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Platform > Planking
According to Federal labor statistics, more scaffold accidents are attributed to planking giving way than any other
cause. Additionally, almost 25% of workers receive no safety training for erecting scaffolds and installing work platforms.
The Planking portion of the OSHA Scaffolding eTool is intended to address the need for specific
and accurate information about arguably the single most critical scaffolding component: The lumber from which platforms are made.
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Lumber grading |
Scaffold-grade lumber is meant to withstand forces not imposed on
ordinary, construction-grade wood (which is only two-thirds the capacity of scaffold-grade). Using construction-grade
lumber on a scaffold platform not only violates OSHA standards, but is also an unsafe practice and an invitation to a deadly accident.
The quality of scaffold-grade lumber
is measured by:
- the number of rings per inch (6 or more),
- the slope of the grain (1 inch to the side for every 16 inches along the length of the board for Douglas Fir, 1/14 for Southern Pine), and
- the number of defects, such as knots and notches.
Solid sawn wood used for scaffold planks should follow the grading rules of a recognized lumber
grading association or an independent lumber inspection agency, and be identified by that
agency or association's grade stamp (see examples below).
Such organizations and their grading rules must be certified by the Board of Review of the American
Lumber Standard Committee, per the U.S. Department of Commerce.
OSHA does not inspect lumber; therefore, any scaffold planking stamped "OSHA Approved" is, at best,
misleading, and should not be assumed to meet the standard on the basis of that stamp alone. An inspection agency can
claim that its product meets OSHA requirements (see example at right). However, because a scaffold plank may still be in service long
after the grade stamp on it has faded, workers should pay attention to the quality and condition of the
planking, whether it bears a stamp or not. |
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Wood Condition |
As wood ages and reacts to usage, it will begin to show checks,
splits and notches. These will vary in degree depending on the loads a plank has carried, the weather it has been exposed to, how long it has been in use, etc.
| Planks with splits
(cracks that go clear through the wood) more than a few inches in length should not remain in service, as they may no longer maintain the necessary load-bearing capacity. |
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| Planks with checks
(cracks that are on the surface only and do not go clear through the wood) should be watched, as the checks may develop into splits over time. |
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| Notches
(small checks on the ends of a plank) should also be watched over time, as they can lengthen and deepen until they become splits. |
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| Scaffold planks that have accumulated
layers of paint, plaster, etc. are not permitted to remain in service [1926.451(b)(9)],
because it is impossible to determine their condition. Dangerous splits may be hidden underneath these coatings. |
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| If a scaffold plank has been used as a mudsill,
it should not be returned to service on a platform. Moisture from standing water, as well as point-loading from the scaffold legs, may
have weakened it, making it unable to bear the weight that will be placed on it. |
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Allowable Spans |
The span of a scaffold plank is the distance it runs between
supports. The longer the span, the more deflection (bend) it will have, and therefore, the less its load-bearing capacity
will be. For 2 x 10 (nominal) or 2 x 9 (rough) solid sawn wood planks, allowable spans for a given load are shown in the table below:
Maximum
Intended Load |
Maximum Permissible Span Using Full Thickness Lumber |
Maximum Permissible Span
Using Nominal Thickness Lumber |
| 25 lbs./square foot |
10 feet |
8 feet |
| 50 lbs./square foot |
8 feet |
6 feet |
| 75 lbs./square foot |
6 feet |
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Because nominal thickness lumber is not cut to its exact dimensions, nominal 2 x 10 is really
more like 1½ x 9¼. As a result, it does not have the same load-bearing capacity of full thickness lumber.
For fabricated planks and platforms, maximum spans are to be recommended by the manufacturer based on the following table:
| Rated Load Capacity |
Intended Load |
| Light-duty |
25 lbs. per square foot applied uniformly over the entire span area |
| Medium-duty |
50 lbs. per square foot applied uniformly over the entire span area |
| Heavy-duty |
75 lbs. per square foot applied uniformly over the entire span area |
| One-person |
250 lbs. placed at the center of the span (total 250 lbs.) |
| Two-person |
250 lbs. placed 18 inches to the left and right of the center of the span (total 500 lbs.) |
| Three-person |
250 lbs. placed at the center of the span and 250 lbs. placed 18 inches to the left and right of the center of the span (total 750 lbs.) |
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Allowable Deflection |
To assure that scaffold planking remains within its safe load-bearing
capacity, it may not be allowed to deflect more than 1/60th of its span between supports [1926.451(f)(16)].
The table below shows how little deflection that is.
| Span of Plank Between Supports |
Calculation |
Maximum Permissible Deflection |
| 10 feet |
120 inches/60 inches |
2 inches |
| 7 feet |
84 inches/60 inches |
1-3/8 inches |
| 5 feet |
60 inches/60 inches |
1 inch |
Workers should be aware of deflection because it can indicate when a platform is overloaded, and a
competent person should not allow employees to occupy a platform that exceeds the 1/60th ratio. The animation below
illustrates the danger posed to workers by planking that has been overloaded.
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