Impact-Resistant Security Gates
by Mark Stokes and Ralph Graham
Idaho Power needed a way to restrict large vehicle access to sensitive areas at its hydro projects that also limited the manpower requirements. To accomplish this task, Idaho Power designed and installed impact-resistant security gates. These gates are designed to be capable of stopping a large truck but also can be simply opened or closed by a single employee.
Security situation at Hells Canyon
With its remote location and high degree of recreational usage for fishing, hunting, and hiking, Idaho Power's 1,167-MW Hells Canyon Complex on the Snake River presents significant security issues. The complex consists of the 585.4-MW Brownlee, 391.5-MW Hells Canyon, and 190-MW Oxbow powerhouses.
After the September 11, 2001, terrorist attacks, Idaho Power began employing security guards to protect sensitive areas at the Hells Canyon Complex, such as the dams, powerhouses, and spillways.
For example, all access to Hells Canyon Dam takes place via one road, which must be used by both plant personnel and recreational visitors. Idaho Power placed a manned security gate at a strategic location on this road, where a guard stopped and inspected all vehicles. The utility also used security guards to safeguard the Brownlee and Oxbow facilities.
Identifying security measures
Idaho Power needed to determine exactly what steps were necessary to secure the Hells Canyon Complex over the long term. The utility quickly realized that adequately ensuring the safety of the power plants, intakes, and spill gates required installing a barricade that could stop a large truck.
Idaho Power first investigated the option of using concrete barricades. However, because of their size and weight, these barricades must be moved using a forklift or other heavy equipment, such as a front-end loader or mobile crane. This would involve extensive time and labor whenever security levels changed. In addition, this situation was impractical because of the need for regular employee access.
The security gates installed at Idaho Power's three-powerhouse Hells Canyon Complex were designed to resist the impact of a large truck but can be easily opened and closed by a single person. Click here to enlarge image
The utility decided some type of large gate would be the best solution. The gate design needed to be heavy enough to resist the impact of a ramming attempt and yet be easily operated for daily access by Idaho Power employees. This meant a single person needed to be able to open or close this gate.
Building the gates
Before designing the security gates, Idaho Power performed an inventory of available resources, such as wide-flange steel beams and heavy wall pipe. Incorporating these materials, personnel then developed a gate design that they believed could resist the impact of a loaded truck. The ultimate goal of the design was to stop the truck or inflict enough damage to disable the vehicle.
The gates for the Hells Canyon Complex are made using wide-flange beams for the cross arms, reinforced with angle braces, and pipe for the posts and sleeves. Idaho Power ordered materials not available at the facilities. Personnel then fabricated the necessary components using the utility's Oxbow maintenance facility. Personnel assembled the gates and tested their balance and whether they would open and close properly.
Installing the gates
Idaho Power installed six gates at vehicle access points that the public could approach. Four of these are double gates that provide a 23-foot-wide opening, and the other two are single gates that provide a 14-foot-wide opening. For each, the top of the main gate beam is 48 inches above the road surface. Total weight of the posts and beams for the 23-foot-wide gates is about 3,700 pounds. Total weight for the 14-foot-wide gates is about 2,950 pounds. Each gate post is embedded in 32,400 pounds of reinforced concrete.
There are two double gates and one single gate at Brownlee, one double gate at Hell's Canyon, and one double and one single gate at Oxbow. All gates are locked.
Since the gates were installed in May 2002, they have performed flawlessly. The only maintenance work consists of painting the gates and reapplying reflectorized sheeting. No incidents have occurred to crash-test the gates.
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