Thermal contact hazards

Precaution Minimize eye, skin contact nnolten material will produce thermal bums Hazardous Decomp. Prods. CO, COj, sulfur dioxide HMIS Health 1, Flammability 1, Reactivity 0 Storage Keep container cl( ed... 

A massive amount of propane is instantaneously released in an open field. The cloud assumes a flat, circular shape as it spreads. When the internal fuel concentration in the cloud is about 10% by volume, the cloud s dimensions are approximately 1 m deep and 100 m in diameter. Then the cloud reaches an ignition source at its edge. Because turbulence-inducing effects are absent in this situation, blast effects are not anticipated. Therefore, thermal radiation and direct flame contact are the only hazardous effects encountered. Wind speed is 2 m/s. Relative humidity is 50%. Compute the incident heat flux as a function of time through a vertical surface at 100 m distance from the center of the cloud. 

Thermal Hazards. These hazards include liot surfaces, fire produced by reacting substances, and flame contacts from heat-producing equipment, welding operations, and so on. 

A solution, prepared by mixing saturated solutions of cadmium sulfate and sodium azide in a 10 ml glass tube, exploded violently several horns after preparation [1], The dry solid is extremely hazardous, exploding on heating or light friction. A violent explosion occurred with cadmium rods in contact with aqueous hydrogen azide [2], A DTA study showed a lesser thermal stability than lead azide [3], It is strongly endothermic (AH°f (s) +451 kJ/mol, 2.32 kJ/g). 

The potential thermal hazards associated with thermally unstable substances, mixtures, or reaction masses are identified and evaluated as in the flow charts Figures 2.3, 2.4, and 2.5. The potential hazards posed by reactivity—water reactivity, pyrophoricity, flammability, oxidizer contact, and so forth—are also included in Figure 2.3. The individual boxes in the flow charts are discussed below ... 

Silver is a white, ductile metal occurring naturally in its pure form and in ores (USEPA 1980). Silver has the highest electrical and thermal conductivity of all metals. Some silver compounds are extremely photosensitive and are stable in air and water, except for tarnishing readily when exposed to sulfur compounds (Heyl et al. 1973). Metallic silver is insoluble in water, but many silver salts, such as silver nitrate, are soluble in water to more than 1220 g/L (Table 7.3). In natural environments, silver occurs primarily in the form of the sulfide or is intimately associated with other metal sulfides, especially fhose of lead, copper, iron, and gold, which are all essentially insoluble (USEPA 1980 USPHS 1990). Silver readily forms compounds with antimony, arsenic, selenium, and tellurium (Smith and Carson 1977). Silver has two stable isotopes ( ° Ag and ° Ag) and 20 radioisotopes none of the radioisotopes of silver occurs naturally, and the radioisotope with the longest physical half-life (253 days) is "° Ag. Several compounds of silver are potential explosion hazards silver oxalate decomposes explosively when heated silver acetylide (Ag2C2) is sensitive to detonation on contact and silver azide (AgN3) detonates spontaneously under certain conditions (Smith and Carson 1977). 

One of the functions of Global Core Technologies R D is the analytical discipline Reactive Chemicals/ Thermal Analysis/Physical Properties (RC/TA/PP). Some of the capabilities of this discipline are testing and data interpretation for reactive chemicals hazard assessment. It is the responsibility of the owner of any chemical process to use this Dow resource to obtain the information which is necessary to design a safe and efficient operation. Information about the analytical RC Testing discipline including contact names can be obtained on the INTRAnet at Reactive Chemicals/Thermal Analysis/Physical Properties web site. 

Several instances of apparently stable solvated metal perchlorates being converted by partial desolvation into explosively unstable materials indicate that this may be a more common potential hazard than has been realised [1]. Neodymium perchlorate tetra-solvated with acetonitrile (obtained by vacuum evaporation of the solution at ambient temperature) had not been found to be thermally- or shock-sensitive, but when vacuum dried at 80°C to the di-solvate, it exploded violently on contact [2]. Erbium perchlorate tetrasolvated with acetonitrile had likewise appeared stable, but when vacuum dried at 150°C to a glassy solid which still contained some solvent, it too exploded when scraped with a spatula [3]. Mercury(II) perchlorate hexa-solvated with DMSO appears stable [4], but when dried to the tetrasolvate, it is impact- and friction-sensitive [5], The fact that the solvating species may also be water suggests that this is not a direct effect of a perchlorate oxidising an organic solvent. Thus,... 

Electrical components which could ignite a hazardous atmosphere either by sparking, arcing or by thermal effects, e.g. the contacts of relays, semiconductors, the windings of transformers or solenoids, can be explosion protected by enclosing them in a compound to avoid immediate contact with the environmental atmosphere. 

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