Police said Lt Col Vikas Sharma (37) was burning garbage when the explosion occurred around 12.30 PM, along with his two sons, Aryan (10) and Shaswat (4), and maid Manjinder. All four of them was injured.
Vikas sustained "pellet wounds", and his condition was serious but stable. Police suspected that "the garbage might have carried some disposed pellets", sources said.
Additional superintendent of police Soumya Chauhan said that they were rushed to the Indira Gandhi Medical College, where they were undergoing treatment.
"It was not yet clear as to what caused the explosion and we are further investigating the matter to ascertain the cause behind it," Chauhan said.
She added that a team of forensic experts had visited the spot and the real cause behind the explosion could be ascertained after their report.
A case has been registered in this regard and further investigations are on.