Two crews from Ballybay and Castleblayney fire service, along with a special unit from Monaghan attended an ammonia gas leak at Americold, Lough Egish industrial business park earlier today.
A number of people were treated on site by the national ambulance service and four people were transported to hospital but have since been discharged.
The source of the leak was determined and the gas was safely vented from the main and adjourning buildings of the Monaghan business park.
A full system safety check was completed and the fire service is no longer on site.