Warning Line System

Under OSHA’s general industry standard, fall protection is required at 4 feet above a lower level (29 CFR 1910.28(b)(1)); on construction work, the trigger is 6 feet (29 CFR 1926.501(b)(1)). General industry also permits a designated area for temporary, infrequent work on low-slope roofs, marked by a warning line at prescribed distances from the edge (29 CFR 1910.28(b)(13)). The warning line is the boundary of that designated area: work stays inside it under the conditions the rule sets, and work outside it or closer to the edge needs a guardrail, restraint, or arrest system.

Fall protection is usually grouped by the hierarchy of controls: elimination, passive prevention (guardrails, covers, and other physical barriers that need no worker action), active fall restraint or fall arrest (harness-and-anchor systems), and administrative controls (warning lines, training, and procedures). A warning line is an administrative control, the lowest tier: it depends on workers respecting the boundary, which is why OSHA limits it to temporary, infrequent work at prescribed distances from the edge (29 CFR 1910.28(b)(13)).

A roof guardrail must have a top rail 42 inches, plus or minus 3 inches, above the walking-working surface and withstand 200 pounds of outward or downward force (29 CFR 1910.29(b) general industry; 29 CFR 1926.502(b) construction). A warning line is not a guardrail and does not meet those criteria: it marks a boundary rather than stopping a fall, so it applies only where the designated-area provision fits the work. Tritech installs warning line systems where that provision applies and guardrail where it does not, based on a Fall Hazard Assessment of how the roof is actually used.