Ignition of flammable atmospheres by mechanical stimuli

As readers of HazardEx will be well aware, following the introduction of the ATEX 95 and 137 directives, there are now requirements on both manufacturers of equipment and employers to consider the likelihood of ignition flammable atmospheres from mechanical impacts/sliding. The aim of this article is not to review legislative requirements, as these are well discussed else where, but to provide insight into the ignition mechanism and relevant research literature to assist those needing to make such assessments. It is certainly not the intention to advocate ignition source control as an appropriate hazard management strategy , particularly with easily ignited gases like hydrogen- this needs to be decided on a case by case basis. Guidance in the design standards i.e. [1] has improved from earlier versions, but still does not convey very well the likely influence of parameters such as material hardness, load, velocities and impact angle

A comparison study into low leak rate buoyant gas dispersion in a small fuel cell enclosure using plain and louvre vent passive ventilation schemes

Hydrogen, producing electricity in fuel cells, is a versatile energy source, but with risks associated with flammability. Fuel cells use enclosures for protection which need ventilating to remove hydrogen emitted during normal operation or from supply system leaks. Passive ventilation, using buoyancy driven flow is preferred to mechanical systems. Performance depends upon vent design, size, shape, position and number. Vents are usually plain rectangular openings, but environmentally situated enclosures use louvres for protection. The effect of louvres on passive ventilation is not clear and has therefore been examined in this paper. Comparison ‘same opening area’ louvre and plain vent tests were undertaken using a 0.144 m3 enclosure with opposing upper and lower vents and helium leaking from a 4 mm nozzle on the base at rates from 1 to 10 lpm, simulating a hydrogen leak. Louvres increased stratified level helium concentrations by typically in excess of 15 %. The empirical data obtained was also used in a validation exercise with a SolidWorks: Flow Simulation CFD model, which provided a good qualitative representation of flow behaviour and close empirical data correlations

Identification of ignition sources in high pressure enriched gaseous oxygen system incidents using flow chart road map diagram methodology

High pressure enriched oxygen is used in a wide number of areas, including aircraft, medical breathing apparatus, and a number of industrial processes including combustion. Unwanted ignition in such systems can cause significant damage to property and danger to life. It is important to gain as much information, and record relevant data for every oxygen incident, enabling both immediate analysis, and post-event evaluations (especially where circumstances are repeated). The lack of clear concise guidance can result in data loss. This work successfully develops investigation ‘road maps’ as guidance documents for investigators to use, even under difficult & time pressured conditions. The work demonstrates their usefulness and importance for information collection and the down-selection’ or elimination of possible ignition causes through their use with a ‘real world’ case study. The benefit of this work will be to enable faster and more effective investigation of oxygen incidents, ensuring key details are recorded (benefitting post-accident academic data & meta-study analysis). The roadmaps can also benefit designers of oxygen systems allowing them to test their designs and operating procedures against specific ignition scenarios

Energy losses during drop weight mechanical impacts with special reference to ignition of flammable atmospheres in nuclear decommissioning: theory and determination of experimental coefficients for impact analysis and prediction

The major purpose of this study is to provide a framework for determination of energy losses resulting from mechanical impacts of the kind that could occur during nuclear decommissioning of waste material. Measurements have been made of final translational and rotational velocities for impacts between projectiles of different length and a massive barrier. This enabled determination of experimental values of the impact coefficients and energy losses. It was found that the total energy losses could be accurately accounted for by the sum of those pertaining to the normal and tangential processes, thus indicating that these include any losses due to vibration. The results obtained clearly support an Amontons–Coulomb friction model and the previously held contention that there is a limiting value for the impulse ratio at low angles of barrier inclination. Although sliding surfaces are likely to be modified during impact, it is shown that any original contamination on the contacting surfaces results in a very large decrease in impulse ratio or friction coefficient. This represents an important finding in the context of mechanical ignition testing indicating that the state of the impact surfaces and their handling need to be taken into account. The difficulties in establishing appropriate values for the impact coefficients and dealing with the effect of mechanical vibrations on the energy losses are discussed and equations derived for determining the tangential and normal energy losses from known initial velocities

A Metabolomic Signature of Acute Caloric Restriction

Context: The experimental paradigm of acute caloric restriction followed by refeeding can be used to study the homeostatic mechanisms that regulate energy homeostasis, which are relevant to understanding the adaptive response to weight loss. Objective: Metabolomics, the measurement of hundreds of small molecule metabolites, their precursors, derivatives, and degradation products, has emerged as a useful tool for the study of physiology and disease and was used here to study the metabolic response to acute caloric restriction. Participants, Design and Setting: We used four ultra high performance liquid chromatography-tandem mass spectrometry methods to characterize changes in carbohydrates, lipids, amino acids and steroids in eight normal weight men at baseline, after 48 hours of caloric restriction (CR; 10% of energy requirements) and after 48 hours of ad libitum refeeding in a tightly-controlled environment. Results: We identified a distinct metabolomic signature associated with acute CR characterized by the expected switch from carbohydrate to fat utilization with increased lipolysis and beta-fatty acid oxidation. We found an increase in omega-fatty acid oxidation and levels of endocannabinoids which are known to promote food intake. These changes were reversed with refeeding. Several plasmalogen phosphatidylethanolamines (endogenous anti-oxidants) significantly decreased with CR (all p≤0.0007). Additionally, 48 acute CR was associated with an increase in the branched chain amino acids (all p≤1.4x10-7) and dehydroepiandrosterone sulfate (p=0.0006). Conclusions We identified a distinct metabolomic signature associated with acute CR. Further studies are needed to characterise the mechanisms that mediate these changes and their potential contribution to the adaptive response to dietary restriction.This work was supported by the Wellcome Trust (to I.S.F.), the NIHR Cambridge Biomedical Research Centre, the European Research Council, the Bernard Wolfe Health Neuroscience Fund (all to I.S.F.), the Swiss National Science Foundation (P3SMP3-155318, PZ00P3-167826, to T.H.C.), and the Uehara Memorial Foundation (to T.S.). This work was supported by the NIHR Rare Diseases Translational Research Collaboration and the NeuroFAST consortium, which is funded by the European Union’s Seventh Framework Programme (FP7/2007-2013) under grant agreement no 245009

Adalimumab for Treating Moderate-to-Severe Hidradenitis Suppurativa: An Evidence Review Group Perspective of a NICE Single Technology Appraisal

As part of its single technology appraisal (STA) process, the UK National Institute for Health and Care Excellence (NICE) invited the manufacturer of adalimumab (AbbVie) to submit evidence on the clinical effectiveness and cost effectiveness of adalimumab for the treatment of moderate-to-severe hidradenitis suppurativa (HS). The appraisal assessed adalimumab as monotherapy in adult patients with an inadequate response to conventional systemic HS therapy. The School of Health and Related Research Technology Appraisal Group was commissioned to act as the independent Evidence Review Group (ERG). The ERG produced a critical review of the evidence for the clinical effectiveness and cost effectiveness of the technology based on the company’s submission to NICE. The evidence was mainly derived from three randomised controlled trials comparing adalimumab with placebo in adults with moderate-to-severe HS. The clinical-effectiveness review found that significantly more patients achieved a clinical response in the adalimumab groups than in the control groups but that the treatment effect varied between trials and there was uncertainty regarding its impact on a range of other relevant outcomes as well as long-term efficacy. The company’s submitted Markov model assessed the incremental cost effectiveness of adalimumab versus standard care for the treatment of HS from the perspective of the UK NHS and Personal Social Services (PSS) over a lifetime horizon. The original submitted model, including a patient access scheme (PAS), suggested that the incremental cost-effectiveness ratio (ICER) for adalimumab versus standard care was expected to be £16,162 per quality-adjusted life-year (QALY) gained. Following a critique of the model, the ERG’s preferred base case, which corrected programming errors and structural problems surrounding discontinuation rules and incorporated a lower unit cost for HS surgery, resulted in a probabilistic ICER of £29,725 per QALY gained. Based on additional analyses undertaken by the company and the ERG following the publication of the appraisal consultation document (ACD), the Appraisal Committee concluded that the maximum possible ICER for adalimumab compared with supportive care was between £28,500 and £33,200 per QALY gained but was likely to be lower. The Appraisal Committee recommended adalimumab (with the PAS) for the treatment of active moderate-to-severe HS in adults whose disease has not responded to conventional systemic therapy

Application of Bayesian methods and networks to ignition hazard event prediction in nuclear waste decommissioning operations

The major purpose of the study is to examine how Bayesian networks can be used to represent and understand potential ignition scenarios in nuclear waste decommissioning. This is illustrated using a network to represent a situation with stacked storage boxes containing pyrophoric material removed from waste storage silos. Corrosion of this material during storage produces hydrogen which is released through a filter medium into the gap between the boxes. The probabilistic relationships used to indicate dependence between network nodes are expressed by conditional probability tables or C++ coded equations that relate to UK nuclear industry corrosion and storage data. The study focuses on optimal prediction of the likelihood of a flammable hydrogen atmosphere arising in the gap between stacked boxes and the conditions necessary to exceed the lower flammable limit. It is concluded that the approach offers a useful means of easily determining the manner in which varying the controlling parameters affects the possibility of an ignition event. The effect of data variation can be examined at first hand using the supplementary Bayesian Network that accompanies the article

Characterising the performance of hydrogen sensitive coatings for nuclear safety applications

The detection of hydrogen gas is essential in ensuring the safety of nuclear plants. However, events at Fukushima Daiichi NPP highlighted the vulnerability of conventional detection systems to extreme events, where power may be lost. Herein, chemochromic hydrogen sensors have been fabricated using transition metal oxide thin films, sensitised with a palladium catalyst, to provide passive hydrogen detection systems that would be resilient to any plant power failures. To assess their viability for nuclear safety applications, these sensors have been gamma-irradiated to four total doses (0, 5, 20, 50 kGy) using a Co-60 gamma radioisotope. Optical properties of both un-irradiated and irradiated samples were investigated to compare the effect of increased radiation dose on the sensors resultant colour change. The results suggest that gamma irradiation, at the levels examined (>5 kGy), has a significant effect on the initial colour of the thin films and has a negative effect on the hydrogen sensing abilities