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This paper deals with the cryogenic risk arising from nitrogen spillage in a box located in Hall A of the underground laboratories of the Gran Sasso National Laboratory, Assergi (L'Aquila). This box will be used as a storage area for some sensitive material (crystals) which will be used for an experiment called "CUORE". Starting from the Fault Tree Analysis (FTA), in order to estimate the global risk for human activities, a consequence analysis has been performed, using EFFECTS software models. The gap between the latest and the real scenario has been covered by a real test during which a "monitored, measured and controlled" gas nitrogen flow has been spilled into the box. Furthermore, a description of a reliable base for computational fluid dynamics (CFD) analysis is treated.

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The aim of this study is the risk analysis evaluation about argon release from the GERDA experiment in the Gran Sasso underground National Laboratories (LNGS) of the Italian National Institute for Nuclear Physics (INFN).The GERDA apparatus, located in Hall A of the LNGS, is a facility with germanium detectors located in a wide tank filled with about 70 m 3 of cold liquefied argon. This cryo-tank sits in another water-filled tank (700 m 3 ) at atmospheric pressure. In such cryogenic processes, the main cause of an accidental scenario is lacking insulation of the cryo-tank.A preliminary HazOp analysis has been carried out on the whole system. The risk assessment identified two possible top-events: explosion due to a Rapid Phase Transition -RPT and argon runaway evaporation.Risk analysis highlighted a higher probability of occurrence of the latter top event. To avoid emission in Hall A, the HazOp, Fault Tree and Event tree analyses of the cryogenic gas extraction and ventilation plant have been made. The failures related to the ventilation system are the main cause responsible for the occurrence. To improve the system reliability some corrective actions were proposed: the use of UPS and the upgrade of damper opening devices. Furthermore, the Human Reliability Analysis identified some operating and management improvements: action procedure optimization, alert warnings and staff training.The proposed model integrates the existing analysis techniques by applying the results to an atypical work environment and there are useful suggestions for improving the system reliability.