Scaffold Accidents: Causes and How to Prevent Them

What the numbers say

When OSHA rewrote the scaffold standard in 1996 it estimated that roughly 65 percent of the construction workforce works on scaffolds frequently, and that the new rule would prevent about 4,500 injuries and 50 deaths a year. A Bureau of Labor Statistics study behind that rule found that 72 percent of workers injured in scaffold accidents attributed the accident to one of three things: the planking or support giving way, slipping, or being struck by a falling object.

The picture has not changed much. The scaffolding standard, 1926.451, has appeared in OSHA's list of the ten most frequently cited standards every year for well over a decade, usually alongside fall protection and ladders. The paragraphs cited most often are the ones about fall protection, platform construction, access and foundations, which map directly onto how people get hurt.

Below are the four ways scaffold accidents happen, the rule aimed at each, and what a site that does not have them looks like.

1. Falls from the platform

Falls are the leading cause of scaffold deaths. They happen from open sides with no guardrail, through gaps in the planking, from climbing the frame instead of a ladder, and during erection and dismantling when the guardrails do not yet exist. Suspended scaffold falls follow rope or rigging failure and a missing or badly anchored lifeline.

The rule: guardrails or personal fall arrest above 10 feet, with top rails at 38 to 45 inches and midrails (1926.451(g)); both systems on suspended scaffolds; fall protection for erectors where the competent person finds it feasible. Our fall protection guide has the full dimensions.

What prevents it: complete guardrails on every open side before the scaffold is released; a tagging system so a scaffold with a rail missing is yellow-tagged with tie-off required; advance guardrail or anchor points for erectors; ladders or stair towers at every platform more than 2 feet above the access point; and a hard rule that nobody climbs cross braces.

2. Planking or support failure

The second leading cause. A plank breaks or slides off its bearer, a leg punches into soft ground, an untied scaffold tips, or an overloaded platform buckles. Almost every one of these traces back to a missing inspection, an overload or a missing tie.

The rule: 4:1 capacity and no loading beyond the rated capacity (1926.451(a), (f)(1)); scaffold-grade planks extending 6 to 12 inches past supports and overlapping 12 inches (1926.451(b)); base plates and mud sills on a firm foundation, and ties or guys once the scaffold exceeds a 4:1 height-to-base ratio (1926.451(c)); a competent person inspection before every shift (1926.451(f)(3)). The planking and load capacity guide covers the numbers.

What prevents it: a load chart from the supplier and someone who has read it; planks inspected and culled every shift; ties installed as the scaffold goes up, not after; and treating "another trade removed a brace" as the emergency it is.

3. Struck by falling objects

Tools, debris, brick and fittings fall from platforms onto the people below. On a multi-level scaffold the victim is often another scaffold worker; on a street-front job it is the public. Dismantling is the high-risk phase, when components are being handed down or dropped.

The rule: hard hats for everyone on the scaffold, and toe boards at least 3.5 inches high, screens, debris nets, canopies or barricades to protect people below (1926.451(h)). Debris may not accumulate on platforms (1926.451(f)(13)).

What prevents it: toe boards that go back on after the platform is swept; screening wherever material is stacked; debris netting and sidewalk sheds on public frontages; a controlled drop zone during dismantling; and tool lanyards, which cost less than one emergency room visit.

4. Electrocution

Less frequent than the first three but usually fatal. A scaffold is a large conductive structure, and it is erected, moved and dismantled by people handling 10-foot lengths of steel or aluminum overhead. Contact with an overhead line, or with a line during a mobile scaffold move, kills the worker holding the component.

The rule: minimum clearances in 1926.451(f)(6). Uninsulated lines: 10 feet for lines up to 50 kV, plus 0.4 inch for every kilovolt above that. Insulated lines: 3 feet below 300 volts, 10 feet from 300 volts to 50 kV. The clearances may be reduced only when the utility has de-energized or relocated the line or installed protective covers. Electrical hazards are also a required topic in user training (1926.454(a)).

What prevents it: a look up before the first frame is set; calling the utility when the scaffold or its planned moves will come inside the clearance; and a rule that mobile scaffolds are never rolled under lines without a spotter.

The violations OSHA cites most

Compliance officers see the same things on scaffold after scaffold. The list below is what fills scaffolding citations, and each is something a competent person would catch in a five-minute walk.

1. Missing or incomplete guardrails on platforms above 10 feet (1926.451(g)(1))
2. No safe access: workers climbing frames and cross braces (1926.451(e)(1))
3. Platforms not fully planked, or planks with gaps wider than 1 inch (1926.451(b)(1))
4. Legs bearing on blocks, bricks or bare soil instead of base plates and mud sills (1926.451(c)(2))
5. Scaffold not tied, guyed or braced beyond the 4:1 ratio (1926.451(c)(1))
6. No competent person inspection before the shift (1926.451(f)(3))
7. Damaged components left in service (1926.451(f)(4))
8. Workers on the scaffold not trained, or erectors not trained by a competent person (1926.454)
9. Toe boards missing, no protection for workers below (1926.451(h))
10. Planks not extending 6 inches past the support, or overhanging too far (1926.451(b)(4), (b)(5))

What a good scaffold safety program looks like

None of the causes above is solved by a sign or a toolbox talk on its own. The sites that do not have scaffold accidents share a handful of habits:

• A named, trained competent person for every scaffold, with the authority to stop work written into their appointment
• A pre-shift inspection that is actually walked, recorded on a tag and in a log
• User training for every trade before they set foot on the scaffold, and erector training for the crew that builds it
• A supplier whose crews are trained and whose equipment arrives rated, tagged and inspected; the directory filters suppliers by the OSHA Compliant qualification and a clean OSHA record
• A rule that any alteration by anyone other than the erection crew takes the scaffold out of service until the competent person has looked at it
• Someone from outside the job walking the scaffold occasionally with fresh eyes, which is what an independent safety audit is for