showstack / glossary / safe-working-load
Safe working load (SWL) / working load limit (WLL) 安全操作負荷
The maximum load a piece of rigging hardware is rated to carry in normal service — not its breaking strength, and not a number to back-calculate yourself from breaking strength by guessing at a safety factor. WLL is the term current US and ISO entertainment-rigging standards use; SWL is the older term, still current in UK and Commonwealth usage, for the same underlying idea. Read the tag or the certificate rather than assume which convention a rider is using.
Easy to get wrong
SWL and WLL usually mean the same number today, but SWL historically implied a fixed safety factor — one that varied by hardware type and could be wrongly assumed rather than checked.
Neither is breaking strength — a lab figure from destructive testing. WLL/SWL already accounts for wear, cyclic and side loading, and is the number you're actually allowed to use.
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Sources
- Understanding Working Load Limit and Breaking Strength in Theatre Rigging — Entertaining Safety primary
- Working Load Limit (WLL) vs Safe Working Load (SWL): Definitions, Differences and Calculations — Safety Lifting Gear
- 起重機械及起重裝置的檢查、檢驗和測試指南 — Labour Department, HKSAR Government primary
Understand the mechanism
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