Novice climber who had limited experience abseiling set themselves up to abseil using a edelrid gigajul in assisted mode. They had been abseiling in manual mode with a prussic previously untill another club member showed them how to use assisted mode. They did not setup the device correctly and did not get anyone to check their abseil setup. They lowered themselves over the edge and the rope slipped through the device. They fell most of the height of the crag ~10m onto their back landing in V shaped groove at the bottom. The climber quickly got up and appeared uninjured to everyone's surprised. They had severe burns from trying to hold the rope but no other significant injuries. I setup a system to haul the casualty up the crag as it was the quickest escape option. The casualtie was driven to hospital for treatment of the burns.