The Quick-Fill System is simply a system that allows for rapid transfer of air from a high-pressure source into a cylinder containing less pressure. This air transfer is based upon one of the oldest and most fundamental laws of physics: Boyles Gas Law. This law demonstrates that when two gas sources of different pressures are connected, they seek to equalize at the same pressure. For example, when an air cylinder pressurized to 2000 psig is connected to an air cylinder of the same size pressurized to 1000 psig, the two cylinders will quickly equalize at 1500 psig each. The patented Quick-Fill System lets MSA Air Mask users refill and transfill air cylinders while the SCBA is worn, without removing the air cylinder - even in IDLH atmospheres.