Architecture and management of a geological repository - Andra

11 – Operational SafetyOver and above these fire precautions, underground installations should be fitted with a smokeextraction system enabling personnel to be evacuated under acceptable temperature, visibility andtoxicity conditions. The installation of warning and alarm systems 166 and a centralised command postable to monitor the situation and direct operations would also contribute to the organisation of thisevacuation under the safest possible conditions.This section assumes that a fire has developed despite the preventative measure described above. Itspurpose is to study the various representative fire scenarios, assess their consequences (temperaturerise, smoke emission, toxic gas emission) and ensure that the personnel evacuation conditions aresatisfactory. It does not deal with fires liable to have radiological consequences, which require furtherdiscussion and which are dealt with in sections 11.5 and 11.6.11.4.1 Fire simulationsSimulation studies [107] have been carried in order to understand the potential consequences of thevarious fire scenarios envisaged, according to their characteristics.11.4.1.1 Description of the various fire scenariosThe plant and machinery used to build the structures (diggers, rock bolters, transporters etc.) orconduct operational activities (transfer cask transporters etc) and a few items of special machinery(conveyer belts for carrying excavated material etc.) may cause potentially high-temperature fires 167 .This type of fire is characterised by its high thermal power, the quantity of toxic gases and the amountof smoke given off.Determining its thermal power requires a realistic scenario to be defined. In the case of an item ofplant machinery, the fire-producing event used in the scenario is usually a liquid fuel leak associatedwith a hot point (spark etc.). The liquid leakage rate considered determines the initial strength of thefire. The fire’s duration depends on the machinery’s calorific potential: the quantities of fuel or oilform a major part of this potential, immediately available in the event of a fire; tyres contribute toincreasing the duration of the fire and the amount of smoke produced. It is also assumed that theoxygen in the air is in sufficient quantity and that the seat of the fire is not extinguished by smothering.The summary of the results for all the various items of machinery studied show that there are twomajor categories of machinery fire. Diesel or diesel-electrical machinery (dump trucks, loaders,excavators, bolting and drilling machines etc.) is that which produces fires which generate the mostheat, approaching 25 MW, whilst electric transporters have a maximum thermal power of around15 MW.In order to overcome the problems associated with modelling of curves presenting transientphenomena, the fire simulations have used standard curves defined by the CETu (French tunnelstudying centre), which cover the above in terms of power and duration. These curves, derived fromfeedback from tunnel fires, correspond to road vehicle fires with respective total powers of 168 30 MWand 15 MW. Also associated with each type of fire are carbon monoxide emissions and smokeproduction.Figure 11.4.1 which represents the evolution of the thermal power of a 30 MW fire over time, is anexample of the standard curves which all have the same profile, with a start ramp, a levelling off and adescending ramp.166 An intersting approach would be to provide personnel with an individual voice system linked to an internal network and centralisedcommand poste. In normal conditions, this system would be used for work organisation; in case of fire, it would be the best real-timealarm system.167 Another type of high-risk fire would be one in an inflammable product store, but this type of fire is not considered at this stage of thestudy, partly because its location and size are unknown and partly because this type of installation can more easily be the subject ofspecial fixed fire-fighting facilities.168 Generally speaking, for this type of fire, two thirds of the total power is dissipated by convection, the other third being dissipated byradiation.DOSSIER 2005 ARGILE -ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL DISPOSAL SYSTEM457/495