LUAS investigators will examine complaints that doors on the tram which crashed into a bus in Dublin earlier this month failed to open on impact, temporarily trapping passengers inside.

It is believed the driver, due to injury, may not have been able to pull an emergency release handle in his compartment which would have allowed the doors to be opened by passengers.

Eye witnesses at the scene, including passengers on the tram, complained of people being trapped onboard.

While the trams are designed for such incidents with emergency release mechanisms on board, a failure or delay in operating these could prove dangerous, particularly if there was a fire. More than 20 people were injured in the accident.

A spokeswoman for Veolia, the owners of the Luas, said the company could not comment on an ongoing investigation.

It is understood all aspects of the crash, including comments made by members of the public in the aftermath, will form part of the investigation.

A member of the emergency services who responded to the incident said the doors on the tram were open when they arrived but that employees of Violia were also on board.

"You would have to ask if the driver opened the doors or disengaged the tram," he said.

"If he was injured and he couldn't do that, would the doors open and I would say not because you just can't have anyone open the doors."

The investigation into how the accident occurred is ongoing. CCTV footage appears to show the driver of the bus had a green light to proceed seconds before impact.

According to reports, the Luas tram was not fitted with head-on CCTV cameras making it unclear from that perspective what may have led to the accident.

Investigators are also gathering CCTV footage from business premises along O'Connell Street in an effort to ascertain the sequence of events.