Crews from Ringwood, Beaulieu and Redbridge were supported by specialist hazmat vehicles from Winchester and colleagues from across the border in Dorset and Wiltshire.
Engines were called shortly before 1pm after a chlorine spillage and a strong smell were reported from an external plant room at the site on Christchurch Road.
The centre was evacuated as three casualties were treated by South Central Ambulance Service paramedics as a precaution and discharged.
The leak was contained by firefighters who then used monitoring equipment to check gas levels within the main building, with no dangerous gas detected.
Crews have now handed the incident back over to the site manager, who will keep the building closed for a couple of hours to allow it to be fully ventilated.
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