Safety

Purpose- To present an overview of the research and development carried out in a European funded framework 7 (FP7) project called SafeHPower for the implementation of neutron radiography to inspect fatigue cracks in vehicle and storage hydrogen fuel tanks. Project background– Hydrogen (H2) is the most promising replacement fuel for road transport due to its abundance efficiency low carbon footprint and the absence of harmful emissions. For the mass market of hydrogen to take off the safety issue surrounding the vehicle and storage hydrogen tanks needs to be addressed. The problem is the residual and additional stresses experienced by the tanks during the continuous cyclic loading between ambient and storage pressure which can result in the development of fatigue cracks. Steel tanks used as storage containers at service stations and depots and/or the composite tanks lined with steel are known to suffer from hydrogen embrittlement (HE). Another issue is the explosive nature of hydrogen (when it is present in the 18-59% range) where it is mixed with oxygen which can lead to catastrophic consequences including loss of life. Monitoring systems that currently exist in the market impose visual examination tests pressure tests and hydrostatic tests after the tank installation [1] [2]. Three inspection systems have been developed under this project to provide continuous monitoring solutions. Approach and scope- One of the inspection systems based on the neutron radiography (NR) technology that was developed in different phases with the application of varied strategies has been presented here. Monte Carlo (MCNP) simulation results to design and develop a bespoke collimator have been presented. A limitation of using an inertial electrostatic Deuterium-Tritium (D-T) pulsed neutron generator for fast neutron radiography has been discussed. Radiographs from the hydrogen tank samples obtained using thermal neutrons from a spallation neutron source at ISIS Rutherford laboratory UK have been presented. Furthermore radiograph obtained using thermal neutrons from a portable D-T neutron generator has been presented. In conclusion a proof in principle has been made to show that the defects in the hydrogen fuel tank can be detected using thermal neutron radiography.

A non-equilibrium two-phase single-component critical (choked) flow model for cryogenic fluids is developed from first principle thermodynamics. Modern equations-of-state (EOS) based upon the Helmholtz free energy concepts are incorporated into the methodology. Extensive validation of the model is provided with the NASA cryogenic data tabulated for hydrogen methane nitrogen and oxygen critical flow experiments performed with four different nozzles. The model is used to develop a hydrogen critical flow map for stagnation states in the liquid and supercritical regions.

The CEP (Clean Energy Partnership) – Berlin is one of the most diversified hydrogen demonstration projects at present. The first hydrogen fuelling station serving 16 cars is fully integrated in an ordinary highly frequented Aral service station centrally located at Messedamm in Berlin. Hydro has supplied and is the owner of the electrolyser with ancillary systems. This unit produces gaseous hydrogen at 12 bar with use of renewable energy presently serving 13 of the cars involved. The CEP project is planned to run for a period of five years and is supported by the German Federal Government and is part of the German sustainability strategy. During the planning and design phase there have been done several safety related assessments and analyses:

• Hydro has carried out a HAZOP (HAZard and OPerability) analysis of the electrolyser and ancillary systems delivered by Hydro Electrolysers.
• Hydro arranged with support from the partners a HAZOP analysis of the interface between the electrolyser and the compressor an interface with two different suppliers on each side.
• A QRA (Quantitative Risk Assessment) of the entire fuelling station has been carried out.
• Hydro has carried out a quantitative explosion risk analysis of the electrolyser container supplied by Hydro Electrolysers.

The aim in the CEP-Berlin project was to follow the guidelines from the European Integrated Hydrogen Project phase 2 (EIHP2) [1] when planning and designing a new hydrogen fuelling station. These guidelines focus on installation and operation of hydrogen refuelling stations and were based upon best practice and knowledge from the industrial partners in EIHP 2. The explosion risk analysis for the CEP-Berlin facility demonstrated that the safety risk was acceptable if certain design modifications were carried out. Both Aral/BP and Hydro accepted the results from the quantitative risk assessments. These companies have also their own standards regarding safety acceptance criteria which have to be complied with. The fuelling station was opened November 12 2004 and was put in normal operation during winter 2005.

We present results from hydrogen dispersion simulations from a pressurized reservoir at constant flow rate in the presence and absence of a wall. The dispersion simulations are performed using a commercial finite volume solver. Validation of the approach is discussed. Constant concentration envelopes corresponding to the 2% 4% and 15% hydrogen concentration in air are calculated for a subcritical vertical jet and for an equivalent subcritical horizontal jet from a high pressure reservoir. The consequences of ignition and the resulting overpressure are calculated for subcritical horizontal and vertical hydrogen jets and in the latter case compared to available experimental data.

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 work provide 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.

Distributed hydrogen optical fiber sensor with Brillouin scattering is an innovative solution to measure hydrogen in harsh environment as nuclear industry. Glass composition is the key point to enhance the sensing parameter of the fiber in the target application. Several optical fiber with different doping element were used for measuring hydrogen saturation. Permeability of optical plays a major role to the kinetic of hydrogen diffusion. Fluorine doped fiber increase the sorption and the desorption of hydrogen.

Although many studies have looked at safety issues relating to hydrogen fuelling stations few studies have analyzed the security risks such as deliberate attack of the station by threats such as terrorists and disgruntled employees. The purpose of this study is to analyze security risks for a hydrogen fuelling station with an on-site production of hydrogen from methylcyclohexane. We qualitatively conducted a security risk analysis using American Petroleum Institute Standard 780 as a reference for the analysis. The analysis identified 93 scenarios including pool fires. We quantitatively simulated a pool fire scenario unique to the station to analyze attack consequences. Based on the analysis and the simulation we recommend countermeasures to prevent and mitigate deliberate attacks.

Hydrogen has potential applications that require larger-scale storage use and handling systems than currently are employed in emerging-market fuel cell applications. These potential applications include hydrogen generation and storage systems that would support electrical grid systems. There has been extensive work evaluating regulations codes and standards (RCS) for the emerging fuel cell market such as the infrastructure required to support fuel cell electric vehicles. However there has not been a similar RCS evaluation and development process for these larger systems. This paper presents an evaluation of the existing RCS in the United States for large-scale systems and identifies potential RCS gaps. This analysis considers large-scale hydrogen technologies that are currently being employed in limited use but may be more widely used as large-scale applications expand. The paper also identifies areas of potential safety research that would need to be conducted to fill the RCS gaps. U.S. codes define bulk hydrogen storage systems but do not define large-scale systems. This paper evaluates potential applications to define a large-scale hydrogen system relative to the systems employed in emerging technologies such as hydrogen fuelling stations. These large-scale systems would likely be of similar size to or larger than industrial hydrogen systems.

A benchmark exercise on vented explosion engineering model was carried out against the maximum overpressures (one or two peaks) of published experiments. The models evaluated are Bauwens et al. (2012-1 and 2012-2) [4 7] models Molkov Vent Sizing Technology 1999 2001 and 2008 models [12 13 6]. The experiments in consideration are Pasman et al. experiments (1974) (30% H2 - 1m3) [1] Bauwens et al. (2012) experiments (64m3) [4] Daubech et al. (2011) experiments (10 to 30% H2 - 1 and 10 m3) [2] and Daubech et al. (2013) [5] experiments (4 m3 – H2 10 to 30%). On this basis recommendations and limits of use of these models are proposed.

Experiments in an obstructed semi-confined vertical combustion channel with a height of 6 m (cross-section 0.4 × 0.4 m) inside a safety vessel of the hydrogen test center HYKA at the Karlsruhe Institute of Technology (KIT) are reported. In the work homogeneous hydrogen-air-mixtures as well as mixtures with different well-defined H2-concentration gradients were ignited either at the top or at the bottom end of the channel. The combustion characteristics were recorded using pressure sensors and sensors for the detection of the flame front that were distributed along the complete channel length. In the tests slow subsonic and fast sonic deflagrations as well as detonations were observed and the conditions for the flame acceleration (FA) to speed of sound and deflagration-to-detonation transition (DDT) are compared with the results of similar experiments performed earlier in a larger semi-confined horizontal channel.