Rigging in depth: truss, wire and safety factor
Why a fitting is never just a detail
Hanging and securing equipment over people's heads is the most dangerous area in the profession — and there is a reason why rigging is treated with a completely different thoroughness than most other backstage tasks. This article goes closer to the technical foundation: truss, wire and the concepts that determine whether a suspension is safe.
§Truss: the skeleton above the stage
Trusses are light, self-supporting structures — typically in aluminium — used to hang lights, sound systems and screens over a stage or floor area. A truss must be properly supported at the ends (and often in the middle on long spans), and each mounting point has a limit to how much load it can bear before the structure bends or fails.
- 01Trusses must be supported according to the manufacturer's span and load tables, not by eye
- 02Everything that hangs on the truss must be included in the total load calculation – not just the heaviest single item
- 03Internationally, the industry often uses the American ANSI E1 standards from ESTA/PLASA as a common reference frame for truss and rigging equipment, although there is no corresponding separate Danish EN standard specifically for stage truss
§Wire, straps and safety factor
Steel wire lines and lifting straps used to secure equipment in the rigging are covered by general European standards for lifting equipment — including EN 13411 for wire terminals and EN 1492 for textile lifting straps. What is common to all lifting equipment is that it must have a safety factor: the breaking strength must be significantly above the working load (WLL — Working Load Limit) the equipment is marked for.
| Concept | Meaning |
|---|---|
| WLL (Working Load Limit) | The maximum load the equipment is permitted to carry in normal operation |
| Safety factor | Ratio between breaking strength and WLL |
| Certificate/marking | Documentation that the equipment has been tested and approved |
| Load angle | Angle of a strap which can significantly increase the actual load |
§Practical check before lifting
Before anything is hoisted or hung up, fittings, wires, and slings must be visually inspected for damage, markings must be readable, and the angle of any slings must be kept as close to vertical as possible — the sharper the angle, the more the actual load on each part of the setup increases. Everything that can fall down must also be secured with an independent fall arrest.
§Why technical language matters
The better you understand the concepts behind rigging – WLL, safety factor, bearing and load angle – the better you can communicate precisely with a rigging supervisor or a rigging equipment rental company, and the more easily you recognize when something deviates from what it should be.