Anchors: certified, engineered and temporary

The anchor is the foundation of every travel restraint and fall arrest system. If it fails, nothing else matters. Anchors fail in fatal falls more often than most workers expect: a lanyard looped around a small pipe, a hook clipped to a guardrail, a temporary roof anchor nailed to sheathing instead of a rafter, a beam clamp on the wrong size of flange. This lesson explains what an anchor must be able to do, the strength requirements, the main types of anchors and how to choose and inspect them.

Anchor, anchorage connector and anchorage

The words are used loosely on site, but the standards distinguish them:

• the anchorage, or anchor, is the structure or element that holds the load, such as a steel beam, a concrete slab, a roof rafter or a column;
• the anchorage connector is the device that attaches the system to the anchorage, such as a beam clamp, a cross-arm strap, a concrete anchor, a roof anchor or a D-ring plate;
• the anchor point is the place on the connector where the lanyard, self-retracting device or lifeline is attached.

An anchorage connector rated for 22 kN or 5,000 lb is only as strong as the structure it is fixed to. A strong strap wrapped around a weak pipe is a weak anchor.

Strength requirements

OSHA sets anchor strengths in 1926.502(d)(15) and 1910.140(c)(13). Anchorages for personal fall arrest must support at least 5,000 lb per worker attached, or be designed, installed and used as part of a complete personal fall arrest system that maintains a safety factor of at least two, under the supervision of a qualified person. ANSI/ASSP Z359 uses similar values for non-certified and certified anchorages. The table summarizes the main values.

Why are anchors so strong when the force on the worker is limited to about 6 to 8 kN or 1,350 to 1,800 lb? Because the anchor must cope with the peak force, which is higher than the average, with dynamic effects, with off-axis loading, with wear and corrosion over time, with errors in installation and with the possibility that the energy absorber is wet, frozen or performs at the top of its range. The large margin is deliberate.

Types of anchors

Anchors fall into a few broad groups.

Permanent engineered anchors

Permanent anchors are installed into a building or structure for repeated use, for example roof anchors for window cleaning and maintenance, anchor posts on rooftops, D-ring plates on steel, and engineered horizontal lifelines. They should be designed and certified by a professional engineer, installed according to the design, labeled with their capacity and intended use, and inspected and recertified at the intervals the engineer or manufacturer specifies. Building owners should keep drawings and certification records and give them to contractors who will use the anchors.

Temporary anchorage connectors

Temporary connectors are installed for a job and removed afterward:

• beam clamps and beam trolleys that grip the flange of a steel beam, sized for the flange width and thickness;
• cross-arm straps and anchor slings wrapped around a structural member, such as a column or beam;
• concrete anchors, such as reusable anchors placed in drilled holes and anchors cast into slabs;
• temporary roof anchors for wood-frame construction, fastened through the sheathing into a rafter or truss with the nails or screws the manufacturer specifies;
• counterweight anchors on flat roofs, which rely on weight and friction and must be used within the manufacturer's limits on roof surface, slope and distance from the edge;
• door and window jamb anchors, which brace across an opening and are rated only for the conditions the manufacturer states.

Each must be installed exactly as the manufacturer instructs. A roof anchor fastened only into sheathing, a beam clamp on a flange it was not designed for, or a counterweight anchor on a wet membrane may hold far less than its rating.

Structural members used directly

A competent person can sometimes use a structural member, such as a steel beam or a concrete column, as an anchorage with a suitable strap or connector, if they are confident it can carry the required load. Using a structure that has not been designed or assessed for the purpose is a judgment call that requires real knowledge of structures. When in doubt, ask an engineer.

What not to use

Many fatal falls involve anchors that looked solid but were never designed for fall loads. Never anchor to:

• vent pipes, plumbing, conduit, sprinkler pipes or cable trays;
• guardrails, handrails or ladder rungs, unless they are specifically designed and rated as anchors;
• light fixtures, ductwork, roof hatches or skylight frames;
• rooftop equipment such as units, antennas or satellite dishes, unless designed as anchors;
• scaffold components, unless the scaffold is designed for it and the manufacturer or engineer allows it;
• the same anchor as another worker, unless the anchor is designed and marked for more than one person.

Anchor location

Where the anchor is placed matters as much as how strong it is. The best location is directly overhead, above the dorsal D-ring, because it:

• keeps free fall short, especially with a self-retracting device;
• reduces total fall distance and the clearance needed below;
• prevents or reduces swing falls;
• keeps the lifeline away from edges.

Anchors at foot level, common on roofs and decks, increase free fall, require leading edge equipment, and create swing hazards when the worker moves to the side. Anchors placed far from the work encourage workers to unhook or to use long lanyards. Plan anchor locations as part of the job, not as an afterthought.

Load direction and slings

Anchorage connectors and slings are rated for loads in particular directions. A strap wrapped around a beam and pulled along its length, or a sling with legs at a shallow angle, may carry far more force than the fall itself. When an anchor sling has two legs meeting at the attachment point, each leg carries more than half the load if the legs are spread apart.

Inspecting and recording anchors

Inspect temporary connectors before each use, like any other component. For permanent anchors, check before use for corrosion, damage, loose bolts, cracked welds, deformation and missing labels, and follow the engineer's or manufacturer's schedule for formal inspection and recertification, commonly every year and after any fall or suspected overload. Remove from service any anchor that has arrested a fall until an engineer or competent person has inspected it. Building owners should mark anchors with their capacity and use, keep a roof plan showing anchor locations, and share it with contractors.

Anchors for suspended access and window cleaning

Buildings that use suspended platforms, bosun's chairs or rope descent systems for window cleaning and facade work need permanent anchors designed for that use. OSHA's 1910.27 requires the building owner to inform the employer in writing, before a rope descent system is used, that each anchorage has been identified, tested, certified and maintained to support at least 5,000 lb in any direction for each worker attached, with inspection at least every year and recertification at least every 10 years. ANSI/IWCA I-14.1 covers window cleaning safety more broadly. Building owners must provide workers with information about the anchors before work begins.

Anchors in different structures

Concrete anchors depend on the strength of the concrete, the embedment depth, the distance from edges and other anchors, and whether the concrete is cracked. Wood anchors depend on the size and condition of the member and on fasteners reaching sound wood, not just sheathing. Steel anchors depend on the size of the member and the welds or bolts that connect it to the rest of the structure. Metal roof decks, in particular, are usually too thin to anchor into without a manufacturer-specific system that spreads the load across several ribs or connects to the structure below. Each material has its own failure modes, which is why permanent anchors are designed and certified by engineers.