521 CMR, § 25.4 - MATS AND GRATES
Door mats 1/2 inch (1/2" = 13mm) thick or less shall be securely anchored at all edges to avoid tripping. Door mats between 1/4 inch (1/4" = 6mm) and 1/2 inch (1/2" = 13mm) thick must be secured with beveled edging that slopes no more than 1:2 (50%). Door mats thicker than 1/2 inch ( 1/2" = 13mm) shall be recessed. Grates shall have openings not exceeding 1/2 inch ( 1/2" = 13mm) in the path of travel. See Fig. 25c.
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