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Time Studies – How can the Ergonomist use this Information?
As an Ergonomist, it may sometimes seem that you are the only one who looks at, or evaluates, a
workstation in great detail. However, your Industrial Engineering counterparts are just as interested
in the elements that make up a job.
What are time studies, and why should Ergonomists be aware of them? A time or motion study is
a detailed analysis of a specific job in an effort to find the most efficient method of performing
tasks in terms of time and effort. Engineers use time studies to determine if an operator is over
or under utilized given the elements of the job. The data collected during a time study is often
very similar to that which is collected for an ergonomic analysis. Ergonomists can benefit from
learning about how time studies are conducted at their facility and by working together with the
engineers.
Benefits may include detailed information about the process that is being studied. Some of the
details which could be incorporated into an ergonomic analysis include:
Frequency (number of motions per cycle/per unit time).
Duration (work/rest per cycle or duration that the posture is held for a static load).
Qualifying posture (i.e. number of movements at a joint, time spent working above shoulder
height).
How much time was allocated to perform a task? Is it appropriate? (i.e. do hand intensive
tasks have sufficient time allocated?)
Metabolic Load: Process information (time, object weights, walk distances, etc.)
As an example, look at the 1991 NIOSH lifting equation. Much of the data needed to complete a
NIOSH lifting analysis can be obtained from information an Industrial Engineer would have collected
to complete a time study.
The NIOSH lifting equation is as follows:
RWL = LC x HM x VM x DM x FM x AM x CM
Definition of NIOSH Variables
| RWL: Recommended Weight Limit | LC: Load Constant |
| HM: Horizontal Multiplier | VM: Vertical Multiplier |
| DM: Distance Multiplier | FM: Frequency Multiplier |
| AM: Asymmetry Multiplier | CM: Coupling Multiplier |
An Industrial Engineer should have the following information about a job, if a time study was completed:
FM – can be calculated from a time study by counting the number of lifts the operator
completes during the job cycle, in addition to measuring how much time each lift takes.
HM, VM, and DM – reach distances and heights are measured while performing the time study
or can be estimated by observation. This information is also useful if one is performing a time
study using a predetermined time standard.
AM – any twisting required during the lift will be observed while performing a time study, and
can be used as an input in some predetermined time standards.
This is only one example of how you can partake in information sharing with your Industrial Engineering
counterparts. Data collected during a time study can not only help you to become more intimate with the
workstations in your facility, but also can save you from having to collect data that may already be available.
Reference:
Badger, Donald W. (1991). Work Practices Guide for Manual Lifting. U.S Department of Health and Human
Services, National Institute for Occupational Safety and Health (NIOSH), Publication No. 81-122, Cincinnati
OH 45226.
Waters, T.R., Putz-Anderson, V., Garg, A. (1994). Applications Manual for the Revised NIOSH Lifting
Equation. U.S. Department of Health and Human Services, DHHS (NIOSH) Publication, Publication No. 94-110,
Cincinnati, OH.
Waters, T.R., Putz-Anderson, V., Garg, A., and Fine, L. (1993). Revised NIOSH equation for the design and
evaluation of manual lifting tables