Consistency Checking of the IEC 61508 PFH Formulas and New Formulas Proposal Based on the Markovian Approach

Safety Instrumented Systems (SISs) are of prime importance in protecting people, assets and environment from hazardous events. Therefore, it is important to be able to assess accurately their performance indicators. For this end, IEC 61508 standard has provided two reliability metrics: the average failure probability of a SIS lowly demanded (PFDavg) and the average failure frequency of a SIS highly or continuously demanded (PFH). The aim of this paper is to investigate the IEC 61508 PFH formulas and to propose new ones based on the Markovian approach. Indeed, the new edition of IEC 61508 provides PFH formulas reflecting the possibility of automatic shutdown of the monitored process upon detection of a dangerous failure in the SIS. However, the IEC 61508 attempt remains incomplete and provide non-conservative results, which is dangerous from a safety point of view.

Frequency of Bonded Bracket Failure in Patients, Undergoing Fixed Orthodontic Treatment

OBJECTIVE: The objective of our study is to determine frequency of bracket bond failure in relation to age, gender, most commonly involved tooth and quadrant. METHODOLOGY: In this descriptive cross-sectional study, a total of 100 patients with ages ranging from 10 to 30 years needing corrective orthodontic treatment were selected for the study. This survey was conducted at Altamash Institute of Dental Medicine, Karachi. The survey was initiated on 30th November 2019 and was concluded on 30th May 2020. A questionnaire was used to evaluate the frequency of bonded bracket failure in patients undergoing orthodontic treatment. The bonded metallic brackets were light cured for 40 seconds, and initial alignment arch wires were inserted. Bonded bracket failure was recorded over a period of six months. RESULTS: The initial debonding results of the present study demonstrated a high number of debonded brackets in mandibular dentition as compared to the maxillary dentition. Whereas, when the teeth were debonded for the second time, a greater number of maxillary teeth were found to be affected by the debonding of the brackets. Both genders demonstrated a greater rate of bracket debonding in the second premolar area and lowest in the molar area. In our study, age and gender had no significant relationship with bracket bond failure and teeth involved in debonding. CONCLUSIONS: The frequency of bonded bracket detachment during orthodontic treatment is very common. Our study concluded that females were more affected by the bracket bond failure as compared to the males along with the second premolar being the most commonly associated tooth during an active orthodontic treatment. KEYWORDS: Bonded brackets, Bracket failure, Frequency, Orthodontic treatment, Orthodontics

A method for assessing of ship fuel system failures resulting from fuel changeover imposed by environmental requirements

Environmental regulations instigated the technological and procedural revolution in shipping. One of the challenges has been sulfur emission control areas (SECA) and requirement of fuel changeover. Initially, many reports anticipated that new grades of low sulfur fuels might increase various technical problems in ship operation. This research develops a simple and easy to use method of the failure severity and intensity assessment in relation to fuel changeover. The scale of failure rate in the ship’s fuel system was evaluated qualitatively and quantitively, using developed failure frequency indicator and the time between failure. Based on 77 records of fuel system failures collected on seven ships, it has been found that frequency of failures related to SECA fuel changeover is on average nearly three times higher compared to the rest of sailing time. Their severity did not significantly change, but the structure of failures changed considerably. The method and presented results may help in improvement of ship’s systems design and on-board operational procedures.

Prosthetic Shoulder Joint Infection by Cutibacterium acnes: Does Rifampin Improve Prognosis? A Retrospective, Multicenter, Observational Study

This retrospective, multicenter observational study aimed to describe the outcomes of surgical and medical treatment of C. acnes-related prosthetic joint infection (PJI) and the potential benefit of rifampin-based therapies. Patients with C. acnes-related PJI who were diagnosed and treated between January 2003 and December 2016 were included. We analyzed 44 patients with C. acnes-related PJI (median age, 67.5 years (IQR, 57.3–75.8)); 75% were men. The majority (61.4%) had late chronic infection according to the Tsukayama classification. All patients received surgical treatment, and most antibiotic regimens (43.2%) included β-lactam. Thirty-four patients (87.17%) were cured; five showed relapse. The final outcome (cure vs. relapse) showed a nonsignificant trend toward higher failure frequency among patients with previous prosthesis (OR: 6.89; 95% CI: 0.80–58.90) or prior surgery and infection (OR: 10.67; 95% IC: 1.08–105.28) in the same joint. Patients treated with clindamycin alone had a higher recurrence rate (40.0% vs. 8.8%). Rifampin treatment did not decrease recurrence in patients treated with β-lactams. Prior prosthesis, surgery, or infection in the same joint might be related to recurrence, and rifampin-based combinations do not seem to improve prognosis. Debridement and implant retention appear a safe option for surgical treatment of early PJI.

Preliminary Failure Frequency Analysis of Receiving Bins in Retention Bunkers Operated in Underground Copper Ore Mines

Ore retention bunkers and receiving bins are important for continuous operation of transport system in a mine. Although the designs of the bins used in the KGHM PM S.A. mines have undergone modifications, their operating principle has remained unchanged since their initial commissioning. Their operation entails many problems, which are caused by the durability and functionality of the entire structure. Preventive actions and research into directions for possible modernizations require the type of damage and its reasons to be identified in the first place. This article presents an evaluation of the documented types of damage and an analysis of the repair works performed for the entire population of the receiving bins operated in one mine. The comparative evaluation of the bin failure rate is here proposed to be performed with the use of a number-based failure indicator and of a mass indicator. The key problem identified in the research was the wear and tear on steel elements due to abrasive processes. The linings of the bin elements were observed to undergo intensive abrasive wear. This abrasive wear of the analyzed bin elements is influenced by a combination of factors, the most important of which include variable physical and mechanical properties of the copper ore.

Definitions and Concepts for Quantitative Rockfall Hazard and Risk Analysis

There is an increasing need for quantitative rockfall hazard and risk assessment that requires a precise definition of the terms and concepts used for this particular type of landslide. This paper suggests to use terms that appear to be the more logic and explicit as possible, and describes methods to derive some of the main hazard and risk descriptors. The terms and concepts presented concern the rockfall process (failure, propagation, fragmentation, modelling) and the hazard and risk descriptors, distinguishing the cases of localized hazards and diffused hazards. For a localized hazard, the failure probability of the considered rock compartment in a given period of time has to be assessed and the probability for a given element at risk to be impacted with a given energy must be derived combining the failure probability, the propagation probability and the exposure of the element. For a diffuse hazard that is characterized by a failure frequency, the number of rockfalls reaching the element at risk per unit of time and with a given energy (reach frequency) can be derived. However, when the element at risk is not replaced or repaired, the probability that it is impacted by at least one rockfall must be considered.

Selection of vehicles for fleet of transport company on the basis of observation of their operational reliability

The exploitation reliability of the contemporary light commercial vehicles of four makes is subject to a quantitative analysis in the article. The issue concerning the quantitative evaluation of the operational reliability of the fleet of the commercial vehicles in the transport company and their selection for this fleet is not very numerously described in the literature. For the purposes of evaluating the operational reliability, results of monitoring failures of 115 vehicles during their several years of exploitation in the similar conditions in the urban area and its surroundings were used. A proposed test method uses the relative quantitative measures of the operational reliability indices targeted at the mileage of vehicles and frequency of the failures. The aforementioned enabled to identify the make of the vehicles, which during exploitation was characterized by the lowest failure frequency and thus reliability. This, in turn, allowed for a favorable selection of the vehicles within the next years of the operation of the company. The results of the study confirmed the possibility of using the proposed method to evaluate the operational reliability of the commercial vehicles in any transport company.

Improving reliability of crankshafts of automotive engines

The article considers the factors influencing the reliability of crankshafts. Analysis of engine complaints was carried out, schedule of change of failure frequency depending on operating time was built. The purpose of the work is to solve the problem of improving the operational reliability of the crankshafts of KAMAZ diesel engines by improving the technological process of manufacturing and processing the crankshaft. Keywords reliability, crankshaft, hardness, complaint analysis

FRAGILITY EVALUATION METHODOLOGY FOR TSUNAMI-BORNE DEBRIS IMPACT

In the safe design and risk assessment of structures in coastal area, it is important to consider tsunami-borne debris impact. Recently, probabilistic analysis has become the preferred form of analysis because of the large aleatory and epistemic uncertainties associated with tsunami effects, which are not captured in deterministic scenario-based assessments. By performing both a probabilistic tsunami hazard assessment (PTHA) and a tsunami fragility assessment (TFA) on structures, their annual failure frequency can be determined. The TFA involves evaluation of the response (e.g. debris impact force exerted on the structure) and the capacity of the structure to resist tsunami effects. Then, a fragility curve shows conditional damage probability of the structure for the tsunami magnitude (e.g., discrete tsunami height around the focused area). This study proposes a TFA methodology for tsunami-borne debris impact, as this has not yet been sufficiently established. Evaluation of the impact speed and impact probability of debris considering various uncertainties in the response evaluation are described in particular detail. Moreover, an assessment of a coastal industrial site was performed and fragility curves and the annual failure frequency of structures against debris impact were shown.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/es-ny8eIUfc