Dangerous goods are important for industrial production as well as everyday life, and they must be transported. However, it is acknowledged that these goods may cause considerable hazards if released in a collision, on open road sections as well as in tunnels. Incidents involving dangerous goods are rare, but may result in a large number of victims and severe material and environmental damage. Special measures are needed to ensure that the transport of dangerous goods is as safe as possible. For these reasons, the transport of dangerous goods is strictly regulated in most countries.
Dangerous goods transport raises specific problems in tunnels because an incident may have even more serious consequences in the confined environment of a tunnel as compared with incidents on the open road.
From 1996 to 2001, the Organisation for Economic Co-operation and Development (OECD) and PIARC carried out an important joint research project to bring rational answers to open questions about transport of dangerous goods through tunnels: Transport of dangerous goods through road tunnels. Safety in Tunnels, Paris: OECD Publishing, 2001 ISBN 92-64-19651-X.
An international survey of regulations regarding the road transportation of dangerous goods in general and in tunnels showed that all investigated countries had consistent regulations for the transport of dangerous goods on roads in general, and that these regulations were standardised within large parts of the world. For instance, ADR (the European agreement concerning the international carriage of dangerous goods by road) is used in Europe and the Asian part of the Russian Federation. Most States in the USA and provinces in Canada follow codes in compliance with the UN Model Regulations. Australia and Japan had their own codes, but Australia has aligned with the UN system.
In contrast, the survey highlighted a variety of regulations regarding the transport of dangerous goods through tunnels. Restrictions applied in tunnels showed considerable variations between countries and even between tunnels within the same country. The inconsistency of the tunnel regulations posed problems for the organisation of dangerous goods transport and led a number of vehicles carrying dangerous goods to infringe restrictions..
As part of their joint project, OECD and PIARC made a proposal for a harmonised system of regulation. This proposal was further developed by the United Nations Economic Commission for Europe (UN ECE), then implemented in Europe in 2007 and in further revisions of the ADR.
The harmonisation is based on the assumption that in tunnels there are three major hazards which may result in numerous victims or cause serious damage to the tunnel structure, and that they can be ranked as follows in order of decreasing consequences and increasing effectiveness of mitigating measures: (a) explosions; (b) releases of toxic gas or volatile toxic liquid; (c) fires. Restriction of dangerous goods in a tunnel is made by assigning it to one of five categories which are labelled using capital letters from A to E. The principle of these categories is as follows:
|Category A||No restrictions for the transport of dangerous goods|
|Category B||Restriction for dangerous goods which may lead to a very large explosion|
|Category C||Restriction for dangerous goods which may lead to a very large explosion, a large explosion or a large toxic release|
|Category D||Restriction for dangerous goods which may lead to a very large explosion, a large explosion, a large toxic release or a large fire|
|Category E||Restriction for all dangerous goods (except five goods with very limited danger)|
The decision on assigning a tunnel to one of these 5 categories can be based on risk assessment using risk assessment tools specifically developed for this kind of application.
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