54,962 research outputs found
A dynamic HAZOP case study using the Texas City refinery explosion
© 2016 Elsevier Ltd. The catastrophic explosion that occurred at Texas City on 23 March 2005 during the start-up of the raffinate splitter resulted in an estimated 15 deaths and 180 injuries. Since the incident, several studies have investigated the root causes of the disaster. Some contributing factors to the incident include wider organisational, process safety management, and human elements. There have also been some attempts to model the sequence of events before the incident, and the consequences of the resulting fires and explosions. This study provides a dynamic model of the sequence of events leading up to the incident and replicates the reported process variables during the isomerisation unit start-up on the day of the incident. The resulting simulation model is used as the framework for a dynamic hazard and operability (HAZOP) study
Phase Transitions in Operational Risk
In this paper we explore the functional correlation approach to operational
risk. We consider networks with heterogeneous a-priori conditional and
unconditional failure probability. In the limit of sparse connectivity,
self-consistent expressions for the dynamical evolution of order parameters are
obtained. Under equilibrium conditions, expressions for the stationary states
are also obtained. The consequences of the analytical theory developed are
analyzed using phase diagrams. We find co-existence of operational and
non-operational phases, much as in liquid-gas systems. Such systems are
susceptible to discontinuous phase transitions from the operational to
non-operational phase via catastrophic breakdown. We find this feature to be
robust against variation of the microscopic modelling assumptions.Comment: 13 pages, 7 figures. Accepted in Physical Review
'Catastrophic Failure' Theories and Disaster Journalism: Evaluating Media Explanations of the Black Saturday Bushfires
In recent decades, academic researchers of natural disasters and emergency management have developed a canonical literature on 'catastrophe failure' theories such as disaster responses from from US emergency management services (Drabek, 2010; Quarantelli, 1998) and the Three Mile Island nuclear power plant (Perrow, 1999). This article examines six influential theories from this field in an attempt to explore why Victoria's disaster and emergency management response systems failed during Australia's Black Saturday bushfires. How well, if at all, are these theories understood by journalists, disaster and emergency management planners, and policy-makers? On examining the Country Fire Authority's response to the fires, as well as the media's reportage of them, we use the 2009 Black Saturday bushfires as a theory-testing case study of failures in emergency management, preparation and planning. We conclude that journalists can learn important lessons from academics' specialist knowledge about disaster and emergency management responses
Assessing Interaction Networks with Applications to Catastrophe Dynamics and Disaster Management
In this paper we present a versatile method for the investigation of
interaction networks and show how to use it to assess effects of indirect
interactions and feedback loops. The method allows to evaluate the impact of
optimization measures or failures on the system. Here, we will apply it to the
investigation of catastrophes, in particular to the temporal development of
disasters (catastrophe dynamics). The mathematical methods are related to the
master equation, which allows the application of well-known solution methods.
We will also indicate connections of disaster management with excitable media
and supply networks. This facilitates to study the effects of measures taken by
the emergency management or the local operation units. With a fictious, but
more or less realistic example of a spreading epidemic disease or a wave of
influenza, we illustrate how this method can, in principle, provide decision
support to the emergency management during such a disaster. Similar
considerations may help to assess measures to fight the SARS epidemics,
although immunization is presently not possible
The effects of climatic fluctuations and extreme events on running water ecosystems
Most research on the effects of environmental change in freshwaters has focused on incremental changes in average conditions, rather than fluctuations or extreme events such as heatwaves, cold snaps, droughts, floods or wildfires, which may have even more profound consequences. Such events are commonly predicted to increase in frequency, intensity and duration with global climate change, with many systems being exposed to conditions with no recent historical precedent. We propose a mechanistic framework for predicting potential impacts of environmental fluctuations on running water ecosystems by scaling up effects of fluctuations from individuals to entire ecosystems. This framework requires integration of four key components: effects of the environment on individual metabolism, metabolic and biomechanical constraints on fluctuating species interactions, assembly dynamics of local food webs and mapping the dynamics of the meta-community onto ecosystem function. We illustrate the framework by developing a mathematical model of environmental fluctuations on dynamically assembling food webs. We highlight (currently limited) empirical evidence for emerging insights and theoretical predictions. For example, widely supported predictions about the effects of environmental fluctuations are: high vulnerability of species with high per capita metabolic demands such as large-bodied ones at the top of food webs; simplification of food web network structure and impaired energetic transfer efficiency; reduced resilience and top-down relative to bottom-up regulation of food web and ecosystem processes. We conclude by identifying key questions and challenges that need to be addressed to develop more accurate and predictive bio-assessments of the effects of fluctuations, and implications of fluctuations for management practices in an increasingly uncertain world
Survival of Casuarina cunninghamiana on a recovering sand-bed stream in the Wollombi Valley of coastal New South Wales
The successful management and restoration of riparian corridors in Australia is currently hindered by our poor understanding of the links between hydrology, fluvial geomorphology and plant population dynamics. The aim of the current study was to determine the survival rates of Casuarina cunninghamiana subsp. cunninghamiana Miq. (family Casuarinaceae) on a sand-bed stream in the Wollombi Valley, a tributary of the Hunter River system, in coastal New South Wales (lat 33°02’S; long 151°10’E). A population planted on the banks of Dairy Arm in 1987, as part of river training works, was used to determine the long-term (24-year) survival rate. A bankfull flood in June 2011 provided an opportunity to examine the survival response of seedlings regenerating naturally within the channel. We found that 24% of the seedlings planted on the banks in 1987 had survived to adulthood. The bankfull flood significantly decreased (d.f. = 14; W= - 30; p = 0.0024) median seedling density within the channel from 12 to 2 individuals per 100 m2. Seedling survival varied with height, with seedlings > 15 cm more likely to survive the bankfull flood. The percentage of seedlings partially buried by sediment was significantly higher (d.f. = 14; W = 13; p = 0.016) after flood compared to before flood. Seedling density was positively correlated with the amount of bare ground prior to the flood (r = 0.61; p = 0.02), but this relationship was no longer significant after flood (r = 0.18; p = 0.53). 37% of the seedlings surveyed showed evidence of grazing. Our results confirm that hydrogeomorphic processes associated with a bankfull flood affect the survival of Casuarina cunninghamiana seedlings. The management implications of our findings are discussed in terms of riparian revegetation techniques and the geomorphic recovery of over-widened sand-bed streams
Jamming transition in a two-dimensional open granular pile with rolling resistance
We present a molecular dynamics study of the jamming/unjamming transition in
two-dimensional granular piles with open boundaries. The grains are modeled by
viscoelastic forces, Coulomb friction and resistance to rolling. Two models for
the rolling resistance interaction were assessed: one considers a constant
rolling friction coefficient, and the other one a strain dependent coefficient.
The piles are grown on a finite size substrate and subsequently discharged
through an orifice opened at the center of the substrate. Varying the orifice
width and taking the final height of the pile after the discharge as the order
parameter, one can devise a transition from a jammed regime (when the grain
flux is always clogged by an arch) to a catastrophic regime, in which the pile
is completely destroyed by an avalanche as large as the system size. A finite
size analysis shows that there is a finite orifice width associated with the
threshold for the unjamming transition, no matter the model used for the
microscopic interactions. As expected, the value of this threshold width
increases when rolling resistance is considered, and it depends on the model
used for the rolling friction.Comment: 9 pages, 6 figure
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