SWL and safety factor of big bags explained
The safe working load is the weight a FIBC is designed to carry; the safety factor is how many times that load the bag withstands in the test rig. Together they define the bag's strength and whether it can be reused.
Every big bag is built for a safe working load (SWL), typically 500 to 2,000 kg, and a safety factor of 5:1 for single-trip or 6:1 for multi-trip use.
A big bag (FIBC) is designed for a specific safe working load (SWL), also written safety work load, which is the maximum weight of product it may carry. Common SWLs are 500 kg, 1,000 kg, 1,200 kg, 1,250 kg, 1,500 kg and 2,000 kg. The safety factor (SF) states how many times the SWL the bag withstood in the test rig: 5:1 for single-trip bags and 6:1 for multi-trip bags. Both values are printed on the label of every DIV Trades big bag.
What is the safe working load (SWL)?
The SWL is chosen by the customer. It is often set so that a full truck carries 24 or 25 tonnes: depending on the bag base, that leads to an SWL of 1,000 kg or 1,250 kg (see the dimension page for the truck table). A higher SWL requires stronger body fabric and loops, which DIV Trades selects for you. The SWL is a property of the bag, not of the product, so a 1,000 kg bag filled with 800 kg is still a 1,000 kg bag.
What is the safety factor (SF)?
In the test rig a filled bag is lifted repeatedly with a load that is a multiple of its SWL. A bag with SF 5:1 fails only above five times its SWL: a 1,000 kg bag bursts above 5 tonnes, a 2,000 kg bag above 10 tonnes. SF 6:1 bags are built stronger and withstand more than six times their SWL.
| SWL | SF 5:1 (single trip) | SF 6:1 (multi trip) |
|---|---|---|
| 500 kg | 2,500 kg | 3,000 kg |
| 1,000 kg | 5,000 kg | 6,000 kg |
| 1,250 kg | 6,250 kg | 7,500 kg |
| 1,500 kg | 7,500 kg | 9,000 kg |
| 2,000 kg | 10,000 kg | 12,000 kg |
Single-trip or multi-trip big bags?
Single-trip big bags (SF 5:1)
Most big bags are used once: filled, sold and emptied at the customer. Collecting the empty bags is usually not economical, in the food industry reuse would not be hygienic, and some bags are never emptied at all because they serve as permanent waste containers. Single-trip bags cannot be repaired and must not be reused.
- Lower fabric weight and price
- No return logistics
- The right choice for food and for one-way distribution
- One filling only; reuse is not permitted
Multi-trip big bags (SF 6:1)
Worthwhile when all bags are emptied at the same place and can be collected easily, and when the product is not food. The bag returns to the filling point and is reused a limited number of times. An optional trip label lets you tick off each cycle. There is no fixed rule for the number of trips, but damaged bags must be taken out of service and the same bag must always carry the same material.
- Lower cost per trip in closed loops
- Stronger construction with SF 6:1
- Heavier fabric and higher unit price
- Return logistics and inspection needed
- Not for food, and never for changing products
Big bags cannot be repaired
Neither single-trip nor multi-trip FIBC may be repaired. A damaged bag must not be filled or lifted, and a multi-trip bag must not be used for a different material on a later trip.
How are SWL and SF certified?
All DIV Trades big bags are tested in-house or certified by recognized testing institutes. The certificates state the SWL and SF of the design, and we deliver the test reports for your FIBC on request. Our quality management is certified to ISO 9001:2015.
Labeling of SWL and SF
Every bulk bag carries a label stating its SWL and SF. Multi-trip bags can have an additional trip label for counting cycles. The label can be sewn into a document pocket or printed directly on the bag, see printing.
UN big bags: SWL and stacking load instead of SF
UN big bags for dangerous goods are certified with an SWL and a maximum stacking load, but they have no safety factor in the sense above. They are always single-trip bags.
What does SWL mean on a big bag?
Safe working load: the maximum weight of product the bag is designed to carry, for example 1,000 kg. It is printed on the label of every bag.
What is the difference between SF 5:1 and SF 6:1?
SF 5:1 bags are single-trip and withstand five times their SWL in testing; SF 6:1 bags are built stronger for multiple trips and withstand six times their SWL.
Can I reuse a 5:1 big bag?
No. Single-trip bags with SF 5:1 are designed for one filling only. Choose SF 6:1 multi-trip bags if you need to reuse them.
How many times can a multi-trip big bag be used?
There is no fixed rule. Use is limited, the bag must be inspected before each trip, damaged bags must be withdrawn, and the material must stay the same.
Can DIV Trades provide test reports?
Yes. Our bags are tested in-house or certified by recognized institutes, and we send the test report for your bag design on request.
Get the right SWL and SF for your product
Send us the product, bulk density and truck or pallet layout, and we will size the bag, fabric and loops to the correct SWL and SF.
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