Six people, including an elderly couple, suffered burn injuries after a water reservoir exploded at a building in the capital's Pallabi area yesterday morning.

Five of them were critically injured. They are Hasan, 28, a tenant of the building, Yakub Ali Khan, 70, owner of the building, his wife Hosena Ara, 60, Yeasmin, 30, another tenant of the house, and her three-year-old daughter Ruhi.

Another injured Mohammad Parvez, 14, a class-VII student and son of a tenant of the house, was given first aid.

Partha Sangkar Paul, a resident surgeon of Dhaka Medical College Hospital's burn unit, said the five were being treated at intensive care and high dependency units.

Of them, Hasan sustained around 87 percent burns, Yakub around 25 percent, his wife around 90 percent, Yeasmin around 41 percent and her daughter around 90 percent.

The blast happened on the ground floor of the six-storey building in Pallabi-12, said Dadon Fakir, officer-in-charge of Pallabi Police Station.

A family member of the house owner told The Daily Star that the water tank had been empty for a long time. The homeowner requested tenant Hasan, a plumber, to clean the tank so that it could be used.

Residents of the building said Hasan, who lives in a rooftop room, went to clean the tank around 9:30am. 

Hasan lifted the iron lid of the tank and lit a match to see inside. Then the explosion happened, creating a fireball.

Yakub and his wife were standing beside the tank when Hasan lit the match. Ruhi was playing on the staircase on the ground floor. Her mother Yeasmin, who lives in a flat on that floor, was injured as she came out to save her daughter. Parvez was in his flat on the ground floor at that time.

Mujibur Rahman, officer of Mirpur fire service station, said the fire was extinguished before firefighters reached the spot.

After visiting the spot, Mujibur said gas had accumulated inside the tank as there was little water inside and the tank was covered.

He said they thought that the explosion happened as fire from the lit match came into contact with the gas.  

He also suggested that such tanks be kept open for two to three hours before cleaning those to disperse the accumulated gas.