Rule 6362.
A bleaching engine, except the Bellmer type, shall have the top covered with the exception of an opening large enough to permit filling but too small to admit an employee. This opening shall be covered with a door. The opening and a platform connecting 1 engine with another shall have standard guardrails that meet the requirements in General Industry Safety and Health Standard Part 2 "Walking-Working Surfaces," as referenced in R 408.16302.
Mich. Admin. Code R. 408.16362