Comprehensive consequence analysis software developed by BakerRisk.
Consequence Analysis Software
SafeSite3G is a comprehensive consequence analysis software capable of simulating chemical discharge, dispersion, pool spread and volatilization, jet and pool fires, vapor cloud explosions, and vulnerability during fire, toxic, and explosion events.
SafeSite3G performs consequence analysis studies for onshore facilities (new and existing), offshore facilities, and transportation routes. During the design phase of a new project, SafeSite3G can efficiently perform study updates for layout and process changes or be utilized for master planning to minimize future facility risk exposures. SafeSite3G is extensively used for our Facility Siting Studies and Quantitative Risk Analyses (with our QRATool©).
SafeSite software showing 3D flammable cloud from single scenario
SafeSite Example of Building Damage Contours for Wood Trailer
SafeSite Example of Vapor Cloud Footprint
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Facilities that handle hazardous materials above threshold quantities are required to assess the impacts due to postulated accidents involving releases of these materials, and to ensure that people are adequately protected from the associated fire, explosion, and toxic hazards. An analysis of these hazards can be based solely on consequences from maximum credible events or can incorporate the likelihood of the events to characterize results in terms of risk. The methods of performing these analyses may vary, but, regardless of the specific techniques used, fundamental principles of thoroughness and defensibility should be achieved. This paper describes best practices and basic requirements for consequence-based and risk-based facility siting studies (FSSs), also commonly referred to as quantitative risk analyses (QRAs), consistent with industry guidance. The fundamental objective of a consequence-based or risk-based FSS is to ensure that the consequences or risks posed by facility operations are minimized to the extent practical.
Facility siting methods to optimize the layout of industrial facilities for risk reduction have been evolving for decades from subjective views, standards, and guidelines to quantitative numerical analysis. The authors of this paper have tossed out the past, moved beyond the present, and taken out their crystal balls to provide a discussion around the future of facility siting by focusing on technology driven enhancements associated with three main themes: mainstreaming of current advanced analysis techniques into the base case methodology, incorporating company and/or site specific data trending and analytics to operationalize the studies, and the potential transformational change to machine learning-based predictive risk management. With technological advancements touching nearly every area of business, it is no surprise that it is also changing the landscape of consequence and risk-based facility siting approaches. As with all markets, the customers will be a key driver for the advancements of technical safety studies to suit their adapting needs. However, as this article will show, personnel conducting facility siting studies are also using technological advancements to challenge the status quo by improving data fidelity, increasing the robustness and depth of analysis, and providing improved insights to aid decision making.
There are a variety of building design approaches that can be considered and employed to mitigate risks to building occupants. Although the preferred and safest approach is to design buildings for worst-case explosion, fire, and toxic events after completion of a consequence study, this can often be infeasible or cost-prohibitive. An alternative building design approach considers the frequency of each scenario and can be achieved through the use of frequency-consequence exceedance curves to determine a design accidental load (DAL) or by use of risk calculations from a Quantitative Risk Analysis (QRA). Using example case studies, the benefits and shortcomings of developing a building design basis employing frequency-consequence exceedance curves versus using a risk-based approach will be examined. Although a risk-based approach may require more complex modelling, additional effort and time compared to determining a DAL, it is important to consider each load (blast, fire, toxic) and the duration of each load to assess the vulnerability to occupants and fully quantify the effectiveness of a building design.
Treating the dynamic effects of accidental discharges of liquefied natural gas (LNG) is important for realistic predictions of pool radius. Two phenomena have important influence on pool spread dynamics, time-varying discharge (blow down) and pool ignition. Time-varying discharge occurs because a punctured LNG tanker or storage tank drains with a decreasing liquid head and decreasing head-space pressure. Pool ignition increases the evaporation rate of a pool and consequently decreases the ultimate pool area. This paper describes an approach to treat these phenomena in a dynamic pool evaporation model.
The first edition of the CCPS book Guidelines to Evaluating Vapor Cloud Explosions, Flash Fires and BLEVEs was published in 1994. The second edition was completed in October 2010. It is a major revision of the Guideline with contents completely reorganized, recent research results added, revised and new prediction methods inserted, with sample problems worked for each prediction method. The treatment of pressure vessel burst was expanded and placed in a dedicated chapter, resulting in a new name for the second edition of the Guideline.
It is common knowledge now that blast effects from vapor cloud explosions (VCEs) are determined by the combustion mode of the cloud.
This paper will review the issues associated with performing an explosion consequence assessment for petrochemical plants along with the available methodologies for conducting the required analyses.
In order to perform consistent and credible quantitative comparisons of pressure histories produced during interior explosive testing, a consistent and clearly defined set of metrics is needed. Additionally, a methodology is needed for estimating those metrics from test data which can be noisy and in which a number of different physical phenomena are overlaid and tend to obscure one another.
Releases of hydrogen at elevated pressures form turbulent jets which may pose vapor cloud explosion (VCE) as well as jet fire hazards. The turbulence induced by the jet release can lead to flame speeds sufficient to produce damaging blast loads if the release is not immediately ignited, even in the absence of confinement or congestion. The VCE hazard posed by such high pressure hydrogen releases is not well-recognized.
ISO shipping containers and blast resistant modules (BRMs) are widely used in petroleum refining and chemical processing facilities, and have the potential for being subjected to blast loading in the event of an accidental explosion. This paper describes full-scale structural response tests performed on an ISO shipping container and a blast resistant wood building (BRWB).
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 (Aobs) to that of the enclosure internal surface area (As) is greater than 0.4 (i.e., Ar ¼ Aobs/As > 0.4). Congestion is accounted for within the correlation at all values of Ar, however when Ar is < 0.4, variations in the level of congestion are not accounted for. The tests described in this paper were performed using an obstacle array with an Ar ratio of less than 0.4.
Modeling discharge and dispersion of materials from processing vessels is an important part of a facility siting study. In this paper, we investigate the dependence of dispersion modeling on physical property data accuracy, including the impact of uncertainty in the lower flammability limit, heat of vaporization, liquid density, and vapor pressure data. Vapor pressure is further analyzed by comparing correlations obtained from the Design Institute for Physical Properties (DIPPR) to the Clausius-Clapeyron equation using the normal boiling point as the reference.
The Deflagration Load Generator (DLG) is a test rig intended to produce blast waves representative of vapor cloud explosions (VCEs) suitable for loading test articles. The test rig is essentially a reinforced steel box with one open side and dimensions of 48 feet long by 24 feet deep by 12 feet high. The rig is outfitted with congestion and filled with a flammable propane-air mixture. The congestion pattern and fuel concentration within the rig can be controlled such that a desired maximum pressure is achieved. The mixture is ignited at the rear wall of the test rig. Large test articles (e.g., tents, trailers, etc.) can be placed in front of the DLG open side, and the standoff distance can be adjusted to give the desired blast overpressure. Smaller test articles (e.g., drums, electrical enclosures, etc.) can be placed internal or external to the DLG.
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 flammable component.
A test was conducted which demonstrates that a detonation wave, once formed due to a 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 and as well as other tests reported in literature.
The most widely used definition of energy for predicting bursting vessels is Brode energy. There are, however, limitations to the application of this definition to many realworld problems due to the assumptions upon which it is based. This paper presents an evaluation of the applicability of the Brode equation, its common interpretation and limitations, and an evaluation of alternative definitions of energy for bursting vessel and Boiling Liquid Expanding Vapour Explosion (BLEVE) prediction. An illustrative example of the recommended approach is provided.
Typically, blast parameters at large distances from an explosive charge can be predicted with reasonable confidence with fast-running engineering models. However, when the charge is in close proximity to a target, the analyst’s confidence in these engineering tools tends to diminish. Generally, there is limited test data available against which such tools can be validated for this purpose.
Making decisions, consciously or unconsciously, resulting in good or bad consequences, presents a challenge for all of us when faced with the opportunities and uncertainties of life. Some decisions are fairly obvious – “no-brainers”, but no-brainers are the exceptions. Most decisions faced by owners and operators of facilities in the chemical, oil and gas industries are difficult and complex. Some of the most challenging decisions involve EHS risk issues.
A set of large-scale vented deflagration tests involving methane- and propane-air mixtures in a congested enclosure has been performed. The enclosure utilized had a 24-foot by 24-foot footprint and a height of 6 feet. Steel plates were attached to the roof and all four sides served as vents. The vent panels weighed 2 lbm/ft2 and were configured to release at 0.3 psig. A regular array of vertical circular tubes provided the congestion for these tests. The tubes were arranged with a pitch-to-diameter ratio of 7.6 and provided area and volume blockage ratios of 13% and 1.5%, respectively. The fuel-air mixture completely filled the congested region in these tests, but did not extend beyond it. The average peak pressures achieved with methane and propane mixtures were 4.0 psig and 5.0 psig, respectively. These pressures are 20 to 40 times the values predicted by the NFPA 68 weak and strong enclosure correlations, respectively, if the constraint imposed by the vent panel release pressure is not explicitly considered. Consideration of the vent panel release pressure constraint increases the predicted pressures to within an order of magnitude of the measured values. On the basis of these tests, it is concluded that NFPA 68 correlations can significantly underpredict the peak pressure achieved in a vented deflagration for an enclosure with moderate congestion levels. This paper also provides comparisons with a simplified predictive method currently under development.
Gaseous explosions occurring in industrial piping and process systems have been recorded and documented since the early days of industrialization. Despite the efforts put forth by the academic and scientific communities in understanding these phenomena, these explosions are still occurring in industry. Often times, operating companies that suffered the explosions were unaware of the possibilities of explosion in their piping systems and as a result, installed control and safety systems were not adequate. The mitigation of gaseous explosions in pipes requires a basic understanding of combustion and detonation theory. These events are not confined to chemical and petroleum refining facilities; potentially, they can occur in any system where a flammable mixture can form in pipes.
A set of large-scale unconfined vapor cloud explosion tests involving ethylene-air mixtures in a congested environment has been performed. The congested region was 48 feet long by 12 wide by 6 feet high. A regular array of vertical circular tubes provided the congestion for these tests. The tubes were arranged with a pitch-to-diameter ratio of 4.5 and provided area and volume blockage ratios of 23% and 4.2%, respectively. The test rig was configured without any confinement (i.e., no wall or roof sections). The fuel-air mixture completely filled the congested region in these tests, but did not extend beyond it. Deflagration to detonation transitions (DDT) were observed near the end of the test rig for mixture concentrations ranging from lean (5.9% C2H4) to rich (9.3% C2H4). On the basis of these experiments, it is concluded that it may be possible for high reactivity fuel mixtures to undergo a DDT with conditions representative of typical process plants.
Pool evaporation models commonly use a correlation for convective heat transfer from the atmosphere developed in 1973. In this model the effect of wind speed on the heat transfer rate is a power law expression with an exponent value of 0.78. This coefficients is incorporated in the US EPA guidelines for dispersion modeling (1996). Several of the experiments forming the basis for this exponent value were conducted outdoor, subject to variable wind speed. We regressed the data developed in an extensive experimental program that used controlled conditions in a wind tunnel and found the effect of wind speed on the mass transfer coefficient for pool evaporation to be 0.10. Furthermore, the data suggest why an erroneous value of 0.78 likely developed from experimental conditions that ranged over too small a wind speed range. A pool evaporation model described here is shown to match observed data with negligible bias for three data sets.
This paper describes the analysis methodologies that are used in the ERASDAC (Explosion Risk and Structural Damage Assessment Code) computer program. As the name implies, ERASDAC was developed to evaluate explosion consequences and risk assessments in and around DoD facilities. The software was designed to handle facility-wide assessments, with all explosion hazards and acceptor buildings being entered into a facility database. ERASDAC can analyze any combination of explosion hazards and acceptors. Standard libraries of explosives, munitions, and structures are included, and user defined items can be added.
Considerable developmental work has gone into modeling dispersion of accidental outdoor releases; less has been applied to indoor releases. Indoor dispersion is characterized by the influence of a ventilation system and confining surfaces that facilitate aerosol rainout. Stratification can occur so that only part of a room contains flammable vapors, giving rise to so-called partial volume deflagrations. Indoor explosions are more complex to treat because there are two important regimes: before and after explosion vents, windows, or other panels open.
Several sets of blast curves are frequently used in the prediction of blast effects from vapor cloud explosions. However, they have not been validated by experiments since systematic experimental data became available only in recently years. The aim of his paper is to present a comparison between the calculated blast curves and available experimental data. Also presented is a comparison between several blast curves.
The Baker-Strehlow methodology was developed to provide an objective approach to prediction of blast pressures from vapor cloud explosions. The complete methodology was first published in 1994. Since then, it has evolved through ongoing research and use in VCE hazard analyses, facility siting studies and accident investigations. This paper presents recent developments in the Baker-Strehlow methodology. The use of the flame speed correlation is reviewed and revisions to the methodology are presented. Methods for handling multiple confined/congested zones within a vapor cloud and the ramifications of multiple blast waves on structures are discussed. The effects of varying degrees of confinement and congestion on VCE blast predictions are also addressed. Lastly, a procedure to determine fuel reactivity for mixtures is presented.
This paper presents the results of a study on the blast effects generated by bursting vessels. The properties of the shock wave and the associated flow field have been determined by solving the non-steady, non-linear, one-dimensional equations numerically by means of the total variation diminishing (TVD) scheme proposed by Harten. The resulting blast curves are, in general, in agreement with Strehlow's at short standoff distances. However, higher values of shock overpressure and impulse at long standoffs were obtained due to the employment of the high resolution shock capturing scheme. Included in the paper are some important parameters, such as negative pressure and impulse, arrival time of the shock front, durations of positive and negative phases, and flow velocity, which have not been published. A parametric study is presented to demonstrate the importance of the ratio of specific heats and initial temperature on blast predictions.
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