1,721,016 research outputs found
IMPROSafety: A risk-based framework to integrate occupational and process safety
Full text linkOccupational Safety and Health (OSH) and process safety are traditionally separated by a fuzzy perimeter, and the need to adopt different management approaches is emphasised in the literature. However, OSH and process safety complement rather than replace each other, and their integration may achieve total safety excellence of organisations. The existing studies about this integration focus on various aspects of the risk management process and provide different types of outputs. In such a context, this paper has the objective to propose IMPROSafety (Integrated risk Management for PRocess and Occupational Safety), a risk-based framework to integrate OSH and process safety. We expand the traditional risk definition considering scenario identification, its occurrence probability, and its consequence severity, to also include other dimensions, i.e. the temporal evolution and spatial extension of the scenario, and the number of workers involved. The framework covers all the steps of the risk management process: hazard identification is performed thanks to the bow-tie chaining structure and the application of the energy theory perspective, risk estimation via quantitative analyses of the considered dimensions, risk evaluation by means of the ranking of each dimension and an overall risk level, and risk treatment through a proper safety measure identification. A case study about three real events occurred in the steel and iron industry in the last decades is used to test the IMPROSafety framework. The investigation of six scenarios highlights the most dominant event sequences and risk dimensions that should receive prioritised attention for developing effective risk reduction controls
Fuel cells for airborne usage: Energy storage comparison
No full textThe global drone market is growing every year. The number of applications is increasing: from search and rescue, security, surveillance to science and research and unmanned cargo systems.
A limiting factor for drone exploitation is that for the energy storage, normally, a battery is used and this solution affects flight time. A possible solution could be the utilization of fuel cells. This paper focuses on the utilization of fuel cells power as an alternative solution for drone propulsion.
The aim of the study is to determine when it is more appropriate, in terms of mass, to use a battery or a hybrid (fuel cell þ battery) system to power drones. To compare the different systems, a numerical simulation model has been developed in order to choose the best power system once the drone operation profile has been defined.
The model allows comparing different type of fuels and battery systems. The data to tune the model have been taken from commercial products, today already available. The simulation model considers a light-weight open-air cathode PEM (Polymer Exchange Membrane) fuel cell. The stack power output is chosen according to the mission profile and rages from 200 W to 1000 W.
The presented results show that, for the considered drone segment, multi-rotor drones with weight of 7 kg at take-off, lithium batteries are still the best choice for time flight shorter than about 1 h. A hybrid system, appears to be interesting for longer flights. For example, it has been calculated that a hybrid quadcopter drone with a mass of 7 kg, considering a flight profile that requires 1089 Wh can be powered with a 4.4 kg hybrid system composed by a 500 W and 1.4 kg PEM fuel cell system, 1.9 kg hydrogen composite pressure vessel and a 0.8 kg lithium battery. The same amount of energy can be stored in a lithium battery with a weight of about 6.6 kg. These means a weight saving of more than 30%. The hybrid system, in term of weight, is even more convenient for flight profiles that require more energy
Performance Assessment of Safety Barriers in Liquid Hydrogen Bunkering Operations Using Bayesian Network
No full textLiquid hydrogen (LH2) has gathered interest as an ecofriendly energy carrier for marine transportation, avoiding carbon emissions and supporting sustainable shipping. However, LH2 intrinsic flammable characteristics pose safety concerns towards people and assets. Ensuring the effectiveness of safety barriers is paramount in preventing accidents and mitigating risks associated with LH2 bunkering operations. In this regard, among several quantitative performance assessment methods, Bayesian Networks (BNs) gained momentum, offering a statistical approach able to account for multifaceted safety factors. This paper evaluates safety barriers’ performance by translating Event Tree-Fault Tree diagrams into BNs. BNs incorporate root nodes representing basic events leading to the failure of the safety barriers, assigning failure probabilities from technical literature and Human Reliability Analysis approaches. Conditional Probability Tables quantify dependencies, mapping safety barrier interconnections. A case study on ship-to-ship bunkering affected by a LH2 release is considered to illustrate the application of BNs in the context of safety barriers performance assessment. Findings highlight BNs' utility in assessing safety barrier performance, providing a tool for regulatory agencies, industry stakeholders, and safety experts to inform LH2 bunkering best practices. This aligns with advancing environmentally responsible LH2 maritime transportation while enhancing safety measures
Modelling of Accident Scenarios from Liquid Hydrogen Transport and Use
Full text linkHydrogen is one of the most suitable candidates to replace hydrocarbons and reduce the environmental pollution and CO2 emissions. Hydrogen is valuable energy carrier, potentially clean and renewable thanks to its peculiar properties. However, hydrogen has a few characteristics, such as high flammability and low density that must be taken into account when stored or handled, especially in relation to the associated safety. For this reason, this PhD study aims to increase the knowledge on safety of hydrogen technologies.
Hydrogen safety is a broad topic which involves several disciplines. This PhD focusses on the modelling of atypical accident scenarios of liquid hydrogen (LH2) technologies by adopting a multidisciplinary approach. This type of accident scenarios is called atypical because they have low probability to happen but high consequences. A few times, the neglection of these scenarios by conventional risk assessment techniques led to major accidents. For this reason, the atypical accident scenario cannot be omitted during a risk assessment and must be further analysed.
Firstly, through a comprehensive literature review, this PhD study investigates the causes of loss of integrity (LOI) and loss of containment (LOC) of hydrogen equipment since the atypical accident scenarios always occurred after these critical events. The consequences of an LH2 release are then analysed. The focus is placed on the boiling liquid expanding vapour explosion (BLEVE) and the rapid phase transition (RPT) explosions for liquid hydrogen technologies because a significant dearth of knowledge is still present.
Secondly, the possibility for the BLEVE to occur after the catastrophic rupture of an LH2 vessel is theoretically assessed by gathering information on previous accident and applying accepted thermodynamic theories for this event. The consequences of a potential BLEVE for LH2 (pressure wave, missiles and fireball) are evaluated. Unique experimental series on LH2 bursting tank scenario and fire tests are simulated. Different approaches are employed for the BLEVE event: analytical models, empirical correlations and CFD analysis. Finally, the time to failure of an LH2 tank exposed to a fire is estimated with a thermal node model.
Thirdly, the RPT event is analysed from a more theoretical approach since no records of LH2 RPT are found in literature. The knowledge gained for other substances such as liquefied natural gas (LNG) and liquid nitrogen (LIN) is applied to LH2. The consequences of a hypothetical LH2 RPT are evaluated by means of an analytical model and compared to the LNG RPT aftermath.
The main contributions of this PhD study are the following:
• investigation on the causes of LOI of hydrogen technology;
• identification of the LH2 release consequences;
• understanding of the BLEVE feasibility for LH2 storage systems;
• determination of the LH2 BLEVE consequences;
• estimation of the time to failure of LH2 tanks exposed to a fire;
• analysis of the theories and mechanisms of RPT explosions;
• determination of the LH2 RPT consequences.
This PhD study provides relevant safety indications on the causes of LOI of hydrogen technologies as well as on the BLEVE and RPT phenomena for LH2 technologies. The knowledge gap in these topics is highlighted and partially fulfilled. The limitations of existing models for the simulation of these explosions are emphasised. The results of this thesis serve as a starting point for future studies
Exploring experimental tests concerning liquid hydrogen releases
Full text linkIn recent years, the adoption of liquid hydrogen (LH2) has increased significantly in industrial and transport applications, driven by its low carbon footprint, thereby aiding the fight against global warming. Additionally, its high volumetric energy density, compared to gaseous or compressed hydrogen, enhances hydrogen storage capabilities.
However, safety remains a major concern due to its physical-chemical properties and inherent hazardous characteristics, especially in the event of spillage scenarios. Therefore, to better understand the consequences of LH2 releases onto or into water, large-scale experimental tests were conducted by Bundesanstalt für Materialforschung und -prüfung (BAM) within the Safe Hydrogen Fuel Handling and Use for Efficient Implementation (SH2IFT) project at the Test Site Technical Safety of BAM, comprising 75 single spill events at varied release rates and orientations. While the rapid phase transition (RPT) phenomenon was not observed, selfignition of the hydrogen-air cloud occurred, accompanied by blast wave overpressure and heat radiation, without a discernible ignition source. These findings emphasize the need for further investigation into LH2 safety. Leveraging experimental data for real-world applications provides insights into safe LH2 infrastructure implementation, laying foundational knowledge for addressing safety challenges and advancing LH2 technology
Cryogenic Hydrogen Storage Tanks Exposed to Fires: a CFD study
Full text linkHydrogen is one of the most suitable candidates in replacing heavy hydrocarbons. Liquefaction of fuels is one
of the most effective processes to increase their low density. This is critical especially in large-scale or mobile
applications such as in the maritime or aeronautical fields. A potential loss of integrity of the cryogenic storage
equipment might lead to severe consequences due to the properties of these substances (e.g. high
flammability). For this reason, this critical event must be avoided. The aim of this study is to analyse the
behaviour of the cryogenic vessel and its lading when it is exposed to a fire and understand how to prevent a
catastrophic rupture of the tank during this accident scenario.
A two-dimensional computational fluid dynamic (CFD) analysis is carried out on a cryogenic liquid hydrogen
(LH2) vessel to investigate its thermal response when engulfed in a fire. The model accounts for the evaporation
and condensation of the substance and can predict the tank pressurization rate and temperature distribution. It
is assumed that the vessel is completely engulfed in the fire (worst-case scenario). The CFD model is validated
with the outcomes of a small-scale fire test of an LH2 tank. Critical indications on the dynamic response of the
cryogenic tank involved in a worst-case accident scenario are provided. Tank pressurisation and temperature
distributions of the case study can be exploited to provide conservative estimations of the time to failure (TTF)
of the vessel. These outcomes represent useful information to support the emergency response to this type of
accident scenario and can aid the selection of appropriate and effective safety barriers to prevent the complete
destruction of the tank
Modelling of Fireballs Generated After the Catastrophic Rupture of Hydrogen Tanks
No full textThe interest towards hydrogen skyrocketed in the last years. Thanks to its potential as an energy carrier, hydrogen will be soon handled in public and densely populated areas. Therefore, accurate models are necessary to predict the consequences of unwanted scenarios. These new models should be employed in the consequence analysis, a phase of risk assessment, and thus aid the selection, implementation, and optimization
of effective risk-reducing measures. This will increase safety of hydrogen technologies and therefore favour their deployment on a larger scale. Hydrogen is known to be an extremely flammable gas with a low radiation flame compared to hydrocarbons. However, luminous fireballs were generated after the rupture of both compressed gaseous and liquid hydrogen tanks in many experiments. Moreover, it was demonstrated that conventional empirical correlations, initially developed for hydrocarbon fuels, underestimate both dimension and duration of hydrogen fireballs recorded during small-scale tests (Ustolin and Paltrinieri, 2020). The aim of this study is to obtain an analysis of hydrogen fireballs to provide new critical insights for consequence analysis. A comparison among different correlations is conducted when predicting fireball characteristics during the simulation of past experiments where both gaseous and liquid hydrogen tanks were intentionally destroyed. All the models employed in this study are compared with the experimental results for validation purposes. Specific models designed for hydrogen can support the design of hydrogen systems and increasing their safety and promote their future distribution
Permitting Process Using Quantitative Risk Analysis of Facilities Handling Hydrogen
Full text linkHydrogen er et lovende alternativt drivstoff på grunn av sine rene forbrenningsegenskaper og høye energiinnhold. Imidlertid utgjør dens lave tetthet lagringsutfordringer. Etterspørselen etter hydrogen forventes å øke, og nå 180 millioner tonn årlig innen 2050. Denne studien kombinerer to studier om risikovurdering for hydrogenanlegg. I begynnelsen utforsker den regulatoriske prosedyrer for tillatelse av hydrogenbehandlingsanlegg og foreslår en risikovurderingsmetodikk ved bruk av kvantitativ risikaanalyse (QRA). Den understreker viktigheten av riktig håndtering og lagring på grunn av hydrogens farlige natur, og benytter retningslinjer fra Vysus Group for en standardisert tilnærming. Senere fokuserer den på å bruke HyRAM+ programvare for å vurdere sikkerheten til hydrogenfyllestasjoner (HRS). Den presenterer tre casestudier med ulike konfigurasjoner for å analysere hvordan designvalg påvirker risiko. Studien beregner nøkkelrisikomålinger og undersøker faktorer som termiske effekter og spredning av hydrogenlekkasje. Ved å vurdere flere systemer og interaksjoner gir denne forskningen et rammeverk for å utforme sikkerhetstiltak og evakueringsprosedyrer for HRS-anlegg, og fremmer sikker implementering av hydrogenteknologier.Hydrogen is a promising alternative fuel due to its clean burning properties and high
energy content. However, its low density poses storage challenges. The demand for
hydrogen is expected to grow, reaching 180 million tons annually by 2050. This study
combines two studies on risk assessment for hydrogen facilities. In the beginning, it
explores the regulatory procedures for permitting hydrogen processing facilities and
proposes a risk assessment methodology using quantitative risk analysis (QRA). It
emphasizes the importance of proper handling and storage due to hydrogen's hazardous
nature, and leverages guidelines from Vysus Group for a standardized approach. Later, it
focuses on applying HyRAM+ software to assess the safety of hydrogen refuelling stations
(HRS). It presents three case studies with varying configurations to analyse how design
choices impact risk. The study calculates key risk metrics and examines factors like
thermal effects and hydrogen leak dispersion. By considering multiple systems and
interactions, this research provides a framework to design safety measures and evacuation
procedures for HRS facilities, promoting the safe implementation of hydrogen
technologies
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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