11. Exceptions: Sections 9 and 10 do not apply when the use of a cover, guardrail or protective screen prevents the carrying out of a task that could not be reasonably performed otherwise.
In such a case, the cover, guardrail or protective screen may be removed, but only while the work is being performed. The wearing of a safety harness is then compulsory for any worker exposed to a danger of falling in the opening, except if the worker is protected by some other device that provides him with equivalent safety or by a safety net.