Known as the silent killer, carbon monoxide has no taste or smell with the affects often mistaken for flu or food poisoning by sufferers.
The death of Susan Henry, aged in her 60s, in Cookstown has once again prompted warnings about the gas which can be impossible to detect without a proper alarm.
William Stockdale (60) was found dead at the property on the Castlewellan Road in Newcastle in May 2016. Five people, including two paramedics were taken to hospital after suffering symptoms while treating the victim.
In 2015 Francis and Nan O'Reilly, a married couple in their seventies, died as a result of carbon monoxide poisoning in their caravan also in Newcastle.
The silent gas also caused the deaths of teenagers Neil McFerran and Aaron Davidson at a Castlerock holiday apartment in 2010, their friend who was found unconscious survived after hospital treatment.
Their deaths prompted a change in the law which requires alarms in all new build properties.
Singer Nadine Coyle has said she almost lost her life to carbon monoxide poisoning, at her LA home that left her "weeks from death".
In 2015 she fronted an awareness campaign about the dangers of the gas.
The Health and Safety Executive, advise that all homes install alarms and regularly service appliances and help protect themselves and their families from the deadly gas.
