When filling a self-contained breathing apparatus cylinder, the cylinder must be:

The correct answer emphasizes the importance of safety and containment when filling a self-contained breathing apparatus (SCBA) cylinder. Placing the cylinder in a fragmentation containment or other shielded device serves as a protective measure that mitigates the risks associated with potential cylinder failure or explosion during the filling process. In the event of a rupture, this containment reduces the risk of injury to personnel nearby by directing shrapnel safely away.

This practice is crucial in maintaining safety protocols, as SCBA cylinders are under high pressure, and any improper handling or failure during filling can lead to catastrophic results. The design of the fragmentation containment specifically addresses the need for shielding, ensuring that high-energy incidents do not pose a threat to firefighters or other personnel involved in the refilling operation.