Existing Joist Size: DH series?? 2

I am doing some preliminary investigation on an existing roof structure of a foundry, era 1970. The existing plans indicate that the joists are 28DH9's spaced at 4'-9" and span 50 ft. The total roof load on each joist is in the 280#/ft range when adjusted for drift load from a proposed addition with a maximum reaction of 8.4 kips. I have researched the Steel Joist Institute's historical manual and have not found a match for a 28DH09. I have found LH, LJ, J and H-series that are 28xx9, but no DH-series. My guess is that it is an error on the plans and is probably either the H or LH. There is a significant difference in capacity with the 28LH09 at 463 #/ft and the 28H9 at only 267#/ft. Does a DH-series exist?