Pressure Relief Devices Research Articles

Numerical simulation of high-pressure jet fire in on-board hydrogen storage cylinders under fire conditions

Hydrogen fuel cell vehicles (HFCVs) may cause fires in the event of an accident. When the high-pressure hydrogen storage cylinders are exposed to fire for a long time, there will be a risk of catastrophic consequences such as leakage, jet fire and explosion. Fire test is the main method to study the safety performance of hydrogen storage cylinders. During the firing process, the wall and internal temperature of the hydrogen storage cylinder rise gradually, and the thermally activated pressure relief device (TPRD) of the cylinder reaches a certain temperature and then releases high-pressure hydrogen to prevent the cylinder from bursting. As the hydrogen storage cylinder is in the fire environment, the release of high-pressure hydrogen will be ignited to form a jet fire and cause damage to personnel and equipment. In this paper, CFD software Fluent was used to numerically simulate the local fire test of the hydrogen storage cylinder with high-temperature air as the fire source. The variation law of cylinder wall temperature, gas temperature and pressure inside the cylinder, and the activation of TPRD were analyzed. At the same time, on the basis of the fire test simulation, a high-pressure hydrogen jet fire simulation numerical model caused by the TPRD action was established. The velocity field, temperature field and hydrogen concentration distribution of the jet fire were obtained, and the overpressure generated by the jet fire and the flame length size were analyzed. The results show that the high-pressure hydrogen released by TPRD was ignited under the fire condition to produce a jet flame and generated an overpressure in the jet direction, and the influence range of the overpressure was smaller than the influence range of the jet flame.

Implementation of Machine Learning Using Deep Neural Networks to Estimate the Failure Risk Caused by Leakage in Pressure Relief Devices

Implementation of Machine Learning Using Deep Neural Networks to Estimate the Failure Risk Caused by Leakage in Pressure Relief Devices

Limitations and Performance of Pressure Relief Devices in On-Load Tap Changer Compartments Under Arcing Faults

Limitations and Performance of Pressure Relief Devices in On-Load Tap Changer Compartments Under Arcing Faults

Experimental Investigation into Shockwave and Flame Characteristics of Hydrogen Released through Various Pressure Relief Devices

This paper presents an experimental investigation into shockwave and flame characteristics of compressed hydrogen released through various types of pressure relief devices (PRDs) for which data have not been previously reported. Burst disks and safety valves with different set pressure (P0) of 22–140 MPa were tested. Shockwave intensity/velocity spontaneous ignition/flame behavior was monitored by in-situ pressure/light sensors, respectively. Previous works have mostly focused on burst disks with low P0 (under 10 MPa), leaving safety valves and high-pressure burst disks uninvestigated. It was found that shockwave/spontaneous ignition behavior differs with PRD types. Spontaneous ignition occurs in all burst disk cases, along with an ignition/self-extinguishment/reignition process with relatively low P0, which has not been revealed previously. In contrast, none of the safety valves cause spontaneous ignition, resulting from the absence of shockwave due to lower overpressure values/rise rate during release. This suggests that shockwave formed by sudden release is the most dominant factor in spontaneous ignition. Also, the occurrence of self-extinguishment does not guarantee the absence of jet flame. This work provides a comprehensive database revealing shockwave and flame characteristics of hydrogen released through different PRDs, which offers basic data and theoretical support for the safety and risk assessment of high-pressure hydrogen facilities.

Thermal responses of a concrete slab under hydrogen fuel cell vehicle fires in a semi-open car park

This work aims to investigate the thermal behaviors of the concrete ceiling slab of a semi-open car park exposed to localized fire in hydrogen fuel cell vehicles. For this purpose, a numerical simulation of the hydrogen fuel cell vehicle fire was performed in the Fluid Dynamic Simulator and then coupled with a subsequent thermal analysis of concrete structure carried out in ANSYS Mechanical APDL. In particular, an automatic procedure was used to extract the output of the fire simulation and apply them as boundary conditions of the thermal model. The one-way coupling procedure involving fire simulation and transient thermal analysis has been validated by comparing it with concrete temperatures of a previous test study. Then, two parameters, the diameter of thermal pressure relief devices (1 mm, 2 mm, 3 mm, and 4 mm) and fire spread time between vehicles (0 min, 20 min, and 30 min), are taken into account to study the thermal properties of concrete. The analysis revealed that an increase in the nozzle diameter of the thermal pressure relief device leads to a rise in the maximum concrete surface temperature. The simulation results also showed that the maximum value of the heat release rate increases with a higher value of the nozzle diameter of the thermal pressure relief device and a shorter fire spread time between vehicles.

Hazards associated with pressure relief devices in hydrogen systems

Hydrogen is increasingly being used as an alternative renewable energy carrier because of its potential to reduce carbon emissions in transportation and heavy industry. Nevertheless, this transition necessitates establishing an infrastructure for storage, transporting, and distributing hydrogen. This infrastructure is typically equipped with pressure relief devices (PRD) to protect systems from uncontrolled pressure increases. Without PRDs, a substantial pressure increase has the potential to rupture equipment and lead to a hydrogen release, which could lead to fires, explosions, and significant damage. However, recent incidents have shown that these PRDs can also be the root cause of leaks and releases. Therefore, there is a need to understand the conditions when PRDs increase the risk versus when these devices effectively mitigate the risk. This paper presents the first comprehensive analysis of past hydrogen incidents involving PRDs and considers when these components succeed and when they fail. We then analyze a diverse, representative subset of events involving PRDs using a root cause analysis (RCA) methodology known as Tripod Beta. Further, we introduce a taxonomy breakdown of the root causes of these incidents. Finally, we provide conclusions related to the observed root causes. The most frequently observed failure modes leading to PRD incidents are 1.) spurious operations of PRDs and 2.) high input to the PRD from components upstream of the PRD, which then activate PRDs. When comparing PRD-mitigated events to PRD-initiated events, we found that PRDs initiated more events than they mitigated; however, it is yet to be seen if this is an artifact of poor (success) data reporting or a true prevalence of PRD activations which undermines their value as a protective feature. The use of Tripod Beta shows that using systematic approaches to incident investigation and analysis provides more causal insight into risk mitigation than simply documenting the occurrence of a single failure. To understand the risk tradeoff that PRD offers, we need more rigorous assessments for the risk & reliability of these components. The results of this study motivate research, design and operational changes, and upcoming codes and standards developments to ensure the continuous, safe, and reliable operation of hydrogen systems.

Hydrogen Safety by Design: Exclusion of Flame Blow-Out from a TPRD

Onboard hydrogen storage tanks are currently fitted with thermally activated pressure relief devices (TPRDs), enabling hydrogen to blowdown in the event of fire. For release diameters below the critical diameter, the flame from the TPRD may blow-out during a pressure drop. Flame blow-outs pose a safety concern for an indoor or covered environment, e.g., a garage or carpark, where hydrogen can accumulate and deflagrate. This study describes the application of a validated computational fluid dynamics (CFD) model to simulate the dynamic flame behaviour from a TPRD designed to exclude its blow-out. The dynamic behaviour replicates a real scenario. Flame behaviour during tank blowdown through two TPRDs with different nozzle geometries is presented. Simulations confirm flame blow-out for a single-diameter TPRD of 0.5 mm during tank blowdown, while the double-diameter nozzle successfully excludes flame blow-out. The pressure at which the flame blow-out process is initiated during blowdown through a single-diameter nozzle was predicted.

Pressure safety approach for PIP-II cryogenic distribution system and cryomodules

The Proton Improvement Plan-II (PIP-II) is a superconducting linear accelerator being built at Fermilab that will provide 800 MeV proton beam for neutrino production. The linac consists of a total of twenty-three (23) cryomodules of five (5) different types. Cooling is required at 2K, 5K and 40K. The Cryogenic Distribution System (CDS) consists of a Distribution Valve Box, ~285 m of cryogenic transfer line, modular Bayonet Cans to interface with cryomodules, and a Turnaround Can. The cryogenic system must provide protection from over-pressure by sizing pressure relief devices for all volumes and process line circuits. The cryomodule cavity circuits have dual pressure ratings, 4.1 bara when cold and 2.05 bara when warm (T>80K). Worst case relieving cases will be identified. The methods for determining heat flux will be presented. For the relieving occurring in the linac tunnel, flow must vent to outside to avoid an oxygen deficiency hazard. Also, we will present vacuum vessel relief sizing to protect the cryogenic distribution system vacuum shells from over pressure during an internal line rupture. The project is funded by US DOE Offices of Science, High Energy Physics.

Fire Risk Mitigation Strategies for Electric and Hydrogen Vehicle Car Parks

As the use of eco-friendly vehicles, such as electric and hydrogen vehicles, is rapidly increasing, the related infrastructure is also expanding, and they have become common in parking areas. The fire safety design of a car park is based on the existing data of internal combustion engine vehicles; therefore, the characteristics of eco-friendly vehicles must be reflected. This study investigated the heat release rate of internal combustion engine vehicles, electric vehicles, and hydrogen vehicles using real-scale fire test data and analyzed the effects of curb weight and battery capacity. The fire growth rate and maximum heat release rate of electric and hydrogen vehicles were similar to those of internal combustion engine vehicles, except for the batteries and hydrogen gas, which are the energy sources of electric and hydrogen vehicles, respectively. When ignited from the battery of an electric vehicle, the fire grew rapidly. When the thermally activated pressure relief device was activated in the storage vessel of a hydrogen vehicle, the heat release rate instantaneously increased to 14.5 MW. To improve fire safety in car parks, the curb weight and fire resistance structure must be designed to reflect the increase in plastic interior materials and battery capacity of vehicles, and firefighting facilities must be installed based on vehicles with greater fire severity.

Uneven exposure of compressed natural gas (CNG) and hydrogen (H2) cylinders: Fire and extinguishment tests

Vehicles that are powered by gaseous fuel, e.g., compressed natural gas (CNG) or hydrogen (H2), may, in the event of fire, result in a jet flame from a thermally activated pressure relief device (TPRD), or a pressure vessel explosion. There have been a few incidents for CNG vehicles where the TPRD was unsuccessful to prevent a pressure vessel explosion in the event of fire, both nationally in Sweden and internationally. If the pressure vessel explosion would occur inside an enclosure such as a road tunnel, the resulting consequences are even more problematic. In 2019 the authors investigated the fire safety of CNG cylinders exposed to localized fires. One purpose of the tests conducted in 2021 reported in this paper is to investigate whether extinguishment with water, e.g., from a tunnel deluge system, may compromise the safety of vehicle gas cylinders in the event of fire. Steel cylinders handles the situation with localizde fire and/or cooling with water well. Composite tanks can rupture if the fire exposure degrades the composite material strength, and the TPRD is not sufficiently heated to activate, e.g., if the fire is localized or if the TPRD is being cooled by water, which prevents its activation.

Shock Wave Evaluation in Shell and Tube Heat Exchanger Tube Rupture Scenario

Abstract Shell and Tube Heat Exchangers (STHEs) are commonly used in oil and gas plants to cool or heat process fluids. A possible issue when designing such systems is represented by the tube rupture scenario, when the internal HP (high-pressure) fluid is suddenly discharged to the LP (low-pressure) fluid in the shell. Since, usually, the tube and shell sides have different design pressures, this scenario must be analyzed to assess if the safety measures are fit to protect the weakest part of the system. The time evolution of this event is characterized by different phases; in the first one, a shock wave is generated and propagated very rapidly in the system, with a time scale in the order of a few ms. The phenomenon is so rapid that pressure relief devices are not effective. This kind of wave is normally not evaluated in the majority of available publications; however, it is deemed that it is of particular relevance for large-size SHTEs, due to their significant investment cost, and hence, a methodology has been developed in this work for the purpose. The main impact of such waves is expected in the LP piping connected to the exchanger. The amplitude of the shock wave at the source location, i.e., at the ruptured tube, is calculated based on the theory of the Riemann problem, with reference to different types of HP and LP fluids. Then, the relevant propagation up to the piping entrance is studied to estimate the wave damping and the effective wave amplitude impacting it. Both validation calculations and calculations referred to new design applications and existing installations are presented, and possible mitigation measures are proposed, if any.

Neuropathic diabetic foot ulcers in the elderly: clinical outcomes and healing

There is little evidence on healing outcomes of neuropathic foot ulcers in elderly patients. Aims: To determine the healing rates of neuropathic diabetic foot ulcers at 12 and 24 weeks achieved by standard care provided at an established multidisciplinary diabetes foot clinic in patients aged 65 years and above. Data on the incidence of falls and hypoglycaemia were also collected due to their perceived clinical risk in the group studied. Methods: This was a retrospective observational study looking at clinical outcomes of neuropathic foot ulcers. Patients aged 65 years or more presenting with a non-infected neuropathic ulcer at the time of their initial review were identified and classified into two groups: Group E patients were aged above 80 years and Group Y patients 65-80 years. Results: A total of 97 patients, presenting with 106 ulcer episodes, were identified. Mean HbA1c was 60 mmol/mol in Group Y and 55 mmol/mol in Group E. Healing rates of all ulcers at 12 and 24 weeks in the elderly group lagged behind rates in the younger group (67.6% at 12 weeks and 73% at 24 weeks in Group E vs. 78.2% at both intervals in Group Y). The elderly group had more falls, 11% vs. 2% in Group Y. In all, 50% of the falls in Group E were attributed to their prescribed pressure relief (off-loading) devices. Conclusions: With standard foot care given in a multi- disciplinary foot service, neuropathic diabetic foot ulcers can heal in the elderly despite their age-related skin changes. The rate of healing of neuropathic ulcers noted in our study provides a benchmark for healing outcomes and enables comparison with other age groups and centres. Our study identifies a risk of falls associated with off-loading devices and highlights the need for structured falls risk and mobility assessments in this group.

Numerical Analysis of the Initial Response to Hydrogen-vehicle Jet-flame Accidents

The hydrogen tank of a hydrogen vehicle is equipped with a thermally activated pressure-relief device, which releases hydrogen gas to prevent explosion above a certain temperature, thus avoiding jet flames. This study analyzed the risk of sudden jet-flame generation during response activities following hydrogen-vehicle accidents through numerical analysis. During the jet flame, heat fluxes of over 9.5 kW/m<sup>2</sup>, which can cause second-degree burns to the driver’s seat and approximately 5 m behind the vehicle, were observed, and a zone of over 37.5 kW/m<sup>2</sup>, which can cause catastrophic damage, was formed at the immediate area, including the lower part of the vehicle. At a distance of 0.5 m from the driver’s seat, a high heat flux of approximately 80 kW/m<sup>2</sup>, which is similar to the test standard for the thermal-protection performance of fire-fighting clothing, was formed. Further analysis indicated that both rescue victims and first responders are at risk if jet flames are generated during rescue activities. The results of this analysis can be used to develop a safe accident-response strategy for hydrogen vehicles.

Numerical Investigation of Hydrogen Jet Dispersion Below and Around a Car in a Tunnel

Accidental release from a hydrogen car tank in a confined space like a tunnel poses safety concerns. This Computational Fluid Dynamics (CFD) study focuses on the first seconds of such a release, which are the most critical. Hydrogen leaks through a Thermal Pressure Relief Device (TPRD), forms a high-speed jet that impinges on the street, spreads horizontally, recirculates under the chassis and fills the area below it in about one second. The “fresh-air entrainment effect” at the back of the car changes the concentrations under the chassis and results in the creation of two “tongues” of hydrogen at the rear corners of the car. Two other tongues are formed near the front sides of the vehicle. In general, after a few seconds, hydrogen starts moving upwards around the car mainly in the form of buoyant blister-like structures. The average hydrogen volume concentrations below the car have a maximum of 71%, which occurs at 2 s. The largest “equivalent stoichiometric flammable gas cloud size Q9” is 20.2 m3 at 2.7 s. Smaller TPRDs result in smaller hydrogen flow rates and smaller buoyant structures that are closer to the car. The investigation of the hydrogen dispersion during the initial stages of the leak and the identification of the physical phenomena that occur can be useful for the design of experiments, for the determination of the TPRD characteristics, for potential safety measures and for understanding the further distribution of the hydrogen cloud in the tunnel.

Effect of TPRD diameter and direction of release on hydrogen dispersion and jet fires in underground parking

The paper presents safety strategies to support choice of diameter and release direction for thermally activated pressure relief device (TPRD) onboard a hydrogen fuel cell electric vehicle. Analytical and numerical modelling campaigns were performed to study hazards of unignited and ignited hydrogen releases from a vehicle in a real underground parking. TPRD diameter to prevent flammable mixture formation during upward release was determined using similarity law for hydrogen concentration decay along jet centreline. Parametric CFD simulations studied effect of different TPRD diameter, release direction, vehicle distance from obstacles, ceiling height, influence of carpark ventilation on hydrogen hazards. Hazards of unignited releases were associated with the lower flammability limit of hydrogen-air clouds. For ignited releases the temperature threshold 70 °C was used as a no-harm criteria for assessment of thermal hazards to people and threshold 300 °C as a damage criteria for mechanical ventilation system following requirements of BS 7346-7-2013 standard for carpark ventilation. Recommendations on TPRD design were formulated to support safe integration of hydrogen-powered vehicles in the existing underground parking facilities and infrastructure.

Analysis and mitigation of the impact of electric vehicle charging on service disruption of distribution transformers

The transition to electric mobility could overload distribution transformers to unprecedented levels. Sustained overloads produce excessive heat within the transformer and hasten insulation deterioration. As EV deployment rises and the severity of overloads increases, the focus shifts from long-term effects that reduce transformer life to more immediate impacts that can disrupt normal functioning. The latter typically manifest as the blowing of protection fuse, the triggering of pressure relief device, or the breakdown of winding insulation, each of which could result in transformer outage. The transformer’s vulnerability can be monitored in terms of its apparent power flow, top-oil temperature and hottest-spot temperature. The IEEE C57.91 standard specifies the permissible range for these parameters, beyond which the transformer operation could get interrupted. A study to determine the range of EV penetration that can be accommodated by a distribution transformer without any discontinuity in its operation is presented in this paper. The non-linear nature of EV charging is incorporated in the analysis to account for the effect of higher-order harmonics on the transformer’s internal temperature. The effectiveness of a controlled charging strategy, which seeks to regulate transformer loading by minimizing its variance, in preventing service disruption is also validated in this simulation study.

Explosion free in fire self-venting (TPRD-less) composite tanks: Performance during fire intervention

This paper describes the performance of explosion free in fire self-venting (TPRD-less) composite tanks in fires of realistic specific heat release rate (HRR/A), i.e., total fire HRR over the source area, A, of HRR/A = 1 MW/m2, during fire intervention. This breakthrough safety technology does not require thermally activated pressure relief devices (TPRD). It provides microleaks-no-burst (μLNB) performance of hydrogen storage tanks in fire. The study investigated two fire intervention strategies, i.e., removal of vehicle with μLNB tank from the fire, and extinction of fire by water. One carbon-carbon and one carbon-basalt double-composite wall tanks were assessed in the removal from fire scenario. Four carbon-basalt prototypes were studied in fire extinction scenarios. All six prototypes of 7.5 L and nominal working pressure of 70 MPa have demonstrated safe release of hydrogen through microchannels of the wall after the liner melting. The μLNB technology allows to apply standard intervention strategies and tactics.

Reenacting the hydrogen tank explosion of a fuel-cell electric vehicle: An experimental study

With the world-wide decision to reduce carbon emissions through the Paris Agreement (2015), the demand for hydrogen-fuelled vehicles has been increasing. Although hydrogen is not a toxic gas, it has a wide flammable range (4–75%) and can explode due to static electricity. Therefore, studies on hydrogen safety are urgently required. In this study, an explosion was induced by applying fire to the lower part of a fuel cell electric vehicle (FCEV). Out of three compressed hydrogen storage tanks installed in the vehicle, two did not have hydrogen fuel, and one was filled with compressed gaseous hydrogen of 700 bar and forcedly deactivated its temperature-activated pressure relief device. The side-on overpressure transducers were installed by distance in main directions to measure the side-on overpressure generated by the vehicle explosion. A 10 m-long protective barrier was installed, on which reflected overpressure, displacement, and acceleration were measured to examine the effect of attenuation of explosion damage in the event of an accident. The vehicle exploded approximately 11 min after ignition, generating a blast wave, fireballs, and fragments. The results of the experiment showed that the protective barrier could almost completely block explosive pressure, smoke, and scattering generated during an explosion. Through Probit function analysis, the probabilities of an accident occurring were derived based on peak overpressure, peak impulse, and scattering. The results of this study can be used to develop standard operating procedures (SOPs) for firefighters as the base data for setting the initial operation location and deriving the safe separation distance.

Breakthrough safety technology of explosion free in fire self-venting (TPRD-less) tanks: The concept and validation of the microleaks-no-burst technology for carbon-carbon and carbon-glass double-composite wall hydrogen storage systems

The paper describes the breakthrough microleaks-no-burst (μLNB) safety technology of explosion free in fire self-venting hydrogen tanks that do not require thermally-activate pressure relief devices (TPRD). The technology implies melting of the hydrogen-tight liner before hydrogen-leaky double-composite wall loses its load-bearing ability. Hydrogen then flows through the wall's microchannels and either burns in microflames on its own or together with resin. The experimental validation of the technology is presented for 7 prototypes with the nominal working pressure of 70 MPa made of carbon-carbon or carbon-glass composites. The prototypes are fire tested at the specific heat release rate HRR/A = 1 MW/m2 characteristic for gasoline/diesel spill fires. The μLNB technology eliminates catastrophic consequences of tank rupture in fire: blast waves, fireballs, and projectiles. The technology limits hydrogen accumulation in naturally ventilated enclosures. It reduces the risk of hydrogen-powered vehicles to an acceptable level below that for fossil fuel automobiles, including underground parking and tunnels. It provides an unprecedented level of life safety and property protection.

Preliminary hazard identification for qualitative risk assessment on onboard hydrogen storage and supply systems of hydrogen fuel cell vehicles

Due to the ever-increasing stringency of environmental policy requirements, hydrogen fuel cell vehicles (HFCVs), which are intended to serve as a substitute for conventional automobiles, are continuously evolving as a new promising technology. It is essential to conduct hazard identification as an early phase in the development of HFCVs in order to describe possible hazards and identify potential safety concerns. The onboard hydrogen storage and supply system is an essential component of HFCVs, serving to store hydrogen and provide it to the fuel cell system to guarantee its proper functioning. In this context, the research is conducted by establishing models of onboard hydrogen storage and supply system that reflected their specifications and elements. In this study, the methods of hazard and operability study (HAZOP) and failure mode and effect analysis (FMEA) are employed to identify and analyze the potential accident scenarios. The risk of each potential accident scenario, including whether to implement safety measures, is analyzed and classified as risk matrix. Medium- and high-risk scenarios in the absence of safety measures include accidental burst of the hydrogen cylinder, debonding of plastic liners and metal bosses, release of hydrogen from a thermally activated pressure relief device or pressure relief device, tiny release of hydrogen from improperly attached tube fittings, and small release of hydrogen from valves with seal failures. Comparing the findings of risk matrices with and without safety measures confirms that the safety measures lower the risk levels of the onboard hydrogen storage and supply systems to a tolerable level.