Short delay blasting

Detonating Relays. These are devices for obtaining short-delay blasting in conjunction with detonating fuse. They consist of two open-end delay detonators coupled together with flexible neoprene tubing. In practice, a relay is inserted in the main line of detonating fuse which is cut at any desired point and the two ends are crimped into either end of the relay. The delay provided is 15 3 millisecs Ref McAdam West water (1958), 60... 

Non-electric, short-interval (millisecond) delay devices for use in delaying blasts which are initiated by detonating cord. 

The reproducibility of the time of a delay element is related to the reproducibility of the primer used for initiation. The times of short" obturated delay elements are very sensitive to variation in primer output (Refs 7 12). Although primers of this type have been additionally tested for blast and gas vol, some opinions have held that, provided the priming mixt is maintained within the prescribed limits, the output is a mere reflection of the pellet wt... 

Where the accidental fuel release is the result of an internal combustion or other reaction, the released fuel is at an elevated temp and contains a concn of free radicals derived from the internal reaction such that the ignition delay is short. (Also, the ignition can be characterized as multipoint where the blast effects approach that of a bursting pressurized sphere)... 

Another more modern type of delay ignition line is known under the tradename of Thermalite Ignitacord. It burns with an external, short, very hot flame and comes in two types 0.75 and 1.5 sec/in. average BT. This type of fuse is used in commercial blasting work. In the same applications, but for multiple hole detonations, the very fast (1 sec/ft) Quarrycord is used. 

The blast pressures produced by the burning of the vapors above a pool of liquid hydrogen are quite small. Measurements were made with both a General Radio Impact Noise Analyzer and a Kistler SLM System. Typical overpressure data obtained 160 ft from the ignition source with the Noise Analyzer are given in Fig. 6. The effect of time delay before ignition is evident from this figure. The maximum overpressure values obtained at several locations indicate that the overpressure is proportional to l//) for distances D between 80 and 160 ft. In this connection, Windes [9] found the overpressure produced by a blast is proportional to l/o for overpressures below 0.01 psi over distances of approximately 200 to 2,000 ft. At short distances, Ireland [10] found the overpressure is proportional to the theoretical value, 1/Z), for pressures in excess of approximately 0.1 psi. 

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