Dum Dum: Two bullets were fired accidentally when a Railway Protection Force constable dropped his rifle in front of a busy ticket counter at Dum Dum Metro station on Friday afternoon, resulting in minor splinter injuries to a nine-year-old boy, his mother and a Metro employee.

An RPF officer said there could have been serious casualties had the Insas 5.56mm bullets not hit the floor first before the splinters ricocheted: "There were scores of people in the area."

The assault rifle was not in the safety lock mode, the mandatory mode when the security forces carry a rifle at a crowded place, RPF and Metro officials confirmed.

The freak 2pm accident happened during a change of guard at an RPF bunker of sand bags barely 10 feet from a ticket counter near the stationmaster's cabin at the western flank of the station.

"The constable whose shift had ended handed the rifle over to his replacement, who dropped it," a Metro official said.

Sangeeta Basu, 36, was standing in queue with son Saptarshi. The splinters hit Sangita in the right arm, Saptarshi in the right leg and Metro employee Narayan Majumdar in the right elbow.

Mother and son, residents of Sonarpur on the city's southern fringes, were taken to RG Kar Medical College and Hospital and later shifted to a private hospital. They were discharged in the evening. Majumdar received first aid at the station.

D.K. Meena, the constable who dropped the rifle, has been suspended and a probe started into why the rifle was not in the safety mode.

It wasn't clear whether any action was being considered against the other constable, who had handed the rifle over without putting it in the safety mode.

"Everything happened in a flash. The queue was fairly long. Before anybody could react, the woman and her son dropped to the floor. They were bleeding profusely," an RPF constable said.

A relative said Saptarshi, a Class III pupil, was returning from his maternal grandparents' home in Barrackpore, where he had spent part of his summer holidays.

The bullet marks were visible on the floor near the ticket counter in the evening. Calcutta police said they had not received any complaint from the Metro authorities or the victims' family, and had not started any case of their own accord.