Sheathed mining explosives—

Effects of Sheaths on Gases from Explosions in Coal Mines. See under Coal Mining Explosives, Permissible, p C454 of Vol 3 of Encycl, and the following addnl Ref B. 

Aluminium detonators with lead azide and other explosives were used in the mining industry for some time, e.g. a No. 8 detonator, contained 1 g of tetryl and 0.3 g of a mixture of lead azide and lead styphnate. These were more powerful than those with a fulminate-tetryl charge, but the use of detonators with aluminium sheathing was soon forbidden in coal-mines due to the danger created by the burning of the aluminium. 

The use of sheaths very slightly weakens the strength of an explosive but does not reduce its sensitiveness to detonation. On the other hand it considerably increases its safety for use in mines with methane and sensitive coal-dust. 

CA 73, 5578m (1970) [Explosives sheathed with. resite salt were tested for use in dusty coal mines using simulated mine drifts and boreholes. It was found that for a borehole with hard walls, the best dispersion on detonation of the sheath was obtd when there was an air gap betw the sheath and borehole walls. For boreholes In soft materials, such as clay, the sheath could fit. tightly in the borehole]... 

Core Explosives or Core Charges. In ordet to lower the temperature of explosion to the level of "permissible explosives, thus avoiding the ignition of firedamp and dust in coal mines, R.W. Lawrence of Hercules Powder Co proposed [USP 2565380(1951) CA 46, 1752(1952)] to place inside of an AN Dynamite cartridge a "core , which can be either hollow or consist of an "inert material, similar to that used for sheaths (See under Enveloped or Sheathed Explosives)... 

Giorgio (Ref 8, p 176) calls them esplosivi quelli avvolti in un mantello di sali refrigeranti 1 (Explosives which are wrapped up in a mantel of cooling salts). Accdg to Belgrano (Ref 3, p 167) and Vettori (Ref 7), the materials of Ital sheaths have been Ca fluoride and Ca sulfate or Na bicarbonate. These expls found wide use in sulfur mines of Sicily... 

Under the term Vzryvchatyiye veshchestva v predokhraniteTnoy obolochke (Explosive substances in protective envelope), sheathed expls have been used in Russia. There are two types of sheaths inert sheath which consists of Na bicarbonate with or without Na chloride and active sheath which consists of Na bicarbonate with ca 10% NG incorporated. The active sheath has the advantage of being pulverized completely on expln of enclosed cartridge, thus filling the mine atmosphere uniformly with non combustible dust (Ref 6, p 514)... 

Esplosivi con guaina (Sheathed Explosives). Accdg to Dr Camillo Belgrano of Codroipo (Udine), as communicated to Dr Omero Vet-tori of Aulla (Massa Carrara), Italian sheaths consist of mixts of Ca fluoride and sulfate with Na bicarbonate. These expls have been used in Sicilian sulfur mines Ref Dr Omero Vettori, private communications July I and August 17,(1964)... 

Effects of sheaths on gases from explosions in coal mines 5 El 5... 

Compex. One of the Brit "permitted mining expls which are designated as EqS (equivalent in safety to sheathed explosives). It is listed in Ref without giving the composition Ref Taylor Gay (1958), 96... 

Ibid 425 (1910) (Explosibility of coal dust) 6)J.J.Rutledge C.Hall, USBurMines Bull 10 (1912) (Use of permissible expls) 7)C. Hall et al, Ibid 15 (1912) (Investigation of expls used in coal mines) 8)Marshall 1 (1917), 44-47 2 (1917), 582-606 (Permitted expls) 8a)Colver (1918), 247 681 (Nauck-hoff s expls) 9)Barnett (1919), 117-42 (Safety coal mine expls) 10)E.Lemaire, AnnMines-Belg 23, 649(1922) (Sheathed expls) 10a)C. A.Taylor W.H.Rinkenbach, USBurMines Bull 219 (1923), 107-14 (The thermochemistry of expln) ll)H.Henkei, SS 22, 173 (1927)... 

Before we launch into a general discussion of commercial explosive materials, a few words about permissible explosives. The term permissible is defined in MSHA regulations as [a]ny substance, compound or mixture which is approved by MSHA and whose primary purpose is to function by explosion. Permissible explosives included on MSHA s Active List of Permissible/Sheathed Explosives are the ONLY explosives that may be used in underground coal mining operations and in certain underground metal and nonmetal gassy mines. ... 

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