Delay detonators

Other problems of the airmen were solved at Picatinny. In 1943, the introduction of skipbombing brought a special request. Because of the low altitude at which the bombing plane had to fly, a bomb with a delay fuze was required to permit the plane sufficient time to get away from die effective range of the explosion. In many instances,bombs were to be dropped from as low as 25 feet. Again, Picatinny came up with the answer a fuze which would delay detonation of the bomb eight to eleven seconds. 

P4 explosives were specifically designed for the operation of ripping with delay detonators (see p. 143) and must satisfy the following tests ... 

Many other methods of making lead azide in a safe form have been described, but the only one to have found commercial importance consists of replacing the dextrine by a small proportion of gelatine. When properly made this form of lead azide is as safe to handle as the dextrinated form and has improved sensitiveness to flame. It can therefore be used by itself in electric and delay detonators, but not in plain detonators as it is not ignited with certainty by safety fuse. 

A real advance in the construction of delay detonators was made by Eschbach, who introduced delay compositions which evolved so little gas that there was no longer need to vent the detonator. This eliminated risk of pre-ignition of high explosive and also made it possible to provide fully waterproofed assemblies which gave delay times much more regular because of the removal of variable venting effects. Delay detonators of this type have now virtually superseded all others. 

Gasless delay detonators are manufactured to fire after pre-arranged delay times, each manufacturer providing a series of detonators with intervals of usually 1 s or 0.5 s. More recently a further type of delay detonator has been introduced, usually known as the millisecond, or short delay detonator. Again, manufacturers provide a series of fixed delay times, but in this case the interval between each number of the series is much shorter and may be from 25 to 50 ms. 

For the manufacture of millisecond delay detonators, faster burning compositions are necessary. Many have been suggested, but the two most commonly used are based on silicon mixed with either red lead or lead dioxide. Typical mixtures would contain between 30 and 50% of silicon and the remainder as oxidising material. 

Delay detonators for use in coal mines must be constructed so as not to ignite methane/air mixtures even if iired accidentally outside a cartridge of a blasting explosive. This requires a suitable selection of fusehead and the provision of the delay element in a form which will not produce large particles of hot slag on burning. In the British design the delay elements are... 

Delay detonator. A detonator in which a time lag is introduced between application of the firing current and explosion of the detonator. 

Electric detonator. A detonator for firing by electric current. The term does not normally include delay detonators. 

Flash past. In assemblies such as delay detonators and military fuzes the possibility of an igniting flash by-passing a delay element. 

Gasless delay detonator. Original name for modern delay detonator. 

Millisecond delay detonator. A short delay detonator. 

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

Short delay detonator. A delay detonator with time interval between individuals of the series of 25 or 50 ms. 

Explosive Wave Shaping by Delayed Detonation, BRL 1022(1957) 49a) J.M. Majowicz... 

A type of British "electric delay detonator with an intermediate charge" is described in Ref 36, p 70 and is shown here as Fig 10. 

Fig 10 BRITISH ELECTRIC DELAY DETONATOR WITH AN INTERMEDIATE CHARGE... 

An other type of British nonmilitary electric detonator, called short type delay detonator" is described in Ref 36, pp 72-3 and is shown here in Fig 11. This detonator con-... 

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