42 CFR 84.172 - Breathing tubes; minimum requirements.
Flexible breathing tubes used in conjunction with respirators shall be designed and constructed to prevent:
(a) Restriction of free head movement;
(b) Disturbance of the fit of facepieces, mouthpieces, hoods, or helmets;
(c) Interference with the wearer's activities; and
(d) Shutoff of airflow due to kinking, or from chin or arm pressure.