6.2 Freight containers

6.2.1       The external and internal dimensions of most freight containers are standardized by ISO.

6.2.2       The maximum gross mass and the permitted payload of a freight container depend on standardized design parameters. The International Convention for Safe Containers requires each freight container to carry a CSC safety approval plate, where the maximum permitted gross mass is specified (see subsection 8.2.1 and annex 4, section 1). Additionally, the tare mass and the payload are marked in painted letters on the door or on the rear end of the freight container.

6.2.3       With the exception of platforms (a container deck without walls), packed freight containers are capable of being stacked. This feature is mainly used in land-based storage areas and on ships during a sea passage. The permissible stacking mass is displayed on the approval plate. Freight containers with a stacking mass equal to or greater than 192,000 kg may be transported without restriction. However, freight containers with a stacking mass value less than 192,000 kg do also exist and require special attention when used for intermodal transport, in particular for the stowage in stacks on seagoing vessels (see subsections 7.3.1 and 8.2.1).

6.2.4       General purpose freight containers are available as closed freight containers, ventilated containers and open top containers. The side walls are capable of withstanding a uniform load equal to 60% of the permitted payload. The front wall and the door end are capable of withstanding 40% of the permitted payload. These limitations are applicable for a homogenous load on the relevant wall area and do not exclude the capability of absorbing higher forces by the framework of the freight container. The container floor is primarily designed to sustain the total payload homogeneously distributed over the bottom structure. This results in limitations for concentrated loads (see annex 7, section 3).

6.2.5       Most general purpose freight containers have a limited number of lashing rings or bars. When lashing rings are fitted, the anchor points at the bottom have a maximum securing load (MSL) of at least 10 kN in any direction. Recently built freight containers have, in many cases, anchor points with a MSL of 20 kN. The lashing points at the top side rails have a MSL of at least 5 kN[1].

6.2.6       Floors on freight containers covered by the CSC are only required to withstand an axle load of 5,460 kg or 2,730 kg per wheel[2] although they may be built to withstand a greater axle load. The CTU operator can provide more precise information.

6.2.7       Closed freight containers generally have labyrinth protected openings for venting (pressure compensation), but these openings do not measurably support air exchange with the ambient atmosphere. Special type "ventilated containers" have weatherproof ventilation grills built into the top and bottom side rails and the front top rail and bottom sill, through which the natural convection inside the freight container is intensified and a limited exchange of air and humidity with the ambient atmosphere is established.

6.2.8       An open top container is similar to a closed freight container in all respects except that it has no permanent rigid roof. It may have a flexible and movable or removable cover, e.g. of canvas, plastic or reinforced plastic material. The cover is normally supported by movable or removable roof bows. In some cases the removable roof is a compact steel construction suitable to be lifted off in one piece. The header (transverse top rail above the doors) is generally movable or removable (known as swinging headers). The headers are part of the container strength and should be fitted to have full strength of the freight container.

6.2.9       Open side containers have a curtain or canvas on one or both sides, a rigid roof and rear doors. While the strength of the end walls is similar to that of closed freight containers, the side curtain provides limited or no restraint capability. Open side containers are not covered by ISO standards.

6.2.10     Platforms and platform based containers are characterized by having no side superstructure except either fixed or collapsible end walls (flatracks) or are designed without any superstructure (platforms). The benefit of collapsible end walls is that the flatrack may be efficiently stacked when transported in empty condition for repositioning.

6.2.11     Flatracks and platforms have a bottom structure consisting of at least two strong longitudinal H-beam girders, connected by transverse stiffeners and lined by solid wooden boards. For securing of cargo units, strong lashing brackets are welded to the outer sides of the longitudinal bottom girders with a MSL of at least 30 kN according to the standard. In many cases the lashing points have a MSL of 50 kN. Cargo may also be secured in longitudinal direction by shoring to the end walls of flatracks. These end walls may be additionally equipped with lashing points of at least 10 kN MSL.

6.2.12     Thermal containers, commonly referred to as reefer containers, are designed for the transport of cargo under temperature control. Such cargo is generally homogeneously packed and tightly stowed from wall to wall. Therefore, the side and end wall strength is similar to that of general purpose freight containers. However, thermal containers are generally not equipped with anchor and lashing points. When a cargo needs to be secured by lashings, specific fittings may be affixed to the “T” section gratings, thus providing the required anchor points.

6.2.13     A tank container comprises two basic elements, the tank shell (or shells in case of a multiple-compartment tank container) and the framework. The framework is equipped with corner fittings and renders the tank suitable for intermodal transport. The frame should comply with the requirements of the CSC. If dangerous goods are intended to be carried in the tank, the shell and all fittings such as valves and pressure relief devices should comply with the applicable dangerous goods regulations.

6.2.14     A non-pressurized dry bulk container is a container especially designed for the transport of dry solids, capable of withstanding the loads resulting from filling, transport motions and discharging of non-packaged dry bulk solids, having filling and discharging apertures and fittings. There are freight containers for tipping discharge, having filling and discharge openings and also a door. A variant is the hopper type for horizontal discharge, having filling and discharge openings but no doors. The front and rear end walls of solid bulk containers are reinforced and so constructed to bear a load equal to 60% of the payload. The strength of the side walls is similar to that of general purpose freight containers.