The undersides of nosings shall not be abrupt. The radius of curvature at the leading edge of the tread shall be no greater than 1/2 inch (1/2" = 13mm). Risers shall be sloped or the underside of the nosing shall have an angle not less than 60 degree from the horizontal. Nosings shall project no more than 11/2 inches (11/2" = 38mm). SeeFig. 27b.
521 CMR, § 27.3