Heavy melting steel (HMS) or heavy melting scrap is a designation for recyclable steel and wrought iron. It is broken up into two major categories: HMS 1 and HMS 2, where HMS 1 does not contain galvanized and blackened steel, whereas HMS 2 does. The Institute of Scrap Recycling Industries breaks up the categories further:
ISRI 200 (HMS 1): Wrought iron or steel scrap 1⁄4 inch (6.35 mm) and larger in thickness. All pieces must be smaller than 60 in × 24 in (1,524 mm × 610 mm)
ISRI 201 (HMS 1): Same as ISRI 200 except pieces must be smaller than 36 in × 18 in (914 mm × 457 mm).
ISRI 202 (HMS 1): Same as ISRI 200 except pieces must be smaller than 60 in × 18 in (1,524 mm × 457 mm).
ISRI 203 (HMS 2): Wrought iron or steel scrap, black and galvanized, 1⁄8 inch (3.175 mm) and larger in thickness.
ISRI 204 (HMS 2): Same as ISRI 203 except pieces must be smaller than 36 in × 18 in (914 mm × 457 mm).
ISRI 205 (HMS 2): Same as ISRI 204 except it may contain automotive scrap except for thin gauge material.
ISRI 206 (HMS 2): Same as ISRI 205 except pieces must be smaller than 60 in × 18 in (1,524 mm × 457 mm).