Two farmers are said to be in a critical condition after being overcome by toxic slurry fumes over the weekend.
The two men, a father and his son, were mixing hen slurry on their family farm in Claudy, County Londonderry when they were overcome by fumes around 4pm on Saturday (16 June).
Emergency services, including an air ambulance, arrived on the farm and took the men, one aged in his 70s and the other in his 40s, to Altnagelvin Hospital.
A spokesman for the Western Trust, which represents hospitals located throughout the west of Northern Ireland said: "Both men are in a stable condition, one more critical than the other."
It is understood the younger man was trying to remove sheep from a shed where slurry was being mixed.
Farmer Ian Buchanan, a friend of the family, said the pair knew the risks involved with mixing slurry.
"They were mixing slurry in the shed and would have known to stay out when they were mixing," he told BBC Radio Foyle.
"But there was a couple of sheep that ran into the shed, a couple of lambs, so he ran in to get them out."
According to the Health and Safety Executive (HSE), incidents involving slurry occur regularly on farms in the UK.
These incidents include people, not just farmers, being overcome by toxic gases, drowning as a result of a fall into slurry or liquid stores, or being injured from the collapse of structures containing slurry.
Slurry is broken down by bacterial action which produces gases. Slurry gas includes methane, carbon monoxide, ammonia and hydrogen sulphide, all of which can create a risk to human and animal health.
Some gases are flammable, others are toxic and some will displace oxygen from the air, causing a risk of asphyxiation.