Warning Line System

A warning line system is a temporary barrier erected on a low-slope roof to mark the area where work can be done without conventional fall protection. It consists of rope, wire or chain supported on weighted stanchions and flagged so it is clearly visible. It does not physically stop a fall; it warns workers that they are approaching an edge.

Use under US rules

OSHA's construction standard (29 CFR 1926.501(b)(10)) allows roofing work on low-slope roofs (4:12 pitch or less) to be protected by a warning line system combined with guardrails, safety nets, personal fall arrest or a safety monitoring system. A safety monitoring system alone is permitted only on roofs 50 ft (15.25 m) or less wide. The detailed construction criteria for warning lines are set out in 1926.502(f).

Set-back distance

For roofing work, OSHA interpretations confirm that a warning line set 6 ft (1.8 m) from the roof edge can protect roofers. Other trades, such as HVAC workers, cannot use the 6-foot roofer provision; under an OSHA enforcement policy they may use a warning line set 15 ft (4.6 m) or more from the edge, provided no work is done between the line and the edge and a work rule forbids crossing it.

How it is used

• Workers inside the line work without harnesses.
• Any worker who must go between the line and the edge needs conventional fall protection, such as a personal fall arrest system.
• Access paths for materials and equipment are planned so lines are not breached.
• A safety monitor, where used, must be competent, stay on the same roof within sight and voice range, and have no other duties that distract them.

Outside the US

Many other jurisdictions do not accept warning lines as fall protection for roofers and instead require guardrails or restraint systems at edges. In the UK and Australia, edge protection with guardrails is the normal expectation on flat roofs.