a diode cutoff block is shown in fig1 . in this drawing , the diode cutoff block ( 10 ) is shown . the block has two through holes 16 , 16 for detonating cord and a channel through the block for focusing the air blast of the detonating cord . detonating cord ( 12 ) passes through the diode block ( 10 ) and then forms a loop ( 14 ) before the cord passes through the diode block in the opposite direction . the diode block functions by focusing the air blast of the detonating cord through the block and severing the adjacent detonating cord section . the length of the loop ( 14 ) must be selected to allow the air blast to sever the adjacent detonating cord before the detonation wave can travel around the loop and pass through the block again . the block can be made out of a variety of materials such as metal , wood , or plastic . from a cost and weight standpoint , the preferred material is usually plastic . the dimensions of the block are determined by the quantity of explosive loading in the detonating cord . typically textile detonating cords have an explosive loading ranging from 4 grains per foot to 400 grains per foot . a typical textile detonating cord for the oil well servicing industry has a coreload of about 80 grains per foot . with a higher coreload detonating cord , the distance between the thru holes must be increased slightly and the block made thicker . the actual dimensions are determined by evaluating the severing capabilities of various samples of detonating cord in different block dimensions . ‘ for an 80 gr / ft detonating cord , the distance between thru holes ranges from 0 . 250 ″ to about 1 . 250 ″. the loop needs to have a minimum detonating cord length of about 6 inches to allow adequate severing of the detonating cord . the diode cutoff block illustrated in fig1 is shown as a solid block . while a solid block performs well , it is difficult to attach and remove the block from the detonating cord . an improved diode block is shown in fig2 . a hinged plastic block ( 20 ) is shown in the open position . a length of detonating cord ( 12 ) is shown passing through the block . a slot for the detonating cord ( 28 ) is molded into both the base of the hinged block ( 34 ) and the lid of the hinged block ( 22 ). the lid and the base of the block are joined by a living plastic hinge ( 30 ) that allows the block portions to be flexed . locking tabs ( 32 ) hold the block fixed in the closed position when the block is shut . by pressing the locking tabs ( 32 ) together , the block can be opened easily . when the hinged block is closed , an air blast channel 26 is formed similar to that in the one - piece block . the functioning of the block 20 is identical to the cutoff block 10 described earlier . when a length of detonating cord detonates , the air blast from the cord will sever the adjacent length prior to the detonation front passing around the loop and back through the block . it is also possible to use a diode block as a directional cutoff device . fig3 shows an arrangement of a diode cutoff block that only permits one - way detonation transfer . the main detonating cord transmission line ( 40 ) goes from the top of the fig3 drawing to the bottom of the drawing . a diode block ( 10 ) is attached to webbing material ( 48 ) to hold the block in the correct position . a jumper detonating cord ( 42 ) is secured to the main detonating cord ( 40 ) with hog rings ( 44 ). the other end of the jumper detonating cord passes through the thru hole 50 in the diode block . the main detonating cord ( 40 ) passes through the other thru hole 52 in the block . silicone rubber tubing ( 46 ) is placed over the jumper detonating cord to prevent the detonation of the jumper cord from damaging the main detonating cord length ( 40 ). the diode cutoff direction is illustrated by the arrow ( 56 ). if the main detonating cord lead 40 is initiated at the top of the figure , the detonation wave will progress towards the bottom of the figure . the main detonating cord will initiate the jumper detonating cord at the hog ring connection ( 44 ). the jumper detonating cord is much shorter than the main detonating cord lead that has a series of loops 40 a , 40 b , 40 c in it . thus the detonation front from the jumper cord 44 will arrive at the diode block 10 and sever the main detonating cord lead at 50 / 52 before the detonation front from the main lead 40 arrives at the block . thus the block 10 will function as an explosive diode , permitting the detonation front to pass through the block only in the direction opposite that of the cutoff direction 56 . fig4 illustrates a packaging transport section for safe packaging of detonating cord . an expanded polystyrene tray ( 70 ) is formed with a series of detonating cord loops ( 72 ) molded into the surface of the plastic . the channel for the detonating cord is slightly wider than the diameter of the detonating cord and slightly deeper than the diameter of the detonating cord . this allows accurate positioning of the detonating cord and makes the packaging easy to assemble . cavities are molded into the tray and sized and dimensioned to receive diode cutoff blocks 74 , 74 . these blocks 74 , 74 may be similar to those described above with reference to fig1 - 3 . if the detonating cord were to be accidentally initiated in some fashion , the detonation would only propagate until it encounters the first cutoff block . the length of each loop is about twelve inches . in this design the maximum length of detonating cord that may be detonated is about eighteen inches before the detonating cord will be severed in a diode cutoff block . each detonating cord transport section holds about eighteen feet of detonating cord . by stacking multiple transport sections , larger quantities of detonating cord can be packaged . for example , stacking twenty - eight transport sections will allow packaging 500 feet of detonating cord in an outer 4 g fiberboard box . fig5 and 6 show a complete packaging for a stack of sheets 70 , 70 such as that shown in fig4 . fig6 shows separator pads 75 between the foam sheets or trays 70 , 70 . thus , block 20 in fig2 provides a slightly arcuate shape for the cord segments contained in the channels and this configuration avoids any necessity for separate severing means to act on the detonating cord when an unwanted percussive signal passes through the adjacent cord segment . the results for this geometry of the containment passageway and the channels has been verified in proprietary tests conducted by an independent testing laboratory . the recommendation of that laboratory was to classify the packaging described herein as meeting federal requirements for transporting by highway , by rail , and by civil aircraft in the usa . the term “ block ” is intended to mean a three - dimensional elongated object with one or more flat faces , and otherwise of any convenient shape for defining the longitudinal blast passageway ( s ) and lateral channel ( s ) called for in the appended claims . the foregoing disclosure and the embodiments shown in the drawings are merely illustrative of the principles of this invention and are not to be interpreted in a limiting sense .