Probabilistic Risk Analysis for Firedamp Explosion (PSAM-0054)


Risk analysis is one of the most modern and powerful tools for making decisions concerning the safety and protection of workers. [1,2]

The so called “quantitative” risk analysis involves the numerical evaluation of the probability (or frequency) of something occurring, as an essential component (along with “damage”) for estimating risk. This level of analysis (generally not required in the area of risks in the workplace applications such as those considered, in the European Union, by the Directive 89/391 and 89/392), is invoked by a specific Regional Circular [3] relevant to tunnel excavation and is, in any case, typical of major accident risk analysis in the frame of the European Directive 82/501 and related laws.

Given the lack of historical data and the complexity of the tunnel “system” (we are not dealing with a “closed” plant), the quantitative risk analysis can be developed via an “expert judgment” approach, that is, through the opinion of experts.

Aim of the paper is to present the development of a quantitative risk analysis relevant to firedamp explosion during tunnel cutting, in road or rail bank. This has been done (at least) for two reasons:

— the prevention and the protection of the bank workers,

— the selection of the proper low requirements.

The second reason is due to the fact that, according to three probability levels, a tunnel segment is classifies as:

— “Code 1”: no firedamp presence probability;

— “Code 2”: low firedamp presence probability;

— “Code 3”: high firedamp presence probability.

In addition, the analyst is required to specify numerical intervals for these probabilities.

Due to lack of data, an expert-judgment-based approach has been adopted, following the structure of the SLIM method. [4] In this frame, a proper group of specialists has been defined, with four experts: two geologists, one risk analyst, one SLIM method facilitator. The team has been working in plenary sessions for 7 days (8 hours each) following all the steps of the SLIM Method, namely:

(a) problem familiarization,

(b) definition of the Performance Shaping Factors, PSF (in this contest defined as “principal shaping factors”),

(c) ordering the PSFs,

(d) weighting the PSFs,

(e) ranking the PSFs,

(f) SLI calculation,

(g) probability estimations.

Quantitative data for each tunnel segment have been assessed and are presented.

  • Summary/Abstract
  • The Methodological Approach
  • Application
  • Identifying the Intervals of Probability
  • Classification of the Sections of the Tunnel and Related Approach Fensters on the Basis of the Methodology Expounded
  • Conclusions
  • References

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