Effects of initial temperature and pressure on explosion characteristics of propane–diluent–air mixtures

The explosion characteristics of propane–diluent–air mixtures under various temperatures and pressures were investigated using a 20-L apparatus. The explosion limits of propane diluted with nitrogen or carbon dioxide were measured at high temperatures from 25 to 120 °C. The results showed that the upper explosion limit (UEL) increased, and the lower explosion limit (LEL) decreased with the rising temperature. The explosion limits of propane diluted with nitrogen or carbon dioxide were also measured at high pressures from 0.10 to 0.16 MPa. The results showed that the UEL increased, and the LEL almost remainedunchanged along with increased pressure. Under the same initial operating conditions, the concentration of nitrogen required to reach the minimum inerting concentration (MIC) point was higher than the concentration of carbon dioxide. Finally, the study investigated the limiting oxygen concentration (LOC) of propane under various initial temperatures, initial pressures, and inert gases. The LOC of propane decreased approximately linearly with increased temperature or pressure, and the LOC of propane dilution with carbon dioxide was greater than dilution with nitrogen from 25 to 120 °C or from 0.10 to 0.16 MPa, which indicated that the dilution effect of carbon dioxide was better than that of nitrogen.     

Effects of obstacles and deposited coal dust on characteristics of premixed methane–air explosions in a long closed pipe

An experimental system including pressure transducer, electric spark ignition device, data acquisition and control unit was set up to investigate methane–air explosions in a horizontal pipe closed at both ends with or without the presence of obstacles and deposited coal dust. The experimental results show that explosion characteristics depended on the methane content, on the layout of obstacles, and on the deposited coal dust. Pressure fluctuation with a frequency of 150 Hz appeared in its crest when the methane content was close to the stoichiometric ratio (9.5% methane percentage by volume). The pressure rise rate increased locally when a single obstacle was mounted in the pipe, but it had little effect on the pressure peak. Repeated obstacles mounted in the pipe caused the pressure to rise sharply, and the mean maximum explosion overpressure increased with the increase of the obstacle’s number. The amplitude of pressure fluctuation was reduced when deposited coal dust was paved in the bottom of the pipe. However, when repeated obstacles were arranged inside, the maximum overpressures were higher with coal dust deposited than pure gas explosions.     

Safety I–II,resilience and antifragility engineering: a debate explained through an accident occurring on a mobile elevating work platform

Occupational health and safety (OHS) represents an important field of exploration for the research community: in spite of the growth of technological innovations, the increasing complexity of systems involves critical issues in terms of degradation of the safety levels. In such a situation, new safety management approaches are now mandatory in order to face the safety implications of the current technological evolutions. Along these lines, performing risk-based analysis alone seems not to be enough anymore. The evaluation of robustness, antifragility and resilience of a socio-technical system is now indispensable in order to face unforeseen events. This article will briefly introduce the topics of Safety I and Safety II, resilience engineering and antifragility engineering, explaining correlations, overlapping aspects and synergies. Secondly, the article will discuss the applications of those paradigms to a real accident, highlighting how they can challenge, stimulate and inspire research for improving OHS conditions.     

The moderating role of calling in the work–family interface: Buffering and substitution effects on employee satisfaction

This research seeks for improved understanding regarding the interaction of meaningful work and the work–family interface. Existing literature suggests that experiencing a sense of calling toward work makes the work domain particularly salient to employees compared to other life domains. In this article, we draw on this idea, rooted in identity theory, to hypothesize that a sense of calling toward work diminishes the effects of work–family conflict and work–family enrichment on employee's job and life satisfaction. We test these ideas in two studies. First, we surveyed an alumni sample of 598 employees from various jobs, industries, and job levels. Then, in a constructive replication, we surveyed 327 employees using a time-lagged design. Calling was found to significantly buffer the effect of work–family conflict on job satisfaction in Study 2, but not Study 1. Calling did not buffer the effect of conflict on life satisfaction in either study. However, both studies demonstrated that calling attenuated (substituted for) the effect of work–family enrichment on job satisfaction. Study 1 supported the idea that calling attenuates the effect of enrichment on life satisfaction; however, this interactive effect was reversed in Study 2, contrary to expectations. We discuss implications for theory and practice related to callings and career choices, as well as for the role of calling and work identity in the work–family interface.     

Should 'Cyrus the Centipede' take a hike? Effects of exposure to a pedestrian safety program on children's safety knowledge and self-reported behaviors

INTRODUCTION: We report the first evaluation of the popular "Cyrus the Centipede" child pedestrian safety program. METHOD: A pre-test/post-test control versus experimental condition design was used to assess Cyrus' impact on third graders' pedestrian safety knowledge, and self-reported pedestrian behaviors. RESULTS: Although some beneficial effects were observed, the program was not reliably effective. In particular, the impact of exposure to Cyrus was strongly influenced by the individual teacher who delivered it, likely due to the highly unstructured nature of the curriculum. SUMMARY: We suggest that: (a) the effectiveness and reliability of such programs be demonstrated before they are widely adopted; and (b) programs that focus on training children in actual or simulated traffic environments may be more effective than those that primarily focus on teaching safety facts and rules.     

Investigation of affecting parameters on treating high-strength compost leachate in a hybrid EGSB and fixed-bed reactor followed by electrocoagulation–flotation process

In this research, treatability of high-load compost leachate in a hybrid expanded granular sludge bed (EGSB) and fixed-bed (FB) bioreactor followed by electrocoagulation–flotation (ECF) system was examined. The operational factors in EGSB–FB were influent chemical oxygen demand (COD), hydraulic retention time (HRT) and COD/nitrogen ratio (COD/N). And, their interactive effects on the efficiency of COD removal and biogas production rate (BPR) as responses were analyzed and correlated by response surface methodology (RSM). The optimum conditions of the hybrid EGSB–FB reactor were acquired at COD = 7800 mg/L, HRT = 35 h, COD/N = 70, in which COD removal efficiency was 83% and BPR 94 mL/h. The amount of confidence interval was 95%. COD (relevant coefficient = 9.8) and HRT (relevant coefficient = −24) were resulted respectively as the most effective parameters on COD removal and BPR. Yet, COD/N parameter imposed negative effect on COD removal and BPR in values less than about 100. The outcomes indicated that operated ECF as post-treatment in constant conditions (electrolysis time = 75 min, electrodes distance = 3 cm, voltage = 20 V) successfully satisfied discharge criteria in the most part of experimental domains.     

Inhibiting effects of gas–particle mixtures containing CO2, Mg(OH)2 particles,and NH4H2PO4 particles on methane explosion in a 20-L closed vessel

The main risk factors from methane explosion are the associated shock waves, flames, and harmful gases. Inert gases and inhibiting powders are commonly used to prevent and mitigate the damage caused by an explosion. In this study, three inhibitors (inert gas with 8.0 vol% CO₂, 0.25 g/L Mg(OH)₂ particles, and 0.25 g/L NH₄H₂PO₄ particles) were prepared. Their inhibiting effects on methane explosions with various concentrations of methane were tested in a nearly spherical 20-L explosion vessel. Both single-component inhibitors and gas–particle mixtures can substantially suppress methane explosions with varying degrees of success. However, various inhibitors exhibited distinct reaction mechanisms for methane gas, which indicated that their inhibiting effects for methane explosion varied. To alleviate amplitude, the ranking of single-component inhibitors for both explosion pressure (P_ex) and the rate of explosion pressure rise [(dP/dt)_ex] was as follows: CO₂, NH₄H₂PO₄ particles, and Mg(OH)₂ particles. In order of decreasing amplitude, the ranking of gas‒particle mixtures for both P_ex and (dP/dt)_ex was as follows: CO₂–NH₄H₂PO₄ mixture, CO₂‒Mg(OH)₂ mixture, and pure CO₂. Overall, the optimal suppression effect was observed in the system with the CO₂–NH₄H₂PO₄ mixture, which exhibited an eminent synergistic effect on methane explosions. The amplitudes of P_ex with methane concentrations of 7.0, 9.5, and 11.0 vol% decreased by 37.1%, 42.5%, and 98.6%, respectively, when using the CO₂–NH₄H₂PO₄ mixture. In addition, an antagonistic effect was observed with CO₂‒Mg(OH)₂ mixtures because MgO, which was generated by the thermal decomposition of Mg(OH)₂, can chemically react with water vapor and CO₂ to produce basic magnesium carbonate (xMgCO₃·yMg(OH)₂·zH₂O), thereby reducing the CO₂ concentration in a reaction system. This research revealed the inhibiting effects of gas‒particle mixtures (including CO₂, Mg(OH)₂ particles, and NH₄H₂PO₄ particles) on methane explosions and provided primary experimental data.