Covers and their use must conform to the following provisions:

(1) Hole covers must be of any material that meets the following strength requirements:

(a) Conduits, trenches, and manhole covers and their supports, when located in roadways, and vehicular aisles must be designed to carry a truck rear axle load of at least two times the maximum intended load;

(b) Hole covers must be capable of supporting, without failure, at least twice the weight of employees, equipment, and materials that may be imposed on the cover at any one time.

(2) All covers must be secured when installed so as to prevent accidental displacement by wind, equipment, or employees.

(3) All temporary covers must be color coded or they must be marked with the word "hole" or "cover" to provide warning of the hazard.

(4) Barriers and screens used to cover openings must meet the following requirements:

(a) Barriers must be of such construction and mounting that, when in place at the opening, the barrier is capable of withstanding a load of at least two hundred pounds applied in any direction (except upward), with a minimum of deflection at any point on the top rail or corresponding member.

(b) Screens must be of such construction and mounting that they are capable of withstanding a load of at least two hundred pounds applied horizontally at any point on the near side of the screen. They may be of solid construction of either grill work with openings not more than eight inches long, or of slat work with openings not more than four inches wide with length unrestricted.