We use can use a warning line system for fall prevention if the roof has a slope of 4/12 or less, is wider than fifty feet and has parapet walls less than 39" high.

The warning lines can be made of wire, rope, or chain and flagged every six feet.  The warning lines must be supported by stanchion posts that can withstand a tipping force of at least 16 pounds.  The height of the warning line from the roof surface must be between 34 and 39 inches.  And the tensile breaking strength of the warning line should be at least 500 lbs.

The open edges around the roof work site should be guarded by warning lines.  These have to be set six feet from all edges when no mechanical equipment is being used.  When mechanical equipment is being operated, the warning lines must be 10 feet from the edge in the direction  the equipment is traveling and six feet  from the roof edge or the sides of the work area.

No materials or mechanical equipment can be stored outside the warning lines.  And workers outside the warning line area must be protected by guardrails, personal fall arrest system or a safety monitoring system.

A safety monitor system is used in conjunction with a warning line system with a 4/12 or less slope and 50 feet wide or wider roofs.  They can be used without another means of fall protection on low slope roofs less than 50 feet across. 

This system has a safety monitor who has been trained and able to recognize and anticipate hazards.  He/she also is authorized to take immediate corrective action.  A safety monitor must be a "competent person" and have no other duties which could interfere with their responsibility.  They must be able to see the employees he/she is monitoring, be on the same working level and able to communicate with them verbally.