— Ergonomic Exposure Limits
Action levels and limit values for manual lifting, noise, vibration,
and heat. Consensus and regulatory values differ — the applicable jurisdiction's
regulation governs.
Revised NIOSH Lifting Equation
RWL = LC × HM × VM × DM × AM × FM × CM,
with load constant LC = 23 kg (51 lb). Lifting Index LI = load weight / RWL.
LI ≤ 1.0 → nominal risk; 1.0 < LI ≤ 3.0 → redesign advised;
LI > 3.0 → redesign required.
| Multiplier | Formula (metric) | Notes |
|---|
| HM — horizontal | 25 / H | H in cm, measured from the ankle mid-point to the hand grasp; HM = 1 if H ≤ 25, HM = 0 if H > 63. |
| VM — vertical | 1 − 0.003·|V − 75| | V = height of hands at the lift origin (cm); VM = 0 if V > 175. |
| DM — distance | 0.82 + 4.5 / D | D = vertical travel of the load (cm); DM = 1 if D < 25, DM = 0 if D > 175. |
| AM — asymmetry | 1 − 0.0032·A | A = trunk twist angle (degrees); AM = 0 if A > 135. |
| FM — frequency | table below | Depends on lifts/min, work duration, and whether V < 75 cm. |
| CM — coupling | table below | Quality of the hand-to-object coupling. |
| Lifts/min | ≤ 1 h | > 1–2 h | > 2–8 h |
|---|
| 0.2 | 1.00 | 0.95 | 0.85 |
| 0.5 | 0.97 | 0.92 | 0.81 |
| 1 | 0.94 | 0.88 | 0.75 |
| 2 | 0.91 | 0.84 | 0.65 |
| 3 | 0.88 | 0.79 | 0.55 |
| 4 | 0.84 | 0.72 | 0.45 |
| 5 | 0.80 | 0.60 | 0.35 |
| 6 | 0.75 | 0.50 | 0.27 |
| 8 | 0.60 | 0.35 | 0.18 |
| 10 | 0.45 | 0.26 | 0.13 * |
| 12 | 0.37 | 0.21 * | 0.00 |
| 15 | 0.28 * | 0.00 | 0.00 |
* value applies only when V ≥ 75 cm; otherwise FM = 0 (task exceeds
the equation's limits). Coupling multiplier CM: Good = 1.00; Fair = 0.95 if V < 75 cm,
else 1.00; Poor = 0.90.
Occupational Noise
| OSHA (29 CFR 1910.95) | NIOSH (Pub. 98-126) |
|---|
| Permissible exposure (8-h TWA) | 90 dBA (PEL) | 85 dBA (REL) |
| Action level (8-h TWA) | 85 dBA — hearing conservation program | — |
| Exchange rate | 5 dB per doubling | 3 dB per doubling |
| Ceiling | 115 dBA (continuous); 140 dB peak (impulse) | — |
| Level (dBA) | OSHA permissible time | NIOSH permissible time |
|---|
| 82 | — | 16 h |
| 85 | 16 h | 8 h |
| 88 | 10.6 h | 4 h |
| 90 | 8 h | 2.5 h |
| 92 | 6 h | 1.6 h |
| 95 | 4 h | 47 min |
| 100 | 2 h | 15 min |
| 105 | 1 h | 5 min |
| 110 | 30 min | 1.5 min |
| 115 | 15 min | 28 s |
Vibration (ISO / EU Directive 2002/44/EC)
| Type | Exposure Action Value, A(8) | Exposure Limit Value, A(8) |
|---|
| Hand-arm vibration (ISO 5349-1) | 2.5 m/s² | 5.0 m/s² |
| Whole-body vibration (ISO 2631-1) | 0.5 m/s² (or VDV 9.1 m/s1.75) | 1.15 m/s² (or VDV 21 m/s1.75) |
A(8) is the vibration magnitude normalised to an 8-hour reference
period: A(8) = ahv√(T/8). The ACGIH TLV for hand-arm vibration ranges from
4 m/s² for ≤ 1 h/day exposure down to about 1.4 m/s² for a full shift.
Heat Stress — WBGT (ACGIH TLV / ISO 7243)
Screening WBGT limits (°C) for an acclimatised worker, by work
intensity and the fraction of each hour spent working. Subtract ~2–4 °C for
unacclimatised workers; adjust for clothing.
| Work / rest per hour | Light (≈200 W) | Moderate (≈300 W) | Heavy (≈415 W) | Very heavy (≈520 W) |
|---|
| 75–100% work | 31.0 | 28.0 | — | — |
| 50–75% work | 31.0 | 29.0 | 27.5 | — |
| 25–50% work | 32.0 | 30.0 | 29.0 | 28.0 |
| 0–25% work | 32.5 | 31.5 | 30.5 | 30.0 |
Posture Assessment Action Levels
| Tool | Score | Action |
|---|
| RULA | 1–2 | Acceptable |
| 3–4 | Further investigation; change may be needed |
| 5–6 | Investigate and change soon |
| 7 | Investigate and change immediately |
| REBA | 1 | Negligible risk |
| 2–3 | Low risk; change may be needed |
| 4–7 | Medium risk; further investigation, change soon |
| 8–10 | High risk; investigate and implement change |
| 11+ | Very high risk; implement change now |
