Safety of Tank Containers Tank containers for the carriage of dangerous goods are regulated by a number of authorities, these include IMDG, ADR, RID, CFR 49 etc. The products that individual tank types are permitted to carry are listed in the tank table. Hazardous products which are not listed, are not permitted to be carried. Each hazardous cargo is identified by its UN No and a packing group in the tank table. In addition special provisions which are also mandatory are indicated in the tank table. The special provisions and tank type are not identical in all regulations. The tank table refers to Portable Tank instruction, this is the minimum construction requirement for a tank container to carry the cargo Below is the Portable Tank instruction for liquid and solid cargoes Portable Tank Minimum Test Minimum Shell Instruction Pressure Bar Thickness (in mm-reference steel) T1 1.5 Note 1 T2 1.5 Note 1 T3 2.65 Note 1 T4 2.65 Note 1 T5 2.65 Note 1 T6 4 Note 1 T7 4 Note 1 T8 4 Note 1 T9 4 6mm T10 4 6mm T11 6 Note 1 T12 6 Note 1 T13 6 6mm T14 6 6mm T15 10 Note 1 T16 10 Note 1 T17 10 6mm T18 10 6mm T19 10 6mm T20 10 8mm

Pressure Bottom Opening Relief Requirements Requirements Normal Normal Normal Normal Note 2 Normal Normal Normal Normal Note 2 Normal Note 2 Normal Note 2 Normal Note 2 Normal Note 2 Note 2 Note 2

Note 3 Note 4 Note 3 Note 4 Not Allowed Note 3 Note 4 Not Allowed Not Allowed Not Allowed Note 4 Note 4 Not Allowed Not Allowed Note 4 Note 4 Note 4 Note 4 Not Allowed Not Allowed

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T21 T22

10 10

10mm 10mm

Normal Note 2

Not Allowed Not Allowed

It is not the function of this document to explain construction parameters but it can be seen that material thickness and test pressure increase with higher T number tank instructions, thus the risk of tank failure decreases. In addition to the above, other tables are used for T23 tanks (self reactive substances) T50 liquefied gas tanks T75 refrigerated gas tanks. All of the above must be considered as a risk assessment which has been carried out by eminent members of international committees. This risk assessment is a major contribution to the undoubted safety of tank containers. The majority of tank containers for the carriage of dangerous goods are manufactured from stainless steel for solid and liquid cargoes and carbon steel for the higher pressure liquefied gas tanks. The malleability of stainless steel allows huge distortion of tanks without any breach in the integrity of the pressure vessel. In addition tanks for the transportation of more hazardous materials have internal stop valves on the discharge orifices which are below liquid level that are closed during transport. This would allow the complete removal of the external valves without a pressure vessel breach. Carbon steel gas tanks require much thicker pressure vessels. A typical vessel would be 18mm thick. In the examples given below tank containers have been involved in serious accidents without loss of cargo The majority of serious accidents occur during road transportation with rollover being the most common. The first series of photographs below illustrate very severe roll over accidents.

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Series 1 Rollover accidents

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Tank in process of recovery

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Before and after recovery

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Before and after recovery

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Before and after recovery

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Before and after recovery

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Series 2 Other forms of accidents

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Container crane lifting gear failure, spreader and loaded tank dropped

Side Impact

Vacuum implosion of an empty tank 10

The severe deformation of this tank indicates the degree to which a tank can distort without the pressure vessel leaking. Fire Damage

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Series 3 tank interiors after accidents

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The above photographs are typical of the damage that can be observed from the interior of a tank which has been involved in a serious accident. Note the material deforms and creases but does not rupture. Millions of transits of tank containers occur throughout the world annually it is rare for serious accidents to be reported. Of the incidents that do occur, losses of hazardous product through physical damage very seldom occur. Most incidents that do involve cargo loss are the result of human error at load / discharge locations. Again this is very rare especially in the more develop parts of the world.

Graham Wood

Technical Secretary ITCO

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Below are the relevant sections of the UN Model regulations. These calculations (sometimes in a slightly different form) are included in the construction requirements for IMDG, ADR,RID etc. As you will see the requirement under total fire engulfment conditions is to maintain a pressure not greater than 20 above the start to discharge pressure of the relief valve. This pressure is less than the hydrostatic test pressure that the tank is subjected to at construction and every five years thereafter. If you require more information please do not hesitate to contact me. Bets Regards Graham