Search

Blast waves from explosion sources such as a pressure vessel burst (PVB) exhibit both positive and negative phases, and the relative magnitude of the positive and negative phases is a function of standoff distance from the explosion source to the target of interest. When an incident blast wave reaches a target building, the blast wave will be reflected off the front wall (i.e., that facing the blast source). Both the blast wave positive and negative phases are affected by this reflection process. A fully reflected blast wave would be produced if the incident blast wave reflected off an infinitely tall and wide wall in a normal orientation. However, when an incident blast wave reflects from a facing wall of finite size, rarefaction waves are created at the edges of the wall and roof, which then sweep inward across the wall. The rarefaction waves result in a clearing effect for both the positive and negative phases. Clearing relieves some of the applied positive phase blast load on the reflected wall. However, clearing may either relieve or enhance the applied negative phase blast load, depending on the blast wave profile and the wall dimensions. This paper focuses on the determination of negative phase clearing as a function of blast wave and structure parameters. Blast load adjustment factors (i.e., ratio of cleared to fully reflected blast loads) are introduced to characterize blast clearing as a function of these parameters. The purpose of the evaluation described in this paper was to generate a database of the blast clearing for engineering modeling of blast-structure interaction.

Kelly Thomas first contacted us briefly—but to us so poignantly—about an earlier publication of ours on Drug-Related Death (DRD) bereavement entitled Sounds of silence. The ‘special grief’ of drug-death bereaved parents (Titlestad et al., 2020). He commented: It is coming up on the 3 years since we lost our daughter at age 21 in a DRD. I have found my wife listening to the song your paper refers to more times than I would like to count. I cried as I read your paper and saw myself, and tears run down my face as I write this. The quote you provided from another father regarding this loss as being “world changing” is highly descriptive. Thank you for your work. At first, we were lost for words, we were so deeply touched by this response to our article, so moved by what he wrote about the title and about his wife listening to the song. We were also grateful for the feedback indicating that Norwegian parents’ experiences are recognisable in other parts of the world. Of course, we went on to respond to him personally and we also drew his attention to a further article that at the time was accepted in OMEGA—Journal of Death and Dying, the one that triggered further correspondence between us, the one which is the subject of this commentary. To step back a little and explain: These two publications are reports on a large-scale, still-ongoing research project that began in 2017 (The END-project), focusing on drug-death bereavement and recovery from the perspective of bereaved family members, close friends and community helpers. This project is close to the hearts of all three of us, as it also is to the extended team of END researchers involved in working on different aspects, all relating to DRD. We are keen to disseminate our findings, for both scientific and applied purposes: To add to knowledge and increase understanding of DRD bereavement, on the one hand, and to contribute to support for DRD bereaved persons and those who care for them professionally and personally, on the other hand. So when we received a second email from Kelly Thomas about the OMEGA—Journal of Death and Dying article, we were moved to suggest its publication as a commentary piece in OMEGA—Journal of Death and Dying: Kelly Thomas’s words vividly illustrate the points we covered in our qualitative analysis. Of course we ourselves included illustrations from the interviews with the participants, in our articles. But here we have an entirely different narrative, namely, the account of one particular DRD bereaved father actually reflecting on the categories—scientific constructions as they are—of feelings and behaviors and attitudes that we identified in our qualitative analysis. We learn from Kelly Thomas how our analysis “spoke” to someone who has himself had to endure the loss of a loved child to DRD. His words speak for themselves.

This paper presents a comparison between the results from a test program carried out to characterize the blast load environment within BakerRisk's Deflagration Load Generator (DLG) test rig, and predictions made using the FLACS computational fluid dynamics (CFD) code. The test data was also compared to internal peak pressure predictions made using the newest version (2018) of the National Fire Protection Association's Standard on Explosion Protection by Deflagration Venting (NFPA 68) (National Fire Protection Association, 2018). The purpose of these tests was to provide data for comparison with standard methods used to predict internal blast loads in a vented deflagration. The tests also provided a characterization of the internal DLG blast load environment for equipment qualification testing. The DLG test rig is 48 feet wide × 24 feet deep × 12 feet tall and is enclosed by three solid walls, a roof, and floor, with venting through one of the long walls (i.e., 48-foot × 12-foot). During testing, the venting face of the rig was sealed with a 6 mil (0.15 mm) thick plastic vapor barrier to allow for the formation of a near-stoichiometric propane-air mixture throughout the rig. The flammable gas cloud was ignited near the center of the rear wall. Congestion inside the rig was provided by a regular array of vertical cylinders (2-inch outer diameter) that occupied the rear half of the rig; the front half of the rig was uncongested (i.e., as would be the case for equipment qualification testing). Forty-three pressure transducers were deployed internal and external to the rig to measure blast pressure histories. Three series of tests were conducted with congestion levels corresponding to area blockage ratios (ABR) of 11%, 7.6%, and 4.2% in test series A, B and C, respectively. The obstacle-to-enclosure surface area ratio (Ar), a parameter used within the NFPA 68 correlations to quantify congestion within the vented enclosure, was equal to 0.39, 0.27, and 0.15 for test series A, B, and C, respectively. The peak pressures and impulses for each test are provided, along with pressure histories internal and external to the rig for selected tests. Comparisons of the test data to predictions made using the FLACS CFD code and NFPA 68 (2018) venting correlations are also provided.

An incident blast wave interacting with a building will diffract around the side walls and roof, resulting in reduced blast loads on the back wall. There is also a region behind the back wall where the blast loads will be attenuated (i.e., lower than the incident blast loads). This paper focuses on defining the attenuated blast load region as a function of the blast wave strength and building dimensions. Characteristic parameters are utilized to present the analysis results, including wave length, wave length normalized by a characteristic building dimension, and normalized standoff distance from the building back wall. Blast load adjustment factors (i.e., ratio of the diffracted to incident blast load) are used to define the blast load attenuation as a function of these characteristic parameters. The purpose of this work was to generate a database of the shock attenuation behind a structure for engineering modeling applications.

This paper presents results from a test program carried out to determine the peak deflagration pressure achieved within a congested enclosure vented through one wall of the enclosure. The industry standard in the United States for predicting the peak pressure developed in a vented deflagration is the National Fire Protection Association's Standard on Explosion Protection by Deflagration Venting (NFPA 68). The NFPA Explosion Protection Committee has compiled a database of published and unpublished explosion venting test data. This data was summarized in a 2008 report (Zalosh) that served as the foundation of the development for the vented deflagration correlations in the latest (2013) edition of NFPA 68. In this latest edition, NFPA 68 (2013), the vent area correlation accounts for varying degrees of congestion if the ratio of the obstacle surface area (A obs ) to that of the enclosure internal surface area (A s ) is greater than 0.4 (i.e., A r = A obs /A s > 0.4). Congestion is accounted for within the correlation at all values of A r , however when A r is r ratio of less than 0.4. These tests were conducted in a rig with a 48-foot width, 24-foot depth, and 12-foot height. The rig is enclosed with solid walls, roof, and floor, allowing for venting through one of the long walls (i.e., 48-foot by 12-foot). The venting face of the rig was sealed with a 6 mil (0.15 mm) thick plastic vapor barrier to allow for the formation of a near-stoichiometric propane-air mixture. The flammable gas cloud was ignited near the center of the rear wall. Steel vent panels (20-gauge, 2 lb m /ft 2 ) were installed over the plastic vapor barrier using explosion relief fasteners. The vent panels were configured to release at 0.3 psig; vent panel restraint devices were not utilized. The congestion inside the rig was provided by a regular array of vertical cylinders (2-inch schedule 40 pipe and 2-inch outer diameter cylinders) giving area and volume blockage ratios (ABR and VBR) within the congestion array of 4.9% and 0.5%, respectively. The obstacle-to-enclosure surface area ratio (A r ) is 0.3 with the array extended throughout the rig and vent panels installed, which is less than the critical value to account for congestion in the NFPA 68 correlation. Four series of tests were conducted with varying vent parameters, flammable gas cloud sizes, and congestion levels. Baseline tests were performed with the congestion array and flammable gas cloud extending throughout the entire rig without vent panels present (i.e., vapor barrier only). The second test series included the addition of vent panels for the same congestion pattern as that employed for the baseline tests. The third test series utilized a flammable gas cloud that filled only the back half of the rig. For the fourth test series, the congestion array occupied only ¼ of the rig. The peak pressures and impulses for each test series are provided, along with pressure histories internal and external to the rig for selected tests. The steel vent panel throw distance is also provided as a function of internal peak pressure. The test data were compared with the predictions of the vent area correlations provided in NFPA 68. For all but the fourth test series (i.e., congestion array occupying ¼ of the rig), the average internal peak pressures were approximately a factor of 2 larger than those predicted by NFPA 68. Adjustments to the NFPA 68 correlation were investigated to improve the agreement with the current test data.

The maximum laminar burning velocity (LBV) of a fuel-air mixture is an important input parameter to vapor cloud explosion (VCE) blast load prediction methods. In particular, the LBV value has a significant impact on the predicted blast loads for high reactivity fuels with the propensity to undergo a deflagration-to-detonation transition (DDT). Published data are available for the maximum LBV of many pure fuel-air mixtures. However, little test data are available for mixtures of fuels, particularly for mixtures of fuels and inert species. Such mixtures are common in the petroleum refining and chemical processing industries. It is therefore of interest to be able to calculate the maximum LBV of a fuel/inert mixture based on the mixture composition and maximum LBV of each component. This paper presents measured test data for the maximum LBV of H 2 /inert and C 2 H 4 /inert mixtures, with both nitrogen and carbon dioxide as the inert species. The LBV values were determined using a constant-volume vessel and the pressure rise method. This paper also provides a comparison of the measured LBV values with simplified LBV prediction methods.

Blast walls are frequently considered as a potential mitigation option to reduce the applied blast loading on a building or structure in cases where unacceptably high levels of blast damage are predicted. There are three general explosion types of interest with respect to blast loading: High Explosive (HE), Pressure Vessel Burst (PVB), and Vapor Cloud Explosion (VCE). The blast waves resulting from these explosion types can differ significantly in terms of blast wave shape and duration. The effectiveness of a blast wall depends on these blast wave parameters (shape and duration), as well as the blast wall parameters (e.g., height, width and standoff distance from the protected structure). The effectiveness of a blast wall in terms of mitigating the blast loading on a protected structure depends on the combination of the blast wave and blast wall parameters. However, little guidance is available on the effectiveness of blast walls as a mitigation option for non-HE explosion sources. The purpose of this paper is to characterize the effect of blast wave parameters on the effectiveness of a blast wall and to provide guidance on how to determine whether a blast wall is an effective and practical blast damage mitigation option for a given blast loading.

A test was conducted which demonstrates that a detonation wave, once formed due to a deflagration to detonation transition (DDT) within a congested region, will propagate as a detonation from the congested region into an uncongested region. This is the expected behavior based on the general behavior of detonation waves as well as other tests reported in literature. The impact of a detonation wave propagating beyond the congested volume in which it is initiated on the resulting blast load was evaluated parametrically. As would be expected, the impact on the blast load is large for flammable clouds which extend well beyond the congested volume. The test rig was 16.5 m (54 ft) long with the first 9.1 m (30 ft) of the rig length comprised of a congested section 3.7 m (12 ft) in width and 1.8 m (6 ft) high. The congestion was made up of a regular array of vertical circular tubes [6 cm (2.375 in.) diameter, pitch-to-diameter ratio of 4.1, area and volume blockage ratios of 23% and 4.2%, respectively]. The last 7.3 m (24 ft) of the test rig length was completely uncongested. The test rig was configured without any confinement (i.e., no wall or roof sections). A near-stoichiometric ethylene-air mixture completely filled both the congested and uncongested portions of the test rig. Prior testing with a similar rig configuration had shown that this flammable mixture would undergo a DDT within the congested portion of the rig. © 2013 American Institute of Chemical Engineers Process Saf Prog, 2013

The standard dust explosibility test is performed in a 20-L vessel with either one or two 5 kJ pyrotechnic igniters. The dust is deemed to be explosible if the ratio of the maximum deflagration pressure to the initial pressure exceeds some threshold value. This type of test is widely accepted and used. However, marginal dusts may be “over driven” in the 20-L standard test and yield a “false positive” result (i.e., indicate that the dust is explosible), even when such a dust is not capable of forming a dust cloud through which a flame would actually propagate any significant distance. This can be avoided by testing such dusts in a larger vessel, where the flame must propagate over a more reasonable distance in order to develop a maximum pressure sufficient to classify the dust as explosible. This article reports on urea dust testing where this type of result was obtained, but the approach taken in this work is applicable to other dusts as well. © 2013 American Institute of Chemical Engineers Process Saf Prog, 2013

An explosion destroyed a small “Gas House” in which aerosol cans were being filled with ethylene oxide on June 24, 1997. At issue was whether the ignition occurred in the Gas House or from a remote catalytic converter. Our investigation of the pattern of blast damage supports ignition at the catalytic converter that generated a burn-back through the ducting. A strong jet ignition reached a flammable atmosphere in the Gas House and ignited an explosion that well exceeded the yield strength of the prefabricated metal Gas House in spite of the vent panels and access doors being released and discharging of the fire suppression system. One of the doors from the Gas House flew off of the building as hazardous debris, which impacted and catastrophically failed a second door located in an adjoining occupied building. This resulted in the only fatality associated with this event. This study illustrates the damage patterns that indicate the direction of the initial explosion wave. © 2007 American Institute of Chemical Engineers Process Saf Prog, 2007.

Enclosed chemical processes, laboratory facilities, boilers and reformer furnaces are typical examples of facilities and equipment where an internal VCE may be postulated to occur. The applied blast load history on the enclosure surfaces is required in order to assess the response of the enclosure to the postulated VCE. The internal blast pressure history and associated applied blast loads depend on a number of factors, such as: (1) the maximum flame speed attained in a flammable cloud, (2) the ratio of the cloud volume to the total enclosure volume, (3) the cloud location within the enclosure, and (4) the environment temperature. The purpose of work described in this paper was to investigate the dependence of internal blast pressure history and applied blast loads on the aforementioned factors. It was found that the applied loads on the enclosure surfaces can be roughly classified into two regimes: quasi-static and dynamic, depending on the combination of these factors. It can be important to identify the appropriate blast loading regime in order to properly analyze the structural response of the enclosure.Copyright © 2015 by ASME

The Baker–Strehlow–Tang vapor cloud explosion (VCE) blast load prediction methodology uses flame speed as a measure of explosion severity. In previous publications, guidance has been presented for selecting flame speeds as a function of congestion, confinement, and fuel reactivity. These recommended values were based on empirical data available from the literature. Over the last 5 years, a series of medium-scale VCE tests have been conducted through a joint industry program to better understand vapor cloud explosions and to allow a more accurate definition of the flame speed applicable to a given combination of congestion, confinement, and fuel reactivity. These tests have demonstrated that the previously published flame speeds are not conservative for all configurations for the case of no confinement (3-D flame expansion). This paper provides an overview of the tests along with an update to the flame speed table where the previously published guidance was not conservative. © 2005 American Institute of Chemical Engineers Process Saf Prog, 2005

During plant start-up, a critical interface exists at block valves located at battery limits of process units. A relatively small leak at a battery-limit isolation point was established as the source of gas that caused an explosion in a 26-foot diameter fractionator on a Fluid Coker nearing the end of a maintenance turn a round. This incident could easily have occurred in any modern oil refinery or chemical plant. This paper shares the technology and learning associated with small release scenarios that are often overlooked in large-scale plant operations. The explosion event did not damage the fractionator shell, but displaced all but two of the sieve trays in the column, and produced minor damage in the overhead condensers and receiver drum. Importantly, the consequent down-time resulted in a major production loss. Damage analysis supports the proposition that a deflagration occurred in the top portion of the fractionator involving under 50 lbs. of fuel. It is believed that relatively small leaks, persisting over a period of a few hours, supplied the required amount of fuel. The accident investigation identified multiple potential pathways whereby natural gas leaking past battery limit block valves could have reached the fractionator. This incident highlights the importance of securing leak tight connections between active and inactive sections of process systems. As a result of this experience, several procedural and organizational reforms have been instituted.

A key component of explosion hazard evaluations is the determination of standoffs to given blast overpressure values. Many such evaluations use a simplified methodology that assumes that the blast wave propagates from the explosion source to the target location without interacting with intervening buildings or structures (i.e., without blast wave shielding). This is obviously a perfectly acceptable approach for a screening study, but blast wave shielding effects can be significant in certain circumstances (e.g., within a building group). A methodology was proposed by the UK Health & Safety Laboratory (HSL) in 2001 to account for blast shielding due to buildings/structures between the explosion source and target location. The HSL methodology is based on the blast waves generated by high explosives (HE). This paper extends the blast shielding evaluation to blast waves generated from pressure vessel bursts (PVB) and vapor cloud explosions (VCE). The influences of blast wave shape parameters (overpressure, duration and rise time) on blast wave shielding are examined. The results indicate that the degree of blast shielding is strongly dependent on the source of the blast wave (i.e., on the blast wave shape parameters) and that the shielding factors obtained with HE blast waves are not always directly applicable for PVB and VCE blast waves.

The ignition of a flammable gas mixture contained within a piping system can lead to damage or failure of the piping or system components. Flame propagation and acceleration within piping systems have been extensively studied. It has been well documented that, given sufficient flame propagation distance and/or the presence of turbulence generating features, flame acceleration within a pipe can lead to a deflagration-to-detonation transition (DDT). The high overpressures associated with a DDT can increase the potential for deformation or failure of the piping system relative to the loads associated with either a fast deflagration or steady-state detonation. This paper presents the results of numerical evaluations to predict the pressure distributions within a pipe run due to a DDT. The blast overpressure associated with a DDT was found to depend on a number of parameters, including: the rate of flame acceleration prior to the DDT, the length of piping occupied by the flammable mixture, the initial gas pressure and the flammable mixture concentration distribution along the pipe. This paper also provides a comparison of the blast loads associated with a steady-state detonation relative to those due to a DDT.Copyright © 2012 by ASME