The injured were labourer Belal Hossain, 28, Md Ziaur Rahman, 45, and his daughters Faria, 8, and Raifa, 4.
The injured were taken to the emergency department of National Institute of Burn and Plastic Surgery around 10:45 pm on Saturday night.
Md Shahporan who brought the injured to the hospital said a worker was cleaning the reserve tank at the house and the explosion took place when an electric bulb was turned on inside the tank presumably due to accumulated gas.
They were first taken to a local hospital and later transferred to the burn institute.
Dr Shawon Bin Rahman, resident surgeon of the institute, said Belal sustained 17 percent burns, Ziaur 4 percent, Faria 5 percent, and Raifa 6 percent, reports UNB.
All are currently out of danger and receiving treatment at the emergency unit, he added.