In the summer of 1985 a severe hydrogen-air explosion occurred in an ammonia plant in Norway. The accident resulted in two fatalities and the destruction of the building where the explosion took place. This paper presents the main findings from an investigation in 1985 and 1986 of the gas explosion and its consequences. The event started when a gasket in a water pump was blown out. The water pump was situated inside a 100 m long, 10 m wide, and 7 m high building. The pump was feeding water to a vessel containing hydrogen gas at pressure of 30 bars. This pressure caused a back flow of water flow through the pump and out through the failed gasket. The hydrogen reached the leakage point after about 3 minutes. The discharge of gas lasted some 20 to 30 seconds before the explosion occurred. The total mass of the hydrogen discharge was estimated at 10 to 20 kg hydrogen. The main explosion was very violent and it is likely that the gas cloud detonated. The ignition source was almost certainly a hot bearing. Several damage indicators were used to estimate the amount of hydrogen that exploded. The indicators include deflection of pipes and panels, distances traveled by fragments, and the distribution of glass breakage. We found that 3.5 to 7 kg of hydrogen must have been burning violently in the explosion. Window glass was broken up to 700 m from the centre of the explosion. Concrete blocks, originally part of the north wall of the building and weighing 1.2 metric tons were thrown up to 16 meters. The roof of the building was lifted by an estimated 1.5 meters before resettling. The displacement of the roof caused a guillotine break of a 350 mm diameter pipe connected to the vessel that was the source of the original gas discharge. The gas composition in the vessel was 65 - 95 %2hydrogen. This resulted in a large horizontal jet fire lasting about 30 seconds. Minor explosions occurred in the plant culvert system.To our knowledge this gas explosion is one of the largest industrial hydrogen explosions reported. We believe this case history is a valuable reference for those who are investigating the nature of accidental hydrogen explosions.

This paper shows the experimental results and findings of field explosion tests conducted to obtain fundamental data concerning the explosion of hydrogen-air mixtures. A tent covered with thin plastic sheets was filled with hydrogen/air mixed gas, and subsequently ignited by an electric-spark or explosives to induce deflagration and/or detonation. Several experiments with different concentrations and/or volumes of mixture were carried out. The static overpressure of blast waves was measured using piezoelectric pressure sensors. The recorded data show that the shape of the pressure-time histories of the resulting blast waves depends on the difference in the ignition method used. The pictures of the explosion phenomenon (deflagration and/or detonation) were taken by high-speed cameras.

A phenomenological approach is developed to calculate the velocity of flame propagation and to estimate the value of pressure peak when igniting gaseous combustible mixtures in a congested space. The basic idea of this model is afterburning of the remanent fuel in pockets of congested space behind the flame front. The estimation of probable overpressure peak is based on solution of one-dimensional problem of the piston (having corresponding symmetry) moving with given velocity in polytropic gas. Submitted work is the first representation of such phenomenological approach and is realized for the simplest situation close to one-dimensional.

The following paper describes researches to evaluate the behavior under various accidental conditions of systems of transport compressed hydrogen. Particularly have been considered gaseous tube trailer and the packages cylinders employed for the road transport which have an internal gas pressures up to 200 barg. Further to a verification of the actual safety conditions, this analysis intends to propose a theme that in the next future, if confirmed projects around the employment of hydrogen as possible source energetic alternative, could become quite important. The general increase of the consumptions of hydrogen and the consequently probable increase of the transports of gaseous hydrogen in pressure they will make the problem of the safety of the gaseous tube trail particularly important. Gaseous tube trailers will also use as components of plant. for versatility, easy availability' and inexpensiveness. The first part of the memory is related to the analysis of the accidents happened in the last year in Italy with compressed hydrogen transports and particularly an accurate study has been made on the behavior of a gaseous tube trailer involved in fire following a motorway accident in March 2003. In the central part of the job has been done a safety analysis of the described events trying to make to also emerge the most critical elements towards the activities developed by the teams of help intervened. Finally in the last part you are been listed, on the base of the picked data, a series of proposals and indications of the possible structural and procedural changes that could be suggested with the purpose to guarantee more elevated safety levels.

Extensive infrastructure exists for the transport of natural gas and it is an obvious step to assess its use for the movement of hydrogen. The Naturalhy project’s objective is to prepare the European natural gas industry for the introduction of hydrogen by assessing the capability of the natural gas infrastructure to accept mixtures of hydrogen and natural gas. This paper presents the ongoing work within both Durability and Integrity Work Packages of the Naturalhy project. This work covers a gap in knowledge on risk assessment required for delivering H2+natural gas blends by means of the existing natural gas grids in safe operation.

Experiments involving several parts of the existing infrastructure will be described that are being carried out to re-examine the major risks previously studied for natural gas, including: effect of H2 on failure behaviour and corrosion of transmission pipes and their burst resistance (link to the Work Package Safety), on permeability and ageing of distribution pipes, on reliability and ageing of domestic gas meters, tightness to H2 of domestic appliances and their connexions. The information will be integrated into existing Durability assessment methodologies, originally developed for natural gas.

An Integrity Management Tool will be developed taking account of the effect of hydrogen on the materials properties. The tool should enable a cost effective selection of appropriate measures to control the structural integrity and maintaining equipment. The main measures considered are monitoring, non destructive examination (pigging and non pigging) and repair strategies. The tool will cover a number of parameters, e.g.: percentage of hydrogen in the gas mixture, material of construction, operating conditions and condition of cathodic protection. Thus, the Integrity Management Tool will yield an inspection and maintenance plan based on the specific circumstances.

Hydrogen is not more dangerous than current fossil energy carriers, but it behaves differently. Therefore hydrogen specific analyses and countermeasures will be needed to support the development of safe hydrogen technologies. A systematic step-by-step procedure for the mechanistic analysis of hydrogen behaviour and mitigation in accidents is presented. The procedure can be subdivided into four main parts:

1. 3D modelling of the H2-air mixture generation
2. hazard evaluation for this mixture based on specifically developed criteria  for flammability,  flame  acceleration  and  detonation  on-set
3. numerical simulation of the appropriate combustion regime using verified 3D-CFD codes
4. consequence analysis based on the calculated pressure and temperature loads.

This paper presents a compilation of the results supplied by HySafe partners participating in the Standard Benchmark Exercise Problem (SBEP) V2, which is based on an experiment on hydrogen combustion that is first described. A list of the results requested from participants is also included. The main characteristics of the models used for the calculations are compared in a very succinct way by using tables. The comparison between results, together with the experimental data, when available, is made through a series of graphs. The results show quite good agreement with the experimental data. The calculations have demonstrated to be sensitive to computational domain size and far field boundary condition.

Interest in the future is not new. Economic constraints and acceptability considerations of today compel decision-makers from industry and authorities to speculate on possible safety risks originating from a hydrogen economy developed in the future. Tools that support thinking about the long-term consequences oftoday's actions and resulting technical systems are usually prognostic, based on data from past performance of past or current systems. It has become convention to assume that the performance of future systems in future environments can be accommodated in the uncertainties of such prognostic models resulting from sensitivity studies. This paper presents an alternative approach to modeling future systems, based on narratives about the future. Such narratives, based on the actions and interactions of individual "agents", are powerful means for addressing anxiety about engaging the imagination in order to prepare for events that are likely to occur, detect critical conditions and to thus achieve desirable outcomes. This is the methodological base of Agent-Based Models (ABM) and this paper will present the approach, discuss its strengths andweaknesses, and present a preliminary application to modeling safety risks related to energy scenarios in a possible future hydrogen economy.

Hydrogen is a convenient energy storage medium; it can be produced from fossil fuels and biomass via chemical conversion processes, or from intermittent renewable sources, like wind and solar, via electrolysis. It is the fuel of choice for the clean fuel-cell vehicles of the future. If the general publicare to use hydrogen as a vehicle fuel, customers must be able to handle hydrogen with the same degree of confidence, and with comparable risk, as conventional liquid and gaseous fuels. For the safe design of retail facilities, through the development of appropriate codes and standards, it is essential to understand all the hazards that could arise following an accidental release of hydrogen. If it is to be stored and used as a high-pressure gas, the hazards associated with jet releases from accidental leaksmust be considered. This paper describes work by Shell and the Health and Safety Laboratory to characterise the hazards from jet releases of hydrogen. Jet release experiments have been carried out using small leaks (circular holes ranging from 1 mm to 12 mm diameter) at system pressures up to 150 barg. Concentration measurements were made in the unignited free jets to determine the extent of the flammable cloud generated. Ignited jets were observed both in the visible and infrared to determine the flame size and shape. The experimental results for the extent of the flammable cloud and jet flame length were found to be in good agreement with model predictions.

A new testing device for cyclic loading of specimens with a novel shape design is presented. The device was applied for investigations of fatigue of metallic specimens under pressurized hydrogen up to 300 bar at tem-peratures up to 200 C. Main advantage of the specimen design is the very small amount of medium, here hydrogen, used for testing. This allows experiments with hazardous substances at lower safety level. Addi-tionally no gasket for the load transmission is required. Woehler curves which show the influence of hydro-gen on the fatigue behavior of austenitic steel specimens at relevant service conditions in hydrogen powered engines are presented. Material and test conditions are in agreement with the cooperating industry.