Architecture and management of a geological repository - Andra

11 – Operational SafetyThis backfilling work is isolated from the disposal cells by seals and cannot cause an explosion.However, if it was decided to return to a cell after sealing, such an operation would only be possibleafter renewing the atmosphere in the disposal cell beforehand in order to vent away any hydrogenpresent (see chapter 10). This would require special provisions to be made, of the sort practiced in firedampproducing coal mines, to avoid any risk of ignition when the ventilation system is put back inplace.11.3.4 ConclusionThe risks associated with the emission of explosive gases (essentially H 2 ) by certain type B wastepackages are controlled during the operational phase by ventilating the various installations, whichdilutes their content. An interruption to the ventilation poses no real danger as a long period of time isavailable to carry out any repairsThe closure steps of the disposal process pose no explosive hazard, except in the event of a return to acell after it has been sealed. In such cases, it will be necessary to re-establish the ventilation in order toextract the gases accumulated in the disposal cell, taking the necessary safety precautions during itsinstallation.11.4 Study into the fire hazard in underground installationsFire remains one of the major preoccupations in an underground environment, since it develops in asemi-confined space, and the associated smoke and toxic gases may spread through the drifts into theinstallations, impede personnel evacuation and endanger a large number of persons.Feedback from fires in underground structures indicates that the calorific potential of the driftsthemselves being low, only the machinery and equipment can be the source of a major fire. Accordingto a study of Swedish mines [115], the three main causes of machinery fires are electrical shortcircuits(around 50 %), oil leaks on hot surfaces (around 25 %) and engine over-heating(approximately 10 % of cases). However, the risk of a collision causing a fire is low, given the slowspeeds and low frequency of vehicles passing each other.The essential fire prevention measures required in underground installations are as follows:- preferred use of non-flammable materials that do not propagate fires and do not emit toxic smoke,- control of inflammable products present (justification of product choice and use, maximumauthorised quantities, transport conditions and utilisation procedures etc.),- restrictions on the quantity of fuel for machinery with thermal engines, protection of sensitivecomponents and choice, where possible of electrically-powered machinery with low heat load ifthe type of activity allows,- implementation of machinery and equipment inspection, maintenance and operating procedures(driving licences for machinery, fire permits etc.) and personnel training in effective reactions inthe event of an anomaly.Fire detection equipment (with smoke, flame or temperature detectors) are also useful to allow rapidintervention in order to get the fire under control before it takes hold. These systems are preferablyinstalled as construction work advances.Fire protection measures consist, firstly, of providing personnel with first aid fire-fighting equipment,with extinguishers and a pressurised firemain fitted close to the work site. Fixed automaticextinguishing systems, fitted in hazardous areas (fuel or oil storage) and systems on board vehiclescould also be effective means to be provided.DOSSIER 2005 ARGILE -ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL DISPOSAL SYSTEM456/495