Such was the tremendous heat generated by the flare that it seared through lead flashing on the roof, burned through a roof timber and even severed a plastic water pipe before finally being extinguished.
Jim McCarthy and Ray McCarthy were Health Service Executive (HSE) paramedics on duty at Castletownbere Hospital and spotted the firework as it landed on the roof at around 12.05am yesterday.
A large number of fireworks were being set off around Castletownbere harbour to mark the New Year but, despite repeated warnings, a number of marine flares were also ignited as part of the celebrations.
"It was Ray who spotted what had happened," Jim said. "He went outside to look at the fireworks and the next thing he spotted this fireball coming in the direction of the hospital. He couldn't believe it when the firework landed on the roof."
The paramedic immediately informed his colleague about what had happened.
"We ran out and realised that the firework hadn't gone out and that it was starting a fire on the roof," Jim said.
Neither of the paramedics realised they were dealing with a marine flare which would have kept burning until it ignited the entire hospital roof - where 30 geriatric patients were being treated inside.
Castletownbere fire brigade was immediately alerted, as were hospital officials.
Emergency services were also ready to trigger the hospital's evacuation plan if deemed necessary.
The two paramedics immediately began trying to douse the firework with water in a bid to buy time until the arrival of the fire brigade. However, because it was a phosphorous-based marine flare, the water didn't extinguish the incendiary device.
Fire brigade officials said the quick-thinking of the two paramedics in dampening the area around the flare did slow its progress in searing into key roof structures.
"It made a big difference and it definitely helped delay the fire," one volunteer said.
The fire brigade was at the scene within minutes but, because phosphorous was involved, was still dealing with the device until 3.30am.
"If Ray hadn't spotted the firework landing on the roof, God only knows what would have happened," Jim said. "I couldn't believe how that firework kept burning and then slowly began to eat into the roof. We could easily have been dealing with a major catastrophe."