R 408.13324 Rigid helmet filter plates.

Rule 3324. (1) A filter plate on a rigid helmet shall fit into the frame and cover the window. (2) Both surfaces of a filter plate shall be well polished and shall be free from striae, waves, or other defects that would impair the optical quality of the surfaces. Filter plate surfaces shall be flat and substantially parallel. (3) Table 2 of R 408.13312 shall be used to select the proper shade number of filter lenses or plates during welding operations. (4) When specified, a filter plate shall be impact-resistant, unless impact-resistant eye protection is worn in conjunction with a welding helmet. (5) A filter plate shall be marked with the shade designation and a permanent and legible marking by which the manufacturer may be readily identified. In addition, a glass filter plate, when treated for impact-resistance, shall be marked with the letter "H." (6) A cover plate made of plain glass, of glass coated on 1 or on both sides with plastic, or of a slow-burning solid plastic sheet shall be used to protect a filter plate from damage. A cover plate shall be the same peripheral size and shape as the filter plate, and the thickness of a cover plate shall not be less than 0.050 inches. A cover plate shall transmit not less than 75% of the luminous radiation and shall be substantially free from optical imperfections.