On May 22, 1994, at 1344 central daylight time, a Burkhart Grob 6103 Twin Astir glider, N156SS, was substantially damaged during descent near Forrest City, Arkansas. The glider, being flown by a private glider pilot, had just departed on what was to have been a local personal flight. There was no flight plan filed and visual meteorological conditions prevailed. The pilot received minor injuries while the passenger was seriously injured. According to the pilot, he was taking his daughter, who occupied the front seat, for her first glider ride. He further stated that the rear canopy came open during the tow at 600 feet AGL. He instructed his daughter to release the tow while he attempted to latch the canopy. The airplane entered an uncontrolled descent. Control was not regained and the glider impacted a 15 foot high, 12 inch diameter, rotary irrigation pipe prior to impacting the ground. The investigation revealed that the rear canopy locking devices were intact on both the canopy and the fuselage and capable of latching.