Episode 41: The K-factor and safety factor

It is a generally known fact that with the tie-down lashing method, some circumstances that cannot be precisely weighed up by the user can influence the securing force. One of these circumstances is the distribution of the pre-tensioning force (STF) from the ratchet side to the opposite side of the load.

Most of those involved know from their gut feeling that less arrives on the opposite side than on the ratchet side. The question that immediately arises is: how much power is lost and can I calculate this?

This is precisely where the discussion between supporters of EN-12195-1 and VDI-2700ff begins. Both sides are staffed with experts, with the difference that only Germans are involved in the VDI-2700ff, but those from 27 countries are involved in the EN-12195-1. Unfortunately, those involved on both sides lose sight of the driver and the shipper, who are supposed to put the sometimes very theoretical considerations into practice.

In the following article, I will try to clear up the jungle a little and present it in a way that is easy to grasp for practitioners. I hope I succeed. But even I am not infallible.

The tie-down lashing method

With the tie-down lashing method, a belt is placed over the load, the hooks of the fixed and loose ends are hooked in and then the pre-tensioning force is applied with the ratchet. The percentages in the diagram are fictitious and are only intended to show that the pretensioning force applied over the corners of the load is becoming less and less.

Regardless of how high the preload force is, it is generally divided into at least three areas:

  • Ratchet side: 100% STF
  • Over the load less than 100%
  • Even less or nothing at all on the opposite side.

If there are more than two deflection points, the clamping force distribution also becomes more fragmented.

VDI-2700 Sheet 2 Edition 07-2014 refers to the transmission coefficient (k), which can assume a value of k=2.0 under certain circumstances. These specific circumstances would be a pre-tensioning force indicator at the slack end or a belt with two ratchets. In practice, a value of k=1.8 is recommended. In my view as a practitioner, that is a very sporting idea. Edge gliders (edge protectors) should generally be used. The remaining force is calculated using Euler’s formula:Fres = F * e -µ*α.

Will the general shippers and drivers be able to cope with this? Rather no!

The formulas for calculation

EN-12195-1 edition 01-2021 refers to the safety factor (fs) because it assumes that the preload force is the same on both sides. The safety factor is used to compensate for uncertainties when securing loads. To the sides and to the rear it should be assumed to be fs=1.1 and to the front fs=1.25.

The equation for calculating the pre-tensioning force of a lashing is as follows:

This is the formula for calculating the securing force. The safety factor (fs) is added at the end of the usual calculation. This means that the calculated preload force is increased by 10% or 25% across the board.

This is the formula for calculating the frictional force for direct lashing.
The coefficient of friction µ is multiplied by the factor fµ=0.75. This means that it is reduced by 25%.

Load weight = 1,000kg
Coefficient of friction µ=0.3
1,000daN * 0.3 = 300daN.
1,000daN * 0.3 * 0.75 = 225daN

Reducing the frictional force automatically results in an increase in the securing force, which is intended to compensate for uncertainties.

EN-12195-1 also attempts to balance out the uncertainties with mathematical considerations, whereby the factors themselves also contain an uncertainty. Nobody knows exactly whether the factors are correct. In principle, however, it is better to work with safety than not to. Such safety factors have always been used in seafaring to safeguard against imponderables. So this is nothing new.

Implementation in practice

How can this problem be put into practice?

Option 1: the responsible person according to §9(2) OWiG, who is appropriately trained and knowledgeable, takes a calculator and calculates each individual charge. From a legal/physical point of view, this is the safest method. The measures should be documented.

Variant 2: the responsible person in accordance with §9(2) OWiG ensures that certain conditions are met. These considerations result from the calculations of variant 1, which could be:

  • Provision of a suitable vehicle
  • Use of suitable and sufficient securing devices. Preferably always use long-lever pull ratchets, edge protection angles (edge gliders) and anti-slip mats. Long-lever tension ratchets because a preload force of more than 400 daN is applied fairly reliably.
  • If no edge protectors are used, only calculate with the preload force on the ratchet side (k-factor = 1.0). If any are used, set the k-factor to 1.5.
  • Create a loading instruction that puts the calculations into practice. This must contain clear instructions such as:
    • Swept clean loading area
    • Form-fit stowage
    • Use of anti-slip mats
    • Use of edge protection angles
    • Correct position of the tension belts
    • Spot check of the preload force
    • The control of all measures

Experience shows that most loads can be transported safely when using variant 2 and the risk is reduced to a minimum.


The considerations described above do not release the person responsible, which in any case is the management, from organizing the entire loading process in their own area in a comprehensible manner. This can be used to counter the accusation of “gross organizational negligence pursuant to §130OWiG”. If inadequate load securing results in a situation that goes beyond an administrative offense and becomes a criminal offense, it must be demonstrated what considerations and measures were taken to avoid or prevent the situation. A good basis is the study of VDI-2700 Sheet 5 “Quality Management Systems”. Here, the entire process is broken down into thin, comprehensible slices that then need to be organized.

It is best to start immediately with the measures described if they have not already been taken.

I wish everyone happy working and a lucky hand.

Yours, Sigurd Ehringer

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