Differential pressure limit for non sterile area

Please any body know the differential pressure limit for non sterile area?

With reference of the limit…

for Same Class the DP not less than 1.0 mm of water column and different class DP not less than 1.5 mm of water column

As per schedule-M, Drugs & Cosmetics act, India.
3.8. Differential pressure between areas of different environmental standards
shall be at least 15 Pascal (0.06 inches or 1.5mm water gauge).