A gas fitter who admitted causing the deaths of two school friends by carbon monoxide poisoning has been given a four-year sentence, two of which he will spend behind bars.
Neil McFerran and Aaron Davidson, both 18, were overcome by noxious fumes at a holiday apartment in Castlerock, Co Derry, in 2010.
Part of the flue from a new gas boiler fitted by George Brown's company became dislodged and filled the flat with the odourless toxin.
At Belfast Crown Court, Brown, from Ballygawley Road in Aghadowey, Co Derry, was sentenced to four years for two counts of manslaughter and was fined £19,000 (€22,700) for a range of health and safety offences.
The 52-year-old had said in court that he did not personally install the boiler and flue.
But he accepted the supply and installation of the heating system was his responsibility.
Mr Justice Weir said Brown's "cavalier attitude" to the dangers presented by carbon monoxide was "reprehensible".
The judge told Brown the deaths of the two young men was a "wholly avoidable tragedy".
Mr McFerran and Mr Davidson, from Newtownabbey near Belfast, had been on a break in the seaside town after doing their A-level exams.
Their friend, Mathew Gaw, survived the incident.
He was rescued when family members broke into the property when they realised something was wrong. By that stage the other two young men were already dead.
Brown ran a gas shop in Coleraine and had been asked to investigate a problem at the apartment earlier in 2010.
He recommended replacing the boiler and flue and converting the burner from natural gas to liquefied petroleum gas.
Experts concluded that part of the flue, used to carry emissions from the boiler to the outside through a void in the apartment ceiling, had separated because sections were not secured properly at a right-angle bend.
At least two screws were missing and the metal sections did not overlap or slot into each other far enough, allowing them to come loose.
Brown initially denied any offending but later pleaded guilty to two charges of manslaughter and a further 19 counts involving failures to comply with health and safety legislation.