Section 193.2907 - Protective enclosure construction(a) Each protective enclosure must have sufficient strength and configuration to obstruct unauthorized access to the facilities enclosed.(b) Openings in or under protective enclosures must be secured by grates, doors or covers of construction and fastening of sufficient strength such that the integrity of the protective enclosure is not reduced by any opening.Amdt. 193-2, 45 FR 70409, Oct. 23, 1980, as amended by Amdt. 193-12, 61 FR 27793, June 3, 1996; 61 FR 45905, Aug. 30, 1996