Farmers have again been warned of the dangers of slurry tanks in the wake of an accident that claimed the lives of a young rugby star, his brother and their father.
Ulster Rugby player Nevin Spence, 22, brother Graham, 30, and 58-year-old father Noel were killed after being overcome by poisonous fumes and falling into an underground slurry tank at the family farm in Co Down on Saturday.
Relatives have said the men died trying to save each other.
The region's Health and Safety Executive, which is investigating the incident, reiterated its advice that farmers should not enter tanks and only mix slurry in ventilated areas.
"Our advice is not to go into slurry pits," said Jim King of the HSENI.
Mr King said he was aware of reports that the incident was triggered after a dog entered the tank but said the exact sequence of events could only be confirmed after consulting eyewitnesses, including grieving family members.
Nevin and Graham's sister Emma, who also inhaled fumes, has been released from hospital following treatment.
Along with her mother Essie and sister Laura, the artist was being comforted by friends and relations at the family home on the Drumlough Road.
Ulster Rugby's next scheduled game on Friday night was yesterday postponed as a mark of respect while a minute's silence will be held at all other RaboDirect PRO12 fixtures over the weekend.
The funerals of the three men are expected to take place later this week. Graham Spence was married with two young children.
Books of condolences were opened at the home of Ulster Rugby at Ravenhill in east Belfast as supporters gravitated to the ground to pay their respects.
Stormont Deputy First Minister Martin McGuinness, Irish Tanaiste Eamon Gilmore and Northern Ireland Secretary of State Theresa Villers were among those who visited the ground to pass on their sympathies.
Former first minister the Rev Ian Paisley also paid a visit to Ravenhill.
Mr King said the incident unfolded in an underground slurry tank on the Spences' diary farm, which has around 250 cows.
"We know that unfortunately both Noel, Graham and Nevin were overcome by the fumes of slurry gas and then fell into some slurry at the bottom of the tank," he told BBC Radio Ulster.
Slurry, a mixture of cow manure and water, is used as a fertiliser. When it is mixed ahead of spreading on fields, poisonous gases including hydrogen sulphide are released.
It is understood the three men had been mixing slurry from outside the tank throughout the day. They entered the tank at around 6pm.
"They were working with the slurry all day, they had been mixing and drawing slurry all day, we understand," said Mr King.
"That brings a particular problem as the slurry levels go down ... the space above the slurry becomes almost covered with an invisible mist of slurry gas which is mostly hydrogen sulphide.
"It's particularly poisonous and it also has the effect that in high concentrations it knocks out your sense of smell and sense of taste."
Mr King said the gas could paralyse the respiratory system.
"Someone can be overcome, unconscious and dead within a very few minutes," he said.
The official said only experienced contractors should enter slurry tanks.
"For the average farmer - don't go in, stay out and keep as much ventilation as you possibly can," he added.
Deputy First Minister Mr McGuinness said it was incumbent on the authorities to look at ways to improve farm safety, particularly around the issue of slurry tanks.
"All of this has had a very profound impact on all of us and I think that we have to remember whenever the publicity is over, whenever the story goes off the headlines, Mrs Spence Snr and Mrs Spence Jnr - Graham's wife - their children and their families will have to deal with this terrible loss," he said.
"The only good thing out of this is that Emma thankfully was spared and is now out of hospital and back home with her family.
"But it is an absolutely grievous blow, there aren't really any words to describe how we all feel except to say that we all feel absolutely shattered that a family could have such a loss inflicted on them as a result of a terrible accident."
Mr Gilmore, who is from a farming background, said the whole island had been rocked by what had happened.
"It's a deep tragedy, it's a great loss and I think that everybody on this island of Ireland will express their sympathy with the Spence family," he said.
Former Free Presbyterian moderator Ian Paisley said he knew the Spence family and invoked biblical references to express confidence that their Christian faith would sustain them.
"It touched me, it really shook me," he said of the tragedy.
"But then having known the family and known their profession of faith in Christ, that was blowing a hard wind that blew away the dark clouds and brought hope and life and assurance.
"It's a warning to us all, we're not here forever, we're travelling home."
He added: "It's a warning to us all, we don't know what a day will bring forth."
On Sunday night the Spence family, in a statement, said: "The families of Noel, Graham and Nevin Spence are trying very hard to come to terms with their tragic loss.
"The three men were very close to each other in life, and that love was expressed in their final moments trying to help one another."
Nevin was a member of the Ulster Rugby squad which reached the European Heineken Cup Final last season, and he was predicted to have a major international future ahead of him in the game.
The former Wallace High School player was last year named Young Player of the Year at the Irish Rugby Union Players' Association Awards.
The Ulster Farmers' Union (UFU) said the deaths had shocked the entire farming community.
Ulster's RaboDirect PRO12 fixture against Zebre, due to be played in Parma on Friday night, has been postponed following Nevin's death.
A statement on the Ulster Rugby website read: "Further to the death of Ulster player Nevin Spence last weekend, the match between Zebre and Ulster due to be played on 21st September 2012 in Parma will be postponed to a later date.
"An announcement will be made in due course with the rescheduled match information. A moment of silence will be observed at all RaboDirect PRO12 matches this coming weekend."