The father, his wife - both thought to be in their 40s - and their young son, aged around 12, were treated at the scene by South Central Ambulance Service for gas inhalation and taken to hospital as a precaution. No-one was seriously injured.
Firefighters used breathing apparatus to enter the plant room. They used dry earth to soak up a small amount of spilled chemical and ventilated the room. Crews from St Mary's, Redbridge and Hightown dealt with the incident.
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A report by the CQC health watchdog has criticised the Southern Health NHS Trust for still not doing enough to protect those in its care.
Amanda Houston presents the late evening forecast for the east of the Meridian region.
Amanda Houston presents the late evening forecast for the west of the Meridian region.