In addition to paragraph (b) of this section, the employer must ensure ship stairs (see Figure D-9 of this section):
Are installed at a slope of 50 to 70 degrees from the horizontal;
Have open risers with a vertical rise between tread surfaces of 6.5 to 12 inches (17 to 30 cm);
Have minimum tread depth of 4 inches (10 cm); and
Have a minimum tread width of 18 inches (46 cm).