Section 84.61 - General construction requirements(a) Respirators will not be accepted by the Institute for examination, inspection and testing unless they are designed on sound engineering and scientific principles, constructed of suitable materials and evidence good workmanship.(b) Respirator components which come into contact with the wearer's skin shall be made of nonirritating materials.(c) Components replaced during or after use shall be constructed of materials which will not be damaged by normal handling.(d) Mouthpieces, hoods, helmets, and facepieces, except those employed in single-use respirators, shall be constructed of materials which will withstand repeated disinfection as recommended by the applicant in his instructions for use of the device.