A carbon-dioxide sampling tube operatively couples a capnograph and an exhaust-gas sampling tube of a mask. The mask has an ambient-to-inside-the mask inflow flapper valve located on a wall of the mask, a fresh-gas inflow tube, an exhaust-gas outflow tube, and a gas sampling tube. A fresh gas inflow tube operatively couples a fresh gas source and the face mask. An exhaust-gas hose operatively couples a scavenging system and the exhaust gas outflow tube.