A Christchurch man has been convicted and ordered to pay nearly $2500 after homemade fireworks exploded and left his brother with serious burns.

Tim Sargeant pleaded guilty in Christchurch District Court to nine charges laid by the Christchurch City Council under the Hazardous Substances and New Organisms Act.

His younger brother received serious burns to a large area of his body when homemade fireworks stored in Sargeant's backyard exploded in May.

Judge Gary MacAskill said the offending arose out of amateur blundering, with Sargeant failing to return gunpowder to a locked gun cabinet where it was usually kept.

He fined him $750 and ordered him to pay reparation of $500 to his brother, plus costs of $1174.

The Council's inspections and enforcement manager Gary Lennan, said the case highlighted the potential danger of mishandling hazardous substances, and Sargeant was lucky his brother had been left with only minor scarring.