STPA Based Approach for a Resilience Assessment at an Early Design Stage of a Cruise Ship

Several definitions and approaches have been proposed to study resilience in different fields like materials, ecology, psychology and infrastructures. A general definition, applicable also to human-made or engineered systems, describes resilience as the ability to maintain capability in case of disruption. Thanks to its systemic, top-down approach, STAMP (System-Theoretic Accident Model and Processes) has been already identified in literature as a very effective and \u201cconductive\u201d reference when reasoning about the possible need of resilience of a complex system. The STAMP-based tool named STPA (System Theoretic Process Analysis) establishes the following steps: identify system accidents, hazards; draw functional control structure; identify unsafe control actions (UCAs); identify accident scenarios; formulate decisions and recommendations. It focuses on what actually is in the hands of the system designer and operator i.e. the possibility to take action on hazards that can be eliminated or controlled. In this paper an approach to design resilience into a cruise vessel will be proposed. An application case will be developed considering the specific hazard of dead ship condition i.e. of energy black-out on board. In case of navigation close to the shore and in heavy weather condition, this situation can rapidly evolve into a loss. The ship energy production and delivery system, both for the propulsion and for the hotel services, will be considered. Running the procedure up to the level of UCAs enables the identification of the possible disruptive events capable to degrade the operational performance of the system. Starting from this point, suggestions will be discussed for a selected UCA, able to prevent or mitigate it. A metric for ship resilience will be proposed as well with the aim to allow comparisons among different design solutions

A New Approach for Human Factor Integration into Ship Design Process

Ship safety and operations are driving issues of ship design and it is well recognized that such performances are strongly related to Human Factor (HF). In the paper a methodology to integrate HF into the ship design process since an early stage is envisaged, with the aim to improve the overall ship resilience when dealing with uncertainty of performance implied by HF element. The System-Theoretic Accident Model Process (STAMP, Leveson 2003) is investigated as a suitable methodology able to provide a significant asset in such perspective. The approach is widely applied in many industrial and transportation fields but in order to better understand its application into the marine context, a specific application will be briefly commented. In the attempt to define a comprehensive procedure, as a preliminary overview, some selected models suitable to classify the human behavior will be considered with specific focus on the reasons for performance degrade and/or uncertainty

Non-invasive diagnostic tests for Helicobacter pylori infection

BACKGROUND: Helicobacter pylori (H pylori) infection has been implicated in a number of malignancies and non-malignant conditions including peptic ulcers, non-ulcer dyspepsia, recurrent peptic ulcer bleeding, unexplained iron deficiency anaemia, idiopathic thrombocytopaenia purpura, and colorectal adenomas. The confirmatory diagnosis of H pylori is by endoscopic biopsy, followed by histopathological examination using haemotoxylin and eosin (H & E) stain or special stains such as Giemsa stain and Warthin-Starry stain. Special stains are more accurate than H & E stain. There is significant uncertainty about the diagnostic accuracy of non-invasive tests for diagnosis of H pylori. OBJECTIVES: To compare the diagnostic accuracy of urea breath test, serology, and stool antigen test, used alone or in combination, for diagnosis of H pylori infection in symptomatic and asymptomatic people, so that eradication therapy for H pylori can be started. SEARCH METHODS: We searched MEDLINE, Embase, the Science Citation Index and the National Institute for Health Research Health Technology Assessment Database on 4 March 2016. We screened references in the included studies to identify additional studies. We also conducted citation searches of relevant studies, most recently on 4 December 2016. We did not restrict studies by language or publication status, or whether data were collected prospectively or retrospectively. SELECTION CRITERIA: We included diagnostic accuracy studies that evaluated at least one of the index tests (urea breath test using isotopes such as13C or14C, serology and stool antigen test) against the reference standard (histopathological examination using H & E stain, special stains or immunohistochemical stain) in people suspected of having H pylori infection. DATA COLLECTION AND ANALYSIS: Two review authors independently screened the references to identify relevant studies and independently extracted data. We assessed the methodological quality of studies using the QUADAS-2 tool. We performed meta-analysis by using the hierarchical summary receiver operating characteristic (HSROC) model to estimate and compare SROC curves. Where appropriate, we used bivariate or univariate logistic regression models to estimate summary sensitivities and specificities. MAIN RESULTS: We included 101 studies involving 11,003 participants, of which 5839 participants (53.1%) had H pylori infection. The prevalence of H pylori infection in the studies ranged from 15.2% to 94.7%, with a median prevalence of 53.7% (interquartile range 42.0% to 66.5%). Most of the studies (57%) included participants with dyspepsia and 53 studies excluded participants who recently had proton pump inhibitors or antibiotics.There was at least an unclear risk of bias or unclear applicability concern for each study.Of the 101 studies, 15 compared the accuracy of two index tests and two studies compared the accuracy of three index tests. Thirty-four studies (4242 participants) evaluated serology; 29 studies (2988 participants) evaluated stool antigen test; 34 studies (3139 participants) evaluated urea breath test-13C; 21 studies (1810 participants) evaluated urea breath test-14C; and two studies (127 participants) evaluated urea breath test but did not report the isotope used. The thresholds used to define test positivity and the staining techniques used for histopathological examination (reference standard) varied between studies. Due to sparse data for each threshold reported, it was not possible to identify the best threshold for each test.Using data from 99 studies in an indirect test comparison, there was statistical evidence of a difference in diagnostic accuracy between urea breath test-13C, urea breath test-14C, serology and stool antigen test (P = 0.024). The diagnostic odds ratios for urea breath test-13C, urea breath test-14C, serology, and stool antigen test were 153 (95% confidence interval (CI) 73.7 to 316), 105 (95% CI 74.0 to 150), 47.4 (95% CI 25.5 to 88.1) and 45.1 (95% CI 24.2 to 84.1). The sensitivity (95% CI) estimated at a fixed specificity of 0.90 (median from studies across the four tests), was 0.94 (95% CI 0.89 to 0.97) for urea breath test-13C, 0.92 (95% CI 0.89 to 0.94) for urea breath test-14C, 0.84 (95% CI 0.74 to 0.91) for serology, and 0.83 (95% CI 0.73 to 0.90) for stool antigen test. This implies that on average, given a specificity of 0.90 and prevalence of 53.7% (median specificity and prevalence in the studies), out of 1000 people tested for H pylori infection, there will be 46 false positives (people without H pylori infection who will be diagnosed as having H pylori infection). In this hypothetical cohort, urea breath test-13C, urea breath test-14C, serology, and stool antigen test will give 30 (95% CI 15 to 58), 42 (95% CI 30 to 58), 86 (95% CI 50 to 140), and 89 (95% CI 52 to 146) false negatives respectively (people with H pylori infection for whom the diagnosis of H pylori will be missed).Direct comparisons were based on few head-to-head studies. The ratios of diagnostic odds ratios (DORs) were 0.68 (95% CI 0.12 to 3.70; P = 0.56) for urea breath test-13C versus serology (seven studies), and 0.88 (95% CI 0.14 to 5.56; P = 0.84) for urea breath test-13C versus stool antigen test (seven studies). The 95% CIs of these estimates overlap with those of the ratios of DORs from the indirect comparison. Data were limited or unavailable for meta-analysis of other direct comparisons. AUTHORS' CONCLUSIONS: In people without a history of gastrectomy and those who have not recently had antibiotics or proton ,pump inhibitors, urea breath tests had high diagnostic accuracy while serology and stool antigen tests were less accurate for diagnosis of Helicobacter pylori infection.This is based on an indirect test comparison (with potential for bias due to confounding), as evidence from direct comparisons was limited or unavailable. The thresholds used for these tests were highly variable and we were unable to identify specific thresholds that might be useful in clinical practice.We need further comparative studies of high methodological quality to obtain more reliable evidence of relative accuracy between the tests. Such studies should be conducted prospectively in a representative spectrum of participants and clearly reported to ensure low risk of bias. Most importantly, studies should prespecify and clearly report thresholds used, and should avoid inappropriate exclusions

A STAMP\u2013based Methodology Enabling the Human Factors Integration into the Design Process for Safer Ships

The increasing of ships complexity is an everyday evidence and more and more tasks, traditionally carried out by crew members, are now managed and executed by the on board automation systems. This research has the aim of modeling the relation among human operators and automation system in order to enhance the whole ship safety. In particular, a methodology will be selected and its suitability for the purpose will be assessed to provide a tool for the ship design decision making process. When addressing safety of very complex systems the cause-effect principle and the linear propagation of failures are not appropriate neither exhaustive inferring models anymore, since safety needs to be necessarily addressed considering its real essence, i.e. an emergent property of the system. In fact, complex systems have the characteristic of being intractable in the sense that not all their behaviours can be easily predicted. This is due to the dichotomy between the so called blunt end and sharp end domains, inherently more pronounced in complex systems and due to the unknowns that are not predictable neither evident during the design stage. In this perspective, an appropriate and innovative safety paradigm is necessary in order to take into consideration, among other aspects, the new human operators\u2019 role in complex systems. In fact, the intense presence of automation on board ships has radically changed the traditional tasks allocation and the way of performing them. Even if many simple and repetitive tasks are more and more in charge of automation, the complex tasks and the related higher responsibilities remain very often assigned to human operators. Designers should be able to consider this relevant change of human operators\u2019 role in the system since the preliminary design phase, investing their resources on the development of a human-centered design. Complex ship design needs to rely on a systemic and systematic approach. Then, in this research System-Theoretic Accident Model Process (STAMP) has been selected and investigated as a suitable methodology that can allow design teams to effectively integrate the so called Human Factors into the ship design process. It has been already used in other complex technology fields, such as aviation, defense, healthcare with successful results. It is a causality model based on Systems Theory and it considers accidents as the result of an inadequate enforcement of safety constraints. The systemic and systematic approach is supported by the Safety Control Structure, that is a hierarchical system model where also the social and organizational layers can be represented. The STAMP accident model has four tools: one is reactive, the others are proactive. The reactive one is called CAST (Causal Analysis based on STAMP), while the second category is composed of STECA (Systems-Theoretic Early Concept Analysis), STPA (System-Theoretic Process Analysis) and STPA-Sec (Systems-Theoretic Early Concept Analysis - Security). CAST and STPA applications have been carried out in the maritime context in order to verify that STAMP approach is applicable for ship design. CAST has been applied to two ship accidents: the Herald of Free Enterprise and the Costa Concordia. It provides a framework to understand the entire accident process and identifies systemic causal factors related to both the organizational and technical system elements, spotting weakness in the existing safety control structure. In this perspective, the application of CAST to the above mentioned ship accidents has proven its effectiveness also in the maritime field to assess the complex influence of human factors into the ship safety control structure. CAST analysis output is the generation of recommendations with the aim of avoiding similar accidents in the future. Then, the focus has been shifted towards the proactive tool STPA. It consists of the following steps: identify system hazards; draw functional control structure; identify unsafe control actions; identify accident scenarios; formulate decisions and recommendations. In this research, an application case has been developed considering a large passenger ship and the specific hazard of dead ship condition (energy blackout). In fact, in case of navigation close to the shore or to another vessel and/or of heavy weather condition, this situation might rapidly evolve into a ship loss. In order to better characterize the human operator\u2019s features and peculiarities, an innovative human mental model (improvement of a mental model already existing in literature) has been implemented in the safety control structure. It has proven to be useful to consider the concept of human performance variation in the design phases. Considering that performance variation could reveal both as a hazard or as a resilience strengthening element, the outcome of this STPA application consists of a set of recommendations focused on adding value to the on board humans operators\u2019 role for enhancing the whole system resilience. In this perspective, specific recommendations have been identified as outcomes of the application case, focused on the improvement of human operator-automation interaction, aimed to the ship blackout avoidance

HUMAN FACTOR AND AUTOMATION: A STPA APPRACH TO ENHANCE SHIP SAFETY

Ships complexity is continuously increasing and lots of action controls, traditionally carried out by crew members, are now managed and executed by the on-board automation systems. The relation among humans and automation system shall be studied with specific attention to their mutual interface and interaction issues, in order to better pursue safety. The STAMP (System-Theoretic Accident Model and Processes)-based tool named STPA (System Theoretic Process Analysis) consists the following steps: identify system hazards; draw functional control structure; identify unsafe control actions (UCAs); identify accident scenarios; formulate decisions and recommendations. In this paper an approach to model the relations among human operator and automation, based on STPA, will be proposed. An application case will be developed considering a large passenger ship and the specific hazard of dead ship condition (energy black-out). In case of navigation close to the shore and heavy weather condition, this situation can rapidly evolve into a ship loss

Human Factors Investigation in Maritime Incident Analysis for Improved Ship Safety: an Innovative Approach Based on System Theory

The complexity of Human Factors interactions with ship safety will be addressed within the field of maritime accident analysis by means of the Causal Analysis using System Theory (CAST). This is a specific tool within the more comprehensive System-Theoretic Accident Model and Processes (STAMP) approach, already applied in other fields like aviation, defence, healthcare with significant outcomes in terms of safety enhancements. CAST can provide a framework to understand the entire accident process and identify the most important systemic causal factors, including the systemic socio-technical ones, since it provides the capability to spot weakness in existing safety control structure in order to possibly implement advances. In this perspective, the application to the Herald of Free Enterprise accident will be discussed, with focus on CAST effectiveness in assessing the complex Human Factors interaction with the ship safety control structure and in providing input to continuously enhance the ship safety and the ship resilience by design

APPLICATION OF CAST to COSTA CONCORDIA ACCIDENT

CAST (Causal Analysis based on Systems Theory) is used to rationally elicit the cause of Costa Concordia accident