3 classes of roof
A little further information about the Temporary Edge Protection PDF Doc. I don't think a lot of people realise the importance of these documents, the HSE have already acted on a number of occasions and prohibition orders have been issued. The ACOP - BS EN 13374:2004 imply that all edge protection handrails must have a drawing showing the calculations for side impact. If you look at the NSG Doc, they show that the puncheon is set at 550mm from the centre of the steel H girder, with the top guardrail at 1.6m from the node point. The node point is the fixing point at the bottom of the puncheon arrangement. This is also where the cruciform strength of the fixing is calculated. According to the calculations on this example, it only takes 240kg of force (side impact) using Class A fittings and 480kg using Class B fittings to start the process of the puncheon arrangement bending at the node point.
The NSG doc is the only drawing I have come across, with calculations provided. The further the puncheon is placed away from the H girder beam, on the supporting tube, (the tube fixed to the beam, with girder clamp fittings), the weaker the puncheon arrangement. It appears designers are reluctant to provide calculations, for puncheon arrangements, the further the puncheon tube is placed away from the supporting girder clamps on the support tube, as the cruciform strength of the bottom fitting (node point) and the elasticity of the supporting tube is considerably weakened on the puncheon arrangement.
You must also take into consideration that the distance from the top hand rail to the bottom fitting at the node point is 1.6m, in this example. The further the distance between these two points the weaker this arrangement of components could be. Design input must be required to erect these handrails or other arrangements should be made to protect persons and materials from falling from roofs.
There other considerations that may also be of interest, BS EN 13374 identifies 3 different classifications of roofs that are determined by the gradient of the roof, for example,
Class A is set at 0º to 10º, where the gaps between the rails are set at 470mm, about 18½ inches
Class B is set at 10º to 30º, where the gaps between the rails are set at 250mm, just over 9 inches
Class C is set at 30º to 60º, where the gap is set at 100mm, 4 inches.