Some €5 million worth of damage was caused by a fire in an industrial estate in Ballincollig, Co Cork last night.
It was the worst of a series of Halloween-night incidents which included the torching of an Orange Hall in Cootehill, Co Cavan and the burning of two houses to the ground in Co Louth.
Two men aged 18 and 20 were questioned about the Cork fire, which damaged commercial units, a youthreach workshop and a mini-bus at the Innishmore Industrial Estate at around 2am.
The two were initially arrested after a Garda car was targeted in a petrol bomb attack but are also being questioned the series of suspected arson attacks in the industrial estate estate.
Mayor of Dublin Paddy Bourke
Three youths were held after a petrol bomb was thrown at gardai on a bicycle patrol in Bray yesterday evening. It exploded and burning petrol splashed on one of the officers but he was not injured.
In Co Louth dozens of hay bales were set alight in a field and two homes in the Carlingford area were gutted by fire.
Two people were injured after being struck by a car at a bonfire in Clondalkin while a man fell into a bonfire in Walkinstown.
Fire and ambulance crews in Dublin answered 1,300 calls in 12 hours from dusk on Wednesday while gardai attended hundreds of incidents.
A spokesman for Dublin City Council said emergency crews answered nearly twice as many calls as last year on Halloween night but there were fewer major incidents to deal with.
In the run-up to the October celebrations 14 young people were injured by fireworks and fires with several losing fingers and suffering bad burns.
Lord Mayor of Dublin Paddy Bourke praised the work of emergency crews. "I want to take this opportunity to thank the fire brigade officers for what was a very hard days and nights work. I am just grateful there seems to have been no serious injuries that we are aware of," he said.
Dublin City Council workers collected more than 400 tonnes of materials in the weeks before Halloween to try to prevent illegal bonfires.
"This time of year, over and over again, no matter how hard the authorities try to get rid of flammable materials from all over the pace, they seem to appear and be available to people," the Mayor said.
"Despite our best efforts these fires do take place. "They are against the law, damage public property and can cause people serious injury and the fire brigade have to work very hard to make sure no serious damage is caused."
Mr Bourke also warned people of severe penalties for illegal use of fireworks. "Fireworks are illegal, and they carry a fine of up to €10,000. But I think there may have been less fireworks available this year than other years," he said.