Investigators are trying to find out what caused an explosion at a Canadian Pacific Railway yard in southeast Calgary on the weekend.

It happened at around 5 p.m. Sunday in CP's Alyth yard in the 1700 block of 30 Avenue S.E.

The blast blew a hole in the wall of a repair shop and sent debris flying .  But there was no fire, officials said.

The building was empty at the time and there were no injuries.