Statistics, lessons learned and recommendations from analysis of HIAD 2.0 database

The manuscript firstly describes the data collection and validation process for the European Hydrogen Incidents and Accidents Database (HIAD 2.0), a public repository tool collecting systematic data on hydrogen-related incidents and near-misses. This is followed by an overview of HIAD 2.0, which currently contains 706 events. Subsequently, the approaches and procedures followed by the authors to derive lessons learned and formulate recommendations from the events are described. The lessons learned have been divided into four categories including system design; system manufacturing, installation and modification; human factors and emergency response. An overarching lesson learned is that minor events which occurred simultaneously could still result in serious consequences, echoing James Reason's Swiss Cheese theory. Recommendations were formulated in relation to the established safety principles adapted for hydrogen by the European Hydrogen Safety Panel, considering operational modes, industrial sectors, and human factors. This workprovide an important contribution to the safety of systems involving hydrogen, benefitting technical safety engineers, emergency responders and emergency services. The lesson learned and the discussion derived from the statistics can also be used in training and risk assessment studies, being of equal importance to promote and assist the development of sound safety culture in organisations

Reaktionskinetische Untersuchungen zur Auslegung von katalytischen Wasserstoffrekombinatoren

In the present study the reaction kinetics of the catalytic recombination of hydrogen and oxygen is investigated experimentally and theoretically. Hydrogen reacts on catalytic surfaces already at ambient temperatures. This fast is used in so-called recombinerswhich remove hydrogen in closed buildings to mitigate the danger of an ignition followed by a detonation. The experiments were carried out at ambient pressure at temperatures of up to 500 $^\circ$C. Air-mixtures of up to 6 vol.-% hydrogen and up to 50 vol.-% steam were used. Plates as used in present recombiners were investigated as substrates as well as wire meshs made of steel. The obtained reaction data on plates covered by the flog can be described by a diffusion formulation. Published data can be caldulated well using the found relations. Wire meshs exhibit higher efficiencies than plates. Furthermore, it is possible to design modular and applicable recombiners. Reaction kinetics on wire meshs can also be described by diffusion. One disadvantage of present systems is insufficient heat removal. In a hydrogen rich atmosphere the ignition temperature can be reached thus leading to an ignition of the hydrogen/air-mixture. Using the found relations innovative recombiner systems shall be designed excluding overheating under all possible conditions. This goal can be reached by improved heat removal and storage as well as bylimiting the catalytic activity