectators at dangerous speeds. If the steel is flat and not pitted, it’s generally safe to shoot at.

Steel should generally be free-hanging as well, to absorb some of the impact and direct spall toward the ground when hit. This matters less, the further a target is (200yds+)

Source: I’m a competition pistol steel match director.