Question 2 of 4: NIOSH Lifting Analysis — Punch Press Stock Reel

Question 2: NIOSH Lifting Analysis — Punch Press Stock Reel (40 marks: a–10, b–10, c–10, d–10)

Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.

Part (a) — RWL and LI at Origin and Destination

Given.

Find. $RWL_{\text{origin}}$, $RWL_{\text{destination}}$, and the corresponding Lifting Indices $LI_{\text{origin}}$, $LI_{\text{destination}}$.

Approach. Read each multiplier directly off the exam's own Appendix 1 tables at the given $H$, $V$, $D$, $A$, $F$ and coupling – interpolating linearly between printed rows where a value (here $V_o=35$ cm and $D=135$ cm) does not land exactly on a table row – then apply $RWL=LC\times HM\times VM\times DM\times AM\times FM\times CM$ and $LI=L/RWL$ once at each end of the lift ($D$ is the same 135 cm travel for both, since it is one continuous lift).

1. Read the multipliers off Appendix 1. Horizontal Multiplier: $H=58\,\text{cm}$ is an exact table row $\Rightarrow HM=0.43$ (both ends, since $H$ is unchanged). Vertical Multiplier: $V_o=35\,\text{cm}$ falls between the printed rows $30\to0.87$ and $40\to0.90$; interpolating, $VM_o=0.87+\frac{35-30}{40-30}(0.90-0.87)=0.885$. $V_d=170\,\text{cm}$ is an exact row $\Rightarrow VM_d=0.72$. Distance Multiplier: $D=135\,\text{cm}$ falls between the rows $130\to0.86$ and $145\to0.85$; interpolating, $DM=0.86+\frac{135-130}{145-130}(0.85-0.86)=0.857$ (the same value applies at both ends, since $D$ is the single travel distance). Asymmetric Multiplier: $A=0^{\circ}\Rightarrow AM=1.00$. Frequency Multiplier: $F\le0.2$ lifts/min, duration $\le1$ h $\Rightarrow FM=1.00$ (both $V<30$ in and $V\ge30$ in columns read 1.00 at this row). Coupling Multiplier: Good, both $V$ ranges $\Rightarrow CM=1.00$.
2. Compute the Recommended Weight Limit at each end. $$RWL_{\text{origin}} = 23 \times 0.43 \times 0.885 \times 0.857 \times 1.00 \times 1.00 \times 1.00 = \boxed{7.50\ \text{kg}}$$ $$RWL_{\text{destination}} = 23 \times 0.43 \times 0.72 \times 0.857 \times 1.00 \times 1.00 \times 1.00 = \boxed{6.10\ \text{kg}}$$ The destination RWL is the lower of the two because $V_d=170\,\text{cm}$ is much further from the NIOSH-ideal $75\,\text{cm}$ knuckle height than $V_o=35\,\text{cm}$ is, so $VM_d \lt VM_o$ even though $H$, $D$, $A$, $F$ and coupling are unchanged.
3. Compute the Lifting Index at each end. $$LI_{\text{origin}} = \frac{L}{RWL_{\text{origin}}} = \frac{25}{7.50} = \boxed{3.33}$$ $$LI_{\text{destination}} = \frac{L}{RWL_{\text{destination}}} = \frac{25}{6.10} = \boxed{4.10}$$

Both lifting indices are far above 1.0, meaning this single-worker lift is not within the NIOSH recommended limit at either end – the destination placement, in particular, is more than four times the recommended weight for that geometry. The dominant penalty is the horizontal multiplier ($HM=0.43$, a 57% reduction on its own) driven by the 58 cm reach to the hand hold, compounded by the large 135 cm vertical travel and, at the destination, a hand height well above the ideal knuckle-height zone.

Part (b) — Safety Issues, Risk Factors and Anatomical Structures

The Part (a) result – $LI\approx3.3$ rising to $LI\approx4.1$ at the destination – places this task in NIOSH's high-risk band, where the majority of the working population would be expected to be at increased risk of low-back injury performing this exact lift, even though it occurs only once per shift. Several risk factors compound rather than acting alone: (1) a large horizontal reach (58 cm) to a bulky 75 cm diameter object, which cannot be held close to the body the way a compact box can; (2) a long vertical travel (135 cm, floor to well above shoulder height), meaning the worker's posture and moment arm both change substantially over the course of one lift, rather than staying constant; (3) a destination height (170 cm) that is above typical shoulder height, requiring an overhead placement motion at exactly the moment (“significant control at the destination”) that precision is also demanded; (4) the reel's cylindrical, bulky geometry makes load balance and grip harder to maintain than a rectangular container even with a hand hold; and (5) the lift is performed solo, with no assistance specified.

The anatomical structures most at risk are the lumbar spine's intervertebral discs and posterior ligaments (compressive and shear loading from the combined weight and long horizontal moment arm, the classic NIOSH low-back-injury target), the erector spinae and other trunk extensor muscles (sustained/peak loading through the lift), and – specifically because of the overhead destination placement – the shoulder girdle (rotator cuff and deltoid), which is loaded in an unfavourable, elevated-arm position exactly when fine motor control is also required. A secondary risk is a dropped-object/crush injury to the hands or feet during the destination placement, given the combination of a heavy, bulky, hard-to-balance object and an overhead reach.

Part (c) — Recommended Lift Assist Devices

Appendix 2 categorizes devices by whether they move loads horizontally (H) or vertically (V) and by which task stage they serve; this task is a single-point vertical reload (floor to machine infeed), so the relevant column is “At Workstation” among the vertical-transport devices, cross-checked against the stated need for “significant control at the destination.”

• Overhead balancer (V, At Workstation). The strongest match to the question's own stated requirement – a balancer counteracts the reel's weight while the operator still guides it by hand, which is exactly what “exercise significant control at the destination” calls for; it also removes essentially all of the 25 kg load from the worker's spine at both the origin pick and the destination placement, directly eliminating the Part (a)/(b) overload rather than only reducing it.
• Scissor lift table or lift/tilt table (V, At Workstation). Raises the reel from floor height toward the machine's infeed height mechanically, cutting the vertical travel $D$ and the unfavourable $V_o=35\,\text{cm}$ starting height that currently drags $VM_o$ down; best paired with the balancer above rather than used alone, since a lift table alone still leaves the operator manually guiding the final placement onto the press.
• Vacuum lifting device (V, At Workstation and Testing). A viable alternative to a balancer if the reel's hand hold is not compatible with a balancer's hook/sling attachment; a vacuum head engages the reel's flat face directly, and vacuum lifters are specifically listed as supporting the fine positioning control this task needs.
• Crane (V, all listed task columns). Feasible but likely oversized/slower for a single-point, once-per-shift reload at one fixed machine – a fixed-position balancer or lift table is the better fit for a repeated task at one location, while a crane suits variable pick-up/drop-off points across a wider area.

Recommendation: an overhead balancer mounted above the press infeed, combined with a low scissor table at the floor-level pickup point – the table removes the awkward, near-floor origin pick, and the balancer carries the load through the full 135 cm travel and gives the operator hands-on control precisely at the destination, addressing both the Part (a) overload and the Part (b) overhead-placement risk simultaneously.

Part (d) — Other Human Factors Resolutions

• Redesign the origin storage height. Storing reels on a stand near waist/knuckle height (close to the NIOSH-ideal 75 cm) instead of the floor raises $V_o$ toward the ideal and shortens $D$, improving $VM_o$ and $DM$ together without needing any mechanical assist device.
• Reduce the horizontal reach. A closer infeed chute or a reel cradle that brings the hand hold nearer the operator's body directly attacks the single largest penalty in Part (a) ($HM=0.43$); even a modest reduction from 58 cm toward, say, 35–40 cm materially raises $HM$ and both $RWL$ values.
• Two-person team lift for the destination placement only. If mechanical assist is not immediately feasible, splitting the overhead, high-control destination placement between two workers reduces the per-worker load well below the single-worker $LI_{\text{destination}}=4.10$, though NIOSH team-lifting guidance cautions this is a lower-confidence mitigation than a mechanical aid and should be a bridging measure, not the final fix.
• Training and technique. Even with assist devices installed, train the operator in a controlled, close-body technique for engaging the balancer/table, since a bulky cylindrical object can still be man-handled poorly around a lift aid.
• Job/task rotation. Rotate the punch-press operator role periodically so no single worker accumulates the cumulative shoulder/back loading of this lift shift after shift, complementing (not substituting for) the engineering fixes above.