42 CFR 84.1132 - Breathing tubes; minimum requirements.
(a) Flexible breathing tubes used in conjunction with respirators shall be designed and constructed to prevent:
(1) Restriction of free head movement;
(2) Disturbance of the fit of facepieces, mouthpieces, hoods, or helmets;
(3) Interference with the wearer's activities; and
(4) Shutoff of airflow due to kinking, or from chin or arm pressure.