(Editor’s Note: This is Part 4 of a series on warehouse labor standards. Click here to read Parts 1-3).
Time studies and predetermined time systems are the two most accurate ways to develop labor standards.
Time studies are easy to understand. These “stopwatch standards” involve consultants timing how long it takes workers to perform different types of tasks. Actually, we’ve gone beyond stopwatches. Today, automated software programs on small terminals make it much easier to collect time study data.
Predetermined times systems are more difficult to explain. Charlie Zosel, a Vice President at TZA, walked me through some of the different pre-determined time system methodologies.
Pre-determined standards are based on tables that document how long it takes for a person to make very elemental motions. These elemental motions have times associated with them which are aggregated to define an activity.
In warehousing, Master Standard Data (MSD) and the Maynard Operations Sequence Technique (MOST) are the two most common methodologies used. MSD is more common than MOST. In production environments, where many tasks are very repetitive, Methods Time Measurement (MTM) is frequently used. Imagine, for example, putting a standard together for grabbing a pencil while sitting at a desk. MTM would break this task into “reach” (18 inches),” “grab,” and “return” time segments. MSD is somewhat less granular. It would have “obtain” as the elemental motion and just one time measurement associated with obtaining the pencil. MOST is even less granular; obtaining a pencil would be part of a larger process sequence.
Let’s move to a more relevant example, building mixed-case pallets. You can decompose this activity with MSD into the following elemental motions, each with a time associated with it: travel to the pick location on a pallet jack; walk from the pallet jack to the slot; bend to pick up the case; grab the case; walk back to the pallet jack; bend; and place the item on the pallet jack. Clearly, elemental motions have very small time units associated with them. These are called Time Measurement Units (TMUs), which equal 1/100,000 of an hour.
In the above mixed-case pallet example, MOST would not break the process down so granularly. MOST would have one time associated with traveling to the slot; all the other elemental tasks would have just one time measurement associated with them.
Even when predetermined systems are the predominant methodology for setting labor standards, they are almost always supplemented with a time and motion study in order to understand how fast forklifts (or other equipment) move.
If you examine the MSD table above, it is pretty easy to see that unless you’ve been trained, you would have a hard time using these tables. Young industrial engineers (IEs) will not provide exactly the same measurements for a process as more experienced IEs. So, there is an element (albeit a small one) of subjectivity.
Consultants who specialize in predetermined time systems will tell you that the days of spending 12 months building very granular standards from elemental motions for an entire warehouse are over. Their customers want faster, more economical results. Over time, consultants have built up elemental motions into patterns that are consistent for almost all DCs. For example, a typical work pattern might be “obtain large dense case from the middle tier of a three tier pallet rack.” This is 60 TMUs. If you purchase RedPrairie’s Labor Management System (LMS), for example, it comes with a database that has thousands of these patterns and associated TMUs. Further, if a pattern does not fit the norm, experienced industrial engineers don’t need to break the activity into all of its components; they just swap out the nonstandard elemental units.
So, which is better, pre-determined time systems or time and motion studies? Not surprisingly, the answer is it depends. They each have their pros and cons, which now that I think about it, would be a good theme for a future posting.