42 CFR 84.72 - Breathing tubes; minimum requirements.
Flexible breathing tubes used in conjunction with breathing apparatus shall be designed and constructed to prevent:
(a) Restriction of free head movement;
(b) Disturbance of the fit of facepieces and mouthpieces;
(c) Interference with the wearer's activities; and
(d) Shutoff of airflow due to kinking, or from chin or arm pressure.