Choosing the Perfect Work Access Lift
Once you have completed your shopping list of work aids to place on the platform, you can begin to add up the total weight on board.
- By Henry J. Renken
- Oct 01, 2012
Safety is the prime purpose of all work access lifts. They are designed to move production personnel, their tools, and materials to ergonomically sound work positions to enhance both worker safety and efficiency. Production tasks are broadly varied and may include welding, painting, assembly, fabrication, inspection, and maintenance.
Because each application is unique to the task being performed and the object being worked on, each lift must be custom designed to the specific application. This guide is designed to help you organize and prioritize your requirements so they may be resolved into appropriate specifications for your work access lift.
Platform Size and Configuration
1. Overall size: The first consideration is the overall room required for personnel, tools, and work aids such as tables, work benches, jib cranes, tool cribs, or boxes, and any other items that will enhance worker efficiency. Be sure the surface area is large enough so personnel are not crowded or cramped. Adequate maneuvering room is assured only when everything on the platform with the worker is accounted for.
2. Cut outs and or platform extensions: When a straight-sided platform does not interface well with the item being worked on, the footprint of the lifting mechanism beneath the work surface often dictates whether it makes more sense to provide platform extensions or to provide platform cut outs. Sometimes both are needed. Extensions may be permanent, fold down (hinged), or powered horizontal extensions. Obviously, the more complicated options are more expensive. Be sure the lift manufacturer is given an accurate dimensioned sketch of the platform profile that is required.
3. Platform surfaces: These may be embossed safety tread (which is most common), smooth steel with silica sand for slip resistance, open grating, or wood surfaced. The materials can be carbon steel, stainless steel, or aluminum and may be finished with industrial enamel, epoxy paint, zinc finishes such as Galvacon, or stainless steel finished with products such as Steel-it. Hot dipped galvanizing is not recommended because it may cause warping. Platform extensions may be of different material than the basic platform.
4. Shear point elimination: When a platform is being elevated to a work height, it is important that personnel on the platform are protected from any shear point that may be created between the edge of the moving platform and the adjacent work object. There are many options. One is to simply position the lift to create a minimum of a 4-inch gap between the platform and the work object. Controls can be positioned on the platform so that the operator must stand back from the working edge in order to elevate the platform. Hinged platform extensions can be used to create a large gap during platform elevation and then lowered to the horizontal position when work is being done. Vertical rising guardrails, swing gates, or removable handrails can be used during elevating operations. Mobile units may be elevated away from work object and then propelled next to the work object after the desired work height is achieved. In some instances, simple signage to stand back and hold onto guardrails during elevating operations may suffice. Industrial engineers can be very creative as long as they remember to address this issue.
5. Safety options: There is a large array of safety options to consider. Guardrails can be designed in any configuration, and they can be equipped with many styles of gates or chains to suit the applications. They can be vertical folding, swinging, removable, and retracting into the platform. There can be electrical interlocks to prevent vertical movement unless guardrails or gates are in place. Electric eyes can be used. Bellows can be used to cover scissor leg assemblies. Personnel harnesses can be used. Common sense is the primary guide.
6. Other options: Work aids such as those mentioned in paragraph 1 above can be added by either the customer or the lift manufacturer. Jib cranes that cantilever loads over the edge of the platform must be approved by the manufacturer to be sure tipping moments are acceptable. Portability/mobility options must be added by the lift manufacturer and are discussed below.
Once you have completed your shopping list of work aids to place on the platform, you can begin to add up the total weight on board. Add the weight of the tools, materials, and work aids. Add the weight of the live load (personnel) and do not forget that, every once in a while, extra supervisors may wish to come along.
Most manufacturers size their lifts in 2,000-pound increments, so you can round up to the next multiple of 2,000 pounds. Do not worry about adding any safety factor because reputable lift builders build to ANSI code MH29.1, which requires 3 to 1 safety factors.
Determine the lift height that you must reach. Subtract the lowered height of the stored platform lift, and that will yield the travel required. Note that most single scissor lifts only can provide vertical travel that is 75 percent of the platform length or less. If the platform length is too short for the desired travel, then you'll have to go to a multiple-scissor lift. This is fine, except the cost of multiple scissors is greater than the cost of single scissor lifts, so if you are close, it may be less expensive to get a platform longer than you need.
Also, multiple-scissor lifts have a higher lowered height than single-scissor lifts; therefore, a step may have to be added on the end or side of the lift. If you are going to add a portability feature, be aware that this may add 2 inches to 10 inches to the lowered height, depending upon the specific features required.
Typical power requirements are 230/460 v, 60 Hz, 3 phase. Other voltages are available on request. The power unit locations are most commonly beneath the platforms, but larger units may require locating the bulkier power units adjacent to the lifts or, in some cases, mounted on the platforms.
The only kind of controls allowed in ANSI MH29.1 for rider scissor lifts are constant pressure push buttons located on the platforms. They may be permanently mounted in fixed locations or they may be on coil cords. Automated "call-send" buttons are not allowed. Manual lowering valves on the base of the unit may be added for lowering if there is a power outage and limit switches for the top of travel also may be added.
ANSI MH29.1 does not allow for drive-around portable lifts, such as self-propelled work platforms covered by ANSI 92.6. The MH29.1 units are limited to self-propelled units that are guided in some way, such as on tracks.
Units equipped with fork pockets or lifting eyes for pick and place portability are common. Manually propelled scissor lifts with casters and floor locks are available. The uniqueness of each work access lift application rules out any standard lift model, but with a little forethought and problem analysis, excellent solutions are fairly easy to achieve. The advantages of lifts over ladders and scaffolding are obvious, and the benefits of worker comfort, efficiency, and safety mean the payback period on these investments is usually very short.
This article originally appeared in the October 2012 issue of Occupational Health & Safety.
Henry J. Renken is president of Advance Lifts, Inc. (www.advancelifts.com), one of the leading U.S. dock lift manufacturers. The company's product lines include production lift tables, tilters, turntables, dumpers, and stretch wrappers. The company has built many configurations of work access lifts and can help clients design one for their applications.