Blast Scaling

The Universal Hopkinson-Cranz and Sachs Laws of Blast Scaling have both been verified by experiment. These laws state that self-similar blast (shock) waves are produced at identical scaled distances when two explosive charges of similar geometry and the same explosive composition, but of different size, are detonated in the same atmosphere [49]. 

ZtNT = scaled distance to the point of interest, feet/(lb)1/3 

When accounting for effective charge weigh t at ground reflection the conversion is [49]  

We = effective charge weight in pounds of TNT for estimating surface burst effects with free air. 

It is assumed that the energy released is proportional to the mass of a specific explosive [40]. 

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Blast scale was determined by use of dispersion calculations to estimate fuel quantity within flammability limits present in the cloud. Initial blast strength was determined by factors which have been found to be major factors affecting the process of turbulent, premixed combustion, for example, the fuel s nature and the existence within the cloud of partial confinement or obstacles. 

In general, a reflected shock wave of 55 psi on a human for 400 milliseconds would be just about the tolerance limit [41] (see Table 7-25B). For a more detailed discussion of blast scaling and overpressure, see Ref [40]. 

The blast scaling law which is almost universally used to predict characteristics of blast waves from explosions at high altitude is that of Sachs (Reference 10). Sachs law states that dimensionless overpressure and dimensionless impulse can be expressed as unique functions of a dimensionless scaled distance, where the dimensionless parameters include quantities which define the ambient atmospheric conditions prior to the explosion. 

A few examples of pheromones will be shown to indicate the diversity of chemical structures. Many sex pheromones of Lepidoptera tend to be long-chain aliphatic aldehydes, acetates, or alcohols. The sex pheromone of a rice borer is Z 11 hexadecenal (11.29).153 The sex pheromone of the Israeli pine blast scale is shown in 11.30.154... 

Firstly, heavy greases, paints and lacquers are removed by hot alkali and cold alkali solutions. Surface contamination is removed by grit blasting. Scales and oxides are removed by pickling solution of H2SO4 or HCl. 

The insensitivity of nitromethane to detonation by shock under normal conditions of handling has been demonstrated by a number of fljH-scale tests. Sensitivity to shock increases with temperature at 60° C, nitromethane can be detonated by a No. 8 blasting cap. Nitroethane can be initiated only when heated near its boiling point under heavy confinement neither it or the nitropropanes can be detonated in unconfined conditions. 

The bitumen in the Athabasca deposit, which has a gravity on the API scale of 8°, is heavier than water and very viscous. Tar sand is a dense, soHd material, but it can be readily dug in the summer months during the winter months when the temperatures plunge to —45° C, tar sand assumes the consistency of concrete. To maintain acceptable digging rates in winter, mining must proceed faster than the rate of frost penetration if not, supplemental measures such as blasting are required. 

The largest use for calcium carbide is in the production of acetylene for oxyacetylene welding and cutting. Companies producing compressed acetylene gas are located neat user plants to minimize freight costs on the gas cylinders. Some acetylene from carbide continues to compete with acetylene from petrochemical sources on a small scale. In Canada and other countries the production of calcium cyanamide from calcium carbide continues. More recentiy calcium carbide has found increased use as a desulfurizing reagent of blast-furnace metal for the production of steel and low sulfur nodular cast iron. 

Slime masses or any biofilm may substantially reduce heat transfer and increase flow resistance. The thermal conductivity of a biofilm and water are identical (Table 6.1). For a 0.004-in. (lOO-pm)-thick biofilm, the thermal conductivity is only about one-fourth as great as for calcium carbonate and only about half that of analcite. In critical cooling applications such as continuous caster molds and blast furnace tuyeres, decreased thermal conductivity may lead to large transient thermal stresses. Such stresses can produce corrosion-fatigue cracking. Increased scaling and disastrous process failures may also occur if heat transfer is materially reduced. 

The scale can also be removed by shot blasting using abrasive grits such as dry sand, less than I mm (p. This method is more suited for components not suited to the dip method and cast iron components, in which the acid may become trapped in the porous surfaces. For sheet-metal components and complicated shapes and crevices, the dip method alone is recommended. 

The reduction of non ores is caiTied out on the large indusuial scale in dre h oir-making blast furnace, where CO is the reducing gas and the product is liquid... 

Fig. 21. Wedge test results for grit blast/silanc surface treatment compared to PAA. Both surfaces were primed with BR127. Note the expanded crack length scale compared to other figures. Data are from Ref [89].

Other methods for removing scale include salt pickling, electrolytic pickling, and blasting blasting is environmentally desirable, where feasible. EAFs produce metal dusts, slag, and gaseous emissions. 

The explosion killed two workers, injured 350 local residents, destroyed property up to 20 miles away, and damaged 50% of Henderson s 17,000 residential and commercial buildings. The two largest blasts registered 3.0 ajid 3.5 on the Richter scale hundreds of miles away in Cdifomia, cars were crumpled, doors blown off their hinges, and windows shattered for miles around. Uninsured losses were more than 20 million, plus 3 million more in insurance deductibles. Just as serious, were the psychological and emotional impact of the explosions, on schoolchildren and adults. 

Investigations of the effects of BLEVEs (Chapter 6) are usually limited to the aspect of thermal radiation. Blast and fragmentation have been of less interest, and hence, not studied in detail. Furthermore, most experiments in thermal radiation have been performed on a small scale. 

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