After medical attention and preferably with a companion, return to the scene as soon as you can with a camera, a long spirit level or straight-edge and a ruler or tape measure. Take a general location shot with the defect identified so that there is no doubt where it is. Then place the straight edge across the hole, resting on either side and bridging it. Measure to the bottom and photograph the measurement. Measure too the length and breadth. The standard definition of dangerous is 40mm deep, 300mm in any other direction and sharp lipped. Visit local residents and ask them if they were aware of the defect, for how long it has been present and whether they have reported it. Record their names, contact details and what they said. Seek advice from the Helpline.