Four people injured in a gas cylinder explosion in Rajshahi Cadet College in Sardah of Rajshahi District on Saturday.The injured were identified as Wahiduzzaman, 30, head plumber of Cadet College, Manjur Rahman, 28, Rubel, 45, son of Hossain Ali of Shiroil Colony, and Selim, 40, son of Makbul of Chotobangram area in the city.Nibaran Chandra Barman, officer-in-charge of Charghat Police Station, said the gas cylinder went off with a big bang around 8 am while the staff and workers were blowing up balloons with the gas as part of their preparation for the annual sports day of the college, leaving four people injured.The injured were rushed to the burn unit of Rajshahi Medical College Hospital.The incident took place two days before the annual sports day of the Cadet College, scheduled to be held on December 28.