Near-field BLEVE overpressure effects: The shock start model

International audienceThis paper presents the results of a small scale experimental study of BLEVE overpressure effects. Testing consisted of a sealed aluminum tube (0.6 L) filled with either water or propane, being heated by a flame until the internal pressure led to catastrophic failure and explosion. Three parameters were controlled during the experiments: the failing pressure, the weakened length on the tube and the fill level. BLEVEs were obtained with tests involving water and propane. Blast gages and optical techniques were used to characterize the shock wave escaping from the failing tube. The results obtained suggest that the lead shock was primarily generated by the vapor space. Overpressure results obtained were compared with the predictions of existing models and found to be in reasonable agreement except for overpressures measured vertically above the cylinder where the overpressures were highest. A prediction model based on only vapor space characteristics was developed. Images show that the shock was fully formed at some distance away from the vessel opening and this was due to the non-ideal opening of the vessel. The model developed was based on the characteristics of the shock when fully formed away from the tube. These characteristics were defined using a combination of imaging, pressure measurements, and predictions from shock tube theory

Invasive Bacterial Infections in Children With Sickle Cell Disease: 2014–2019

Background: Children with sickle cell disease (SCD) are at a high risk of invasive bacterial infections (IBI). Universal penicillin prophylaxis and vaccination, especially against Streptococcus pneumoniae, have deeply changed its epidemiology. Analysis of IBI in children with SCD in a post-13-valent pneumococcal vaccine era is limited. Methods: Twenty-eight pediatric hospitals from 5 European countries retrospectively collected IBI episodes in SCD children aged 1 month to 18 years between 2014 and 2019. IBI was defined as a positive bacterial culture or polymerase chain reaction from a normally sterile fluid: blood, cerebrospinal, joint, or pleural fluid and deep surgical specimen. Results: We recorded 169 IBI episodes. Salmonella spp. was the main isolated bacteria (n = 44, 26%), followed by Streptococcus pneumonia (Sp; n = 31, 18%) and Staphylococcus aureus (n = 20, 12%). Salmonella prevailed in osteoarticular infections and in primary bacteremia (45% and 23% of episodes, respectively) and Sp in meningitis and acute chest syndrome (88% and 50%, respectively). All Sp IBI occurred in children ≤10 years old, including 35% in children 5 to 10 years old. Twenty-seven (17%) children had complications of infection and 3 died: 2 because of Sp, and 1 because of Salmonella. The main risk factors for a severe IBI were a previous IBI and pneumococcal infection (17 Sp/51 cases). Conclusions: In a post-13-valent pneumococcal vaccine era, Salmonella was the leading cause of bacteremia in IBI in children with SCD in Europe. Sp came second, was isolated in children ≤10 years old, and was more likely to cause severe and fatal cases.info:eu-repo/semantics/publishedVersio

Analysis of BLEVE overpressure using spherical shock theory

International audienceThe near-field hazards from BLEVE including blast, ground force, drag loading from the rapid liquid phase change and projectiles. There are several correlations available in the literature for the far field blast overpressure from a BLEVE, usually requiring the calculation of the available expansion energy and the application of correction factors. However, there is very little information available for near-field effects and how this is affected by the details of vessel failure.This work presents near-field blast overpressure data and prediction models to fill in this gap. First, experimental measurements of overpressure in the near-field of a small scale cylindrical controlled BLEVE experiments with propane (V = 0.6 L, d =50 mm, L = 300 mm) were performed. Then, this work establishes a prediction model based solely on the vapour phase properties at failure, using shock tube overpressure prediction and spherical shock propagation models.The model predicts well the strongest tests and is conservative with all the others. Scaling the model up to larger scale experimental data from literature shows that it is transposable, proposing a simple physics-based prediction model for BLEVE overpressure

Ground loading from BLEVE through small scale experiments: experiments and results

International audienceThe ground force generated by a BLEVE is a hazard that has been seldom studied, even though BLEVE has been source of many research works in the past decades. However, emergency responders have been asking questions the risk and consequences of a BLEVE on a bridge and other critical infrastructures for a while, with no answer so far. Moreover, a tank truck accident in Bologna in August 2018 has shown that bridge collapse may result from such scenario.This paper presents the experimental work done with a small scale apparatus reproducing realistic BLEVE failure with a cylindrical tube. Load cells were placed under the base plate holding the tube to measure the local ground force generated by the explosion. Forces from 10 kN to 55 kN were measured for a 50 mm diameter tube with 300 mm length failing at pressures from 10 to 32 Bar. The ground force signals are interpreted together with the imaging and internal pressure signal. The synchronization between violent boiling, repressurization in the vessel and strong ground force is clear through this comparison. Different ground force signals were observed depending on the fill level and weakened length of the tube. The maximum ground force and impulse vary almost linearly with failure pressure and liquid fill level. It is less clear for the influence of weakened/opening length of the tube. More data is required to conclude on this parameter influence

Early moments of BLEVE: From vessel opening to liquid flashing release

International audienceThe boiling liquid expanding vapour explosion (BLEVE) is well known but not well understood. Some still argue about what comes first, the BLEVE or the vessel rupture. Some believe the BLEVE is triggered by some pressure transient inside the vessel and this causes a superheat limit explosion which causes the vessel to rupture. Others believe it is the vessel rupture by some weakening process that leads to the BLEVE. This paper will provide evidence that the latter description that is correct for most, if not all BLEVEs observed in practice.This paper describes small scale experiments of aluminum tubes that were weakened by machining a thinned wall area over a specified length. The tubes were filled to a desired level with liquid propane and then the propane was uniformly heated electrically until the tubes failed. The failure pressures ranged from 10 to 33 bar.The tube was instrumented to capture failure characteristics (pressure, temperature) and consequences: blast overpressure and imaging of the propane cloud and shock around the vessel; ground force under it; transient pressure and imaging of the boiling process inside the vessel. The work was done to improve our understanding of the fluid – structure interactions during the fire heat induced failure of a pressure vessel holding a pressure liquefied gas. We were specifically interested in the near field hazards including blast overpressure and ground force. This paper will focus on the early milliseconds of the process where the vessel begins to open and a shock wave is formed and moves out into the surroundings. The imaging reveals presence of a Mach shock at the exit of the vessel at the early stage of the opening. A chronology of the event also shows that the lead shock is generated early in the explosion process, and is long gone before the liquid starts boiling, arguing that vapour expansion is the main contributor to the first shock overpressure

Near field blast effects from BLEVE

cited By 2International audienceThere is a need to have a better understanding of the near field blast and impulse from boiling liquid expanding vapour explosions. Emergency responders and response planners need to know the ground loading on a bridge if there is a tank truck BLEVE, or the loading on a building if a tank truck suffers a BLEVE near a high rise building.When a tank suffers a BLEVE the vessel opens fully to release the contained energy. The release is strongly directional since the tank wall does not move away instantaneously. The piston effect of the expanding vapour generates a shock at some distance away from the tank. This shock then propagates into the surroundings. Behind this shock is an additional blast wind caused by liquid flashing. This may also produce a shock. When the tank opens fully and is flattened on the ground this produces a large impulse load. Long range projectiles are also possible.Experiments have been conducted using 50 mm diameter tubes filled with water or propane. These tubes have been heated until failure to produce a BLEVE release. The tube failure mode and kinematics was representative of pressure vessel failures. The tube supports contained load cells to measure the ground force. Pencil blast gages were located close to tube to measure overpressures. High speed shadowgraph imaging was used to capture the formation and movement of the shocks.The results include detailed data on near field blast and ground loading effects from a boiling liquid expanding vapour explosion