ABSTRACT

Some residential areas of the iron basin of Lorraine (in the North-East of France) are affected by noxious gas emissions (under oxygenated, carbon dioxide loaded and radon loaded gas mixtures). Site investigations showed that the gas flow was mainly due to natural thermal air circulation between old mines and the external atmosphere. The main hazards associated with this flow of gas and its potential accumulation in confined volumes within buildings are asphyxiation and intoxication. A further study is in progress in order to better understand the origin of the gas generation within the old iron mine workings. Following the first hypothesis, the carbon dioxide emission is mainly due to the specific hydro-geo-chemical process associating the pyrite oxidation with the acid dissolution of carbonates.

ZUSAMMENFASSUNG

Einige Wohngebiete der Eisenmulde Lothringen (im Nordöst Frankreich) werden von Ausgasung gesundsheitsschadlichen sauerstoffarmen Mischungen, die mit Kohlendioxid und Radon beladen sind, betroffen. Untersuchungen am Ort haben gezeigt, wie diese Gasstroemung von natuerlichem thermischen Luftumlauf zwischen den alten Bergwerken und der externen Atmosphare ausgelöst wird. Erstickung und Vergiftung sind die wichtigste Risiken, die mit dieser Gasströmung und ihrer möglichen Speicherung in begrenzten Lokalen zusammenhangen. Eine weitere Untersuchung wird durchgefuehrt so dass man die Herkunft der Gaserzeugung in den alten Grubenraume besser versteht. Der ersten Hypothese folgend, Ausgasung von Kohlensaure liegt vor allem an dem hydro-geo-chemischen Prozess, der Pyritrösten mit der sauren Auflösung von Karbonate verbindet.

RESUME

Certaines agglomerations du bassin ferrifère lorrain (au Nord-Est de la France) sont affectees par des emanations de melanges gazeux sous-oxygenes et charges en certains gaz nocifs (dioxyde de carbone, radon…). Les investigations effectuees in situ ont montre que les ecoulements gazeux à l'origine de ces emanations sont liees au phenomène de tirage naturel entre les anciens travaux miniers et la surface. Les principaux risques engendres par ces emanations de gaz et son accumulation possible dans des endroits confines sont l'asphyxie et l'intoxication. Une etude est en cours afin d'expliquer l'origine de la modification de l'air au sein des vieux travaux miniers. Les emissions de dioxyde de carbone seraient dues à des processus hydro-geo-chimiques associant l'oxydation de la pyrite et la dissolution de carbonates.

Introduction

A measurements campaign carried out in the iron basin of Lorraine (North-east of France) put the spot on the existence of under-oxygenated and noxious gas emissions in vast built-up areas related to former mining works. The most spectacular phenomenon occurred in the built-up area of Moyeuvre-Grande in Moselle (figure1), especially in the district of the town located very close to the former underground mine workings, in which some inhabitants observed the dysfunctioning of gas cookers and boilers.

(Figure in full paper)

In 1999, following the Lorraine local office of the French Ministry of Industry, Research and Environment (DRIRE) request, INERIS (the French National Institute for Safety and Risks) started some investigations to assess the geographical extend of the problem. These studies brought to the fore the existence of noxious gas emissions in relation with former mining workings that were not completely submerged. High level CO2 content (up to 6 %) and low level O2 content (down to 13 %) have been measured. At the same time, the Institute for Radioprotection and Nuclear Safety (IRSN) and the DASS (a government organisation responsible to the national Ministry of Health) investigated and measured high level radon content (up to 15000 Bq/m3) in the gaseous mixture.

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