The tech manual for the SPH-4 is located on this site. It's 16 pages.
http://www.gentexcorp.com/default.aspx?pageid=2687If anyone is interested.......
This is a link to the the U.S. Coast Guard's Aviation Life Support Systems Manual (COMDTINST M13520.1C). Anything UCCG aviation uses is discussed in this manual......rafts, vests, pyro, O2, masks, clothing, knives, MRE's, pumps, etc. I don't know if this will help much but the SPH-5CG is on page 7-15. I have (and used) this helmet. There is a lot of great info in this manual and it gets updated often.
www.uscg.mil/directives/cim/13000-13999 ... 520_1C.pdf