United States

The potential for particulates entrained in hydrogen releases to generate electrostatic charge and induce electrostatic discharge ignitions was investigated. A series of tests were performed in which hydrogen was released through a 3.75-mm-diameter orifice from an initial pressure of 140 bar. Electrostatic field sensors were used to characterize the electrification of known quantities of iron oxide particulates deliberately entrained in the release. The ignition experiments focused on using charged particulates to induce spark discharges from isolated conductors and corona discharges. A total of 12 ignition events were observed. The results show that electrification of entrained particulates is a viable self-ignition mechanism of hydrogen releases.

Hydrogen is seen as an ideal energy carrier for stationary and mobile applications. However the use of high energy density condensed hydrogen storage materials such as NH3BH3 comes with risks associated with their high reactivity with water exposure and their decomposition products reactivity in air. To predict their behaviour under these circumstances idealized finite element models of hypothetical accident scenarios have been developed. Empirical thermodynamic calculations based on precise thermal gravimetric analysis (TGA) and calorimetric experiments have been performed in order to quantify the energy and hydrogen release rates and to quantify the reaction products resulting from water and air exposure.

Experiments are described in which hydrogen was released at the center of the floor of a real-scale enclosure having dimensions of a typical two-car residential garage. Real-time hydrogen concentrations were monitored at a number of locations. The hydrogen/air mixtures were ignited at pre-determined local volume fractions ranging from 8% to 29%. The combustion behavior and structural effects were monitored using combinations of high-speed pressure transducers and ionization gauges standard thermocouples hydrogen sensors and digital infrared and high-speed video cameras. Experiments were performed both for empty garages and garages with conventional automobiles parked above the hydrogen release location.

We have developed a web-based hydrogen safety class and are developing a hands-on hydrogen safety class. The 4-h web-based class is directed to laboratory researchers who need basic hydrogen safety information (free online access at http://www.h2labsafety.org/) and it addresses hydrogen fundamentals: properties pressure and cryogenic safety emergency response and codes and standards. Technical operators in charge of building and testing experimental hydrogen equipment will also soon benefit from a more comprehensive 3-day hands-on safety class that will present detailed information for installation testing and operation of hydrogen pressurized systems. The hands-on class includes a full day of classroom instruction followed by two days of laboratory work where students assemble test and operate a pressure system based on a schematic and component description.

This paper provides an introduction to the powered industrial truck application of fuel cell power systems the safety similarities with the automotive application and safety lessons learned. Fuel Cell niche markets have proven their value to many early adopters. How has the automotive market provided a springboard for these niche applications? How are niche markets revealing gaps in current safety approaches? What is different about the powered industrial truck application and what new codes and standards are needed to accommodate those differences?

Liquid hydrogen (LH2) storage is viewed as a viable approach to assure sufficient hydrogen capacity at commercial fuelling stations. Presently LH2 is produced at remote facilities and then transported to the end-use site by road vehicles (i.e. LH2 tanker trucks). Venting of hydrogen to depressurize the transport storage tank is a routine part of the LH2 delivery and site transfer process. The behaviour of cold hydrogen plumes has not been well characterized because of the sparsity of empirical field data which can lead to overly conservative safety requirements. Committee members of the National Fire Protection Association (NFPA) Standard 2 [1] formed the Hydrogen Storage Safety Task Group which consists of hydrogen producers safety experts and computational fluid dynamics modellers has identified the lack of understanding of hydrogen dispersion during LH2 venting of storage vessels as a critical gap for establishing safety distances at LH2 facilities especially commercial hydrogen fuelling stations. To address this need the National Renewable Energy Laboratory Sensor Laboratory in collaboration with the NFPA Hydrogen Storage Task Group developed a prototype Cold Hydrogen Plume Analyzer to empirically characterize the hydrogen plume formed during LH2 storage tank venting. The prototype analyzer was field deployed during an actual LH2 venting process. Critical findings included

• Hydrogen above the lower flammable limit (LFL) was detected as much as 2 m lower than the release point which is not predicted by existing models.
• Personal monitors detected hydrogen at ground level although at levels below the LFL.
• A small but inconsistent correlation was found between oxygen depletion and the hydrogen concentration.
• A negligible to non-existent correlation was found between in-situ temperature measurements and the hydrogen concentration.

The prototype analyzer is being upgraded for enhanced metrological capabilities including improved real-time spatial and temporal profiling of hydrogen plumes and tracking of prevailing weather conditions. Additional deployments are planned to monitor plume behaviour under different wind humidity and temperature conditions. The data will be shared with the Hydrogen Storage Task Group and ultimately will be used support theoretical models and code requirements prescribed in NFPA 2.

Laboratory measurements were made on the concentration and temperature fields of cryogenic hydrogen jets. Images of spontaneous Raman scattering from a pulsed planar laser sheet were used to measure the concentration and temperature fields from varied releases. Jets with up to 5 bar pressure with near-liquid temperatures at the release point were characterized in this work. This data is relevant for characterizing unintended leaks from piping connected to cryogenic hydrogen storage tanks such as might be encountered at a hydrogen fuel cell vehicle fuelling station. The average centerline mass fraction was observed to decay at a rate similar to room temperature hydrogen jets while the half-width of the Gaussian profiles of mass fraction were observed to spread more slowly than for room temperature hydrogen. This suggests that the mixing and models for cryogenic hydrogen may be different than for room temperature hydrogen. Results from this work were also compared to a one-dimensional (streamwise) model. Good agreement was seen in terms of temperature and mass fraction. In subsequent work a validated version of this model will be exercised to quantitatively assess the risk at hydrogen fuelling stations with cryogenic hydrogen on-site.

Hydrogen sensors are recognized as an important technology for facilitating the safe implementation of hydrogen as an alternative fuel and there are numerous reports of a sensor alarm successfully preventing a potentially serious event. However gaps in sensor metrological specifications as well as in their performance for some applications exist. The U.S. Department of Energy (DOE) Fuel Cell Technologies Office published a short list of critical gaps in the 2007 and 2012 Multiyear Project Plans; more detailed gap analyses were independently performed by the Joint Research Centre (JRC) and the National Renewable Energy Laboratory (NREL). There have been however some significant advances in sensor technologies since these assessments including the commercial availability of hydrogen sensors with fast response times (t90 < 1 s which had been an elusive DOE target since 2007) improved robustness to chemical poisons improved selectivity and improved lifetime and stability. These improvements however have not been universal and typically pertain to select platforms or models. Moreover as hydrogen markets grow and new applications are being explored more demands will be imposed on sensor performance. The hydrogen sensor laboratories at NREL and the JRC are currently updating the hydrogen safety sensor gap analysis through direct interaction with international stakeholders in the hydrogen community especially end users. NREL and the JRC are currently organizing a series of workshops (in Europe and the United States) with sensor developers end-users and other stakeholders in 2017 to identify technology gaps and to develop a path forward to address them. One workshop was held on May 10 in Brussels Belgium at the Headquarters of the Fuel Cell and Hydrogen Joint Undertaking. A second workshop is planned at NREL in Golden CO USA. This paper reviews improvements in sensor technologies in the past 5 to 10 years identifies gaps in sensor performance and use requirements and identifies potential research strategies to address the gaps. The outcomes of the Hydrogen Sensors Workshops are also summarized.

Studying thermal ignition mechanisms is a key step for evaluating many ignition hazards. In the present work two-dimensional simulations with detailed chemistry are used to study the reaction pathways of the transient flow and ignition of a stoichiometric hydrogen-air mixture by moving hot spheres. For temperatures above the ignition threshold ignition takes place after a short time between the front stagnation point and separation location depending upon the sphere's surface temperature. Closer to the threshold the volume of gas adjacent to the separation region ignites homogeneously after a longer time. These results demonstrate the importance of boundary layer development and flow separation in the ignition process.

Hot surface ignition is relevant in the context of industrial safety. In the present work two-dimensional simulations with detailed chemistry and study of the reaction pathways of the buoyancy-driven flow and ignition of a stoichiometric hydrogen-air mixture by a rapidly heated surface (glowplug) are reported. Experimentally ignition is observed to occur regularly at the top of the glowplug; numerical results for hydrogen-air reproduce this trend and shed light on this behaviour. The simulations show the importance of flow separation in creating zones where convective losses are minimized and heat diffusion is maximized resulting in the critical conditions for ignition to take place.

A properly trained first responder community is critical to the successful introduction of hydrogen fuel cell applications and their transformation in how we use energy. Providing resources with accurate information and current knowledge is essential to the delivery of effective hydrogen and fuel cell-related first responder training. The California Fuel Cell Partnership and the Pacific Northwest National Laboratory have over 15 years of experience in developing and delivering hydrogen safety-related first responder training materials and programs. A National Hydrogen and Fuel Cell Emergency Response Training Resource was recently released. This training resource serves the delivery of a variety of training regimens. Associated materials are adaptable for different training formats ranging from high-level overview presentations to more comprehensive classroom training. This paper presents what has been learned from the development and delivery of hydrogen safety-related first responder training programs (online classroom hands-on) by the respective organizations. The collaborative strategy being developed for enhancing training materials and methods for greater accessibility based on stakeholder input will be discussed.

Safety is of paramount importance in all facets of the research development demonstration and deployment work of the U.S. Department of Energy’s (DOE) Fuel Cell Technologies Program. The Safety Codes and Standards sub-program (SC&S) facilitates deployment and commercialization of fuel cell and hydrogen technologies by developing and disseminating information and knowledge resources for their safe use. A comprehensive safety management program utilizing the Hydrogen Safety Panel to raise safety consciousness at the project level and developing/disseminating a suite of safety knowledge resources is playing an integral role in DOE and SC&S efforts. This paper provides examples of accomplishments achieved while reaching a growing and diverse set of stakeholders involved in research development and demonstration; design and manufacturing; deployment and operations. The work of the Hydrogen Safety Panel highlights new knowledge and the insights gained through interaction with project teams. Various means of collaboration to enhance the value of the program’s safety knowledge tools and training resources are illustrated and the direction of future initiatives to reinforce the commitment to safety is discussed.

The U.S. Department of Energy supports the implementation of hydrogen fuel cell technologies by providing hydrogen safety and emergency response training to first responders. A collaboration was formed to develop and deliver a one-day course that uses a mobile fuel cell vehicle (FCV) burn prop designed and built by Kidde Fire Trainers. This paper describes the development of the training curriculum including the design and operation of the FCV prop; describes the successful delivery of this course to over 300 participants at three training centers in California; and discusses feedback and observations received on the course. Photographs and video clips of the training sessions will be presented.

Quantitative Risk Assessment (QRA) can help to establish a set of design and operational requirements in hydrogen codes and standards that will ensure safe operation of hydrogen facilities. By analyzing a complete set of possible accidents in a QRA the risk drivers for these facilities can be identified. Accident prevention and mitigation features can then be analyzed to determine which are the most effective in addressing these risk drivers and thus reduce the risk from possible accidents. Accident prevention features/methods such as proper material selection and preventative maintenance are included in the design and operation of facilities. Accident mitigation features are included to reduce or terminate the potential consequences from unintended releases of hydrogen. Mitigation features can be either passive or active in nature. Passive features do not require any component to function in order to prevent or mitigate a hydrogen release. Examples of passive mitigation features include the use of separation distances barriers and flow limiting orifices. Active mitigation features initiate when specific conditions occur during an accident in order to terminate an accident or reduce its consequences. Examples of active mitigation features include detection and isolation systems fire suppression systems and purging systems. A concept being pursued by the National Fire Protection Association (NFPA) hydrogen standard development is to take credit for prevention and mitigation features as a means to reduce separation distances at hydrogen facilities. By utilizing other mitigation features the risk from accidents can be decreased and risk-informed separation distances can be reduced. This paper presents some preliminary QRA results where the risk reduction potential for several active and passive mitigation features was evaluated. These measures include automatic leak detection and isolation systems the use of flow limiting orifices and the use of barriers. Reducing the number of risk-significant components in a system was also evaluated as an accident prevention method. In addition the potential reduction in separation distances if such measures were incorporated at a facility was also determined.

Experiments were conducted to assess detectability of a low-level leak of hydrogen gas and the uniformity of hydrogen concentration at selected sensor placement locations in a realistic setting. A 5%2hydrogen/95%2nitrogen gas mixture was injected at a rate of 350 L/min for about 3/4 hour into a 93m3 residential garage space through a 0.09 m2 square open-top dispersion box located on the floor. Calibrated catalytic sensors were placed on ceiling and wall locations and the sensors detected hydrogen early in the release and continued to measure concentrations to peak and diminishing levels. Experiments were conducted with and without a car parked over the dispersion box. The results show that a car positioned over the dispersion box tends to promote dilution of the hydrogen cause a longer time for locations to reach a fixed threshold and produce lower peak concentrations than with no car present.

In the United States requirements for liquid motor vehicle fuelling stations have been in place for many years. Requirements for motor vehicle fuelling stations for gaseous fuels including hydrogen are relatively new. These requirements have in the United States been developed along different code and standards paths. The liquid fuels have been addressed in a single document and the gaseous fuels have been addressed in documents specific to an individual gas. The result of these parallel processes is that multi-fuel stations are subject to requirements in several fuelling regulations codes and standards (RCS). This paper describes a configuration of a multi-fuel motor vehicle fuelling station and provides a detailed breakdown of the codes and standards requirements. The multi-fuel station would dispense what the U.S. Department of Energy defines as the six key alternative fuels: biodiesel electricity ethanol hydrogen natural gas and propane. The paper will also identify any apparent gaps in RCS and potential research projects that could help fill these gaps.

Hydrogen jet flames resulting from ignition of unintended releases can be extensive in length and pose significant radiation and impingement hazards. One possible mitigation strategy to reduce exposure to jet flames is to incorporate barriers around hydrogen storage and delivery equipment. While reducing the extent of unacceptable consequences the walls may introduce other hazards if not properly configured. This paper describes experiments carried out to characterize the effectiveness of different barrier wall configurations at reducing the hazards created by jet fires. The hazards that are evaluated are the generation of overpressure during ignition the thermal radiation produced by the jet flame and the effectiveness of the wall at deflecting the flame.<br/>The tests were conducted against a vertical wall (1-wall configuration) and two “3-wall” configurations that consisted of the same vertical wall with two side walls of the same dimensions angled at 135° and 90°. The hydrogen jet impinged on the center of the central wall in all cases. In terms of reducing the radiation heat flux behind the wall the 1-wall configuration performed best followed by the 3-wall 135° configuration and the 3-wall 90°. The reduced shielding efficiency of the three-wall configurations was probably due to the additional confinement created by the side walls that limited the escape of hot gases to the sides of the wall and forced the hot gases to travel over the top of the wall.<br/>The 3-wall barrier with 135° side walls exhibited the best overall performance. Overpressures produced on the release side of the wall were similar to those produced in the 1-wall configuration. The attenuation of overpressure and impulse behind the wall was comparable to that of the three-wall configuration with 90° side walls. The 3-wall 135° configuration’s ability to shield the back side of the wall from the heat flux emitted from the jet flame was comparable to the 1-wall and better than the 3-wall 90° configuration. The ratio of peak overpressure (from in front of the wall and from behind the wall) showed that the 3-wall 135° configuration and the 3-wall 90° configuration had a similar effectiveness. In terms of the pressure mitigation the 3-wall configurations performed significantly better than the 1-wall configuration

This paper discusses the preliminary results of the Risk Management subtask efforts within the International Energy Agency (IEA) Hydrogen Implementing Agreement (HIA) Task 19 on Hydrogen Safety to develop uniform harm criteria for use in the Quantitative Risk Assessments (QRAs) of hydrogen facilities. The IEA HIA Task 19 efforts are focused on developing guidelines and criteria for performing QRAs of hydrogen facilities. The performance of QRAs requires that the level of harm that is represented in the risk evaluation be established using deterministic models. The level of harm is a function of the type and level of hazard. The principle hazard associated with hydrogen facilities is uncontrolled accumulation of hydrogen in (semi) confined spaces and consecutive ignition. Another significant hazard is combustion of accidentally released hydrogen gas or liquid which may or may not happen instantaneously. The primary consequences from fire hazards consist of personnel injuries or fatalities or facility and equipment damage due to high air temperatures radiant heat fluxes or direct contact with hydrogen flames. The possible consequences of explosions on humans and structures or equipment include blast wave overpressure effects impact from fragments generated by the explosion the collapse of buildings and the heat effects from subsequent fire balls. A harm criterion is used to translate the consequences of an accident evaluated from deterministic models to a probability of harm to people structures or components. Different methods can be used to establish harm criteria including the use of threshold consequence levels and continuous functions that relate the level of a hazard to a probability of damage. This paper presents a survey of harm criteria that can be utilized in QRAs and makes recommendations on the criteria that should be utilized for hydrogen-related hazards.

The International Energy Agency’s Hydrogen Implementing Agreement (www.ieahia.org) initiated a collaborative task on hydrogen safety in 1994 and this has proved to an effective method of pooling expert knowledge to address the most significant problems associated with the barriers to the commercial adoption of hydrogen energy. Presently there are approximately 10 countries participating in the task and it has proven a valuable method of efficiently combining efforts and resources. The task is now in the fifth year of a six year term and will end in October 2010. This paper will describe the scope of the task the progress made and plans for future work. There are also a number of other tasks underway and this paper will give a brief summary of those activities. Because of the nature of the International Energy Agency which is an international agreement between governments it is intended that such collaboration will complement other efforts to help build the technology base around which codes and standards can be developed. This paper describes the specific scope and work plan for the collaboration that has been developed to date.

For hydrogen fuelled vehicles to attain significant market penetration it is essential that any potential risks be controlled within acceptable levels. To achieve this goal on-board vehicle hydrogen storage systems should undergo risk analyses during early concept development and design phases. By so doing the process of eliminating safety-critical failure modes will help guide storage system development and be more efficient to implement than if undertaken after the design-freeze stage. The focus of this paper is the development of quantitative risk analyses of storage systems which use onboard reversible materials such as conventional AB5 metal hydrides the complex hydride NaAlH4 or other material candidates currently being researched. Collision of a vehicle having such a hydrogen storage system was selected as a dominant accident initiator and a probabilistic event tree model has been developed for this initiator. The event tree model contains a set of comprehensive mutually exclusive accident sequences. The event tree represents chronological ordering of key events that are postulated to occur sequentially in time during the accident progression. Each event may represent occurrence of a phenomenon (e.g. hydride chemical reaction and dust cloud explosion) or a hardware failure (e.g. hydride storage vessel rupture). Event tree branch probabilities can be quantified using fault tree models or basic events with probability distributions. A fault tree model for hydride dust cloud explosion is provided as an example. Failure probabilities assigned to the basic events in the fault tree can be estimated from test results published data or expert opinion elicitation. To account for variabilities in the probabilities assigned to fault tree basic events and hence to propagate uncertainties in event tree sequences Monte Carlo sampling and Latin Hypercube sampling were employed and the statistics of the results from both techniques were compared.

The United Nations Economic Commission for Europe Global Technical Regulation (GTR) Number 13 (Global Technical Regulation on Hydrogen and Fuel Cell Vehicles) is the defining document regulating safety requirements in hydrogen vehicles and in particular fuel cell electric vehicles (FCEVs). GTR Number 13 has been formally adopted and will serve as the basis for the national regulatory standards for FCEV safety in North America (led by the United States) Japan Korea and the European Union. The GTR defines safety requirements for these vehicles including specifications on the allowable hydrogen levels in vehicle enclosures during in-use and post-crash conditions and on the allowable hydrogen emissions levels in vehicle exhaust during certain modes of normal operation. However in order to be incorporated into national regulations that is to be legally binding methods to verify compliance with the specific requirements must exist. In a collaborative program the Sensor Laboratories at the National Renewable Energy Laboratory in the United States and the Joint Research Centre Institute for Energy and Transport in the Netherlands have been evaluating and developing analytical methods that can be used to verify compliance with the hydrogen release requirements as specified in the GTR.

Hydrogen is a notoriously difficult substance to store yet has endless energy applications. Thus the study of long-term hydrogen storage and high-pressure bulk hydrogen storage have been the subject of much research in the last several years. To create a research path forward it is important to know what research has already been done and what is already known about hydrogen storage. In this review several approaches to hydrogen storage are addressed including high-pressure storage cryogenic liquid hydrogen storage and metal hydride absorption. Challenges and advantages are offered based on reported research findings. Since the project looks closely at advanced manufacturing techniques for the same are outlined as well. There are seven main categories into which most rapid prototyping styles fall. Each is briefly explained and illustrated as well as some generally accepted advantages and drawbacks to each style. An overview of hydrogen adsorption on metal hydrides carbon fibers and carbon nanotubes are presented. The hydrogen storage capacities of these materials are discussed as well as the differing conditions in which the adsorption was performed under. Concepts regarding storage shape and materials accompanied by smaller-scale advanced manufacturing options for hydrogen storage are also presented.

In order to face the coming shortage of fossil energies a number of alternative methods of energy production are being considered. One promising approach consists in using hydrogen in replacement of the conventional fossil fuels or as an additive to these fuels. In addition to conventional hydro-electric and fission-based nuclear plants electric energy could be obtained in the future using nuclear fusion as investigated within the framework of the ITER project International Thermonuclear Experimental Reactor. However the operation of ITER may rise safety problems including the formation of a flammable dust/hydrogen/air atmosphere. A first step towards the accurate assessment of accidental explosion in ITER consists in better characterizing the risk of explosion in gaseous hydrogen-containing mixtures. In the present study laminar burning speeds ignition delay-times behind reflected shock wave and detonation cell sizes were measured over wide ranges of composition and equivalence ratios. The performances of five detailed reaction models were evaluated with respect to the present data.

Element One Inc. Boulder CO is developing novel hydrogen gas leak indicators to improve the safety and maintenance operations of hydrogen production and chemical processing facilities and hydrogen fueling stations. These technologies can be used to make visual gas leak indicators such as paints decals and conformal plastic films as well as RF sensors for wireless networks. The primary advantage of the Element One hydrogen gas indicators is their low cost and easy deployment which allows them to be used ubiquitously at each and every potential hydrogen leak site. They have the potential to convert safety problems into routine maintenance problems thereby improving overall safety and decreasing operational costs.

The formation of elongated zirconium hydride platelets during corrosion of nuclear fuel clad is linked to its premature failure due to embrittlement and delayed hydride cracking. Despite their importance however most existing models of hydride nucleation and growth in Zr alloys are phenomenological and lack sufficient physical detail to become predictive under the variety of conditions found in nuclear reactors during operation. Moreover most models ignore the dynamic nature of clad oxidation which requires that hydrogen transport and precipitation be considered in a scenario where the oxide layer is continuously growing at the expense of the metal substrate. In this paper we perform simulations of hydride formation in Zr clads with a moving oxide/metal boundary using a stochastic kinetic diffusion/reaction model parameterized with state-of-the-art defect and solute energetics. Our model uses the solutions of the hydrogen diffusion problem across an increasingly-coarse oxide layer to define boundary conditions for the kinetic simulations of hydrogen penetration precipitation and dissolution in the metal clad. Our method captures the spatial dependence of the problem by discretizing all spatial derivatives using a stochastic finite difference scheme. Our results include hydride number densities and size distributions along the radial coordinate of the clad for the first 1.6 h of evolution providing a quantitative picture of hydride incipient nucleation and growth under clad service conditions.