42 CFR 84.135 - Half-mask facepieces, full facepieces, hoods, and helmets; fit; minimum requirements.
(1) By providing more than one facepiece size; or
(2) By providing one facepiece size which will fit varying facial shapes and sizes.
(c) Hoods and helmets shall be designed and constructed to fit persons with various head sizes, provide for the optional use of corrective spectacles or lenses, and insure against any restriction of movement by the wearer.
(d) Facepieces, hoods, and helmets shall be designed to prevent eyepiece fogging.