Figure 5. Completed explosive assembly. Figure 6. Charge assembled away from bridge. Top cartridge was located just below the stemming. Figure 7. Loading holes on the concrete pier. so that the detonating cord and the nonelectric detonators could each be threaded through the cartridge. The explosive charge for each hole was pre-assembled on the surface. A single 25/500 nonelectric initiator was loaded into the bottom cartridge and another similar detonator was placed in one of the last cartridges near the top of the charge for insurance. A wrap or two of duct tape was used to secure the cast boosters in the desired position along the detonating cord/nonelectric line. The length of each assembly was calculated to determine where the stemming should start. The detonating cord did not extend up into the stemming, as it stopped at the top cartridge. The drill holes were checked for depth and blown clean with a blowpipe and compressed air when it was necessary. 12 Access to the top of the piers inside of the cofferdam was limited to a man basket via the crane on the work bridge. After the drill holes were checked and cleared, the explosives assemblies were transferred to the crew members in the cofferdam individually for each hole. In order to protect the fragile nonelectric initiation tubing from the weight of the blasting mats that would cover each pier, a wood channel was created by bolting two lengths of framing lumber to the top of the concrete. All the wiring was kept inside of this channel and when the hookup was complete it was covered with a narrow piece of plywood that was nailed in place. The initiation sequence was designed to start with one of the center holes firing first, then by using a 17 ms delay on one side the detonation progressed away from the center at 25 ms intervals. The Journal of Explosives Engineering January/February 2015