Defective boiler flue killed two teen friends Neil McFerran and Aaron Davidson
Teenagers Neil McFerran and Aaron Davidson tragically died from carbon monoxide poisoning in August 2010 after a gas leak in a holiday apartment in Castlerock, Co Londonderry.
The 18-year-olds had been staying at the apartment with a third friend, Matthew Gaw, who survived. The three friends were found by relatives.
In 2012, in response to the Castlerock deaths, carbon monoxide alarms became a legal requirement in all new homes in Northern Ireland.
The new law came in as research at the time suggested half of the UK population mistakenly believed their household smoke alarms would alert them to the gas.
In 2014, Aghadowey gas fitter George Brown was sentenced to two years in prison and two on licence and fined £19,000 following his guilty plea to manslaughter by gross negligence in connection with the deaths from carbon monoxide poisoning of the two young men.
An investigation found that the gas leak had been caused by a defective flue in a boiler.
After the sentencing, PSNI Detective Chief Inspector Rachel Shields said: "The families of Aaron and Neil have and continue to highlight the issue of carbon monoxide poisoning.
"It is an issue that all households should be aware of and I would remind service providers who work with installing heating systems or maintaining heating systems of the legal requirements and responsibilities that govern this area of business."
Louis Burns of the Health & Safety Executive for Northern Ireland said after the court hearing: "The tragic and untimely deaths of Neil and Aaron from carbon monoxide poisoning serve as a potent reminder of the dangers this deadly gas poses."
Carbon monoxide is a highly poisonous gas which is impossible to see, taste or smell, and anyone who uses an appliance that burns a fossil fuel including gas, oil and coal, as well as peat and wood, is potentially at risk from carbon monoxide poisoning.