Permitted explosives

Figures 6.30 and 6.31 present the same information for saturated hydrocarbons. In Figure 6.30, the saturated liquid state is on the lower part of the curve and in Figure 6.31 it is on the upper part of the curve. Below T y, the line width changes, indicating that the liquid probably does not flash below that level. Note that a line has been drawn only to show the relationship between the points a curve reflecting an actual event would be smooth. Note that a liquid has much more energy per unit of volume than a vapor, especially carbon dioxide. Note It is likely that carbon dioxide can flash explosively at a temperature below the superheat limit temperature. This may result from the fact that carbon dioxide crystallizes at ambient pressure and thus provides the required number of nucleation sites to permit explosive vaporization.

P (Explosives). Brit permitted expls categorized as PI, P2, P3, P4 and P5. See under Permissible and Permitted Explosives in this Vol Ref S. Fordham, High Explosives and Propellants , Pergamon Press, NY (1966), 90—96... 

Permissible or Permitted Explosives. In many coal mines there is a continual evolution of methane (firedamp) into the air of the workings. 

From the days of Nobel to about 1950 the scientific basis of commercial explosives remained relatively unchanged, although continuous and numerous improvements in manufacturing methods occurred throughout the world. There were, however, many advances in military explosives, note of which will be made later. These advances were, of course, largely due to the two world wars, which occurred since the death of Alfred Nobel. There were also many advances in the development of permitted explosives designed for use in gassy coal mines. 

It will, therefore, be seen that the best and safest practice is to use in each situation in the coal mine an explosive which is best adapted for the operation in hand. The use of unnecessarily weak explosives, even though apparently safer in some tests, is often a disadvantage and can be dangerous. These considerations have led to the development of a series of types of explosives suited for particular purposes in coal mines and subjected to tests relevant to their individual uses. Thus, in Britain there are now five classes of permitted explosives. In Germany there are three classes. In the U.S.A. geological conditions are different and the hazards are less than in Europe, and it has been possible to work throughout with the strongest types of permissible explosives. 

It was early recognised that an explosive is more hazardous in a coal mine if it is fired in a borehole from which the stemming is omitted or blown out early by the explosive than if it is fired in a properly stemmed hole and does adequate work in bringing down rock or coal. The tests which led to the original permitted explosives, now called P1 explosives, were therefore designed to test the product under these conditions. 

The original permitted explosives are now known as P1 explosives and must pass the following tests ... 

It must be remembered that methane can be liberated in a coal mine, not only in the coal itself, but in the nearby stone. It is therefore necessary to use permitted explosives, both in and near a seam of coal. Further, before any shot is fired in a coal mine, tests are made for the presence of methane in the air by means of a safety lamp. This safety lamp is the well-known Davy lamp and an experienced operator can judge the presence of methane in the air from the appearance of the flame. Tests are made... 

The method of mining is somewhat like driving two sets of tunnels at right angles through the strata. Most mines of this type do not present any hazard from methane and therefore non-permitted explosives can be used. The selection of powder or gelatine type of explosive depends on the nature of the rock and particularly on the wetness of the mine. 

Eq.S. Equivalent to Sheathed. The original name for Group P3 Permitted Explosives. 

P3. Class of Permitted Explosives for general use with instantaneous detonators. 

P4. Class of Permitted Explosives particularly for ripping with short delay detonators. 

Permissible Explosive. The American equivalent to British Permitted Explosive. 

Permitted Explosive. An explosive which is authorised for use in gassy coal mines. 

Haswelite. A British permitted explosive which passed the Buxton Test (See Vol 2, p B 394). 

The word detonics in the title is chosen in preference to the word detonation to indicate the physics of detonating high explosives and their mechanical effects. The major emphasis is on commercial high explosives for rock blasting, with the exclusion of Permitted Explosives and the many complicated problems connected with these... 

Corresponding explosives are known in Belgium as explosifs SCP (securite-grisou-poussiere), and in the USA as permissible explosives. In Great Britain they are called permitted explosives, and are to be distinguished from authorized explosives which... 

Chapter 6, 1 Assessment of Explosives", which includes Power or Strength (pp 65-8) Velocity of Detonation (69-72) Sensitiveness, to Friction and to Impact (72—6) Stability on Storage (76—8) Fume Test (78—9) and Miscellaneous Tests, such as for. Brisance and Speed of Gelatinization of NC (79—80). Chapter 7 Gallery Testing of Permitted Explosives (85—9)... 

Civil explosives are further sub-divided into permitted or permissible explosives and non-permitted explosives. Two types of civil explosives namely ammonium nitrate-fuel oil (ANFO) and emulsion explosives dominate the rock blasting scene in the USA. 

Explosives which produce a flash on detonation and create hazards for workers in coal mines are called non-permitted explosives. Basically these explosives include compositions based on aluminum powder and other HEMs with negative oxygen balance. 

In Great Britain the first explosives which passed the test in the testing gallery at Woolwich were approved for use in mines under the name of Permitted Explosives. At Woolwich the charge of explosive in the test mortar was stemmed with dry clay, a practice that differed from that followed in other countries. 

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