Inherent safety is a proactive approach to process safety in which hazards are removed or minimized so as to reduce risk without engineered (add-on) or procedural intervention. Four basic principles are available to attain an inherently safer design—minimization, substitution, moderation, and simplification. The subject of the current paper is the principle of moderation as it applies to the prevention and mitigation of dust explosions.
Moderation can be achieved by processing a material under less severe operating conditions or by processing the material in a less hazardous form. With respect to the latter approach, it may be possible to alter the composition of a dust by admixture of solid inertants, or to increase the dust particle size so as to decrease its reactivity. Additionally, avoidance of the formation of hybrid mixtures of explosible dusts and flammable gases is an application of moderation of the material hazard.
Several examples are given for each of the above three forms of moderation. The discussion on admixture of solid inertants includes examples from the following industrial applications: (i) refractory materials manufacturing, (ii) food processing, (iii) power generation, (iv) industrial recycling, and (v) foundry shell mold fabrication. The importance of particle size consideration is explained first from the perspective of engineering tools such as the Dow Fire & Explosion Index, and professional guidance on the definition of a dust and suitable particle sizes for explosibility testing. Industrial examples are then drawn from the following areas: (i) rubber recycling and textile manufacturing, (ii) industrial recycling, (iii) wood processing, (iv) dry additive handling (polyethylene facility), (v) polyethylene production, (vi) carbon block recycling, and (vii) coal mining. The concluding discussion on hybrid mixtures includes brief cases from the process safety literature. 相似文献
Mixtures of biodiesel, glycerol, and ethanol/methanol are commonly processed and stored in biodiesel production. In this work, non-ideal models are used to calculate the Flash Points (FPs) of binary and ternary mixtures, using data available from different feedstocks. Despite the fact that biodiesel is considered safer than common diesel fuels, results show a synergistic effect of biodiesel/methanol and biodiesel/ethanol mixtures, resulting in a reduction of the flash point of mixtures to values lower than the ones of pure compounds. Most soluble ternary mixtures were found flammable, the only exception being mixtures with a relatively lower alcohol content (45% mol. ethanol or 42% methanol) at temperature lower than 303 K. Accidental increase in temperature can cause domino effect, due to the higher solubility and the formation of new flammable ternary mixtures. 相似文献
The Hydrocarbon Release Database (HCRD) contains data on loss of containment events in the UK sector of the North Sea. The data shows a decrease in the annual number of releases. A study was carried out to determine whether statistically significant trends are apparent when categorizing releases by severity and specific cause. It was investigated whether the relative contribution of some causes as compared to all releases, had changed over time.The main conclusion is that over the analysed period (1993–2014), the relative contribution of “Procedures” as a cause for release has decreased with statistical significance. “Design” improvements seem to lead to a reduction in releases too. Finally, “Equipment” was improving at the slowest rate, if at all, until 2005. Since then, it appears to improve as well. These findings are robust, at least for the total set of data, and the releases of Significant severity. For releases of Major severity, the number of incidents is too small to justify any conclusion on trends.The conclusions suggest that over the analysed period improvements in offshore safety have been mainly driven by improvements in management, covering elements like procedures, competence and compliance. 相似文献
Quantitative risk analysis (QRA) has been widely used to conduct the assessment of offshore accidental risks. However, the accuracy and validity of QRA is significantly affected by uncertainties when subjective judgments are involved. Therefore, it is unrealistic to determine the probability of a hazardous event by using one single explicit value when safety experts have a relatively low confidence level in their judgments. This paper proposes a new methodology for incorporating uncertainties into conventional QRA using the concept of confidence level. Offshore hydrocarbon release hazards are focused on and a barrier and operational risk analysis (BORA-Release) method is selected as the basic model to illustrate the proposed methodology. A left–right (L–R) bell-shaped fuzzy number is employed and its membership curve is able to control its shape to represent different confidence levels. As to the complex geometry of the bell-shaped fuzzy number, an α-cut operation is introduced to conduct the arithmetic operations of the fuzzy number, and a defuzzification method with total integral value is chosen to match the α-cut operations and acquire complete information for the fuzzy numbers. In the meantime, an optimism index is used to describe the attitude of the decision-maker. One case study is provided in this paper to demonstrate the implementation of this method. 相似文献
A novel sorbent based on 2% grape stalk wastes encapsulated in calcium alginate beads was investigated for the removal of Cr(VI) and Cr(III) from aqueous solutions. The sorbent proved to be efficient for chromium removal in both hexavalent and trivalent forms from aqueous solution at pH 3.0. In binary mixtures, the presence in solution of one of the forms enhances the sorption of the other which results in an increase of the amount of total chromium removed. This study suggests that the proposed sorbent can be used for the removal of chromium from wastewaters through a cost-effective and environmentally friendly process. 相似文献
Contamination of aquatic ecosystems with heavy metals has been receiving increased worldwide attention due to their harmful e ects
on human health and other organisms in the environment. Most of the studies dealing with toxic e ects of metals deal with single
metal species, while the aquatic organisms are typically exposed to mixtures of metals. Hence, in order to provide data supporting
the usefulness of freshwater fish as indicators of heavy metal pollution, it has been proposed in the present study to investigate the
bioaccumulation and depuration of chromium in the selected organs of freshwater fingerlings Cirrhinus mrigala, individually and in
binary solutions with nickel. The results show that the kidney is a target organ for chromium accumulation, which implies that it is also
the “critical” organ for toxic symptoms. The results further show that accumulation of nickel in all the tissues of C. mrigala is higher
than that of chromium. In addition, the metal accumulations of the binary mixtures of chromium and nickel are substantially higher
than those of the individual metals, indicating synergistic interactions between the two metals. Theoretically the simplest explanation
for an additive joint action of toxicants in a mixture is that they act in a qualitatively similar way. The observed data suggest that C.
mrigala could be suitable monitoring organisms to study the bioavailability of water-bound metals in freshwater habitats. 相似文献
This paper presents an argument that improvement in operational safety can be achieved concurrently with increased operational efficiency. This is a fundamentally different viewpoint on the investment in safety. Traditionally, the cost of providing safety barriers is offset by the expected benefits of reducing the occurrence and severity of accidents. Our approach departs from this method of accounting for safety improvements and focuses on planning as a means of managing systems' response uncertainty and consequently reducing both major accident risk and the cost of operations. The scope of the paper is limited to interventions such as maintenance and repairs and defined in the context of major accident prevention e.g. hydrocarbon leaks. However, the developed methodology is general enough to be applied across the spectrum of process industry facilities and operations. 相似文献
Loading and unloading operations produce 8% of all accidents which occur in process plants and in the transportation of hazardous materials. A survey of 738 accidents was performed, allowing the identification of the accident type distribution and of their cause. Some considerations on flammable mixtures are also presented, and the procedures to avoid these mixtures occurring when filling or emptying a tank are briefly discussed. 相似文献