Merciless physics: Drivers and loaders are both responsible for load securing
Over the last few years, the subject of load securing has become very important. However, in spite of all the efforts some basic mistakes are still being made, meaning that many loads are not adequately secured. This results in major accidents with serious injuries and high levels of material damage – especially in domestic goods transport.
(01.06.2010) If the driver of a truck has to brake abruptly or swerve to avoid a hazard, for instance if he has to change lanes suddenly because of another driver's mistake, it becomes very obvious: the laws of nature also apply on the loading space of a truck – and they are merciless. Consequently, the argument "That's so heavy it can't move", can safely be changed to "That's so heavy, it has to be secured especially well."
The vehicle brakes, but what brakes the load – and where does it go? Is it not a good feeling when you have secured the load and can thus "keep your options open"? In Germany, load securing is covered by several statutory regulations, such as Section 22 (1) of the German Road Traffic Regulations (StVO): "The load, including equipment for securing the load and loading devices are to be stowed and secured so that they cannot slide, fall over, roll forwards and backwards, fall down or cause avoidable noise even during emergency braking or sudden evasive action in compliance with state-of-the-art technology."
This text lists the specific situations where this counts: emergency braking or sudden evasive action. At the latest then, the argument: "I drive with care, therefore I don't have to secure the load" loses all credence. The actual specification is in the sentence "in compliance with state-of-the-art technology" – in particular, this means German industrial standards (DIN) and European (EN) standards, as well as the guidelines of the Association of German Engineers (VDI), currently, for example, VDI Guideline 2700 "Securing of loads on road vehicles". It must be remembered that Section 22 of the German Road Traffic Regulations applies not only to the driver but also to the loader. When considering load securing you have to consider the question of which forces could affect the load. As already suggested, load securing must compensate for the forces that could occur during normal driving situations. This means that the load must be secured for emergency braking, sudden evasive actions and bad roads – but not for traffic accidents. According to the specifications of VDI Guideline 2700 ff. and the European standards for load securing, every load must be secured as follows:
* In the driving direction: with 80 per cent of its loaded weight
* To the sides: with 50 per cent of its loaded weight
* To the back: with 50 per cent of its loaded weight
The friction force is part of natural load securing, as it exists as soon as the load is placed on the loading area. The extent to which load securing is covered by friction depends on the materials.
In daily loading situations you can use four values.
* Metal on metal µD = 0.1 (corresponds to 10 per cent load securing through friction)
* Metal on wood µD = 0.2 (corresponds to 20 per cent load securing through friction)
* Wood on wood µD = 0.3 (corresponds to 30 per cent load securing through friction)
* Anti-slip mat µD = 0.6 (corresponds to 60 per cent load securing through friction)
These values are guiding values only and can be assumed only with well-swept and grease-free surfaces. Friction force has an enormous effect on load securing. If anti-slip materials with a sliding friction coefficient of µD = 0.6 are used, the friction force is greater – which means that less securing force is needed. Nevertheless, the following still applies: "sweep first, then load."
What must be used to secure the load? It doesn't matter whether lashing straps, lashing chains, lashing wire or other aids are used to secure the load, the issues are always the different forces and how these are to be overcome. However, each lashing material or aid has its advantages and disadvantages; therefore, the user must decide which one to use. For example, lashing straps: lashing straps are the most commonly used – but also the most frequently overestimated – lashing material. "My strap holds 5 tons – it says that on the label, doesn't it?" This statement is correct, but also incorrect. To understand this you have to read a lashing strap label and know what the abbreviations mean.
"My lashing strap holds 5 tons". This is correct if you use it to apply head loop strapping and are able to use the Lashing Capacity (LC) in the strapping. But it does not apply if you use it as tie-down lashing and are thus able to use only the Standard Tension Force (STF). How must the load be secured? The regulations demand that the load is adequately secured – but do not specify how this is to be done. The type of load securing is left up to the users, and they often come to the following conclusion: load securing = tie-down lashing. However, tie-down lashing is not effective for most goods. With tie-down lashing the lashing material exerts pressure on the load with its standard tension force (STF) and presses this down on to the loading area. The lashing material does not secure the load, it increases the friction force and the friction force secures the load.
With diagonal lashing the load is kept in position by the lashing capacity (LC) of the lashing material with direct pull if, for example, it tries to move when the truck brakes. The lashing is inserted into lashing points on the load and into lashing points on the loading area and is then pre-tensioned just slightly.
With head loop strapping the load is held in the lashing by the lashing capacity of the load securing material. The load securing material is inserted into lashing points on the vehicle; lashing points on the load are not necessary.
With head loop strapping the load is held in place with the lashing straps. However, the load securing devices can do this only if they are locked into the anchor rails with suitable adapters.
With positive securing using the vehicle body the load is loaded directly on to the end of the truck or against the sides or stanchions of the truck. Wedges or chocks can also be used. But these must be fixed to the loading area, for example, with perforated rails or nails.
If the vehicle body is to be used to secure the load, it must guarantee the required securing force. For vehicles over 3.5 tons gross vehicle weight (GVW) the European vehicle structure standard DIN EN 12642 specifies certain load-carrying capacities. But this standard has applied only since 2002 and also makes an exception: curtainsiders (tautliners) with a standard body are not suitable for load securing; therefore, the German employers' accident insurance fund for vehicle operators (BGF) also describes them as weather protection. Now, at the latest, the idea that "every strap in the tarpaulin holds 2 tons" no longer qualifies.
In January 2007, the standard was extended by the annex "Code XL" – and this also applies to curtainsiders. Vehicles with a body according to "Code XL" have a certificate listing the load, the loading conditions and the chassis number. Vehicles whose body stability complies with this standard may secure such things as bales of paper for recycling, beverages or general cargo under certain conditions.
Containers may also be secured on the truck with variable blocking facilities in front of and on the sides of the container. Load securing to the back of the vehicle is a problem. Although it is hard to believe, snap hooks are not suitable for this.
On trailers the containers are generally secured by Y-lashing; this is based on the principle of tie-down lashing. But because the containers and the surface of the load-carrying vehicle are made from smooth metal the standard tension force needed for securing the load must be very high.
The securing principle of Y-lashing is tie-down lashing. The load must be pressed down on to the loading area with a very high standard tension force (STF). If a container with a mass of 10 tons sits freely on the loading area, lashing with a standard tension force (STF) of at least 15,000 daN (corresponds to 15 tons) with direct pull is needed on each side. Even if the container is blocked to the front, each of the two lashings must still have a standard tension force (STF) in direct pull of at least 7,500 daN (corresponds to 7.5 tons).
When you see these figures, you will ask yourself how the containers can possibly be secured. But the answer is quite simple: by direct lashing. If the lashing chains are used as X-lashing, a free-standing container weighing 10 tons can be secured adequately with four chains (two on each side) with a lashing capacity (LC) of 6,400 daN each and suitably dimensioned lashing points.
"I've been driving for 20 years like this and nothing has ever happened." This achievement deserves recognition, but it does not mean that it would have applied in every extreme situation. Load securing is a complex subject and there are several aids available. For example, on the Internet a lot of information is available at www.ladungssicherung.de; details about training can also be requested by e-mail from email@example.com
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