Ventilation calculations for residential stairwells

(1) Looking for someone like a mechanical building/HVAC engineer/surveyor to calculate the stairwell pressure in a 4 storey stairwell. The fan is at top of the stairwell and creates a positive pressure when the fire alarm is activated. (There are actually 2 stairwell fans which need calculating.)
(2) Confirm this fan pressure is ok for UK building control regs in the case of a fire.

I can provide all stairwell measurements to help you, or you can visit the site in Luton, UK.