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From SCDigest's On-Target E-Magazine

- July 17, 2013 -

Supply Chain News: The Fatigue Factor in Labor Management and Engineered Standards

Many Companies Apply Simple Flat Allowance, but More Nuanced Calculation is Usually Better; Personal, Fatigue and Delay Factors

SCDigest Editorial Staff

The essence of Labor Management Systems in distribution is the calculation of goal times for each task a worker performs, based on the specific details and ergonomics of that piece of work (discrete engineered standards).

But there are certainly many nuances to standards development and resulting goal time calculations. One of the most important of those is how so-called "fatigue" factors are applied to standards, under the logical assumption that as a shift proceeds, workers are inherently likely to be less productive as they tire.

SCDigest Says:

Companies should also have a bias towards simplicity, such that the approach is both fair and understandable to DC workers.

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SCDigest asked several LMS experts for their thoughts on the process, and as with many issues in supply chain its clear LMS users have a number of considerations to work through to get this right.

It starts with understanding that fatigue is almost always factored into standards overall from the get go, says Mark Messinger, director of services for labor management at Manhattan Associates.

"All companies with engineered standards include a fatigue factor, as standard industrial engineering practice," Messinger says. In other words, standards are first developed based on how long the task should take in sort of unconstrained mode, but then modest relaxation of the goal times is then applied based on the fact engineers know there will be some fatigue, Messinger says.

He added that there are standard industrial engineering tables that are used to apply this factor based on task type, usually adding a 3-5% factor for expected fatigue.

It gets a little bit more complicated after that.

For example, fatigue is often combined with other factors that are used to relax goal times, generally grouped under what are called Personal, Fatigue and Delay (PF&D) allowances.

Beyond fatigue alone, "Personal time is generally considered to be about 5% of the working day for all task types and delay time [factors in DC processes that get in the way of doing a task] typically ranges from 2% to 4% by task type," according to Tom Stretar, a director at consulting firm enVista.

Stetar observes that there are many factors specific to a given DC operation and task that have to be considered to come up with the right fatigue allowances. Those include physiological factors (weights of products being handled, posture required for the task, etc.), psychological factors (concentration level required, level of monotony), and environmental factors (how hot it is inside the DC).

Nafe Hagen of JDA Software offered the following example of how these differences play out in practice: "A case picker on a double pallet jack in a general merchandise warehouse would and should have a different fatigue allowance calculation than a putaway driver on a forklift in a freezer warehouse," Hagen told SCDigest. "The case picker exerts a lot of physical effort handling cases whereas the forklift driver has less physical fatigue but the environmental fatigue factor is higher."

The purpose of all of this, says Manhattan's Messinger, is to provide a standard that is fair and equitable for worker and company.

The PF&D approach is "especially useful in environments where the amount of time worked or amount of weight lifted can vary. It can also be used to give an additional allowance at certain times of day, for example in the heat of the afternoon," Messinger told SCDigest "If these types of variability are present in your distribution environment, what we call progressive PF&D is a good way to account for that variance. If this variance is not significant, fatigue time can simply be applied evenly throughout the day."

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Some companies choose to simply set a modestly generous fatigue allowance and then not bother with additional allowance for say delays or environment, says Hagen - but while this approach may be easier, it usually isn't optimal.

Hagen does not believe that a single basic allowance across tasks is appropriate but rather that companies should "determine the proper allowance percent and apply it to each task performed."

How to Get PF&D Right

enVista's Stretar notes that the level of sophistication of a company's labor management software has a big impact on how far that company can take the PF&D approach.

"Without a true LMS, all you can do is apply a flat percentage by task type," Stretar told SCDigest. "The most advanced LMS systems have capabilities for escalated or ramped fatigue or an incremental or step fatigue when thresholds are met based on factors such as the number of hours worked and total cumulative weight picked."

Messinger adds that "PF&D can either be a gradual slope by hour of the day or weight lifted, or it can be done at certain thresholds of work performed. We have customers who do it each way."

He adds that one Manhattan labor management customer set its PF&D based on some obvious thresholds. The company had a group of part-timers who only worked four hours a day, and full-timers who usually worked eight hours but regularly worked overtime. So the company set three different thresholds: up to four hours worked, workers were a lot a certain PF&D allowance. Between four and eight hours, they received a little more. Beyond eight hours they received even more.

"It was simple to explain and a big win for their associates," Messinger said.

"If you go with progressive PF&D, you need to do some calculations to make sure you're giving the right total amount of PF&D on average," Messinger added. "In other words, progressive PF&D should not be a blanket "loosening" of the standards, relative to using a flat PF&D amount throughout the day, but rather a intelligent approach to creating fair standards but not being overly generous."

The bottom line: getting Personal, Fatigue and Delay allowances for labor management in distribution right takes more work and expertise than just flat lining a given percentage allowance over all tasks. Taking a more intelligent approach that looks at the specifics of tasks, progress during the day and other factors does a better job of getting such factors more accurate for associates - and distribution operations.

But companies should also have a bias towards simplicity, such that the approach is both fair and understandable to DC workers.

Management should be very involved in these decisions, even if using outside consultants, as getting this right can have be a big factor in costs and associate satisfaction with the program.

What are your thoughts and experience with Personal, Fatigue and Delay factors? Let us know your thoughts at the Feedback section below.

Recent Feedback

Nice piece on the often overlooked "F" factor of PF & D. The Fatigue factor should vary from work task to work task.

This approach goes back a long way, but was nicely documented by the late Dr. Benjamin Niebel in his seminal work measurement text "Motion and Time Study", which is regarded as one of the foundational reference books for the work measurement field. This textbook was also summarized and included as a chapter in the Handbook of Industrial Engineering. The fatigue reference tables scientifically generated by the International Labour Organization (Geneva, Switzerland) were applied for differentiating fatigue factors from work task to work task in Niebel's text.

Many practictioners in recent years have strayed from this, which is dangerous, and applied "blanket" fatigue factors the same for all tasks, mainly due to the abandonment of teaching of work measurement in the industrial engineering curricula in U. S. universities. As for progressive fatigue factors, while this certainly can be handled by a robust LM software calculation, I agree that it has to be simple, applied clearly for a reason, and be understood and accepted by associates and supervisors. Also, I might add that "D" should also vary from work task to work task and kept up with in time studies, as the incidental delay that results can vary widely. Thanks for a good piece on work measurement!

Steve Johnson
Principal
Johnson Stephens Consulting
Jul, 17 2013