National Safety Stand-Down: Warning Lines - How to Prevent Roof Falls National Safety Stand-Down: Warning Lines - How to Prevent Roof Falls

Warning lines are one of the oldest forms of fall protection mandated by OSHA for low slope roof projects. The basics of the system are that warning lines must be made of rope, wire or chain. The flags must be visible, present every six feet, 34 to 39-inches from roof level and erected at a minimum of six feet from the fall hazard. Most workers generally think about warning lines and safety monitors as a means of fall protection for the unprotected edge; but warning lines can be used to establish a barrier for multiple rooftop fall hazards. The warning line system continues to be a versatile tool in the roofing industry even with the increasing use of temporary guardrails and engineered systems.


Prior to commencement of any roofing project, a warning line system is established to create a working perimeter for the crews. The bright flags provide the crews with a clear indicator of their distance from the unprotected edge. This perimeter allows the crews to work freely within the designated work area.

Once access/egress to roof level has been determined and the work perimeter erected, a clear indicator of where to access/egress must be established. Warning lines can be used to accomplish this task as well.

Warning lines may also be set-up to establish a walkway to the intended scope of work. This provides roofers with a clear path of travel to the main work area. This use allows crews to steer clear of hazards at roof level, such as skylights, areas where the decking is suspect and customer specific equipment.

Warning lines are often used to flag-off skylights in the main work area. This provides the crews with an understanding of how close they can get to skylights before additional means of fall protection is required, such as conventional fall protection systems.

An underdeck inspection is conducted when bidding roof projects. One of the main reasons for this inspection is to locate potential areas of deteriorated decking. These areas of deteriorated decking may fall within areas of the proposed scope of work or paths to the prospective work area. There are limited cases where a majority of the decking must be replaced due to degradation, but these areas are isolated in most cases. Warning lines can be used to make the crews aware of these isolated locations at roof level. Warning lines are a clear indicator of where you can work up to before conventional fall protection is necessary.

To summarize, although the warning line system was established as one of the earliest forms of fall protection, unlike the body belt, there are still many uses for the system in modern day rooftop safety.

Robert Wilson, Northern Safety Manager, Franklin, OH