I was going to guess he meant High Pressure, thanks. Well...those engines are built on the previous rendition of the Ferrara Ultra Chassis. They were built to VERY closely mimic the other engines in service. Unlike the current HazMat 1, which is built (as correctly stated above) on the Inferno Chassis, the High Pressure engines were built to exact FDNY specifications, on a completely new and unique chassis, just like the current FDNY products emerging from Ferrara.
Will the FDNY replace those engines just to have a unified fleet? No...because they're not that far off the mark. However, the HM rig is almost at it's replacement age and is a completely unique rig. I'll bet the shops can't wait to see it replaced. Why was the Ferrara engine, donated by Louisiana, so happily returned after Katrina? Why is the ALF sitting on Governors Island? Why was the Spartan Aerialscope sent to City Island? Because they're not helpful in maintaining a smooth and unified fleet for parts and labor reasons.