A warning line system is a barrier of rope, wire or chain on stanchions placed on a roof to warn workers that they are approaching an unprotected edge.
A warning line system is a barrier made of rope, wire or chain held up by stanchions and set back from the edge of a roof. It warns workers that they are approaching an unprotected side or edge and marks out an area where roofing work can be done without guardrails, safety nets or personal fall arrest systems.
A warning line does not stop a fall. It is a visual and physical reminder that keeps workers and equipment away from the edge. For that reason, OSHA only allows warning lines on low-slope roofs, and workers who need to go between the warning line and the roof edge must be protected by another method.
Under OSHA's construction definitions, a low-slope roof has a slope of 4 in 12 or less. See roof work safety for the broader rules that apply to roof work.
Under 29 CFR 1926.501(b)(10), employees doing roofing work on low-slope roofs with unprotected sides and edges 6 feet or more above lower levels must be protected by guardrails, safety nets, personal fall arrest systems, or a combination of a warning line system with one of those systems or a safety monitoring system. On roofs 50 feet or less in width, a safety monitoring system alone is permitted.
In practice, many roofing contractors set up warning lines around the main work area and use a safety monitor or fall arrest for any work between the line and the edge.
The construction standard at 29 CFR 1926.502(f) sets these key requirements:
Mechanical equipment on roofs may only be used or stored in areas protected by a warning line system, guardrail system or personal fall arrest system.
For non-construction work, such as maintenance on low-slope roofs, OSHA uses designated areas under 29 CFR 1910.28 and 1910.29(d). These work in a similar way to warning lines but have their own distance and construction rules.
A roofing contractor was replacing the membrane on a 120-foot-wide low-slope warehouse roof. The crew set up a warning line 10 feet from the edges perpendicular to the direction the roofing kettle cart would travel, and 6 feet from the edges parallel to it, with red flags every 6 feet.
When the crew needed to install flashing at the roof edge, they worked from a tie-off anchor using a personal fall arrest system. During the job, a supervisor found that wind had knocked over two stanchions. The crew replaced them with heavier bases and added a check of the warning line to the start of every shift.
It is part of an approved system on low-slope roofs, but it does not stop a fall. It must be combined with guardrails, safety nets, personal fall arrest or a safety monitor for any work between the line and the edge.
No. On steep roofs, OSHA requires guardrails with toeboards, safety nets or personal fall arrest systems.
At least 6 feet, and at least 10 feet from edges perpendicular to the direction of mechanical equipment operation.
Part of SafetyIQ's EHS glossary: plain-English definitions of workplace health and safety terms.
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