# SYN-ERGO-001 Rev A / Workstation redesign method

**SYNTHETIC DEMONSTRATION. All task measurements, transfer quantities, schedules and timings are fictional. No real workplace implementation, worker observation, injury prediction or approval is implied.**

Factory SYN-OPS-01, operator SYN-021; station SYN-ST-A01; source K1, work area A1; factory factory-1.0, task ergo-1.0. Route: /engineering-lab/ergonomics/.

## Problem, scope and responsibility

Review one stable component-tote lift beside an assembly fixture. The visitor acts as the improvement engineer: change hand geometry, load, grip or work pattern; inspect validity and the controlling endpoint; propose redesign and verification. The tote is a fictional work-study handling unit, not an inferred real component mass, lot allocation or weekly schedule. K1 supplies it; RNLE assesses the local adjacent lift at A1, not carrying between factory areas. Layout proposals provide A1's location context only. They do not alter measured hand geometry or approve a workstation.

Baseline gross load is 12 kg, including an assumed 2 kg empty tote and 10 kg payload. Pickup H=45 cm, V=30 cm, A=45 degrees; placement H=35 cm, A=0 degrees, bench=85 cm. A declared 15 cm grip offset places destination hands at V=100 cm. The offset is a schematic assumption; real grip height must be measured. Placement requires significant control, so both endpoints are assessed and the smaller Recommended Weight Limit controls. The baseline assumes fair coupling, a representative 15-minute frequency of 1 lift/min, 45 minutes classified lifting work followed by 45 minutes of recovery, standing two-handed stable lifting, clear access, normal motion, suitable environment and firm footing.

## Reference and approach

[NIOSH Applications Manual for the Revised Lifting Equation (September 2021 revision)](https://stacks.cdc.gov/view/cdc/110725), DHHS (NIOSH) Publication 94-110, revised September 2021. [Official PDF](https://stacks.cdc.gov/view/cdc/110725/cdc_110725_DS1.pdf). The method uses metric constants/formulas in section 1.3, Table 5 frequency factors, Table 7 coupling and section 1.2 scope. It uses the corrected short-duration recovery ratio of 1.0. It does not implement a Composite Lifting Index, discontinuous-work special procedure, multi-session schedule or multi-task exposure.

RWL (kg) = 23 x HM x VM x DM x AM x FM x CM. LI = gross mass / controlling RWL.

- HM = 25 / max(25,H). H below 25 cm uses 25; H above 63 cm is excluded.
- VM = 1 - 0.003 x abs(V-75). Both hand heights must be 0-175 cm.
- D = abs(destination V - pickup V); effective D = max(25,D). DM = 0.82 + 4.5/effective D. D above 175 cm is excluded.
- AM = 1 - 0.0032 x A, with A from 0-135 degrees at each endpoint.
- FM uses the ORIGIN hand-height column (below 75 cm or at/above 75 cm) for both endpoints, classified duration and representative lifting frequency. Rates below 0.2 use 0.2. Rates between positive supported table rows use linear interpolation. A rate above the last positive row in that regime is excluded; the calculator does not interpolate into a zero-factor regime to produce a misleading finite weight limit.
- CM is 1.0 for good coupling, 0.9 for poor coupling, and 0.95 for fair coupling below 75 cm / 1.0 at or above 75 cm, assessed separately at both endpoints. Coupling choice is a declared assumption; suitable handle/container geometry must be verified against the manual.

## Duration and validity decisions

Short duration is up to 60 minutes and requires recovery at least equal to work time before another session. Moderate duration is over 60 through 120 minutes and requires at least 0.3 times work time. Long duration is over 120 through 480 minutes and assumes standard industrial rest allowances. Insufficient recovery is flagged rather than silently assigning a favorable duration: combine inadequately separated work periods to classify the actual job, which this single-task workspace does not model.

One-handed, seated/kneeling, unstable, restricted, high-speed, unfavorable-environment and inter-area carrying tasks are outside this model. Mechanically assisted transfer also receives no RNLE rating: the calculator does not subtract assistance force from mass and call the residual safe. Unsupported tasks retain their inputs for repair, but RWL, LI and index improvement are null in exports and shown as not assessed. Reasons remain inspectable. A lower index, including one at or below 1, does not establish safety for every worker or cover all hazards.

## Proposed countermeasures and implementation

- **Raise and bring closer:** Present hands at 75 cm, shorten both horizontal distances, remove asymmetry and specify suitable handles. Assume 14 s per transfer; verify by work study.
- **Split the payload:** Two 5 kg payloads in 2 kg totes replace one 10 kg payload: 7 kg gross each. Double the lift rate and transfer count; assume 12 s each. Lighter loads can add handling work.
- **Use a lift assist:** Conceptual assisted transfer, assumed 24 s. RNLE does not rate this task; assess residual manual work and equipment suitability separately.

These are complete predefined examples from the baseline, not optimizations of an arbitrary custom task. Choosing one creates a visitor proposal. Custom edits are stored separately from the immutable baseline. Raised presentation changes both hand positions and handle quality. Split payload preserves 10 kg payload per reference bundle: two 7 kg gross totes each contain 5 kg payload plus 2 kg tare, with twice the frequency. The lift-assist example illustrates changing method and the need for another assessment.

## Computed results

| Scenario | Controlling RWL / kg | LI | Payload / bundle | Assumed handling / bundle |
| --- | --- | --- | --- | --- |
| Baseline | 7.471 | 1.606 | 10.0 kg | 18.0 s |
| Raise and bring closer | 21.620 | 0.555 | 10.0 kg | 14.0 s |
| Split the payload | 7.233 | 0.968 | 10.0 kg | 24.0 s |
| Use a lift assist | Not assessed | Not assessed | 10.0 kg | 24.0 s |

The lifting values are computed from the documented inputs. Time is a separately editable work-study assumption: transfers per reference bundle x assumed seconds per transfer. It has no fitted biomechanical equation and does not automatically improve when geometry changes. Time differences are shown only when payload per bundle matches. No conversion to throughput, staffing, elapsed lead time or weekly capacity is made. Splitting reduces per-lift load but increases tare moved and assumed handling work; frequency is included in the lifting assessment.

## Conceptual reach and clearance

Pickup and placement schematics each use their own ankle datum and display H/V/A. They are dimensioned endpoint views, not a human simulation or a carrying trajectory. A 35 cm horizontal design reference supports comparison; it is not an anthropometric reach percentile or universal reach limit. Clear access is declared, not computed from worker dimensions. Toe, knee and fixture access require a measured workstation review. A factory-level clear aisle cannot certify task-level access.

## Draft standard work, evidence and lessons

Export workstation assessment includes both tasks/assessments, factors, scope reasons, timing assumptions, payload equality, layout context, source, versions and a draft SYN-SW-A01-ERGO Rev A with the visitor rationale. Proposed sequence: present stable tote beside the fixture; keep access clear; use proposed grip/geometry; place under control with declared work/recovery pattern. For assistance, define residual manual tasks and equipment suitability. The draft is unverified and unapproved.

Verification requires representative-worker measurement of gross mass, hand positions, asymmetry, grip, access and environment; full-shift work/recovery and other-task review; hazards beyond RNLE; repeated equal-payload timing with variability; and workplace review/approval. No measured trial, image, calibration certificate or signature is invented. Lessons: reach, asymmetry and pickup height can dominate load stress; lighter packaging can require more work; assistance changes assessment scope; and modeled ergonomic/handling results do not resolve quality gates.

## Architecture, state and reproduction

Task assumptions and Table 5: data/factory/ergonomics.ts. Pure calculation: lib/factory/ergonomics.ts. Session parsing and export: lib/factory/ergonomics-session.ts. Workbench/diagram: components/factory/ErgoWorkbench.tsx. Summary: components/factory/ErgoSummary.tsx. Factory schema 3 migrates schema 1/2 while retaining planning/layout/quality state. Reset workstation clears only this task; factory reset clears all. Weekly demand does not change the assumed task-window frequency.

Generate with pnpm docs:ergonomics; verify with pnpm check:ergonomics. Checks include exact metric-factor arithmetic, minimum-distance treatment, Table 5 and interpolation/limits, endpoint coupling, duration/recovery boundaries, unsupported tasks, countermeasure tradeoffs, state migration/reset and export consistency. NIOSH Example 3's closer-load redesign is adapted to the manual's metric minimum H=25 cm; its rounded LI agrees with the published 1.2. The printed US-customary worksheet uses rounded multipliers and different nominal constants, so its RWL is an approximate cross-check rather than an exact metric golden value. The independent metric formula checks remain exact.

## Limits

- Fictional geometry, loads, schedules and timings; no employee observation, injury prediction or workplace approval.
- One task only; no Composite Lifting Index or multi-task/day exposure model. Frequency is an assumed representative 15-minute task rate, independent of weekly skid demand.
- Both lift endpoints are checked because fixture placement needs significant control. FM uses origin hand height for both endpoints.
- Scope assumes firm footing, suitable temperature/humidity, normal motion, unrestricted standing access and little other strenuous handling. Unsupported conditions receive no RWL or LI.
- A lifting index at or below 1 does not establish safety for every worker or eliminate other ergonomic hazards.
- The reach reference is a conceptual design target, not an anthropometric percentile, reach limit or clearance certification.
- Times are editable work-study assumptions per reference bundle, not measured improvement, capacity, staffing or a simulation.
- Mechanical assistance is not rated by subtracting support force from the load. Residual manual tasks need a separate assessment.