Flameproof equipment that has flanged joints is required to be spaced a minimum distance from solid obstacles For example, steelworks, walls, weather guards, mounting brackets, pipes, or other electrical equipment that might interfere with the venting and dispersal of the products of combustion created by internal explosions.. The clearances are given in Table 505.7(D).The distances are based on the chemical group of the flammable material and are measured from the flange opening to the obstacle.