For many, “manual material handling” (MMH) is just a fifty-dollar phrase for “lifting.” But, taken from a broader perspective, careful planning of MMH activities affect the efficiency of an operation, as well as the impact on individual workers.
Often, one of the simplest ways to reduce the cumulative, total amount of weight lifted is to eliminate double handling of objects. How many times is a part, object, supply box, container, etc., lifted or moved? Sometimes, this is not obvious until a videotape or formal time study analysis of a job is performed.
Simply moving a single box or object around a workplace can add up to several hundred pounds of unnecessary, no-value-added lifting per day. Cluttered workplaces or storage areas are notorious for needing multiple parts or objects to be removed or relocated in order to access the item needed; each of these is an unnecessary lift.
Work-in-progress or batch processed jobs often require multiple handling of parts, including repetitive packing and unpacking items into totes, bins or boxes. Continuous flow processing eliminates much of this double handling, and is consistent with just-in-time manufacturing. Organized workspaces save steps and lifting.
A second key strategy is to eliminate as many lifts as possible by converting them into low force transfers at the same elevation. Powered or un-powered rollers or conveyors are good examples of this, and even a low friction surface, such as plastic laminate or polished steel, can allow a worker to slide a box or part with relatively low force, and without lifting it.
In a case study, a company producing products in 50 pound net weight containers required their workers to check weigh five boxes every 30 minutes on a scale located approximately two feet away, and six inches higher than the production line. Since each box must be lifted and carried to the scale, then lifted and carried back to the line, this required:
2 (lifts each) x 5 (boxes) x 50 (pounds) x 2 (times per hour) x 8 (hour shifts) = 8,000 pounds (or 2 tons) of unnecessary lifting per day.
Similarly, these 50 pound boxes were carried a cumulative distance of 320 feet, which is about the length of a football field, and lifted or lowered a cumulative distance of 80 feet, which is approximately the height of a six story building.
Placing the check weight scales in-line, or mounting rollers on the scales at the same height as, and adjacent to, the line, would eliminate almost all the physical stress associated with this task, and even allow it to be classified as a “light duty” job.
Looking at a process as a complete cycle also helps improve the MMH perspective. When work-in-progress is placed into a storage tote or bin, consideration needs to be given both to how the object gets into the container and how it gets out. Bin tilters and false bottom containers help at both ends; however, smaller bins can also help. These should be designed for how far and low a worker needs to reach, rather than just the size of the storage slot in the warehouse.
The same can be said for product packaging. Consideration should be given for how the customer removes the finished product, as well as how the worker places it into the final package. Too often, short sightedness affects parties at both ends. For example, floor-loading semi-trailers are sometimes seen as a cost saving measure, as many shipments are billed by weight, and as one shipping manager told me bluntly, “I ain’t paying to ship pallets!”
But floor loading is slower and more physically demanding than unloading pallets with a fork truck at both ends, and this adds to total costs. A little communication with interim and final customers may go a long way with improving the value for everyone involved.
Proper planning of material handling tasks requires careful selection of hoists and slings, conveyors and casters, hand truck and fork lifts. A little extra planning that reduces the amount of manual handling can not only increase efficiency by reducing tasks that need to be performed or the total weight handled, but also increase the number of workers capable of performing those tasks.
Philip Jacobs, CPE, CSP
President – Jacobs Consulting, Ltd.
Saint Paul, Minnesota
This article originally appeared in The Ergonomics Report™ on 2003-09-01.