Lessons learned from hazardous chemical incidents--Louisiana Hazardous Substances Emergency Events Surveillance (HSEES) system

Since 2001, the Louisiana Department of Health and Hospitals (LDHH) has participated in the Hazardous Substances Emergency Events Surveillance (HSEES) system. In 2001, there were 815 events qualified for HSEES surveillance. Data for each event was gathered and analyzed. During these hazardous substances events, there were 1164 chemicals released resulting in injuries to 63 people, most with respiratory system irritation. Even though more people were injured in fixed-facility events, injuries were more likely to result from transportation-related events. The quantity and frequency of hazardous substance releases do not always positively correlate with the number of injuries sustained during those releases. A higher percentage of "Rail" transport events was observed in Louisiana when compared with other HSEES states. By collecting and analyzing more data and disseminating results to the public, it is expected that further adverse public health consequences from hazardous releases/spills in Louisiana can be reduced and/or minimized.     

Human error and time of occurrence in hazardous material events in mining and manufacturing

Human error has played a role in several large-scale hazardous materials events. To assess how human error and time of occurrence may have contributed to acute chemical releases, data from the Hazardous Substances Emergency Events Surveillance (HSEES) system for 1996-2003 were analyzed. Analyses were restricted to events in mining or manufacturing where human error was a contributing factor. The temporal distribution of releases was also evaluated to determine if the night shift impacted releases due to human error. Human error-related events in mining and manufacturing resulted in almost four times as many events with victims and almost three times as many events with evacuations compared with events in these industries where human error was not a contributing factor (10.3% versus 2.7% and 11.8% versus 4.5%, respectively). Time of occurrence of events attributable to human error in mining and manufacturing showed a widespread distribution for number of events, events with victims and evacuations, and hospitalizations and deaths, without apparent increased occurrence during the night shift. Utilizing human factor engineering in both front-end ergonomic design and retrospective incident investigation provides one potential systematic approach that may help minimize human error in workplace-related acute chemical releases and their resulting injuries.     

The role of adverse weather conditions in acute releases of hazardous substances, Texas, 2000-2001

High winds, flooding, lightning, and other phenomena associated with adverse weather can cause power failures, equipment damage, and process upsets resulting in chemical releases. Of the 5000 events in Texas that were reported to the Hazardous Substances Emergency Events Surveillance (HSEES) system during 2000-2001, adverse weather conditions contributed to 110 (2%) events. Rain was the most frequent adverse weather condition. Most events to which adverse weather conditions contributed occurred during June or September; these months correspond with the high temperature and hurricane season in Texas. Most events occurred in coastal counties with large numbers of industrial facilities. Three industries reported the majority of events: industrial and miscellaneous chemicals manufacturing; petroleum refining; and plastics, synthetics, and resin manufacturing. Power failures were associated more often with adverse weather-related events than with nonweather-related events. Releases occurred most commonly from ancillary process equipment and process vessels. Events associated with adverse weather-related conditions involved nine victims. System and process design improvements, such as improved backup power generation and redesigned secondary containment systems, could be explored to reduce the potential negative effects of severe weather.     

Sources of acoustic emission during fatigue of Ti-6Al-4V: effect of microstructure

The fundamentals of acoustic emission (AE) analysis of fatigue cracking were applied to Ti-6Al-4V. The effect of microstructure on the characteristics of the AE events generated and the failure mechanisms which produced AE in Ti-6Al-4V were established. Lamellar microstructures generated one to two orders of magnitude more emission than equiaxed microstructures. The combination of larger grain size, more continuous / interfaces, more tortuous crack-front geometry, cleavage and intergranular fracture in lamellar microstructures accounts for the greater amount of emission. For lamellar microstructures, most AE events were generated in the upper 20% of the stress range, whereas in equiaxed microstructures, most events were generated at lower stresses. Most AE events were generated during crack opening and also at low stresses. AE events having high level intensities were also generated at stresses other than the peak stress. This is because in titanium alloys, which have both high strength and toughness, AE events are generated from both plastic zone extension and crack extension.     

Clustering of Event Sequences for Failure Root Cause Analysis

Many types of complex electromechanical equipment exhibit several (often hundreds) fault states. When there are so many fault states, it is often very difficult to know the root cause of failure from a purely engineering consideration. We have developed a technique based on the analysis of the sequence of events preceding the failure state to classify large numbers of failure types into a smaller number of categories. These categories, when investigated closely enough, might reveal the actual causes of such failures. In doing so, we will be able to assign certain root causes to each of these groups of failure types. From the maintenance department's point of view, this approach has a tremendous benefit because when a fault occurs the repairperson/service mechanic will have clear knowledge about what is the most likely cause of failure and hence he/she can act accordingly (instead of just trying things blindly or based on his/her own subjective judgment).     

Estimation of cracking and damage mechanisms of rock specimens with precut holes by moment tensor analysis of acoustic emission

This work presents an experiment on the acoustic emission (AE) of coarse grain granites with two square-shaped precut holes under uniaxial loading. Studies were carried out on the temporal–spatial evolution behavior of micro-cracks by AE mechanisms with the use of the simplex location method and the moment tensor theory, with further analysis in comparing the numerical simulations using the software RFPA \(^\mathrm{2D}\) (Rock Failure Process Analysis). The results show that during the loading process, from beginning to rock failure, shear-mode micro-cracks are prominent, constituting more than 60 % of the total events; next most common are tensile-mode micro-cracks a less than 35 % of the total events. Variations of micro-cracks of the three modes during the loading process have the same increase tendency, i.e. fewer were generated in the initial loading stage, with a rapid increase when the stress values are between 40 and 60 % of the peak stress, and a rate dimunition before rock failure. It is observed that the tensile stress concentration is prone to appear at the tops of the two holes in the form of tensile type cracks, while the shear stress concentration usually appears at the bottom in the middle region of the specimen in the form of shear type cracks. The findings of the present work may serve as guidance for the prevention of roof and floor collapse in the stope exploration of mines.     

Hazardous substances events associated with the manufacturing of chemicals and allied products

This report describes events involving the acute release of hazardous substances reported to the Hazardous Substances Emergency Events Surveillance (HSEES) system for 1993-2000. HSEES, maintained by the Agency for Toxic Substances and Disease Registry (ATSDR), collects data on the industries/services associated with events. This analysis focuses on fixed-facility events that occurred during the manufacturing of chemicals and allied products (i.e. categorized according to the 1990 Industrial Classification System (ICS) of the US Bureau of the Census). This is the most frequently reported industry category in the surveillance system, with over 12000 events (28% of all events and 35% of fixed-facility events). Further classification found that the majority (71%) of these events involved the manufacturing of industrial and miscellaneous chemicals (ICS code 192), and 21% plastics, synthetics, and resins (ICS code 180). A total of 2676 persons reported injuries in 307 fixed-facility events. Most of the injured persons were employees (42%), followed by the general public (38%), students (15%), and responders (5%). Thirty-five percent of all injured persons and 46% of all injured employees had respiratory symptoms. Releases frequently occurred in processing vessels, and the majority was due to equipment failure. A review of the data indicates that manufacturers of chemicals and allied products could help reduce morbidity and mortality by taking preventive actions such as performing regular maintenance of processing equipment, regular training of employees and encouraging them to wear respiratory protection, and educating the public on what to do in the event of a release from these facilities.     

Risk implications of digital reactor protection system operating experience

This paper summarizes an in-depth review of the US nuclear operating experience with the first generation of digital reactor protection systems. The accumulated operating experience from 1984 to 2006 on these first generation digital reactor protection system functions exceeds 1.27 million hours (145.5 yr). A review of failure event reports identified 141 specific events associated with these systems on seven US nuclear power plants. Twenty-six of these events involved some type of common cause failure mechanism (predominantly redundant sensors/channels being out of calibration), which temporarily rendered redundant portions of the overall trip function degraded. Most of these failures were found not to be unique to digital systems. Six of the common cause failure events were more severe and involved situations where incorrect addressable constant data sets were systematically loaded into all redundant computer channels due to personnel errors. One of these events involved a latent software design change error introduced during a software update, which would prevent proper operation, given an unlikely event involving failure of three out of four sensors of one type.Based upon this review of digital system operating experience, a series of risk assessment calculations were performed to evaluate the safety significance of the observed failure events. From the insights gained in this work, it is possible to develop a framework for establishing digital reactor protection system reliability requirements that can be related back to regulatory safety goal objectives and operating experience.     

Assessing the effects of manufacturing infrastructure preparation prior to enterprise information-systems implementation

Reports on the success or failure of enterprise information system (EIS) implementation have been decidedly mixed. In this study, we focus on manufacturing infrastructure preparation prior to EIS implementation and report the results of a survey of 152 US manufacturing companies that have implemented EIS. We have provided four major findings in this study: (1) the requirements from customers and trading partners are more powerful drivers motivating US manufacturing firms to implementing enterprise systems than internal business planning needs; (2) one manufacturing infrastructural issue often has implications for other infrastructural items in implementing technology, so various manufacturing infrastructural issues should be prepared simultaneously; (3) manufacturing infrastructure preparation prior to EIS implementation has significant positive effects on customer-focused performance, production/operations performance, and financial performance; and (4) better customer-focused performance contributes to better financial performance.     

Injuries to the elderly in the traffic environment

Two hundred ninety-seven persons, all aged 60 or over (180 women, 117 men), injured in the traffic environment, and treated at the Regional Hospital in Ume?, over a one-year period, were analysed. Injuries were grouped into three main categories: falls (52%), vehicle-associated events (44%), and "other" injury events (4%). In women, falls were a more common cause of injury than vehicle events, whilst in men there was a tendency for a converse relationship. Two-thirds of the falls involved slipping on ice and snow. Ice- and snow- related injuries (all categories) accounted for 37% of the total cost of all injuries in the elderly in the traffic environment. The main groups in the vehicle-associated injury category were cyclists (48%), car occupants (34%), other occupants (14%), and pedestrians (4%). Vehicle-associated injuries became more common with advancing age, resulted in the most severe and critical [Maximum Abbreviated Injury Scale (MAIS) greater than or equal to 4] injuries and the most fatalities, and cost (total and mean) more than falls. In conclusion, from the injury cost point of view, it is most important to prevent vehicle-associated injuries. However, when total frequencies are considered, falls deserve to be given just as much priority in injury prevention programs as vehicle-associated injuries, to make the traffic environment safer for this growing population.     

Acute public health consequences associated with hazardous substances released during transit, 1993-2000

Massive quantities of hazardous substances are transported each day throughout the United States. While most arrive safely at their destination, uncontrolled releases of substances in transit do occur and have the potential of causing acute public health consequences for those individuals at or near the release. Data from 16 state health departments participating in the Agency for Toxic Substances and Disease Registry's (ATSDR) Hazardous Substances Emergency Events Surveillance (HSEES) system were analyzed to determine the public health consequences that occurred from actual releases in transit. Of the 9392 transportation events analyzed, 9.1% resulted in 2008 victims, including 115 deaths. The population groups injured most often were employees and the general public. The most common injury sustained was respiratory irritation. Evacuations were ordered in 5.5% of events effecting at least 63,686 people. Human error and equipment failure were the most common factors leading to events. These findings underscore the importance of job safety training, community planning, and effective emergency response to prevent adverse public health consequences from occurring or lessen their effect on the public.     

Production reliability in flexible manufacturing systems

A typical flexible manufacturing system, Westland Helicopters' sheet metal detail manufacturing complex, has been analysed for reliability. The techniques of fault tree analysis and event tree analysis are presented and their applicability to this study investigated. Event tree analysis has been found to be a more effective method for analysing manufacturing systems. The failure states of the system have been identified from the construction of an event tree which considers random hardware faults that influence production. Failure rate data have been used to quantify the critical production failure states in terms of machine failures. Estimates are made of the system's MTTF and percentage availability using typical MTTR figures. The probability that a selected production route fails to complete the manufacture of a set of parts is also evaluated. A dependency of systems reliability on the production demand has been discovered, and a possible method for modelling and assessing the reliability of systems capable of producing several products is proposed.     

Developments on standoff detection of explosive materials by differential reflectometry

Differential reflectometry (DR) is an effective tool to supplement existing explosives detection systems thus making the combined unit more effective than one tool alone. It is an optical technique in which the light beam (UV) emanates from an extended distance onto the substance under investigation, thus rendering it to be a standoff method. DR allows the measurement of the energies that electrons absorb from photons as they are raised into higher, allowed energy states. These electron transitions serve as a "fingerprint" for identifying substances. The device can be made portable; it is fast, safe for the public, does not require human involvement, is cost effective, and most of all, does not require ingestion of a suspicious substance into an instrument. Various embodiments are presented.     

Quantitative Failure Analysis Using a Simple Finite Element Approach

Failure analysis encompasses the examination of a failed component and assessment of the failure situation in order to determine the causes of failure. Metallurgical and manufacturing defects often initiate a crack that subsequently propagates under service conditions, leading to premature failure and/or catastrophic fracture of the component. Traditional failure analysis performed on failed section often constitutes only of qualitative metallurgical and microstructure studies in establishing the causes of failure. Since the failed parts have likely been subjected to tensile overload, localized fatigue damage and/or excessive creep strains, the mechanics aspects of the failure should also be considered in the failure analysis. This includes load and stress analyses, fatigue life calculations, and failure simulations. In this respect, finite element (FE) analysis offers a simple, yet effective approach in establishing the causes of failure by predicting the internal states of strains and stresses in the material relative to the strength of the material during the fracture event. Qualitative metallurgical and fractographic results complement such FE-based prediction of the failure.     

The anomalous heat capacity of cerium magnesium nitrate

It has been demonstrated in several laboratories that the heat capacity of cerium magnesium nitrate is anomalous above 20 mK. The origin of the anomaly is unknown. We have measured the heat capacity of three samples of cerium magnesium nitrate from 0.15 to 0.6 K. The samples were: (a) from a cloudy region of a large single crystal grown from nominally 95% starting material, (b) from an optically clear region of the same single crystal, and (c) from a single crystal grown from 99.9% starting material. Within the scatter of the data the three heat capacity determinations showed the same anomaly as observed elsewhere; after subtracting an appropriate lattice contribution, the heat capacity above 0.1 K is more than twice that expected for a set of interacting magnetic dipoles on a regular lattice. The cloudy sample versus clear sample results ruled out crystal growth problems as the source of the anomaly. Chemical analysis by neutron activation analysis, mass spectrographic analysis, and optical absorption spectroscopy all showed the presence of approximately 0.06% praseodymium to cerium ratio in the two single crystals. The heat capacity arising from the hyperfine splitting of the non-Kramers doublet ground state of that concentration of praseodymium ions in cerium magnesium nitrate accounts for the heat capacity anomaly in magnitude and temperature dependence. No serious consequences are expected regarding the use of cerium magnesium nitrate as a primary thermometric substance.Supported by the National Research Council of Canada.     

Case histories

This article describes the results of several case history studies of the failure of polymer-matrix composite (PMC) components to provide not only some representative types of failures one can encounter, but also to provide some insight into the investigative process. These case histories deal mainly with structures that exhibit an initial material and/or manufacturing defect or anomaly—failures that are most prevalent and most easily solved. Component failures traced to some initial material- and/or manufacturing-related defects seem to have fewer fracture surfaces compared with those that do not have any initial defects. In addition, more complex failures (those without defects and those having transverse fractures) often require the use of stress analysis in addition to fractographic analysis. In the investigations presented here, final analysis often was considerably more involved than is possible to describe in a brief summary. However, the results of these investigations hopefully will enable the reader to understand the need not only for careful technical analyses, but also the need for insight, patience, persistence, and experience to solve the myriad tyes of problems related to the failure anlaysis of composite structures.     

Defects tracking in mass customisation production using defects tracking matrix combined with principal component analysis

One of the most important quality control tools for mass customisation production (MCP) is defects tracking. Classical statistical process control and design of experiment technologies are not useful for MCP quality control due to the extensive difference in organisational structures, values, management roles and systems, learning and training techniques and customer relations with the traditional mass production. Defects tracking work is often affected by the frequent reconfiguration of the production line and the interruption of the quality information flow. The purpose of this research is to develop an effective and efficient tool for defects tracking in MCP. A defect tracking matrix (DTM) based on house of quality is constructed to directly connect manufacturing technologies with quality defects within a production module. An AHP method is employed and a new correlation coefficients calculation algorithm is proposed to build the ‘house’. The matrix, which is called ‘defect-gene matrix’, contains core defects and manufacturing technologies extracted from DTM by using principle component analysis. The defect-gene matrix can identify and track defects in mass customisation production without being affected by the frequent reconfiguration of the production line and the interruption of the quality information flow. The application revealed that the proposed DTM and defect-gene matrix was an effective and efficient tool for defects tracking in MCP. The defect-gene matrix brings a novel idea to defects tracking. The results of this research will help systematically in defects tracking in MCP.     

Reliability analysis of systems with discrete event data using association rules

With the popularization of big data, an increasing number of discrete event data have been collected and recorded during system operations. These events are usually stored in the form of event logs, which contain rich information of system operations and have potential applications in fault diagnosis and failure prediction. In manufacturing processes, various levels of correlations exist among the events, which can be used to predict the occurrence of failure events. However, two challenges remain to be solved for effective reliability analysis and failure prediction: (1) how to leverage various information from the event log to predict the occurrence of failure events and (2) how to model the effects of multiple correlations on the prediction. To address these issues, this paper proposes a novel reliability model, which integrates Cox proportional hazards (PHs) regression into survival analysis and association rule mining methodology. The model is used to evaluate the probability of failure event, which occurs within a certain period of time conditional on the occurrence history of correlated events. To estimate parameters and predict occurrence of failure events in the model, an effective algorithm is proposed based on piecewise-constant time axis division, Cox PHs model, and maximum likelihood estimation. Unlike the existing literature, our model focuses on the interactions among events. The applicability of the proposed model is illustrated through a case study of a manufacturing company. Sensitivity analysis is conducted to illustrate the effectiveness of the proposed model.     

Reliability evaluation of distribution systems considering optimal restoration sequence and variable restoration times

Switching sequence, available restoration resources and customer reliability requirements have an important impact on customer interruption times in distribution system failure restoration. An optimal restoration sequence based on the minimum interruption cost of customers has been proposed and incorporated in the reliability evaluation of distribution systems. A fault-traversal algorithm has been used to dynamically trace the affected areas of failure events and the switches involved for the failure isolation and supply restoration. Multi-state models for sequential, parallel and hybrid switching processes have been proposed to determine variable restoration times of different load points. A test distribution system is used to illustrate the technique.