Residents in Wisbech were forced to keep their windows closed for almost two hours after ammonia leaked from a factory.
Specialist ambulances and firefighters wearing gas tight suits were called to the Moy Park factory in Mount Pleasant Road on Wednesday morning last week after the gas was detected.
Six workers from the site were taken to hospital as a precaution following possible exposure to ammonia.
An investigation by firefighters found that the leak had originated from a refrigeration unit at the factory.
Firefighters were called to the factory just before 8.40am after the leak was detected.
Soon after the service issued an appeal to residents in the Mount Pleasant Road area to keep their windows and doors closed to prevent possible exposure.
Firefighters wearing breathing apparatus and gas tight suits isolated the leak alongside onsite specialists.
But by 10am firefighters issued a notice to state that the area was safe and no longer a threat to public safety.
Two crews from Wisbech, one crew from St Neots and a rescue vehicle from Dogsthorpe attended along with fire officers.
The fire service remained on site to monitor the levels of ammonia.
But all crews left the scene at 10.50am.
East of England Ambulance Service sent two ambulances, a rapid response vehicle, and the hazardous area response team (HART) to the scene.
A spokesman for Moy Park said: “On Wednesday, a small ammonia leak was detected from a piece of refrigeration equipment at the Moy Park factory in Wisbech.
“The piece of equipment is located in a controlled environment within the site plant room.
“A well rehearsed incident plan was followed, the fire service was called to the factory and the leak was quickly contained.”
The Wisbech factory is one of Moy Park’s 13 production sites in England and Ireland.
It employs 10,600 people across those 13 factories, which include sites in Peterborough, Grantham, Huntingdon, Crewe and Ballymena.
The company produces free range chickens and turkeys.
It also produces a number of poultry products including the Jamie Oliver and Castle Lea ranges.