Safety thermal characterization

The fine chemicals business is characterized by a small volume of products manufactured. Therefore, batch production predominates and small-scale reactors are used. The need to implement fine chemistry processes into existing multiproduct plants often forces the choice of batch reactors. However, safety considerations may lead to the choice of continuous processing in spite of the small scale of operation. The inventory of hazardous materials must be kept low and this is achieved only in smaller continuous reactors. Thermal mnaways are less probable in continuous equipment as proven by statistics of accidents in the chemical industries. For short reaction times, continuous or semicontinuous operation is preferred. 

The explosive was exhaustively characterized for thermal behavior, impact sensitivity and electrostatic discharge sensitivity etc. Based on this data, CP has been described as much less sensitive to accidental initiation than primary explosives such as LA but at the same time, initiation grows rapidly to detonation when properly confined. Its performance evaluation in a test detonator or hardware indicates that CP can replace primary explosives in many hot wire detonator applications especially if safety considerations are of prime importance [239]. 

Since a reaction product catalyses the reaction, the initial concentration of product also has a strong effect on the TMRad. In the case illustrated in (Figure 12.6), an initial conversion of 10% leads to a reduction of the TMRad by a factor of 2. This also has direct implications for process safety the thermal history of the substance, that is, its exposure to temperature for a certain time increases initial product concentration, leading to effects comparable to those illustrated in Figure 12.5. Hence it becomes obvious that substances showing an autocatalytic decomposition are very sensitive to external effects, such as contaminations and previous thermal treatments. This is important for industrial applications as well as during the experimental characterization of such decompositions the sample chosen must be representative of the industrial situation, or several samples must be analysed. 

It was outlined in chapter 2 in detail that screening tests primarily have the purpose, to provide a first characterization of the safety relevant substance properties as part of the basic assessment. It was further explained that the determination of the thermal stability of a substance is of the greatest importance. The most fi-equently used methods for this puipose are those that investigate thermal stability using very small amounts of sample material only. The most widely used test equipments to perform such investigations are the DTA ( difference thermal analysis ) and DSC ( differential scanning calorimetry). 

These salts were characterized by IR, Raman and NMR spectroscopy, mass spectrometry, elemental analysis. X-ray, and initial safety testing (impact and friction sensitivity). Low impact sensitivities were demonstrated. Densities and thermochemical characteristics of substituted amino, amino-methyl, and polymethyl tetrazolium salts are summarized in Table 5. All of these new salts exhibit thermal stabilities > 170°C based on DSC/TGA studies (except the azide). The densities of l-amino-4,5-dimethyl tetrazolium perchlorate (45b) and l-methyl-4,5-diamino tetrazolium dinitramide (50b) are markedly higher than the others. 

The testing of concrete specimens with respect to the level of carbonation is carried ont by applying a phenolphthalein solution to a freshly fractured or sawn snrface. Noncarbonated areas become red while carbonated areas remain grey. The rate of carbonation in ordinary concrete elements exposed to the atmosphere is schematically shown in Figure 11.25. It is assumed that the depth of cover d of steel-reinforcement should be bigger than the depth of carbonation estimated after 100 years to ensure safety of reinforcement (CEB 1992). In normal conditions, half of that depth can be reached within 15 years. A simplified formula proposed for the carbonation rate is d = 10 V t, here d is in mm and t in years b is a numerical coefficient that characterizes the quality of concrete, for example, for a very good quality concrete b = 0.15. Carbonation is usually deeper on those sides of a structure that are exposed to sunshine because the process of conversion into calcium carbonate CaCOj by carbon dioxide CO2 is quicker in frequently variable hydro-thermal conditions. 

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