Dublin Fire Brigade is the latest group of frontline workers to test how they would deal with a terrorist attack.
They have staged an event where a car was deliberately driven into a Luas, and two gunmen started firing.
It follows the Garda simulation of an attack in Dublin's Docklands last week.
John Keogh from Dublin Fire Brigade says officers practiced assessing the injured tram passengers.
"They're graded red, and they're marked with a red marker to say that they're the most seriously injured people.
"If someone has a green tag it means they're walking wounded and can make their own way out of the incident.
"If someone is tagged yellow, it's not immediate but it is still serious."