Safety is first priority during blasting at hydro project
Nov 27, 2015
Blasting of bedrock to prepare for the construction of a powerhouse is proceeding as designed at the Red Rock Hydroelectric Project (RRHP) near Pella, IA. Approximately 21,000 cubic yards of bedrock has been removed from the powerhouse excavation, with approximately 11,300 cubic yards yet to be removed. Blasting began Oct. 28 to loosen the bedrock so that it can be removed from the site.
The safety of the public and workers continues to be of the utmost importance; therefore, additional safety precautions are taken before, during, and after each blast. In preparation for each blast, explosives are placed into holes that are strategically drilled into the bedrock. Large rubber pads are placed on top of the explosives to minimize flying rock and debris.
Before the explosives are ignited, a warning siren sounds throughout the area to indicate the blast will take place in 10 minutes and all workers move to designated safe areas. A second warning siren sounds 5 minutes before the explosives are ignited. Traffic is stopped and Highway T-15 is closed during the entire blasting sequence. Variable message boards and additional signage provide advance warnings of the road closures.
Spotters watch each blast for any irregularities or other problems. Following the blast, the spotters check in and give their reports. Next, a worker goes down to the blast site to verify that a device called the “tattletale” has received the blast signal. The charges are wired together in a series with an electrical charge setting off the explosives one at a time. The tattletale is the last device in the series. If the tattletale received the signal, the crew can be assured that all of the explosives have discharged. Once that assurance is verified, the “all clear” signal is given and Highway T-15 is immediately reopened. Road closures have typically been only 10 to 15 minutes in duration. However, longer closures may be needed in the future if one or more of the charges fails to ignite.
Excavation using the blasting method is expected to continue through mid-December.