Warning lines (1926.502(f))
Distance from the roof edge:
- No mechanical equipment: at least 6 feet.
- With mechanical equipment: at least 6 feet from edges parallel to the direction of equipment operation, and at least 10 feet from edges perpendicular to it.
Using 6 ft on the perpendicular edge is the named common error. 15 ft is not in the warning-line rule.
Height above the walking/working surface: lowest point, including sag, no less than 34 inches; highest point no more than 39 inches. 34 in. is a height, never a distance from the edge. A 30-to-34-inch range sets the line too low.
Personal fall arrest (1926.502(d)(15)-(16))
With a body harness:
- maximum arresting force 1,800 pounds (8 kN);
- free fall no more than 6 feet, with no contact with any lower level;
- deceleration distance no more than 3.5 feet.
900 lb is the old body-belt limit; body belts have not been acceptable for fall arrest since January 1, 1998. A 10-ft free fall and 6-ft deceleration exceed the limits.
Anchorages
Each anchorage supports at least 5,000 pounds (22.2 kN) per employee attached, unless designed by a qualified person with a safety factor of at least 2. Two roofers on separate non-engineered anchorages: 5,000 lb each. 1,800 lb is the force on the worker, not the anchorage strength; 2,500 lb halves the requirement and is not a Subpart M value.
Guardrails (1926.502(b))
- Top edge 42 inches plus or minus 3 inches (39 to 45 in.).
- Withstands at least 200 pounds applied within 2 inches of the top edge in any outward or downward direction; under that load the top edge may not deflect below 39 inches.
- On steep roofs, guardrails also need toeboards.
Keep the numbers in their boxes
- 34 to 39 in.: warning-line height. 42 ± 3 in.: guardrail height. A 36-inch nominal guardrail is too low.
- 200 lb: guardrail top-edge load. 1,800 lb: arresting force. 5,000 lb: anchorage.