Maximum injection pressure. The owner or operator shall limit injection pressure to the lesser of:

(a) A value which will not exceed the operating requirements of § 144.28(f)(3) (i) or (ii) as applicable or

(b) A value for well head pressure calculated by using the following formula:

Pm = (0.600−0.433 Sg)d where: Pm = injection pressure at the well head in pounds per square inch Sg = specific gravity of inject fluid (unitless) d = injection depth in feet.