Ten people were taken to hospital after inhaling chemicals released from a fish tank in an Oxfordshire village.
The "potentially toxic" fumes were emitted from coral being cleared from an aquarium at a house Hanney Road, Steventon, on Monday evening.
About 50 emergency services personnel attended, including a hazardous area response team and three ambulances.
Scientist Dr Mike Leahy said the people were probably exposed to "palytoxins" released by the coral.
Six members of a family and four firefighters were taken to the John Radcliffe Hospital in Oxford, and three family members were kept in overnight after suffering "flu-like symptoms" and eye irritation.
TV presenter Dr Leahy said he was caught inside the police cordon while visiting his mother, who lives on the same road.
He said after hearing about what happened he realised the coral was likely to have released "palytoxins" that can be "incredibly lethal".
"In the main they're absolutely harmless but sometimes if you stress certain types of coral, they can produce a toxin," he said.
He added that "if ingested it can be lethal" but that inhaling fumes was far less dangerous.
Two dogs were also removed from the house and the remaining coral was dealt with by firefighters in "full body cover, gas-tight suits".
Went for a cuppa with Mum. When I left confronted by this. Trapped within police cordon. Palytoxin incident due to a neighbour cleaning his coral tank. Second deadliest naturally occurring toxin in the world (allegedly) but rarely kills, & only if eaten! Over-reaction? pic.twitter.com/iTlpLvyXSn— Dr Mike Leahy (@OfficialDrMike) March 26, 2018
Police officers remained at the scene overnight and windows were left open to ventilate the house.
Owen Hughes said on Twitter local residents were "told to stay indoors" by police but they were "not in any danger".