Papers by Seshu Dharmavaram
Process Safety Progress, Sep 20, 2010
Preventing loss of containment of materials and/or energy is a primary goal of industrial Process... more Preventing loss of containment of materials and/or energy is a primary goal of industrial Process Safety Management programs. A thorough understanding of the hazards, identification of a complete range of failure events, detailed analysis of the consequences of failure events, and the analysis of process risks accounting for all the safeguards can help significantly in preventing and mitigating loss of containment incidents. In this article, additional details are provided on hazard assessment approaches, consequence analysis of potential events, and risk analysis for minimizing risks.
Process Safety Progress, Jun 7, 2012
A surprising number of process incidents occur due to a lack of general understanding of process ... more A surprising number of process incidents occur due to a lack of general understanding of process hazards and lack of basic hazards assessment, subsequently resulting in the absence of or inadequate Process Hazards Analysis (PHA) to provide appropriate safeguards for minimizing process risks. Comprehensive assessment of intrinsic hazards that are present in a chemical process or facility is one of the first steps necessary in documenting process safety information and technology prior to conducting PHAs and requires much more than, for example, just a review of the material safety data sheets of materials used in the process. This article reviews practical approaches for conducting and documenting intrinsic hazards assessments. 2012 American Institute of
Process Safety Progress, May 6, 2012
Many facilities have now implemented and maintained process safety management (PSM) programs for ... more Many facilities have now implemented and maintained process safety management (PSM) programs for 20 years or more, but these facilities continue to have sometimes serious incidents and injuries suggesting a continuing need to improve their PSM performance. Of course, new requirements are often added to upgrade PSM programs, due to near-miss learnings, audit findings, and new recommended and generally accepted good engineering practices, for example, but often overall performance improvements have not occurred or have not achieved the desired level of performance. How can significant performance improvements be obtained? Although performance issues at different facilities will certainly vary, this article provides several key approaches for improving overall PSM performance and for helping prevent injuries and incidents.
Atmospheric Environment, Sep 1, 2004
The FLACS CFD model, which can be used to estimate the flow and dispersion around buildings and o... more The FLACS CFD model, which can be used to estimate the flow and dispersion around buildings and other large roughness obstacles, has been evaluated with tracer data from several field experiments involving obstacle arrays. The following experiments were used in the evaluation exercise: Kit Fox (52 trials with puff and plume releases of slightly dense CO 2 gas in arrays of billboard-shaped obstacles), MUST (37 trials with puff releases of neutrally buoyant tracer gas in an array of 120 shipping containers), Prairie Grass (43 trials with continuous plume releases of neutrally buoyant tracer gas over a flat agricultural field), and the EMU L-shaped building (a wind tunnel experiment involving a release from an open door in the courtyard area of an L-shaped building). The primary focus is on the maximum concentration on the monitoring arcs. The performance statistics are consistently fairly good, with a median of 86% of the predictions within a factor of two of the observations, a median relative bias suggesting a 20% underprediction, a median relative scatter of about 50%, and a median 20% underprediction of the overall experiment maximum. These results are all well within the criteria of acceptance for dispersion models. Evaluations with the EMU L-shaped building data show that 72% of FLACS predictions are within a factor of two of observations, and that the model can predict the dimensions of the recirculating cavity behind the building within a factor of two. It is suggested that these extensive data sets involving tracer releases in obstacle arrays be used to evaluate other CFD models.
Process Safety Progress, Dec 4, 2017
Water spray curtains are often advertised as means to mitigate the consequences of released chemi... more Water spray curtains are often advertised as means to mitigate the consequences of released chemicals from high pressure tanks. Spray curtain effectiveness claims by certain vendors are misleading-a curtain placed at the periphery of a tank will only scrub a puff of a release. A spray curtain that can effectively contain a consequential release will look very different and cost much more. Studies that demonstrate spray curtains to be effective assume low gas velocities. However, calculations show that pressurized liquid NH 3 or HF when released from an orifice to the atmosphere comes out at a high velocity and momentum in the form of a twophase jet. The jet must travel quite a distance before the velocity drops enough to be effectively scrubbed by a water curtain. The water curtain therefore needs to be at this large distance and consequently the diameter of the water curtain manifold ring needs to be quite large to be effective. This paper presents engineering calculations to estimate jet velocity, diameter & concentration, calculations to evaluate the efficiency of water sprays and discussion of water spray curtain designs that are more effective. V
Process Safety Progress, Dec 1, 2005
Several models are currently available to model the discharge and dispersion of toxic or flammabl... more Several models are currently available to model the discharge and dispersion of toxic or flammable materials to the environment. A few of the Gaussian dispersion modeling tools allow the representation of the complex environment within a manufacturing plant or urban area in determining the impact of continuous releases from a plant. For atmospheric dispersion of dense gases, a correction is made for the presence of the buildings and other complexity by using a surface roughness parameter, which is only a crude approximation. A need exists to obtain realistic estimates of plume dispersion in a complex environment, particularly accounting for buildings/obstructions at a plant and the associated turbulence. With the advance of computational technology, and greater availability of computing power, computational fluid dynamics (CFD) tools are becoming more available for solving a wide range of problems. A CFD model, called FLACS (flame acceleration simulator), developed originally for explosion modeling, has been upgraded for atmospheric dispersion modeling. CFD tools such as FLACS can now be confidently used to understand the impact of releases in a plant environment consisting of buildings, structures, and pipes, and accounting for all complex fluid flow behavior in the atmosphere and predicting toxicity and fire/explosion impacts. With its porosity concept representing geometry details smaller than the grid, FLACS can satisfactorily represent geometry even when using a coarse-grid resolution to limit the simulation time. The performance of FLACS has recently been evaluated using a wide range of field data sets for sulfur dioxide (Prairie Grass), carbon dioxide (Kit Fox), and ethylene (EMU), for example. In this paper, details about the improvements made to FLACS, model validation exercises, and results from the modeling of releases from an industrial facility are presented.
Process Safety Progress, Sep 1, 2008
Six widely-used dense gas dispersion models (ALOHA, HGSYSTEM, SLAB, SCIPUFF, PHAST, and TRACE) we... more Six widely-used dense gas dispersion models (ALOHA, HGSYSTEM, SLAB, SCIPUFF, PHAST, and TRACE) were used to calculated downwind chlorine gas concentrations following three railcar accidents. The accidents, where as much as 60 tons of chlorine were released, were located at Festus, MO (release from a ruptured 1-in. line while offloading), and Macdona, TX, and Graniteville, SC (release from a large hole due to an accident). Public sources such as National Transportation Safety Board (NTSB) reports were used to develop input data. Source emissions rates were refined based on source modeling with PHAST and TRACE and derivations using fundamental thermodynamic equations. No chlorine removal mechanisms, such as photolysis, chemical reactions, or deposition were accounted for. Given the same source emissions rates, the models' simulations of 10-min averaged cloud centerline concentration, at downwind distances ranging from 0.1 to 10 km, agree with each other within plus and minus a factor of two most of the time. For a very large release (Graniteville), the 2,000, 400, and 20 ppm contours are predicted to extend downwind about 1.3, 3.1, and 14 km, respectively, from the source. There is also agreement among the models simulations of the plume widths and heights to the 2,000, 400, and 20 ppm contours. A major conclusion of the study is that estimation of the source or release term is important for reliable results, since the calculated chlorine concentrations are approximately proportional to the mass release rate. It must also be stressed that observed concentrations would be expected to be less than those calculated here, because removal by dry deposition at the surface and by chemical reactions in the plume have not been accounted for.
Journal of Hazardous Materials, Jun 1, 1994
<scp>Red Squirrel</scp> Tests: Air Products' ammonia field experiments
Process Safety Progress, Apr 10, 2023
The Red Squirrel ammonia field experiments were conducted at the DNV Spadeadam site in the UK in ... more The Red Squirrel ammonia field experiments were conducted at the DNV Spadeadam site in the UK in 2022. Field test data currently exists for high‐pressure (ambient temperature) two‐phase releases of ammonia from Desert Tortoise (1983) and FLADIS (1996) experiments. No field tests have ever been done for cold (refrigerated) ammonia liquid spills on dry land or into water. The handling of liquified ammonia, during storage/processing and transportation, in a cold (refrigerated) state is inherently safer than in a high‐pressure (ambient temperature) liquified state. The main objective of the Air Products’ Red Squirrel Tests was to determine the source term and dispersion characteristics for high‐pressure (ambient temperature) liquified ammonia and low‐pressure (cold/refrigerated) liquified ammonia in form of two‐phase releases and liquid spills, respectively. Liquid spills on concrete and water were studied, along with the process conditions that led to the transition from liquid spills to two‐phase flow regimes based on discharge pressures for cold liquified ammonia. Details on the equipment, instrumentation, secondary containment, and ammonia sensors and their layout are presented. An initial analysis of the source terms and dispersion behavior for two‐phase releases and contained liquid spills over a range of weather conditions is also provided.
Integrating cybersecurity into the risk‐based process safety (RBPS) program
Process Safety Progress, Jul 13, 2022
With the industry's increasing reliance on computer systems for basic process control and saf... more With the industry's increasing reliance on computer systems for basic process control and safety functions, industrial processes have become more vulnerable to cybersecurity threats. The recently released CCPS book, Managing Cybersecurity in the Process Industries, A Risk‐based Approach, discusses the need for proactive and effective cybersecurity management in the interest of process safety. This paper will share some of the highlights from the book illustrating areas where cybersecurity considerations parallel and complement the key principles of Risk‐Based Process Safety (RBPS) elements. This paper will share some lessons from recent cybersecurity incidents impacting process safety and identify avenues where cyberattacks can gain access to the control or safety instrumented systems to cause harm. Finally, we will discuss a sampling of the RBPS elements in more detail to illustrate how cybersecurity can be integrated into the RBPS program.
Process Safety Progress, Sep 1, 2008
Oleums are mixtures of sulfur trioxide in sulfuric acid and are produced in several strengths. Ch... more Oleums are mixtures of sulfur trioxide in sulfuric acid and are produced in several strengths. Chlorosulfonic acid (CSA) is formed by reacting sulfur trioxide with hydrochloric acid (HCl). These chemicals are used as sulfating and sulfonating agents in many applications. When accidentally released from vessels or pipes, they react instantaneously with water available from all sources like atmosphere, concrete, soil, and so forth, to form a fine acid mist that disperses downwind, based on atmospheric conditions. Unlike most other chemicals, the vaporization of sulfur trioxide from oleum spills depends not just on its partial pressure, but a variety of conditions. Complex chemical reaction and heat generation that occur in the liquid phase determine the amount of sulfur trioxide released above a pool of liquid. The sulfur trioxide or CSA vapors then react instantaneously with the moisture in the atmosphere generating sulfuric acid and/ or HCl and heat. Water and/or foam are used effectively in mitigating oleum and CSA spills. However, very limited laboratory or field data are currently available that describe the complex behavior of these chemicals. Several theoretical models have been developed to predict the vaporization and dispersion of the chemical upon loss of containment. These models and methods have not been validated. In this article, details are provided on field tests conducted in Nevada in 2003 and 2006 for spills of 65% oleum and CSA. A description of the spill mitigation, field measurement methods, and some preliminary results are included.
Springer eBooks, Jul 22, 2008
Six widely-used dense gas dispersion models (ALOHA, HGSYSTEM, SLAB, SCIPUFF, PHAST, and TRACE) we... more Six widely-used dense gas dispersion models (ALOHA, HGSYSTEM, SLAB, SCIPUFF, PHAST, and TRACE) were used to calculated downwind chlorine gas concentrations following three railcar accidents. The accidents, where as much as 60 tons of chlorine were released, were located at Festus, MO (release from a ruptured 1-in. line while offloading), and Macdona, TX, and Graniteville, SC (release from a large hole due to an accident). Public sources such as National Transportation Safety Board (NTSB) reports were used to develop input data. Source emissions rates were refined based on source modeling with PHAST and TRACE and derivations using fundamental thermodynamic equations. No chlorine removal mechanisms, such as photolysis, chemical reactions, or deposition were accounted for. Given the same source emissions rates, the models' simulations of 10-min averaged cloud centerline concentration, at downwind distances ranging from 0.1 to 10 km, agree with each other within plus and minus a factor of two most of the time. For a very large release (Graniteville), the 2,000, 400, and 20 ppm contours are predicted to extend downwind about 1.3, 3.1, and 14 km, respectively, from the source. There is also agreement among the models simulations of the plume widths and heights to the 2,000, 400, and 20 ppm contours. A major conclusion of the study is that estimation of the source or release term is important for reliable results, since the calculated chlorine concentrations are approximately proportional to the mass release rate. It must also be stressed that observed concentrations would be expected to be less than those calculated here, because removal by dry deposition at the surface and by chemical reactions in the plume have not been accounted for.
International Journal of Chemical Kinetics, Jan 7, 2014
The hydrolysis of acetic anhydride in the presence of water is an exothermic reaction that produc... more The hydrolysis of acetic anhydride in the presence of water is an exothermic reaction that produces acetic acid. Most of the research has focused on low ratios of acetic anhydride to water. The major concern in the industry is the accidental addition of a small amount of water to large quantities of acetic anhydride stored in tanks, or as handled in a manufacturing process. This paper focuses on isothermal and adiabatic experiments that were conducted to understand the effect and rate of hydrolysis at high ratios of acetic anhydride to water. The acetic acid produced in the reaction also affects the rate of reaction. Detailed calorimetric data and specific rate expressions that have been developed are presented in this paper.
Integrating cybersecurity into the risk‐based process safety (RBPS) program
Process Safety Progress
With the industry's increasing reliance on computer systems for basic process control and saf... more With the industry's increasing reliance on computer systems for basic process control and safety functions, industrial processes have become more vulnerable to cybersecurity threats. The recently released CCPS book, Managing Cybersecurity in the Process Industries, A Risk‐based Approach, discusses the need for proactive and effective cybersecurity management in the interest of process safety. This paper will share some of the highlights from the book illustrating areas where cybersecurity considerations parallel and complement the key principles of Risk‐Based Process Safety (RBPS) elements. This paper will share some lessons from recent cybersecurity incidents impacting process safety and identify avenues where cyberattacks can gain access to the control or safety instrumented systems to cause harm. Finally, we will discuss a sampling of the RBPS elements in more detail to illustrate how cybersecurity can be integrated into the RBPS program.
INTRODUCTION AND FLACS MODEL SUMMARY Computational Fluid Dynamics (CFD) models are useful for sim... more INTRODUCTION AND FLACS MODEL SUMMARY Computational Fluid Dynamics (CFD) models are useful for simulating air flow and plume transport and dispersion within arrays of obstacles such as buildings or pipe racks and tanks. The FLACS CFD model (Hansen, O. et al., 1999) is being used by the authors to estimate flow and dispersion in the atmosphere around chemical processing plants. This paper contains the results of recent evaluations of FLACS with extensive field observations involving tracer gas releases in three independent field experiments (Kit Fox, MUST, and Prairie Grass) and wind tunnel data from the EMU L-shaped building.
Process Safety Progress, 2017
Water spray curtains are often advertised as means to mitigate the consequences of released chemi... more Water spray curtains are often advertised as means to mitigate the consequences of released chemicals from high pressure tanks. Spray curtain effectiveness claims by certain vendors are misleading—a curtain placed at the periphery of a tank will only scrub a puff of a release. A spray curtain that can effectively contain a consequential release will look very different and cost much more. Studies that demonstrate spray curtains to be effective assume low gas velocities. However, calculations show that pressurized liquid NH3 or HF when released from an orifice to the atmosphere comes out at a high velocity and momentum in the form of a two‐phase jet. The jet must travel quite a distance before the velocity drops enough to be effectively scrubbed by a water curtain. The water curtain therefore needs to be at this large distance and consequently the diameter of the water curtain manifold ring needs to be quite large to be effective. This paper presents engineering calculations to estim...
Process Safety Progress, 2018
When a liquid mixture, such as an aqueous formaldehyde solution, is released into the environment... more When a liquid mixture, such as an aqueous formaldehyde solution, is released into the environment, the rate of evaporation into the atmosphere depends strongly on chemical reactions that regulate the evolution of formaldehyde vapors. Most of the consequence modeling methods and models currently used in the industry usually ignore any reaction phenomena. This article describes a dynamic model developed using the Aspen® Custom Modeling (ACM) tool kit. In the case of formaldehyde solutions, the thermodynamics and reaction kinetics of a mixture of formaldehyde (HCHO), water and methanol (CH3OH) are computed from models available in the open literature. The liquid‐phase, reversible, chemical reactions between water and formaldehyde, as well as methanol and formaldehyde, form oligomers—most of which are nonvolatile. The mass transfer and heat transfer coefficients between the surface of the spill and the atmosphere are computed by established correlations for flow over a semi‐infinite fla...
Modeling Spills of Reactive Chemicals
When materials such as Oleums and Chlorsulfonic Acid are released into the environment they react... more When materials such as Oleums and Chlorsulfonic Acid are released into the environment they react with all available water to generate heat and form an acid mist. Most of the consequence modeling methods and models currently used in the industry usually ignore the reaction phenomena. This paper describes a dynamic model developed using the Aspen Custom Modeling (ACM) tool kit. The DuPont-ACM model employs various methods for solving simultaneous systems of nonlinear algebraic and ordinary differential equations. This makes it possible, for example, to solve coupled differential mass and energy balances which are implicit in temperature and composition. Also, even though temperature and composition are not state variables, they can be given initial conditions. The algorithms do not always tolerate discontinuities, so smoothing techniques are used where needed. In the case of oleum, the thermodynamic behavior of the mixture is represented by the vapor-liquid equilibrium of the H2O-H2S...
Assessment of Chemical Reactivity Hazards for Nitration Reactions and Decomposition of Nitro-Compounds
ACS Symposium Series, 2013
Process Safety Progress, 2005
Several models are currently available to model the discharge and dispersion of toxic or flammabl... more Several models are currently available to model the discharge and dispersion of toxic or flammable materials to the environment. A few of the Gaussian dispersion modeling tools allow the representation of the complex environment within a manufacturing plant or urban area in determining the impact of continuous releases from a plant. For atmospheric dispersion of dense gases, a correction is made for the presence of the buildings and other complexity by using a surface roughness parameter, which is only a crude approximation. A need exists to obtain realistic estimates of plume dispersion in a complex environment, particularly accounting for buildings/obstructions at a plant and the associated turbulence. With the advance of computational technology, and greater availability of computing power, computational fluid dynamics (CFD) tools are becoming more available for solving a wide range of problems. A CFD model, called FLACS (flame acceleration simulator), developed originally for explosion modeling, has been upgraded for atmospheric dispersion modeling. CFD tools such as FLACS can now be confidently used to understand the impact of releases in a plant environment consisting of buildings, structures, and pipes, and accounting for all complex fluid flow behavior in the atmosphere and predicting toxicity and fire/explosion impacts. With its porosity concept representing geometry details smaller than the grid, FLACS can satisfactorily represent geometry even when using a coarse-grid resolution to limit the simulation time. The performance of FLACS has recently been evaluated using a wide range of field data sets for sulfur dioxide (Prairie Grass), carbon dioxide (Kit Fox), and ethylene (EMU), for example. In this paper, details about the improvements made to FLACS, model validation exercises, and results from the modeling of releases from an industrial facility are presented.
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Papers by Seshu Dharmavaram