A police spokeswoman said police were called when Powergel and a detonator cord were found on the property of a person who had died.
The blast could be heard in the North End and some residents complained of their buildings shaking.
The explosion prompted calls to the emergency services and speculation on social media.
Jamahl Edwards, who filmed it, said it was ``very impressive''.
``When the sound came it was a wall of pressure hitting you, like on the movies.''
The spokeswoman said police did not notify nearby residents of the explosion.
``It was not anticipated that it would cause any more disturbance or disruption than the normal quarry operations,'' she said.
``If people wish to raise concerns with police directly, they are welcome to contact us.''
The explosives were ``all legal and above board'' and finding explosives lying around in old sheds was not uncommon, the spokeswoman said.
Powergel is an explosive used in mining.
