We were so excited to have such a great turnout for our web course this week, Ergonomics for Manual Material Handling. Below are the answers to questions asked during the event.
Q: Are you going to talk about frequency independent lifts?
A: This feature of the NIOSH lifting equation is very important because it calculates the recommended weight limit (RWL) without the influence of frequent lifting. Therefore, the frequency independent RWL provides the not-to-exceed weight of a load within an 8 hour period.
Q: In one of Humantech’s applied ergonomics manuals, there are some rules that explain how to determine duration. Could you please speak to that?
A: Duration is based on the patterns of continuous work-time and recovery-time periods. A continuous work-time period is defined as a period of uninterrupted work. Recovery-time is defined as the duration of light-work activity (e.g. sitting at a desk or table, monitoring operations, light assembly work, etc.) following a period of continuous lifting. Duration can be classified into three categories; short, moderate, and long.
Short duration is when an operator is lifting objects with work durations of one hour or less, followed by a recovery time equal to 1.2 times the work time. Moderate duration is characterized by lifting objects for greater than one hour, but not more than two hours, followed by a recovery period of at least .3 times the work time. Finally, long duration pertains to lifting durations between two and eight hours, with stand industrial rest allowances (e.g. morning, lunch, and afternoon rest breaks).
Q: When you are unloading a pallet, what scenarios do you consider to use the equation?
A: This type of task should be analyzed by the composite NIOSH lifting equation. The composite NIOSH is similar to the standard NIOSH in that it produces a recommended weight limit and corresponding lifting index, but differs because it combines up to 10 sequential lifts at a time. A good method to adopt, when applying the composite NIOSH to a task such as this, would be to enter in the measurements for the closest, lowest position on the pallet. Second, you would measure the next closest, lowest position and then the furthest, lowest position. Continue this same method for the middle and top row of objects on the pallet to get a comprehensive view of unloading the pallet. The composite NIOSH will compile up to 10 separate lifts and create a single recommended weight limit and composite lifting index.
Q: Can you repeat what you said about the operator choosing to twist versus must twist in using the NIOSH calculator?
A: During the webinar, we were discussing the difference between an operator needing to twist their torso in order to access an object and choosing to twist because they did not want to move their feet into the appropriate position. Often times we observe the latter of the two because the object is within an arm’s reach of the operator but at an angle of which the operator does not perceive it to be unsafe. In either case, the root cause of both of these situations is due to workplace dimensions.
Needing to twist to the torso in order to access a load is typically due to a lack of space provided for the operator. Contrastingly, choosing to twist is due to a lack of utilization of the space provided. These issues can be resolved if one ensures that the workplace is designed using industry standard design guidelines. Many sources are readily available including Humantech’s Handbook of Ergonomic Design Guidelines.
Q: We load material rolls on unwind spindles. Is there a push pull calculator for this task?
A: No, you would perform the NIOSH lifting equation while loading the material rolls to their staging location. Then, you would use the Snook and Ciriello tables to analyze any pushes or pulls necessary to move the spindles throughout the facility.
Q: What is your definition of restricted areas that the NIOSH equation cannot be used for?
A: A restricted work space is any area within the anterior, posterior, medial, lateral, and vertical planes that would affect an operator’s natural ability to lift/lower a load. For example, if a maintenance worker needs to remove a 35-lb guarding plate from a piece of machinery, the NIOSH should not be applied if there were objects impeding a clear path of lifting/lowering the guarding throughout the movement.
Q: What if the frequency is less than .2 lifts/min (1 lift every 5 minutes)? For example one lift every 35 seconds (20 lbs)? Do you use that above category (.2)
A: Yes, the frequency would be set at .2 lifts per minute for any lifts that are performed faster than every 5 minutes.