Adjustable work tables

REACHING THE HEIGHTS

By Chris McIntyre

We don't buy shoes three sizes too big and compensate by tightening up the laces. Nor do we buy everyone the same "average size" shoes and hope that everyone will make do. Likewise, workers shouldn’t be expected to work comfortably and efficiently at work tables that are not suitable for their physical dimensions. Whether it is fine electronics assembly or rebuilding engines in a machine shop, a one-size work table clearly does not fit all. Ideally, a work table should provide the same personal fit as a good pair of shoes.

Height-adjustable work tables can help to reduce work-related injuries and improve worker productivity. Here’s how to select a work table to fit the needs of your company and your workers.

Although it’s almost cliche, people do come in all shapes and sizes. Take a look around your facility and you'll see employees of vastly different physical dimensions. Does your organization provide work tables that account for these size variations? Or, like in many workplaces, are the work surfaces a standard height that cannot be changed?

Fixed height work tables force many workers to alter their postures to "fit" their work. For example, a petite female has to raise her arms from the shoulders, as if having a constant "shrug". Conversely, a tall male must bend his back to work at the same work table. Working in such awkward body postures for even short periods of time is physically strenuous, resulting in fatigue, discomfort and reduced job performance. More important, long-term exposure to such postures has been closely linked to the development of work-related musculoskeletal disorders.

A better, more ergonomically sound approach is to give workers the ability to work at their preferred postures by providing height-adjustable work tables. When individual employees can adjust the work table height to optimize their posture, the muscular demands of the work are reduced and job performance can actually improve. Height adjustability also allows the worker to alternate between sitting and standing, another valuable method of preventing fatigue. The result is a more physically efficient and productive worker who is at a lower risk of injury.

HOW TO SELECT

There are many "ergonomically designed" work tables on the market, and this can make the selection process appear overwhelmingly complicated. It shouldn’t be. By determining your company’s particular needs, you can make finding the right product a simple process.

Determine who will be using the work tables. Many purchasers tend to look only at the mechanical and aesthetic features of adjustable work tables. However, don’t forget the objective -- to allow the table height to be customized to your workers. This is becoming increasingly important with the continuing changes in the ethnic makeup, gender and age of workers in today’s workplace.

In order to design or purchase appropriate work tables, you must have information regarding the physical dimensions of your workers. While it is possible to measure your current employees, the physical characteristics of your work force will likely change over the table’s lifetime. The preferred method is to use anthropometric tables (charts of body measurements for a given population), which can be obtained from many ergonomics textbooks and resources. Ensure that you use information based on a population similar to your employees: anthropometric tables based on male army recruits will not be suitable for a female work force.

Determine the work to be performed. There are three key issues to consider:

* The size of the products being handled can influence the posture the worker has to adopt. For example, if the product is 14 inches high on a 32 inch high work table, the actual distance of the hands from the floor is 46 inches.

* The weight and dimensions of the products will affect the load-bearing requirements and surface dimensions of the work table.

* The type of work being performed will also influence the optimal working height. As a general rule, precision or inspection work should be two inches below elbow height; light assembly work should be two to four inches below elbow height; heavy work should be four to eight inches below elbow height.

Determine if the work is to be performed in a seated or standing position, or both. For seated work, a fixed-height work table may be quite acceptable when working with products of similar sizes if a height-adjustable chair is provided. However, most chairs have a relatively small range of vertical height and can only be properly adjusted to lower work tables with very small variations in part height. Also, very tall or very short workers may not be able to properly fit the fixed-height work table, even with an adjustable chair.

For standing work, an adjustable work table is critical because a fixed height is frequently too high or too low for many workers.

For "sit/stand" work, both the chair and the work table will need to be adjustable to allow for optimal working posture.

Determine the features required. Adjustment mechanisms should make adjusting the table easy. The controls must be easy to reach, easy to understand and easy to use. Otherwise, the employees will likely not adjust the work table. Spring-loaded, hydraulic or electric work tables are generally preferred to manual crank or pin adjustment systems. Also consider the type of work performed and the expected frequency of adjustments. (For example, when a task requires frequent adjustments in table height while supporting a part in the hands, a foot-operated mechanism is preferable.)

The required range of height adjustment will depend on the range in elbow height of the particular working population. In order to accommodate the majority of workers, the anthropometric range from the 5th percentile female to the 95th percentile male is typically used when both males and females will use the table. The occasional worker who falls outside this range may require individual accommodations to work comfortably at the work table.

As an example, an industrial firm specializing in small automotive components has a department where male and female workers are performing light assembly work on a five inch high part while standing. Let’s assume the anthropometric work tables for this particular population indicate the standing elbow height is 37.1 inches (5th percentile female) to 46.1 inches (95th percentile male). However, light assembly work should be two to four inches below elbow height so the resulting height range is 33.1 inches (four inches below the 5th percentile female) to 44.1 (two inches above the 95th percentile male). Finally, subtracting the five inch part height results in a range of 28.1 inches to 39.1 inches above the floor. This is the height-adjustment range you will require for this particular work table.

If the goal in this example was for the workers to be able to perform the work in either sitting or standing positions, similar measurements can be used to determine the required height adjustment ranges for both the work table and chair.

Special features ensure that the work table has the necessary power supplies, storage space, and other accessories that the workers require. Also consider table tilt options, task lighting, leg clearance, reach distances and any jigs, fixtures or balancers that may help to make the workers more comfortable and efficient.

There are several other considerations to keep in mind when introducing height-adjustable work tables into your company.

* An adjustable work table must meet the needs of both the company and its workers by considering both the current operation and possible future changes to the products, work methods or work force. Many companies have achieved this objective through the formation of "purchasing teams" consisting of individuals such as managers, employees, health and safety coordinators, engineers, purchasing agents, suppliers and outside experts.

* Resist the temptation to simply purchase a work table directly from a catalogue. Don’t hesitate to ask several suppliers for demonstration models that can then be tested and evaluated.

* Not all companies need to purchase adjustable work tables. Many organizations have access to in-house resources which can "retro-fit" existing work tables with a height adjustment mechanism.

* Finally, "ergonomically-designed" equipment is a misnomer as it implies you simply place the equipment on the shop floor and the problem is solved. The latest ergonomic features and adjustments are of little or no value if the workers do not know how or why to adjust the work table properly, or choose not to do so. Supervisors and management must also understand these issues and provide an environment that encourages such adjustment.

Introducing work tables into your organization does not need to be overwhelming. Consider who will be using the table, the type of work they will be performing, and any special features they will require to perform their work. Once you have carefully evaluated the options and found the appropriate work table, train your supervisors and employees to use the tables properly. Following this approach will ensure you make a wise investment for your company and your workers.

Chris McIntyre is the principal ergonomist for Ergonomics at Work, a consulting firm in Waterloo, Ont.

Top

Back to contents