Compact 12 kg loads are inspected for damage and lifted with two hands directly

Question

Compact 12 kg loads are inspected for damage and lifted with two hands directly in front of the body from shelf 1 to shelf 2 at rate of 3/min for a duration of 45 minutes/day, as illustrated in Fig 1. For this example, assume that the worker cannot take a step forward when placing the object at the destination, and assume that significant control of the object is required at the destination. The containers are optimal design, but without handles (fair coupling). Use the NIOSH equation to calculate the RWL and the Lifting Index. Comment on the safety of the task. Identify the risk factors and propose solution

Explanation / Answer

Solution:

a) The RWL (Using NIOSH equation) is defined by the following equation:

RWL = LC X HM X VM X DM X AM X FM X CM

Where,

Load Constant, LC = 23 kg (Standard)

Horizontal Multiplier, HM = 25/H = 25/25 = 1

Vertical Multiplier, VM = 1-(.003 [V-75]) = 1-(.003 [55-75]) = 0.94

Distance Multiplier, DM = .82 + (4.5/D) = .82 + (4.5/95) = 0.87 (D is Vertical Travel Distance variable in our case 150-55 = 95cm)

Asymmetric Multiplier, AM = 1 (Since it is in front of the body therefore no Asymmetric angle) Frequency Multiplier, FM = 0.88 (Since frequency of lifting is 3 / min and for 45 min/day)

Coupling Multiplier, CM = 0.95 (Since it is a fair coupling)

Now, put all the above value in below equation

RWL = LC X HM X VM X DM X AM X FM X CM

RWL = 23 x 1 x 0.94 x 0.87 x 1 x 0.88 x 0.95

RWL = 15.7 kg

The LI is defined by the following equation:

LI = Load Weight (L) / Recommended Weight Limit (RWL)

LI = 12/15.72 = 0.76 (Safe)

b) The task is very safe as lifting index is 0.76 at first level lifting from shelf 1. It is not safe for frequency 3/min at destination level shelf 2, it can be improved by reducing the frequency.

c) Risk - Shelf 2 is very high. Either shift shelf 2 some down or shift shelf 1 some upside.

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