This is a general term used to describe Cargo Transport Units (CTU) or simply Freight Units (FU's) that can be handled by conventional container handling equipment.
Not all freight units are ISO Standard Containers, variants have evolved to satisfy the ever changing demands in this industry and many now carry specialised equipment rather than cargo. The legacy of the past has, however, left millions of obsolete containers scattered around the globe that may still have a viable use, even as scrap, and may need lifting. Fortunately many incorporporated corner castings that complied with the original ISO Standards thus guaranteeing that they can, at least, be coupled with conventional lifting lugs. Whether or not they are in a fit state to be lifted may need sanctioning by an engineering surveyor especially if badly corroded and may present safety issues when being lifted.
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Cargo Transport Units CTU's
Containerisation slowly replaced traditional cargo handling during the 1950's and 60's after developments in containerized cargo handling during WW2. During this time international trade was transformed by reducing handling times, increasing security and ultimately lowering the cost of traded goods.
A comprehensive history of containerisation in the UK is given at
It soon became apparent that standardisation was essential with respect to geometry, strength and certification of containers enabling their smooth throughput internationally. This started in the late 1960's and developments in
continues to this day in the light of experience and technological advances.
The first major ISO publication was R668, this covered:- Terminology, Dimensions and Ratings followed by ISO R1161 for corner castings that specified their dimensions, aperture profiles and material specification for weldability and impact resistance.
Nowadays container dimensions, construction and strength testing to which they must conform to are:
BS ISO 668 (Series 1 Freight containers.Classification, dimensions and ratings) and
BS ISO 1496 (Series 1 Specification and Testing).
A full comprehensive publication concerning container construction, testing and Rules for Certification of Cargo Containers
Series 1 Containers Size Designation from BS ISO 668
External height ranges for A,B,C,D & E containers.
Maximum Gross Weight (MGW)
This information should be prominantly displayed on containers.
The Maximum Gross Weight (MGW) or Gross Rating (GR) is the sum of the empty container weight T (Tare) and its payload P. Both should be quantified in units of mass, kg or lb.
A detailed explanation of units is given at
Mass Force Weight.
Up untill 2005 the MGW of Series 1 containers was linked to the types A,B,C,D as defined in ISO 668 995 and Plated containers up to 2005 will be limited to Certified Test Weight displayed on CSC plate. After 2005 all Series 1 containers, other than Type D (10ft length) were re-rated as "Heavy Tested" to 30,480kg or 30Ton. Specification for 45ft containers were also added and became Type EE, EEE also rated at 30,480kg.
(Non ISO compliant containers may be rated at higher MGW typically 35,000kg and will be prominantly displayed together with other relevant information.)
Table 1 giving past and present MGW's for ISO containers.
Pre 2005 kg
Post 2005 kg
Table 1 From ISO 3874
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Container Safety Convention (CSC)
When released for world-wide use, CTU's that conform to the relevant standards are certified and carry a Container Safety Convention Plate. The essential part is shown here, other information might include ownership, a complete list of all loading tests undergone and timber treatment for their wooden floors.
What is significant is the Maximum Gross Weight (MGW), when loaded and presented for lifting, it is best to assume that it is fully laden up to the rated MGW.
An up to date CSC plate is essential for containers used in international trade and an identification plate is displayed in a prominant place safe from being damaged. It acts as an international passport, guaranteeing the security of their contents besides being fit for purpose.Information appertaining to strength capacity of the container presented on the plate is covered in great detail in Amendments to the International Convention for Safe Containers of 2 December 1972
Perhaps the most comprehensive source of information for both Cargo Transport Units and CSC plating is available on the GDV link below.
Over 17 million containers have accumulated around the world since their introduction, many of which may not be up to date nor even standard, but they may need shifting and when called upon to handle them and there are problems with identification, it would be wise to consult the
Main Transport Unit Types
Standard Series1 Containers
Universal dry cargo containers
These are by far the most common type of CTU's in use and were the first units to be standardized under the Freight Container Certification Scheme introduced by Lloyd's Register of Shipping in 1968. These are referred to as General Cargo Dry Containers and originally had an 8ft square section so they could pass through railway tunnels and came in lengths of 10ft increments up to a maximum of 40ft.
Applies to the space envelope defined by the Standard Series1 Container volumes and any cargo that extends beyond their limits is classified as Out of Gauge (OOG).
Nowadays the height is more usually 8ft6in but universally 8ft wide. A varient known as European overland container has an internal width of 8ft making the external width 8ft 6in. Non standard corner fittings are used that allow the the base and top pickup points to correspond to standard ISO dimensions for handling and securing purposes, but standard lifting lugs CANNOT be used in bottom corner fitting apertures with overhanging top flange.
Out Of Gauge Flat
This may be carried by various freight units but generally by open topped containers, platforms or flat racks. Depending on the nature of this cargo it is subclassified as Standard OOG where cargo does not extend beyond the space envelopes of the equivalent container type, usually 20ft and 40ft lengths, and Non Standard OOG where it does. Cargo that could be contained but is deemed unsuitable for being enclosed eg fertilizers and uncured animal hides is often carried on platforms as OOG deck cargo.
The example opposite of an OOG lift shows a uniformly distributed loaded 40ft platform with both corner and inboard lifting points (corner castings). The inboard points have 30ft centres, resulting with greater lifting angles and, therefore, lower sling forces. These particular early platforms were very flexible and when fully laden this lifting arrangement, using inboard points rather than the corners, was widely practiced. Modern 40 ft types use end lifting points only on account of their increased rigidity.
20ft and 40ft ISO Flats
These come in two standard lengths of 20ft and 40ft and are mainly for OOG cargo. There may be height restrictions on platforms when stowed as deck cargo. Ratings vary from one manufacturer to another but for general use are taken as 25 ton for 20ft unit and 40 ton for 40ft platform. What is paramount for this type of freight conveyor is that loading is central, and any eccentricity of load is not permitted.
Flatrack High Cube 40ft Platform
Like platforms these come in two standard lengths of 20ft and 40ft and are also for OOG cargo. These units have evolved to cater for ever increasing cargo profiles but basically have either fixed or collapsable ends. The fixed end types range from rigid corner pillars, topped with top corner fittings, to substantial end panels again with top corner fittings. These flat racks can be lifted by their ends with standard container gantry cranes using twistlocks that couple with top horizontal apperture of corner fittings for vertical lifting only. The collapsable type make it easier to transport because they can be stacked when empty. Their total MGW must obviously be within limits hence need for tare weight to be clearly marked. With both types their top end apertures are blanked of to prevent hooks being used for lifting. In any case they should never be lifted by the top end corner fittings using side lifting lugs but only from the very bottom corners and with slings fitted with spreaders to prevent contact with cargo. The same MGW and loading limitations for platforms also apply to flat racks.
Generic Tank Container
These are generally 20ft long, and can be used to carry liquid, gases, dry powder or granules and are usually rated in Litres. When filled with liquids or solids, tanks may present problems when being lifted because of their mobile centre of gravity. There are three types:- Beam Tank
having 27,000 litres capacity for gases only, where the tank acts as a monocoque structure with corner fitting attachments welded to it resulting with low tare weight but limited strength.
This is by far the most common type where a self contained tank is built into ISO dimensioned rigid frame for maximum protection. Capacity ranges from 17,000 Litres to a maximum of 26,000 Litres but when carrying dry materials Maximum Gross Weight is limited to 33.5ton.
have an increased capacity of 35,000 Litres and are made for ease of intermodal transfer but being non standard they don't have the same degree of protection as the Generic Tank.
Non-standard Specialised Containment Units.
This class covers a vaste range of container units, below are just two examples at the extreme end of the customised freight unit spectrum where applicable standards have been incorporated into their design. One houses a specialized mobile process unit, the other is for carting rubbish.
The process unit is a self contained water filtration system comprising generator, suction and discharge pumps, to be transported via modified 40ft container lorry. The other unit is used by City of London Council to convey domestic rubbish from riverside depots along the Thames, by barges, to incinerators down river where they are offloaded by standard container handling equipment onto specialised vehicles for the last leg of their journey. These fully sealed reinforced bins have the same base and roof dimensions as a 20ft Series 1C container.
If non-standard types are to be transported across international borders, it is advisable to incorporate pick up points that conform to applicable ISO standards in order that they can be handled with conventional container lifting equipment. Process units such as electricity generators, pumps etc should at least be mounted on a rigid platform type base, fitted with ISO bottom corner fittings at positions given in ISO 668 for standard containers.
40ft Process Unit with 8 standard
ISO bottom corner lifting points.
20ft Ton Waste Transporter.
CX type since height less than 8 ft.