NIOSH Lifting Equation Example - Package Inspection - Free Printable

To solve this problem, we need to calculate the Recommended Weight Limit (RWL) using the NIOSH Lifting Equation. This equation helps determine how much weight is safe for a person to lift based on specific conditions.

The formula for the RWL is:
$$RWL = LC \times HM \times VM \times DM \times AM \times FM \times CM$$

Here are the standard values and multipliers we will use:
* Load Constant ($LC$): 51 lbs (This is the maximum recommended load under ideal conditions).
* Horizontal Multiplier ($HM$): $10 / H$ (where $H$ is the horizontal distance in inches).
* Vertical Multiplier ($VM$): $1 - (0.0075 \times |V - 30|)$ (where $V$ is the vertical height in inches).
* Distance Multiplier ($DM$): $0.82 + (1.8 / D)$ (where $D$ is the vertical travel distance in inches).
* Asymmetric Multiplier ($AM$): $1 - (0.0032 \times A)$ (where $A$ is the angle of asymmetry in degrees).
* Frequency Multiplier ($FM$): Looked up from a table based on lifts per minute and duration.
* Coupling Multiplier ($CM$): Based on hand-hold quality (Good, Fair, Poor).

Step 1: Identify the Variables from the Diagram

Let's extract the numbers from the image:

1. Horizontal Distance ($H$): The diagram shows the load is 10 inches away from the body (midpoint between ankles). So, $H = 10$.
2. Vertical Height ($V$): The lift starts at Shelf 1. The height of Shelf 1 is given as 22 inches. So, $V = 22$.
3. Vertical Travel Distance ($D$): The load moves from Shelf 1 (22 inches) to Shelf 2 (59 inches).
* $D = 59 - 22 = 37$ inches.
4. Angle of Asymmetry ($A$): The person is facing forward, and the shelves appear to be directly in front. There is no twisting mentioned or shown. So, $A = 0$ degrees.
5. Frequency ($F$): The task is "Package Inspection." This usually implies a slow, controlled pace. Without a specific rate given, we assume a low frequency, typically less than 1 lift per minute or very few lifts per hour. For infrequent lifting (less than 1 lift every 5 minutes), the Frequency Multiplier ($FM$) is 1.0.
6. Coupling ($C$): The object is a box ("25 LBS"). Boxes usually have handles or allow for a good grip unless stated otherwise. We will assume a "Good" coupling. For a Good coupling, the Coupling Multiplier ($CM$) is 1.0.
7. Significant Control Required: The note says "Assume Significant Control Required." This confirms that the lift is precise and likely slow, supporting our choice of $FM = 1.0$. It also reinforces that we are looking at the *destination* or the most difficult part of the lift, but since the start point (lower shelf) is usually the most stressful due to biomechanics, we analyze the lift starting at V=22.

Step 2: Calculate Each Multiplier

Now, let's plug the numbers into the multiplier formulas.

1. Horizontal Multiplier ($HM$):
$$HM = 10 / H$$
$$HM = 10 / 10 = 1.0$$

2. Vertical Multiplier ($VM$):
$$VM = 1 - (0.0075 \times |V - 30|)$$
$$VM = 1 - (0.0075 \times |22 - 30|)$$
$$VM = 1 - (0.0075 \times |-8|)$$
$$VM = 1 - (0.0075 \times 8)$$
$$VM = 1 - 0.06 = 0.94$$

3. Distance Multiplier ($DM$):
$$DM = 0.82 + (1.8 / D)$$
$$DM = 0.82 + (1.8 / 37)$$
$$DM = 0.82 + 0.0486$$
$$DM \approx 0.869$$ (We'll round to 0.87 for simplicity, but keep precision for calculation).

4. Asymmetric Multiplier ($AM$):
$$AM = 1 - (0.0032 \times A)$$
$$AM = 1 - (0.0032 \times 0) = 1.0$$

5. Frequency Multiplier ($FM$):
Assuming infrequent lifting (inspection task):
$$FM = 1.0$$

6. Coupling Multiplier ($CM$):
Assuming Good coupling (box):
$$CM = 1.0$$

Step 3: Calculate the Recommended Weight Limit (RWL)

Now multiply all the factors together with the Load Constant ($LC = 51$ lbs).

$$RWL = 51 \times HM \times VM \times DM \times AM \times FM \times CM$$
$$RWL = 51 \times 1.0 \times 0.94 \times 0.869 \times 1.0 \times 1.0 \times 1.0$$

Let's do the math:
1. $51 \times 1.0 = 51$
2. $51 \times 0.94 = 47.94$
3. $47.94 \times 0.869 \approx 41.66$

So, the Recommended Weight Limit (RWL) is approximately 41.7 lbs.

Step 4: Compare with the Actual Load

* Actual Load: 25 lbs (shown on the box).
* Recommended Weight Limit (RWL): ~41.7 lbs.

Since the actual load (25 lbs) is less than the recommended limit (41.7 lbs), the lift is considered safe according to these guidelines.

Often, homework questions like this ask for the Lifting Index (LI), which compares the actual load to the recommended limit.

$$Lifting Index (LI) = \frac{\text{Actual Load}}{\text{RWL}}$$
$$LI = \frac{25}{41.66} \approx 0.60$$

An LI of less than 1.0 indicates a low risk of injury.

Final Conclusion

The problem asks to analyze the package inspection task. Based on the NIOSH lifting equation calculations:

1. The Recommended Weight Limit (RWL) for this specific lift is approximately 41.7 lbs.
2. The Lifting Index (LI) is approximately 0.6.

Because the Lifting Index is less than 1.0, the task is within safe limits.

Final Answer:
The Recommended Weight Limit (RWL) is 41.7 lbs, and the Lifting Index (LI) is 0.6. Since the actual weight (25 lbs) is below the RWL, the lift is safe.