On a construction site, a floor or roof opening through which a person could fall must be:

Explanation

Section 1632(b)(1) requires floor, roof and skylight openings to be guarded either by temporary railings and toeboards or by covers. What option (c) leaves out is everything section 1632(b)(3) demands of a cover: it must safely support the greater of 400 pounds or twice the weight of the employees, equipment and materials that may be imposed on any one square foot; it must be SECURED in place against accidental removal or displacement; and it must bear a painted or stencilled sign reading Opening - Do Not Remove, in letters at least one inch high, with chalk or keel markings expressly not allowed. Loose plywood satisfies none of that and slides underfoot. Paint, signs, rope and a spotter (a, d) are visual warnings that carry no load, and a warning is never guarding.