Walking the Straight and Narrow
Providing a safe work surface is an important part of overall worker safety. OSHA regulations require that all work surfaces be completely decked or planked, allowing no more than a one-inch gap between two planks laid side-by-side, or between the plank and an outside vertical member. However, there are three scenarios where exceptions are made: 1) during scaffold erection, 2) in demonstrated confined areas after scaffold erection is completed, and 3) when planking is used solely as a walkway. Since most scaffold manufacturers use a five-foot-wide frame, what exactly does this mean?
First, let's talk about wood plank. There are two types of wood plank: manufactured (i.e., laminate) and sawn plank. Sawn plank is typically produced from Southern yellow pine, Douglas fir or spruce. It is available rough-sawn or dressed, which is differentiated by thickness and the amount of surface treatment. Nominal two-inch rough-sawn dry lumber is usually 1-3/4 inches to 1-7/8 inches thick, and receives no surface treatment. Nominal two-inch dressed lumber is surface planed on four sides and commonly 1-1/2 inches thick after kiln drying.
Wood planks are graded by a certified lumber grader and must meet the minimum grade of DI65 or better to be considered scaffold grade. Common lumber is not considered scaffold grade. The scaffold grade designation is critical because most lumber is graded for other uses, such as floor joists where the board face is vertical and loads rest on the edge of the board. Scaffold plank, on the other hand, is tested for use horizontally with loads bearing on its face.
Most scaffold-grade plank nominally measures two inches by 10 inches, while actual dimensions are typically 1-1/2 inches by 9-1/2 inches. This applies to both sawn and manufactured plank. With this being the usual case, it will take six planks to completely deck a five-foot-wide frame.
Many times, in addition to workers, heavy tools and building materials are placed on the plank. Contractors need to remember to review the plank's load chart that is part of the OSHA Regulations for Scaffolding to ensure the maximum load capacity of the plank is not exceeded.
In the case of laminated plank ? a manufactured, wood plank product that's made from layers of thin, dried veneers ? it is both visually and ultrasonically graded to meet specific standards.
|Full Thickness Undressed Lumber||Nominal Thickness Lumber|
|Working Load Lbs./Sq. Ft.||25 50 75||25 50|
|Permissible Span (ft.)||10' 8' 6'||8' 9'|
Similar safety rules apply for manufactured walkboards as well. Walkboards are typically made from aluminum with either a plywood top or aluminum top and measure 19 inches wide. Load-bearing capacities are normally stamped right on the walkboard and are usually either 50 pounds per square foot (psf) or 75 psf, depending on the length and width of the walkboard. Capacities for both plank and walkboards assume uniform loading to reach their rated capacities, not point loads. Point loads have the entire load centered in one spot instead of a uniform distribution of the weight along the entire length and width of the plank or walkboard.
Other walkboards can be constructed of steel, or steel and expanded metal. Use of these materials will allow contractors to attain higher load capacities than are normally attainable with either wood or manufactured plank.
Selecting Scaffold Plank
When buying or renting scaffold frames and planking, contractors need to consider their needs carefully and be prepared to answer three important questions.
- What materials will be used on the job?
- How will those materials be stocked and stored?
- How many workers will be working from a scaffold plank at one time?
Masonry work generally is considered light-duty (25 psf) or medium-duty (50 psf) loading, but this doesn't always hold true. A scaffold plank that must hold palletized brick or block, or accommodate several workers at a time, may need to be rated for heavy-duty (75 psf) loading.
Instead of assuming uniform loading, contractors should assess their material loading process and determine how much actual point loading they have. For example, each worker with tools is considered a 250-pound load. OSHA and ANSI standards define one-person loading as 250 pounds placed at the center of the plank or deck span. Two-person loading is 250 pounds placed 18" to the left and right of midspan. Three-person loading assumes 250-pound loads at each of the points noted above, one in the center and one 18 inches left and right of midspan.
The distance a plank spans between supports is also important. The permissible span depends on the size, strength and stiffness of the plank, as well as the loads imposed.
Proper Installation and Use
Selecting adequate plank is only part of the overall plank safety. Plank also must be correctly installed and used properly to help prevent accidents.
Ideally, planking should come within a few inches of the wall, although OSHA does allow a distance of up to 14 inches. Adjacent parallel planks should be no more than one inch apart to prevent workers or tools from falling through any gaps. All planks should be securely tied to supporting brackets, bearers or ledgers to minimize plank movement. Plank ends should extend six to 12 inches beyond the supporting members and overlap other planks by at least 12 inches, with the overlap at the supports, not the midspan.
Although not equipped to perform sophisticated deflection testing on used plank, most mason contractors can visually monitor their plank for excessive deflection. As a general rule, Southern yellow pine, Douglas fir and manufactured plank that deflects under loading more than two inches for a 10-foot span, one inch for an eight-foot span, or 3/4 inches for a seven-foot span is considered overloaded. When this occurs, the load should be redistributed or, if the planks are new, they should be rejected.
Maintaining Scaffold Plank
Mason contractors should treat scaffold plank as the important safety equipment it is. Here are a few tips:
- Because impact loads can affect a plank's serviceability, don't drop or throw it.
- Load planks carefully and store them in a safe place, away from potential damage from forklifts or other machinery.
- Don't use the "gorilla jump" testing method.
- Laminated veneer lumber is most susceptible to damage.
- Bank plank ends with metal to prevent splitting.
- Clean mortar off plank and store it properly between jobs.
- Don't use plank for mud sills and then reuse it on the scaffold, as this will overload and weaken it.
- Routinely inspect plank for visible damage. Never paint scaffold plank since it can conceal defects.
- If notches, cracks or saw kerfs are found in plank, they must be cut shorter to eliminate hazards.
- Metal banding or rodding may reinforce plank with splits.
Be aware that not all damage is visible. Plank that has been overloaded or subjected to severe impact may be weakened, even if it's apparently intact. Some people advocate periodic retesting and recertification of scaffold plank to detect such damage, but this procedure is neither required nor widely practiced. Still, if a contractor suspects that a plank has been overstressed and has any doubts about its condition, it should be rejected.
Consider the reduction in a plank's load-carrying capacity caused by high moisture content (above 19%). If plank is used green or treated with fire-retardant chemicals, refer to grading standards for any necessary adjustments to safe spans and loadings.
Rainwater on the face surface of plank normally has little effect on its moisture content, but water entering the ends of plank can. Plank ends should be sealed, while the ends of cut plank should be resealed. Check the weight of plank that gets thoroughly wet on the job. If a plank is unusually heavy, it may have absorbed enough water to negatively affect its strength.
Manufactured wood plank may be more susceptible to moisture absorption than solid-sawn plank. If manufactured wood plank gets soaked, or even if it is exposed to prolonged periods of high humidity, consult the equipment's manufacturer.
By treating your plank and walkboards with the same respect you might other safety equipment, your investment will last and the safety of your crewmembers will be increased.
About the Author
Chuck Hutchinson is the Vice President of Sales & Marketing for Bil-Jax, Inc. He also has over 28 years of construction equipment manufacturing and distribution experience.