An investigation is under way after 48 farm workers suffered breathing difficulties at a Kent commercial site.
They were treated for suspected exposure to carbon monoxide at Rumwood Green Farm, in Sutton Road, Langley. Four people were taken to hospital.
Residents nearby spent the night in temporary accommodation as a precaution after Tuesday afternoon's incident.
Officials from the Health and Safety Executive have been at the scene carrying out initial inquiries.
Three ambulances, seven fire engines, hazardous material officers and a specialist chemical unit were sent to the scene near Maidstone just before 15:00 GMT.
A spokesman for Kent Fire and Rescue said: "Initial indications suggested those experiencing breathing difficulties may have been exposed to carbon monoxide, and symptoms displayed were conducive with exposure to this gas.
"Paramedics treated patients accordingly in line with this and the condition of those affected improved as a result of treatment."
It is understood the incident was contained to the site.
Rumwood Green Farm was closed on Wednesday, with police officers parked at the entrance and lorries being turned away.