Mark Vaughns
Director of Product Safety & Reliability
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JLG Industries
A common question the JLG® Safety team gets asked by equipment operators is: “Are we allowed to utilize cribbing under aerial lifts?” This topic comes up often because these machines today are only rated to work on firm, level surfaces (with 5 degrees or less of grade) — and, most job sites aren’t flat.
More often than not, aerial lifts need to \be able to work on uneven or inclined terrain.
This leads operators to coming up with alternative ways to make the equipment be able to work in these types of situations, such as cribbing. Cribbing is a temporary wooden structure purpose-built to provide a level work surface for an aerial lift to operate from, making sure the machine is working within safe limits.
Although not an ideal solution, the answer to the question is: Yes, cribbing can be utilized under certain aerial lifts. However, it’s very limited, and it should only be done following the manufacturer’s recommended guidelines — and you should not use cribbing on any aerial lift not approved by the original equipment manufacturer. Cribbing instructions for approved JLG aerial lifts can be found in the JLG Cribbing Manual.
Below are excerpts from the JLG Cribbing Manual to help you better understand how to crib an approved JLG aerial lift on your next job site.
Follow all safety precautions
It is important to follow all of the manufacturer’s safety precautions for cribbing an aerial lift. This includes making sure that the job site’s ground conditions are able to support the aerial lift’s maximum load. Cribbing should only be used on surfaces capable of supporting the weight of the machine without cribbing.
Machines that are on a slope greater than 5 degrees (9%) should not be cribbed, and cribbing should never be used over a hole, depression or bump in the supporting surface.
Only crib two wheels on the same side or one end of the aerial lift; cribbing in two directions should not be used.
And, you should not drive the machine onto the cribbing with the platform raised; wait to raise the boom above horizontal until the machine has been leveled with the cribbing.
Conduct a workplace inspection
Prior to constructing and using cribbing, it is important to conduct a workplace inspection to determine if the site is suitable for safe machine operation.
During the inspection, be aware of — and avoid — the following hazardous situations when using cribbing:
- Unstable surfaces that could shift under cribbing
- Surfaces that cannot support cribbing
- Slippery surfaces that could cause cribbing to slide or skid
- Slopped surfaces of greater than 5 degrees
- Drop-offs or holes
- Raised ground, bumps or uneven surfaces
The workplace must be inspected before each use of the aerial lift to determine if any changes have occurred that could affect the safe operation of the machine.
Construct cribbing to manufacturer’s specifications
It is important to only use cribbing that is built to the manufacturer’s specifications.
JLG specifies that cribbing for its approved aerial lifts should be constructed to the following guidelines:
- Use APA certified plywood sheets. Each sheet must be a minimum of ¾-in (1.9 cm) thick and measure a minimum of 24-in. by 24-in. (60.9 cm by 60.9 cm).
- Plywood sheets must be layered together with a minimum of 24-in. (60.9 cm) of overlap for joints
- Layers are to be secured with 6D ring shank nails, placed a minimum of 8-in. (20.3 cm) on-center edge and face.
- You should use 8D ring shank nails for plywood over 1-1/8-in. (2.8 cm) thick.
- Each end of the cribbing is to have a chock that extends the full width of the cribbing. The chock must be a minimum of 6-in. by 6-in. (15.2 cm by 15.2 cm).
- Ramps are to be constructed in a series of steps. Each step should be a minimum of 12-in. (30.4 cm) long.
- The maximum total ramp height when cribbing one end should not exceed 8-in. (20.3 cm). The maximum total ramp height when cribbing on one side only should not exceed 6-in. (15.2 cm).
- Make sure that the machine wheels have 24-in. (60.9 cm) square surface or twice the tire width, whichever is larger, to rest on when the aerial lift’s platform is elevated.
- When cribbing one side only, the minimum length for the top surface should be at least equal to the wheelbase +24-in. (60.9 cm) or twice the tire width whichever is larger.
- Cribbing must not be constructed to accommodate turns or curves.
- Check the cribbing material for cracks, pitch pockets, dry rot or knots, which can weaken the wood and cause uneven compression. Do not use any wood that exhibits these features.
Follow the instructions for safe use
In addition to completing operator training specific to the aerial lift you are operating, you must also be trained in the safe use of aerial lifts on cribbing.
Specific to approved JLG aerial lifts, guidance for cribbing includes, but is not limited to, the following instructions for use:
- Make sure the JLG machine has been modified with a DRIVE/STEER DISABLE lock-out switch that disables the drive/steer function.
- With the machine in the stowed position, drive onto the cribbing. The base of the machine must be level on the cribbing, and both tires must be centered on the cribbing — not off to one side.
- Move the DRIVE/STEER DISABLE switch to lock out the drive/steer function. Ensure that these functions are disabled prior to elevating the aerial lift’s platform. You can test this by carefully attempting to drive off the cribbing in the direction opposite of the chock.
- Operate the machine lift function according to the aerial lift’s specific Operation and Safety Manual.
When work at height is completed, position the boom in the stowed position, move the DRIVE/STEER DISABLE switch to reengage the drive/steer function and drive off the cribbing.
For additional details about cribbing approved JLG aerial lifts, click here.
The safe use of aerial lifts on job sites is very important to JLG. To help you and your crew be informed on best practices for operating this type of equipment, JLG provides information on everything safety-related, from inspections and manuals to how-to’s and manlift safety videos. To access essential aerial lift safety, product and training information relating to JLG equipment, click here.
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