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 as safe a transportation 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. The following questions must be addressed:
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 the above questions: OECD. Transport of dangerous goods through road tunnels. Safety in Tunnels, Paris: OECD Publishing, 2001 ISBN 92-64-19651-X. The following paragraphs summarise the outputs of this project and the further developments.
The first step of the joint OECD/PIARC research project was an international survey of regulations regarding the road transportation of dangerous goods in general and in tunnels.
The survey 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 the 2007 and further revisions of the ADR.
The harmonisation is based on the assumption that in tunnels there are three major hazards which may cause numerous victims or 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)|
More information on this topic is available on the following websites:
Banning dangerous goods from a tunnel does not eliminate the risks, but modifies them and moves them to a different location, where the overall risk may actually be greater (diverting through a dense urban area for instance). For this reason, the joint OECD/PIARC research project recommended that decisions on authorisation/restriction of dangerous goods in a tunnel should be based on a comparison of various alternatives and should take into account the tunnel route as well as possible alternative routes.
A rational decision process was proposed, with the structure shown in the figure below. The first steps would produce objective risk indicators, based on quantitative risk analysis (QRA). The last steps would take into account economic and other data, as well as the political preferences of the decision maker (risk aversion for instance). These later steps could be based on a decision support model(DSM).
The OECD/PIARC project has developed a QRA model as well as a DSM. The QRA model is currently used in a number of countries. It is a system-based risk analysis model (see chapter 2.4 for definition) and produces indicators of the societal risk (F-N curves for the tunnel users and for the permanent neighbouring population), as well as the individual risk (for people permanently living in the neighbourhood of the tunnel) and damage to the tunnel and the environment. It is applicable both to routes including tunnels and to open-air routes, so that the risks on various alternative routes can be compared. The model is based on 13 scenarios representative of each of the five tunnel categories (although categories D and E cannot be distinguished because they lead to similar risks). This model can be bought from PIARC and is described in more detail in its website.
Additional information as well as examples of application can be found in the following PIARC references:
The joint OECD/PIARC research project also included an investigation of measures that could reduce the probability and/or consequences of an incident involving dangerous goods in a tunnel, where such goods are allowed.
Firstly a state of the art was established, resulting in identification and description of all possible measures, most of which are described in part 2 of this manual (chapters 6-9). The second, more challenging step was an attempt at evaluating the cost-effectiveness of these measures with respect to dangerous goods hazards. Costs were not examined in detail as they will be specific to a particular tunnel project and can be studied for each individual project. The focus was put on the effectiveness of measures.
Some of the possible risk reduction measures are directly taken into account in the QRA model developed under the project (see above). These were called "native" measures. The effectiveness of each of these measures, or each combination of measures, can be assessed by running the model with and without the measure(s) and comparing the results. A large number of tests were made and showed that no general conclusion could be drawn regarding the effectiveness of measures because the effectiveness very much depends on the specific case. Assessment of effectiveness should thus be made on a project basis.
The effectiveness of the other, "non-native" measures was much more difficult to assess and methods were proposed to take a number of them into account. More information can be found in chapter VII of the OECD project report (Risk reduction measures).