HVAC system designing for a swimming pool, why consider negative pressurization?

There is ventillation requirement (Freshair) in swimming pool we caanot say that its negative pressure altough concept is same but actually this is ventillation air as per ASHRAE so the humidity and smeel can be controlled in closed swimming pool area.

 In general outdoor air is introduced into a building to dilute the off-gassing of humans and materials and thus provide an acceptable air quality in the building. In all public indoor swimming pools the use of a chemical to disinfect the water is required by code. These chemicals have a bad effect on the indoor air quality when they off-gas from the pool water and often cause eye irritations or even asthma. Consequently ASHRAE has increased the amount of outdoor air required for indoor swimming pools in comparison with standard office buildings.