Which key component connects the SCBA to the user's facepiece?

The regulator is the key component that connects the SCBA to the user's facepiece because it is responsible for controlling the flow of breathable air from the cylinder to the user. It reduces the high pressure of the air in the cylinder to a breathable pressure and ensures that the air reaches the facepiece in a consistent and safe manner.

The regulator also incorporates features that allow the user to easily inhale and exhale while using the SCBA, making it essential for effective breathing in hazardous environments. The proper connection and functioning of the regulator are crucial for the overall effectiveness of the self-contained breathing apparatus during firefighting or other emergency situations.

In contrast, while the mask strap provides support for the facepiece and the cylinder valve controls the flow of air from the cylinder, they do not directly connect the SCBA to the facepiece in the same critical way that the regulator does. The backpack serves as a harness for carrying the cylinder and other equipment but does not play a role in the air supply connection to the facepiece.