Patients in life threatening emergencies who need a 999 ambulance are at serious risk because of the way Dublin Fire Brigade manages its calls.
According to the safety watchdog, some patients in critical situations are having to wait 10 minutes longer than they should for a 999 ambulance to arrive, as a result of the manner in which Dublin Fire Brigade is operated.
A key problem is the ongoing lack of integration between the Dublin Fire Brigade service and the HSE-run National Ambulance Service, despite improvements in co-operation in recent years, the report by the Health Information and Quality Authority (Hiqa) said.
Dublin Fire Brigade is run by Dublin City Council while the National Ambulance Service, which caters for the rest of the country, is part of the HSE.
The lack of proper integration between both means that if a patient with a potentially life threatening condition in Dublin dials 112/999 for an ambulance, current arrangements for call handling and dispatch can result in a delay in response.
This is due to the way calls are transferred from Dublin Fire Brigade to the National Ambulance Service.
Hiqa warned of the dangers in a previous report in 2014.
Two years later, it found the situation had worsened as demand for ambulances increased.
It discovered that over 24 hours a high proportion of calls being queued were potentially life-threatening.
Hiqa said it escalated its concerns to Dublin City Council.
A Dublin Fire Brigade ambulance may continue to be dispatched to the patient even though a nearer National Ambulance Service ambulance may have been available and better placed to respond.
"The status quo puts patients at risk and cannot be allowed to continue," warned Sean Egan, Hiqa's acting head of healthcare regulation.
Firefighters last month voted for strike action over proposed reforms to the service operated by the Dublin Fire Brigade. This has now been deferred to allow for mediation by the former director general of the Workplace Relations Commission, Kieran Mulvey.