Two men are in a critical condition in hospital after they were both overcome by toxic slurry fumes on their farm.
The father and son were mixing hen slurry at the Hazlett family farm in County Londonderry over the weekend.
Police say the men are aged in their 40s and 70s.
A spokesman for the Western Trust 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, told BBC Radio Foyle: "They were mixing slurry in the shed and would have known to stay out when they were mixing."
"But there was a couple of sheep that ran into the shed, a couple of lambs, so he ran in to get them out."
Mr Buchannan said the elder man went into the shed to help and" he went down as well".
"The fact there was someone to raise the alarm was crucial," he said.
"Farming can be so often a lonely job and there are so many cases where the farmer is farming by himself."
Sinn Fein councillor Sean McGlinchey said the farming community in the area was ’shocked but relieved that we are not coping with two fatalities’.
"The farming community is totally shocked and stunned by the whole thing," he told the Belfast Telegraph.
"There is a lot of information and details these last few years about these type of incidents, so it is a shock that it has happened again.
"We are very lucky that we are not looking at two deaths today.
"We are just so thankful that the emergency services were here so quickly, especially with the helicopter to take them to Altnagelvin.
"That was a lifesaver."
The Health and Safety Executive has been informed.