Key takeaways
- Safe working load (SWL) is the most a bag may carry in normal use.
- A 5:1 bag is designed for a single trip; a 6:1 bag can be reused.
- Never fill a bag beyond its SWL, and never reuse a single-trip bag.
Every jumbo bag label carries two numbers that matter more than anything else: the safe working load (SWL) and the safety factor (SF).
Safe working load
The SWL is the maximum weight the bag is designed to carry in normal use — for example 1,000 kg or 1,500 kg. It is a limit, not a target: filling beyond it puts the loops, seams and fabric under loads they were not designed for.
Safety factor
The safety factor is the margin built into the design. It is the ratio between the load the bag must survive in testing and its SWL.
| Safety factor | Meaning | Use |
|---|---|---|
| 5:1 | Withstands at least 5 × SWL in testing | Single trip — use once |
| 6:1 | Withstands at least 6 × SWL in testing | Multi-trip — can be reused after inspection |
So a 1,000 kg SWL bag at 5:1 has been designed to survive 5,000 kg in a test. The international standard for these tests is ISO 21898.
Single-trip or multi-trip?
- Single-trip (5:1) bags are the right choice when bags leave your site with the product and are not returned.
- Multi-trip (6:1) bags make sense in closed loops — for example between your plant and a customer who returns empty bags. Inspect each bag before every reuse and retire any with damaged loops, seams or fabric.
Choosing the right SWL
Work out the weight of product per bag from its bulk density and the bag's volume, then choose the next SWL above it. Our team can do this calculation for you from your product data.
Frequently asked questions
What does 1,000 kg SWL at 5:1 mean?
The bag may carry up to 1,000 kg in use, and its design must withstand five times that load in testing. It is a single-trip bag.
When do I need a 6:1 bag?
When you want to fill, empty and refill the same bag. Multi-trip bags are built to a 6:1 safety factor and should be inspected before every reuse.
What SWL can Blue Line Pack make?
We make jumbo bags with safe working loads up to 1,500 kg, in 5:1 single-trip and 6:1 multi-trip designs.