2. Means of protection shall—
(a)be of sufficient dimensions, of sufficient strength and rigidity for the purposes for which they are being used, and otherwise suitable;
(b)be so placed, secured and used as to ensure, so far as is reasonably practicable, that they do not become accidentally displaced; and
(c)be so placed as to prevent, so far as is practicable, the fall of any person, or of any material or object, from any place of work.