17.4 RULA, REBA, the Strain Index, and the ACGIH HAL TLV

RULA, REBA, the Strain Index, and the ACGIH HAL TLV

The NIOSH equation evaluates two-handed sagittal lifting only. Most workplace ergonomic risk is postural, repetitive, or upper-limb, which is what the observational and semi-quantitative tools in this section are built to score.

1. Rapid Upper Limb Assessment (RULA)

Developed by McAtamney and Corlett in 1993, RULA is a survey tool designed for use in ergonomics investigations of workplaces where work-related upper limb disorders are reported. It evaluates postural loading, muscle use, and external forces on the neck, trunk, and upper limbs in seated or standing sedentary/light assembly tasks (e.g., VDT operations, sewing, electronics assembly, inspection).

   +-------------------------------------------------------------------------+
   |                     RULA SCORING ARCHITECTURE                           |
   +-------------------------------------------------------------------------+
   |                                                                         |
   |  [GROUP A: Upper Limb]              [GROUP B: Neck, Trunk, Legs]        |
   |  • Upper Arm Posture (1-6)          • Neck Posture (1-6)                |
   |  • Lower Arm Posture (1-3)          • Trunk Posture (1-6)               |
   |  • Wrist Posture (1-4)              • Legs Support (1-2)                |
   |  • Wrist Twist (1-2)                |                                   |
   |          |                          |                                   |
   |          v                          v                                   |
   |    Table A Score              Table B Score                             |
   |          +                          +                                   |
   |  Muscle Use Score (0 or +1)   Muscle Use Score (0 or +1)                |
   |  (Static > 1 min or           (Static > 1 min or                        |
   |   Repetitive > 4x/min)         Repetitive > 4x/min)                     |
   |          +                          +                                   |
   |  Force/Load Score (0 to +3)   Force/Load Score (0 to +3)                |
   |  (<4.4 lb: 0, 4.4-22 lb: 1-2, (<4.4 lb: 0, 4.4-22 lb: 1-2,              |
   |   >22 lb/shock: +3)            >22 lb/shock: +3)                        |
   |          |                          |                                   |
   |          v                          v                                   |
   |     Score C                    Score D                                  |
   |          \                        /                                     |
   |           \                      /                                      |
   |            v                    v                                       |
   |                   Table C Score                                         |
   |                 GRAND SCORE (1 - 7)                                     |
   +-------------------------------------------------------------------------+

RULA Action Levels

• Action Level 1 (Score 1–2): Posture is acceptable if not maintained or repeated over long periods. (Negligible risk).
• Action Level 2 (Score 3–4): Further investigation is needed and changes may be required. (Low risk).
• Action Level 3 (Score 5–6): Investigation and changes are required soon. (Medium risk).
• Action Level 4 (Score 7): Investigation and changes are required immediately. (High risk).

---

2. Rapid Entire Body Assessment (REBA)

Developed by Hignett and McAtamney in 2000, REBA was formulated specifically to address dynamic, unpredictable, whole-body postures encountered in healthcare (patient handling, bed transfers), warehousing, heavy maintenance, construction, and service industries where lower extremity postures and unpredictable load coupling are critical.

   +-------------------------------------------------------------------------+
   |                     REBA SCORING ARCHITECTURE                           |
   +-------------------------------------------------------------------------+
   |                                                                         |
   |  [GROUP A: Trunk, Neck, Legs]       [GROUP B: Upper Arm, Lower Arm, Wrist]|
   |  • Trunk Posture (1-5)              • Upper Arm Posture (1-6)           |
   |  • Neck Posture (1-3)               • Lower Arm Posture (1-2)           |
   |  • Legs Posture (1-4)               • Wrist Posture (1-3)               |
   |          |                                    |                         |
   |          v                                    v                         |
   |    Table A Score                        Table B Score                   |
   |          +                                    +                         |
   |  Load / Force Score (0 to +3)       Coupling Score (0 to +3)            |
   |  (<11 lb: 0, 11-22 lb: 1,           (Good: 0, Fair: 1,                  |
   |   >22 lb: 2, Shock: +1)              Poor: 2, Unacceptable: 3)          |
   |          |                                    |                         |
   |          v                                    v                         |
   |       Score A                              Score B                      |
   |          \                                    /                         |
   |           \                                  /                          |
   |            v                                v                           |
   |                          Table C Score                                  |
   |                                +                                        |
   |                     Activity Score (0 to +3)                            |
   |                     (+1: Static > 1 min)                                |
   |                     (+1: Repetitive > 4x/min)                           |
   |                     (+1: Rapid unstable posture change)                 |
   |                                |                                        |
   |                                v                                        |
   |                       REBA FINAL SCORE (1 - 15)                         |
   +-------------------------------------------------------------------------+

REBA Action Levels

• Action Level 0 (Score 1): Negligible risk; no action necessary.
• Action Level 1 (Score 2–3): Low risk; change may be needed.
• Action Level 2 (Score 4–7): Medium risk; further investigation; change soon.
• Action Level 3 (Score 8–10): High risk; investigate and implement change promptly.
• Action Level 4 (Score 11–15): Very high risk; implement changes immediately.

Summary Comparison: RULA vs REBA

---

3. Moore-Garg Strain Index (SI) and ACGIH HAL TLV

For hand-intensive, mono-task repetitive industrial operations (e.g., meat packing, poultry processing, small parts manufacturing), ergonomists employ specialized distal upper extremity tools.

The Moore-Garg Strain Index (SI)

Published by Moore and Garg in 1995, the Strain Index (SI) is a semi-quantitative job analysis method that evaluates the risk of distal upper extremity (wrist, hand, elbow) musculoskeletal disorders.

$\mathbf{\text{Strain Index (SI)} = \text{IE} \times \text{DE} \times \text{EM} \times \text{HWP} \times \text{SW} \times \text{DD}}$

Where the six multiplicative exposure parameters are:

1. Intensity of Exertion (IE): Borg CR-10 rating / % MVC (1.0 Light to 13.0 Near Maximal).
2. Duration of Exertion (DE): Percent of cycle time performing exertion (0.5 for <10% to 3.0 for >80%).
3. Efforts per Minute (EM): Frequency of exertions (0.5 for <4/min to 3.0 for ≥ 20/min).
4. Hand/Wrist Posture (HWP): Wrist extension/flexion/ulnar deviation (1.0 Perfect to 3.0 Extreme).
5. Speed of Work (SW): Perceived pacing (1.0 Normal to 2.0 Very Fast).
6. Duration per Day (DD): Exposure hours per day (0.25 for <1 hr to 1.5 for ≥ 8 hr).

• Strain Index Risk Classification:
  • SI ≤ 3: Job is probably safe.
  • 3 < SI ≤ 7: Job is uncertain; elevated risk for some workers.
  • SI > 7: Job is strongly associated with distal upper extremity disorders; high risk requiring ergonomic intervention.

The ACGIH Hand Activity Level (HAL) TLV

The ACGIH Hand Activity Level (HAL) TLV applies to repetitive mono-task hand work performed for 4 or more hours per day. It integrates two primary parameters:

1. Hand Activity Level (HAL): A 0-to-10 scale assessing repetition and duty cycle (ratio of exertion to rest), determined by visual observation or video analysis.
2. Normalized Peak Force (NPF): A 0-to-10 scale assessing peak hand grip/pinch force normalized to the worker population's maximum voluntary contraction (where 10 = 100% MVC, using the Borg CR-10 scale or EMG).

   +-------------------------------------------------------------------------+
   |                  ACGIH HAND ACTIVITY LEVEL (HAL) TLV MATRIX             |
   +-------------------------------------------------------------------------+
   |                                                                         |
   |  Normalized Peak Force (NPF: 0 - 10)                                    |
   |  10 |                                                                   |
   |   8 |              UNACCEPTABLE REGION (Above TLV)                      |
   |   6 |                            /----------------- TLV Boundary        |
   |   4 |              ACTION REGION /----------------- Action Limit (AL)   |
   |   2 |  SAFE REGION              /                                       |
   |   0 +--------------------------+--------------------------->            |
   |     0                          5                          10            |
   |                      Hand Activity Level (HAL: 0 - 10)                  |
   +-------------------------------------------------------------------------+

• Threshold Equations:
  • ACGIH TLV Line: NPF = 0.56 × (10 - HAL) (or NPF/(10 - HAL) = 0.56)
  • Action Limit (AL) Line: NPF = 0.40 × (10 - HAL) (or NPF/(10 - HAL) = 0.40)
• Interpretation: If the intersection of NPF and HAL lies above the TLV line, the job is unacceptable and mandates immediate engineering redesign. If the point lies between the Action Limit and TLV, administrative controls, medical surveillance, and ergonomic hazard evaluations are required.

---

4. Worked Step-by-Step Calculation Examples

Worked Example 16.2.1: Full RNLE & Lifting Index Calculation for a Warehouse Packing Job

Problem: A warehouse worker manually lifts boxes of machine parts from a low conveyor pallet and places them onto a high packing table for 1.5 hours per day. The job parameters are measured as follows:

• Actual box weight (L) = 32 lb
• Horizontal distance at origin (H) = 15 in
• Vertical origin height (V) = 18 in
• Vertical destination height (Vdest) = 42 in (Travel distance D = 42 - 18 = 24 in)
• Asymmetry angle (A) = 30°
• Lifting frequency (F) = 3 lifts/min
• Frequency Multiplier (FM) from NIOSH table (for 1.5 hr, V < 30 in, 3 lifts/min) = 0.88
• Coupling (CM) = Fair containers (V < 30 in → CM = 0.95)

Calculate the Recommended Weight Limit (RWL) and the Lifting Index (LI). Interpret the risk.

Solution Steps:

1. Identify Load Constant (LC): $LC = 51.0\text{ lb}$

2. Calculate Horizontal Multiplier (HM): $HM = \frac{10}{H} = \frac{10}{15} = 0.667$

3. Calculate Vertical Multiplier (VM): $VM = 1 - (0.0075 \times |V - 30|) = 1 - (0.0075 \times |18 - 30|) = 1 - (0.0075 \times 12) = 1 - 0.090 = 0.910$

4. Calculate Distance Multiplier (DM): $DM = 0.82 + \frac{1.8}{D} = 0.82 + \frac{1.8}{24} = 0.82 + 0.075 = 0.895$

5. Calculate Asymmetric Multiplier (AM): $AM = 1 - (0.0032 \times A) = 1 - (0.0032 \times 30) = 1 - 0.096 = 0.904$

6. Multiply all factors to find RWL: $\text{RWL} = LC \times HM \times VM \times DM \times AM \times FM \times CM$ $\text{RWL} = 51.0 \times 0.667 \times 0.910 \times 0.895 \times 0.904 \times 0.88 \times 0.95$ $\text{RWL} = 51.0 \times 0.667 = 34.017$ $34.017 \times 0.910 = 30.955$ $30.955 \times 0.895 = 27.705$ $27.705 \times 0.904 = 25.045$ $25.045 \times 0.88 = 22.040$ $22.040 \times 0.95 = \mathbf{20.94\text{ lb}}$

7. Calculate the Lifting Index (LI): $\text{LI} = \frac{L}{\text{RWL}} = \frac{32\text{ lb}}{20.94\text{ lb}} = \mathbf{1.53}$

8. Risk Interpretation & Recommendations:

   • Because 1.0 < LI = 1.53 < 3.0, the job poses an increased risk of lower back injury for a portion of the industrial workforce.
   • Primary Hazard Driver: The largest penalty is HM = 0.667 (horizontal reach of 15 in). Redesign recommendations: bring the pallet closer to the worker to reduce H to 10 in (HM = 1.0) and utilize a scissor lift table to raise V from 18 in to knuckle height (30 in). This would increase RWL to 34.5 lb and drop LI to 0.93 (safe).

---

Worked Example 16.2.2: ACGIH Hand Activity Level (HAL) TLV Evaluation

Problem: A worker in a meat processing plant uses a boning knife for 6 hours per day. Video analysis establishes a Hand Activity Level of HAL = 6.0. Electromyography (EMG) and subjective Borg CR-10 ratings determine a Normalized Peak Force of NPF = 3.0.

Determine whether this task exceeds the ACGIH Action Limit or TLV.

Solution Steps:

1. Calculate the TLV Peak Force threshold at HAL = 6.0: $\text{NPF}_{\text{TLV}} = 0.56 \times (10 - \text{HAL}) = 0.56 \times (10 - 6.0) = 0.56 \times 4.0 = 2.24$

2. Calculate the Action Limit Peak Force threshold at HAL = 6.0: $\text{NPF}_{\text{AL}} = 0.40 \times (10 - \text{HAL}) = 0.40 \times (10 - 6.0) = 0.40 \times 4.0 = 1.60$

3. Evaluate against actual exertion:

   • Actual NPF = 3.0.
   • Since Actual NPF (3.0) > NPFTLV (2.24), the task lies in the Unacceptable Region above the TLV.
   • Conclusion: The task presents a significant risk of distal upper extremity WMSD. Corrective engineering controls (knife blade sharpening protocols, powered cutting tools, or reduced duty cycle) are legally and professionally required.