Mode factors are the calculations used to determine the tension when lifting with two or more slings/chains at an angle greater than vertical. 

When a sling is being used in a vertical position (a straight pull), a Working Load Limit (WLL) applies. 

Even though the term WLL is very important, it is slowly coming out of use. People find it confusing because sometimes, they don’t get taught the difference between WLL and Safe Working Load (SWL). So SWL is now the more popular to use.

Here’s the difference:

As explained, WLL is the maximum weight the sling has been designed to lift. SWL is the adjusted WLL, depending on what configuration the sling is in.

The calculated tension/force going through each sling is classed as the Safe Working Load (SWL).

In this scenario, the sling or chain used directly relates to the weight of the load being lifted. I.e. a 1te sling for a 1te load, a 1te sling for a 2te load, and so on. 

This changes when two or more slings or chains are used at an angle. The greater the angle of the accessories, the more tension is on them.

Here’s a diagram to show that theory.

As you can see, as the angles of the accessories increase, the strain on them increases. So, let’s take the 150° angle as an example. Even though the load only weighs 1te, there is 6te of strain on each sling. Therefore, 6te slings or bigger need to be used at that angle. But lifts would not be done at that angle. This diagram is purely to indicate what happens to the SWL when the sling angles increase.

The maximum recommended angle is 90°. The maximum angle permitted is 120°.

Mode factors help slingers decide what accessories to use, in relation to the load weights and accessories angle.

Let’s explore how they do this.

But before we do, there’s a free gift for you at the bottom of this page, to help you work in confidence. Followed by services we provide.

Uniform Load Method

The Uniform Load Method is the standard practice European sling manufacturers use to calculate the sling rating for multi-leg configurations.

Here’s a basic example:

Let’s use the golden angle. The internal angle at the master link is 90°, which makes the internal angles where the slings meet the load 45°. Each sling is under 0.7te of tension. Adding them together gives 1.4te. So, lifting a 1te load with slings at a 45° angle gives a mode factor of 1.4.

This is shown in the load chart below.

Using more than two slings

Lifts are sometimes done with four slings. When this happens, the mode changes. Here’s how:

Using the golden angle again, you begin by using the same method as with two slings. However, one sling gets cancelled out. This is because slings can vary slightly in length. One leg is often longer, so this acts as a stabiliser. It stabilises the load. Unlevel loads could also be a factor. Sometimes It’s a combination of both.

You can see the mode for using four slings in this load chart.

When do you need to use mode factors?

There are two scenarios where mode factors need to be used.

• If you know the weight of the load.
• If you don’t know the weight of the load. 

Here are the two formulas to use when calculation for each:

• If you know the load, divide by the mode.
• If you don’t know the load, times by the mode.

If you know the load

Let’s say a slinger is lifting steel beam that they know weighs 2te. Using the Uniform Load Method, they divide that 2te by the mode. They know the mode is 1.4 at the Golden Angle.

2te ÷ 1.4 = 1.42te 

This means there will be 1.42te of tension on each leg.

The slinger now knows they’ll need 2te slings. 1te slings won’t be sufficient.

If you don’t know the load

Let’s say a slinger is lifting a steel beam, but this time they don’t know what the weight is. Experienced people generally have a rough idea of how much things weigh. So, the slinger estimates that the beam weighs 2te. For this they’ll need 2te slings.

They’ll multiply the 2te slings by the mode factor 1.4. 

2te × M1.4 = 2.8te.

By this calculation, 2.8te is the maximum the slinger can lift using 2te slings at an angle no greater than 90° at the master link.

The slinger will now do a test lift. They’ll instruct the driver to take tension on the beam until the crane is holding the maximum weight the slings can take. In this case, 2.8te. If the load is still on the ground when this weight is reached, the slinger will need to use bigger slings.

Choke Hitch

When lifting loads, cradle slinging is no longer permitted on site unless ratchet strapped around the side of the load. Some sights allow only to lift low level from a lorry, locally to the ground.

Loads should be choke hitched. With regards to slings, this is where the sling is wrapped around the load and fed through the eyelet of the other end of the sling until tension squeezes the load intact.

When using lifting chains, the chain wraps around the load, then the latch hook hooks onto the chain. As the tension increases when the load gets lifted, the slinger makes sure the gap between the latch hook and the load decreases, to tighten the grip. This is much like tightening a tie or noose.

When choking loads, the sling’s lifting capacity reduces by 20%. This is the case for both single wrapping and double wrapping loads.

There are two ways of doing the calculations, as follows:

Either minus 20% or times by 0.8.

Single sling

Very rarely will a lift be done with a choked single sling. But if it is, 20% of the sling’s SWL gets reduced.

So, if a single 1te sling is used to lift a 1te load, the calculation is 1te – 20 = 0.8. So, we now have a 0.8 mode factor because of the choke hitch, which means the sling is capable of lifting 800kg in that configuration.

The other way is 1te × 0.8 = 0.8te (800kg).

Two slings

On most building sites, there are long loads to be lifted, like scaffolding, rebar, steel beams, etc. For these lifts, two slings would be used, double wrapped and choked. If the loads are single wrapped, they usually have to have banding or ratchet straps around the load.

Using the Uniform Load Method, with 1te slings, for example. We know the mode factor is 1.4, with the slings at no more than 90° at the master link and 45° internal at the load.

The calculation is: (1te × 1.4) – 20% = 1.12

Or more simply, M1.4 – 20% = 1.12

The other method is:

1te × 1.4 × 0.8 = 1.12

Or more simply, 1.4 × 0.8 = 1.12

Therefore, the maximum that can be lifted with the two 1te slings is 1.12te. Which means those slings are okay to use up to that weight.

To finish off

This information can be a lot to think about for a slinger. Especially an inexperienced slinger. And particularly on very busy sites that don’t allow much time to think.

In these situations, it’s important to stay calm and take time to think about what you’re doing. These calculations might seem daunting at first, but they become like second nature.

If you’re unsure, all slings should have a label on that shows a simplified load chart that gives the mode factors. This is also the case for lifting chains.

A crane supervisor or appointed person (AP) will also be able to help if you’re unsure. Also, LOLER provides all the information you need regarding lifting regulations.

You can always invest in yourself and do extra training to give you the proper skills and enhance your chances of employment.

The important thing to take away is, there is no room for cutting corners in the lifting industry. No cheating, no ‘that’ll do’, and no negligence.  

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For a visual demonstration of the information shown in this article, watch this video.

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Here’s a nice gift. A free Mode Factors PDF that gives you all the information in this article. You can download it to your device to help you work in confidence knowing you can whip it out to refer to whenever you need it.

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