Design of PE Piping Syste 158 (1-1) (1-2) WHERE PR = Pressure rating, psi HDS = static Design Stress, psi (Table 1-1) A F = Environmental Application Factor (Table 1-2) NOTE: The environmental application factors given in Table 1-2 are not to be nfused with the Design Factor, DF, used in previous editions of the PPI Handbook and in