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.
More top news
A GP in Surrey has launched a petition calling for a £90m fine handed to two drugs companies, to be reinvested in the NHS and epilepsy care.
Friday evening's weather update for the east
Friday evening's weather update for the west