Experiment-based investigations of magnesium dust explosion characteristics

An experimental investigation was carried out on magnesium dust explosions. Tests of explosion severity, flammability limit and solid inerting were conducted thanks to the Siwek 20 L vessel and influences of dust concentration, particle size, ignition energy, initial pressure and added inertant were taken into account. That magnesium dust is more of an explosion hazard than coal dust is confirmed and quantified by contrastive investigation. The Chinese procedure GB/T 16425 is overly conservative for LEL determination while EN 14034-3 yields realistic LEL data. It is also suggested that 2000-5000 J is the most appropriate ignition energy to use in the LEL determination of magnesium dusts, using the 20 L vessel. It is essential to point out that the overdriving phenomenon usually occurs for carbonaceous and less volatile metal materials is not notable for magnesium dusts. Trends of faster burning velocity and more efficient and adiabatic flame propagation are associated with fuel-rich dust clouds, smaller particles and hyperbaric conditions. Moreover, Inerting effectiveness of CaCO₃ appears to be higher than KCl values on thermodynamics, whereas KCl represents higher effectiveness upon kinetics. Finer inertant shows better inerting effectiveness.     

基于风险的突发事件应急准备能力评估方法

建立基于风险的突发事件应急准备能力评估指标体系,为应急能力建设提供参考。主要根据《中华人民共和国突发事件应对法》和我国应急管理体系＂一案三制＂的基本框架,选择反映突发事件应急准备能力的定性与定量指标,并采用简单加权求和方法分别计算其得分;根据四大类突发事件造成的人口死亡和经济损失等方面选择突发事件固有风险指标,并采用秩和比法计算相对风险水平得分;然后集成三类指标得分并作归一化处理得到反映突发事件应急准备能力的标准分。结果表明该评估指标体系能查找应急管理工作中的缺陷与脆弱性,评估方法能识别突发事件应急准备能力与突发事件固有风险降低需求之间的符合程度。该评估指标体系总体结构合理,方法可行。     

基层公安消防部队应急救援能力构成要素研究

近年来,我国公安消防部队主动拓展职能,承担了灭火之外的,以抢救人民生命为主的应急救援任务,已成为了我国常态下应急救援的主力军。本文根据新时期、新形势下应急救援工作建设的实际需要,系统的研究了应急救援能力的概念和构成要素,并从人员、装备、组织管理指挥体系和社会救援资源四个方面对基层公安消防部队的应急救援能力进行了分析,对各要素及各要素之间的关系分别进行了研究,分别提出了各要素的衡量方法,可对基层公安消防部队应急救援能力的科学评价和管理决策提供参考。     

区域地震灾害承载力评价的突变模型

为提高区域地震灾害承载力评价的准确性,基于拓扑学与系统论的基本原理,运用突变理论,构建区域地震灾害承载力评价突变模型。首先,在区域地震灾害承载力与突变理论结合分析的基础上,构建区域地震灾害承载力评价指标体系;其次,进行原始数据标准化处理;接着采用相应的突变归一公式和突变原则进行递归计算区域地震灾害承载力突变隶属值,并与评判标准比较得其地震灾害承载力等级;最后计算29个城市的地震灾害承载力,并将所得计算结果与模糊可变识别评价方法、指数评价方法所得结果进行比较。结果表明,该方法评价结果与模糊可变识别评价方法、指数评价方法的评价结果基本一致。     

Determination of the minimum ignition energy on the basis of a statistical approach

Based on existing MIE test results and new measurements, a statistical analysis for the MIE of hydrogen, ethene and propane is made by means of the logistic regression. The conditions necessary to carry out such an approach are discussed. It is shown that MIE values which are connected with a certain ignition probability could be determined adequately and lead to a more sophisticated result, also with regard to measurement uncertainties. This, in turn, leads to a better comparability and a higher informative content. At the same time, the MIEs of hydrogen, ethene and propane are reviewed. In doing so, a useful contribution to the discussion concerning the MIE of propane is made.     

Ignition of dust-air atmospheres by ultrasonic waves

This paper shows the results of our investigations on the ignition source ultrasound in dust-air atmospheres. Ultrasound is, on the one hand, considered to be an ignition source according to international safety standards (EN 1127–1 (2011)). On the other hand, though, ultrasound is used for various applications in gases and air, such as level and flow measurement, or in the process industry, but no explosion accidents have yet been reported. Our research now shows that it is indeed possible to ignite dust-air mixtures in ultrasound fields under certain conditions. We conducted our experiments in an ultrasound standing wave field and used maize starch, calcium stearate and sulfur dust. For ignitions, an absorbing target was needed to convert the acoustic energy into heat. From theoretical estimations and experiments critical conditions that provoke ultrasonically triggered explosions are identified.     

Testing of dust clouds for the electrostatic-spark ignition hazard in industry. Need for a modified approach?

Current standard test methods for electric-spark minimum ignition energies (MIEs) of dust clouds in air require that a series inductance of at least 1–2 mH be included in the electric-spark discharge circuit. The reason is to prolong the spark discharge duration and thus minimize the spark energy required for ignition. However, when assessing the minimum electrostatic energy ½CU² for dust cloud ignition by accidental electrostatic-spark discharges, current testing standards require that the series inductance of at least 1–2 mH be removed from the spark discharge circuit. No other changes of apparatus and test procedure are required. The present paper questions whether this simple approach is always adequate. The reason is that in practice in industry accidental electrostatic-spark discharge circuits may contain large ohmic resistances due to corrosion, poor electrical grounding connections, poorly electrically conducting construction materials etc. The result is increased spark discharge durations and reduced mechanical disturbance of the dust cloud by the blast wave emitted by the spark. Therefore, testing for minimum ½CU² for ignition by accidental electrostatic spark discharges may not only require removal of the series inductance of 1–2 mH from the standard MIE spark discharge circuit. Additional tests may be needed with one or more quite large series resistances R_s inserted into the spark discharge circuit. The present paper proposes a modified standard test procedure for measurement of the minimum electrostatic-spark ignition energy of dust clouds that accounts for these effects.     

Screening for a new Streptomyces strain capable of e cient keratin degradation

Keratinous wastes could be degraded by some microorganisms in nature. Native human foot skin （NHFS） was used as sole nitrogen source to screen microorganisms with keratin-degrading capability. From approximately 200 strains, a strain of Streptomyces sp. strain No. 16 was found to possess the strongest keratinolytic activity, and the total activity in the culture was 110 KU/ml with specific activity of 2870 KU/mg protein （KU： keratinase unit）. Substrate specificity test indicated that the crude keratinase could degrade keratin azure, human hair, cock feathers and collagen. The optimal pH of the crude keratinase ranged from 7.5 to 10 and the temperature ranged from 40℃ to 55℃. Metal chelating agent ethylenediamine tetraacetic acid obviously stimulated the keratinolytic activity but suppressed the proteolytic activity. To our knowledge, this is the first report on specific induction of keratinases by NHFS from an actinomycete. Moreover, excellent characteristics of its crude keratinase may lead to the potential application in waste treatment and recovery, poultry and leather industry, medicine, and cosmetic development.     

塔河县环境监测能力建设的必要性和可行性分析

文章从塔河县环境监测站现状出发,分析了塔河县环境监测能力建设的必要性和可行性。最后提出了塔河县环境监测站建设标准。     

Inerting effect of CaCO3 powder on flame spread of wood dust layer

The effect of CaCO₃ powder, a typical inert dust, on the flame spread characteristics of wood dust layers was studied using an experimental device to understand the ignition characteristics of and develop inert explosion-proof technology for deposited wood dust. The results showed that the flame spread velocity (FSV) of the mixed dust layer was affected by the dispersion effect of CaCO₃ powder and physical heat absorption. As the CaCO₃ powder mass fraction increased, the FSV of the dust layer first increased and then decreased, reaching a peak at a 50% mass fraction. Moreover, the front-end temperature of the flame gradually decreased, and the red spark faded. The combustion reaction of the mixed dust layer could be more completed, and the colour of the combustion residue changed from charcoal black to charcoal grey. The coupling effect of the initial temperature and wind speed can promote an increase in the FSV in the mixed dust layer. The Gauss–Amp model of the FSV of the wood dust layer and mass fraction of CaCO₃ powder showed that the peak of the FSV occurred when the mass fraction of CaCO₃ powder was between 40 and 50%. Thus, a good inerting and explosion-proof effect can be achieved by using CaCO₃ powder with a mass fraction of more than 50%; it can improve the whole inerting process. Inert explosion-proof technology should be considered when assessing fire and explosion risk of dust in real process industry situations.