Why a Skylight Is Treated as a Hole
Why this matters
Treat every skylight, light panel and translucent roof panel as an open hole from the moment you step onto the roof: do not stand on one, kneel on one, set a tool bag on one, lean a ladder against one, or walk within reach of one without the same protection you would use at an unguarded edge. The glazing is not a walking surface and it has no fall-arrest rating unless a specific unit has been tested and labelled for it, which is rare and which you have to see documentation for rather than assume. What makes this hazard different from an edge is that the edge looks like an edge. A skylight looks like part of the roof, it is often the same colour as the roof under snow or dust, and the people it kills are usually walking backwards, carrying something, or working at night.
This card is mostly about what does not protect a skylight, because almost everything a crew reaches for on the day falls into that list.
What the standards actually say
Both Parts treat a skylight as a hole in a walking surface rather than as a special category.
- Construction, 29 CFR 1926.501(b)(4): each worker on a walking or working surface with a hole, including a skylight, more than 6 ft above a lower level must be protected from falling through it by a guardrail system, a cover, or a personal fall arrest system. The same paragraph separately addresses stepping into a hole and objects falling through one, which is why a cover has more than one job.
- General industry, 29 CFR 1910.28(b): holes are among the listed hazards, and the general industry trigger is 4 ft rather than 6 ft. If your work is maintenance rather than construction, the lower number is the one that applies to you, and a roof that was outside a construction trigger is not outside this one.
The word "hole" is doing the work. Once the skylight is a hole, the question stops being "how strong is this dome" and becomes "which of the three permitted protections is in place", and none of the three is the glazing.
The five things people use instead, and why each one fails
The glazing itself. Acrylic and polycarbonate dome units lose impact strength over their service life through ultraviolet exposure, thermal cycling and abrasion, and there is no field test that tells you where a given dome sits on that curve. A unit that would have held a worker at installation can be brittle enough to shatter under a knee at fifteen years, and it looks identical. Wired glass is worse than it looks: the wire is a fire-rating feature that holds fragments together, not a load-carrying element, and it is routinely mistaken for reinforcement.
A screen nobody can trace. A mesh screen over a curb is only protection if it meets the cover criteria of the applicable Part, or if it is a manufactured fall-protection screen with a published rating and an installation you can confirm was followed. A screen fabricated on site from stock mesh and self-tappers is a decoration with a load path through fasteners nobody sized.
The curb. A skylight curb is typically several inches to a foot or so tall. That height is a trip hazard, not a guardrail. Only where a curb or a rail around it actually meets the guardrail criteria of the applicable Part - the height band, the top rail load applied in any outward or downward direction, the midrail - does the curb protect anyone, and that is a measurement rather than an impression. The library's guardrail card carries those criteria.
Awareness. Paint, tape, cones, a photograph in a briefing, a line of chalk. Every one of these depends on a worker seeing the hazard at the moment they are least likely to be looking at their feet, which is when they are backing up with a load. Marking is required on covers and it is useful, but it is a supplement to a physical protection, never a substitute for one.
A harness that will not close its clearance. This is the subtle one. Arrest at a skylight is legitimate, and it only works if the fall distance available below the opening is greater than the system needs. Below a skylight the available distance is the full interior height of the building to the floor or to the machinery under it, which sounds generous and often is not, because the anchorage is usually a long way inboard and low. Compute it rather than assuming the drop is large. The library's clearance card carries the stack-up and the reason people get it short.
What a cover has to be
If the protection is a cover, the criteria are specific and they are not what a crew usually builds.
Under 29 CFR 1926.502(i) for construction, a cover has to support without failure at least twice the weight of the workers, equipment and materials that may be imposed on it at any one time; where vehicular traffic can cross it, the criterion instead is twice the maximum axle load of the largest vehicle expected to cross. It has to be secured to prevent accidental displacement by wind, equipment or workers. And it has to be colour coded or marked with the word HOLE or COVER. 29 CFR 1910.29(e) carries the general industry equivalent: capable of supporting at least twice the maximum intended load, secured, and marked.
Two details in that wording get missed and both run in the dangerous direction.
The factor of two is already the standard's, and it is applied once. You establish the intended load, you double it, and that doubled figure is the capability the cover must have. You do not then add a second factor because it feels safer, and more importantly you do not treat "it held me when I stood on it" as evidence of compliance, because holding the intended load once is exactly half of what the criterion asks for.
"Secured" is a wind requirement as much as a foot requirement. An unsecured sheet over a roof opening is a sail with a hole under it, and the way it fails is that it moves in the night and the marking is now over solid deck while the hole is bare.
The cover spec for one opening
A 4 ft by 4 ft curbed opening on a low-slope roof, cover needed for a two-week period while a replacement unit is on order. Every load figure below is an estimate of intended load for this job and should be re-established for yours.
| Line | Value | Why |
|---|---|---|
| Workers who could be on it at one time | 2 | Realistic for a two-person crew crossing together, not the minimum case |
| Weight per worker with tools and PPE | 250 lb | Illustrative working figure; use your own crew's realistic loaded weight |
| Material that could be set on it | 150 lb | A bundle staged during the unit swap |
| Intended load | 650 lb | 2 workers at 250 lb plus 150 lb of material |
| Standard's factor | times 2 | The factor required by 1926.502(i), applied once and not compounded |
| Required capability | 1,300 lb without failure | This is the number the cover must carry over its span |
| Clear span | 4 ft, plus bearing onto the curb on all four sides | The capability above is meaningless without the span it is carried over |
| Who owns whether a given sheet does that over 4 ft | not you | A material and thickness that carries 1,300 lb over a 4 ft span is a structural question; take it from a manufactured cover's published rating or from an engineer, not from what is on the truck |
| Securing | mechanically fastened to the curb, all four sides | Prevents wind displacement and prevents a worker sliding it |
| Marking | HOLE or COVER on the top face, legible | Required, and the last line of protection rather than the first |
| Not rated for | any wheeled equipment | Vehicular crossing is a separate criterion at twice the maximum axle load, and nothing about this cover addresses it |
The failure mode here is precise and common. A crew cuts a sheet of whatever is on the truck, lays it over the curb, sprays an X on it, and it now looks exactly like a compliant cover. Two weeks later a different trade steps on it. The marking made it more dangerous rather than less, because the marking is what told the next person it had been engineered.
The other half of the failure is the span. A material that carries 1,300 lb across 2 ft may carry a fraction of that across 4 ft, and a cover sized by the load alone with no attention to span is the most common way a cover that "meets the number" does not.
What changes the answer
The unit is rated and labelled. Some manufactured skylight assemblies are tested to a fall-protection criterion and carry a label. That rating belongs to the unit as manufactured and as installed, in its original condition. It does not survive a re-glaze with a generic dome, it does not survive fasteners that have been out, and it does not transfer to the identical-looking unit two bays over that was replaced by a different contractor. Documentation from the manufacturer plus the building's own records, or treat it as a hole.
Snow or standing debris. A skylight under snow is not a covered hole, it is a hidden one, and the correct response is to establish where every opening is from the building's records before anyone walks the roof, not to probe for them.
The work is at the skylight rather than near it. Servicing or replacing the unit means the protection has to survive the opening being open, which is a different plan: the cover comes off and something else has to be in place before it does, not after.
How to tell you got this right
Walk the roof once before the work and once after, and count the openings against the building's records rather than against memory. The number that matters is not how many you protected, it is whether any opening on the roof is currently unprotected, and those are different questions the moment a cover has been moved to get a unit through.
Then check the one thing that decays: pull on each cover's fastening. A cover that can be slid by hand can be slid by wind and by a boot, and it will be, on the day the person crossing it is not from your shop.
References
- 29 CFR 1926.501(b)(4), construction fall protection for holes including skylights, and 29 CFR 1910.28(b), the general industry counterpart with its lower trigger height.
- 29 CFR 1926.502(i) and 29 CFR 1910.29(e), the cover criteria including the factor of two, securing, and marking.
- Manufacturer documentation for any skylight or screen claimed to carry a fall-protection rating, plus the building's roof records for locating openings.
- See related: the library's cards on what a guardrail has to withstand, on computing fall clearance, and on fragile roof surfaces.