Page 48 - Security Today, October 2017

Attack Prevention
While all new barriers being considered for embassy projects should be tested to ASTM standards, the DOS SD-STD-02.01 Rev A ratings are still used frequently in project specifications. These ratings were assigned based on impact speed, similar to ASTM ratings. Products successfully tested with vehicles travelling at 30 mph were as- signed a K4 rating, at 40 mph a K8 rating, and at 50 mph a K12 rating.
Property owners should first seek to un- derstand the threat conditions for the par- ticular site they want to secure, and then make a determination as to the performance level required. For reference, the DOS typi- cally requires that barriers used on embassy projects must be tested with a medium-duty truck (15,000 pounds) traveling 50 mph and have less than a 1 meter penetration distance, which is equivalent to the ASTM F2656 M50-P1 rating.
Separately, the Department of Defense maintains a list of vehicle barriers and fenc- ing that are approved for use. While the DOD doesn’t have its own unique crash testing standard, the U.S. Army Corps of Engineers reviews crash test reports and independently validates the barriers. It’s important to note that not every product that obtains a crash test performance rating is placed on DOD Anti-Ram Vehicle Barrier List.
Differentiating the Various Types of Anti-Ram Fencing
Choosing an anti-ram fence largely comes
down to two options—post and beam or cable-based—and the differences lie right in the name.
Post and beam anti-ram fencing systems rely on a single steel, horizontal beam that is mounted between two anchor posts. These are typically spaced around 30 feet apart, de- pending on the crash rating and manufactur- er. Post and beam systems that utilize tubular steel offer a clean, aesthetic look, and simple connection points with minimal hardware.
Cable-based fences use anchor and inter- mediate posts spaced as close as 8 feet apart, to which a tensioned cable is attached. The tensioned cable is relied upon to stop all ve- hicular threats, and is either exposed or often ornamentally hidden in the fence. Multiple runs of cable line the posts, and the amount of cable needed largely depends on the level of crash test certification that is desired. Cable-based fence may include tall pickets, which act as anti-pedestrian security and add another level of protection.
However, the real difference between the two types of fence lies in the installation.
Purchase Price vs. Total Cost
Purchasing an anti-ram perimeter security fence system is only half the financial battle to securing a property’s border against ve- hicle-borne attacks—what still looms is the cost of installation. Contractors, architects and owners can realize significant savings by looking beyond the initial purchase price of the fence system and exploring the steps, ma-
terials and equipment necessary to complete the project.
Extensive amounts of hardware, interme- diate posts, wire rope and concrete are all re- quirements of traditional cable-based fence systems that drive up the total project cost and lengthen the construction schedule. Post and beam perimeter fences eliminate these components to cut installation costs nearly in half while still providing crash tested cer- tification to ASTM F2656 standards.
More than a 1,000 meter span, a DOS K12 or ASTM F2656 M50-P1 cable-based fence system can include up to 20 anchor posts and 380 line posts, while supporting multiple runs of cable. With up to 400 post holes in just a 1,000 meter stretch, the cost of materials and labor hours begins to add up quickly when you consider that each hole re- quires auguring, concrete fill and a rebar cage.
To effectively prevent vehicles from pene- trating the fence, spools of cable must be run in multiple lines—sometimes up to eight— through line posts and anchor posts in time- consuming fashion. The whole system also requires a significant amount of hardware to maintain its safety standards, using cable clamps and nuts to tension each cable.
Furthermore, the maintenance and work isn’t finished when the cable-based fence in- stall is complete. Cables must be checked and re-tensioned periodically to adjust tension- ing and maintain the fence’s ability to prevent vehicle penetration.
All of this work is above and beyond what’s needed to install a post and beam anti-ram fence. A post and beam solution to the anti-ram fence installation dilemma is straightforward—simplicity in design.
Vertical anchor posts are spaced approxi- mately 30 feet apart in the case of M50-P1 systems and rely on a single tubular beam to absorb the energy of a crash as opposed to multiple runs of wire rope and the line posts that support them. The result is 110 posts in a 1,000 meter span, versus the 400 posts used with a cable-based fence system. That’s nearly 75 percent less holes to dig—and that’s before factoring in the different-sized holes, and the time it takes to switch back and forth between auger bit sizes.
While the rebar cage must always be priced and built separately with a cable- based fence system, rebar sticks are included with some post and beam fence designs. To install, contractors simply insert the rebar
GS22
GOVERNMENT SECURITY OCTOBER 2017
Stefano Carnevali/Shutterstock.com