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
It's looking warm! Holly has the details.
Abby King has seen life-changing results after undergoing weight loss surgery in 2016. Her surgeon says many more people could benefit.
Progress has been made in talks under the chairmanship of the conciliation service Acas.