A. Where are you?
B. Smoke vent in UK is highly specialised and I would think it is in any Western Country (Or antwhere for that matter)
I worked for a company who made smoke vent eqpt and we had specialist designers.
Currently, BS5588 covers smoke vent
It can be natural or mechanical.
Flow rates are determined from an assessment of the fire hazard. It may be assessed that the fire size is 5MW (Mega Watts) and an associated amount of smoke is attributable to this fire size. The size and shape of room and the affects of balconies, atrium etc have a big effect.
Also effects of 'plugging'(where air is entrained through the opening rather thamn purely smoke) are taken into consideration.
Smoke temperature is also a factor and smoke curtains that are used to reduce excess smoke cooling if the smoke travels too far...(It cools and drops to prevent escape of occupants)
I would not try to do the design. There are many companies that offer a design or design and install package.
If you are in teh UK I can give you a couple of companies that will give you a good service.
Friar Tuck of Sherwood