A Crash Course on Hardening Soft Targets

How vehicular perimeter security systems can play into your overall facility design

Keeping retail shoppers safe, shielding structures from accidental or intentional automobile crashes, protecting hotel patrons from suicide car bombers, and keeping employees and visitors from harm have always been a concern...today more so than ever. From pedestrian-filled farmers markets and universities to new and used car lots, a wide variety of businesses and agencies find peace of mind through the use of barriers, bollards, barricades and crash gates for vehicle-based physical access control at the perimeter.

For those areas where a vehicle will never enter, fixed bollards and barriers are the norm. However, at entrances, barriers that go up and down are needed to let authorized vehicles through.

Risk Assessment Starts With Physics 101

To evaluate the security risk for a given facility, particular attention must be focused on the weights and velocities of vehicles that would be used to attempt penetration into sensitive areas.

A vehicle moving towards a barricade has kinetic energy, the major measure of how much "hitting power" it possesses. Mathematically, kinetic energy is derived from the vehicle velocity and its weight (mass). On impact, some of this energy is converted to heat, sound and permanent deformation of the vehicle. The barricade must absorb the remainder of this energy if the vehicle is to be stopped.

The amount of remaining energy depends on many factors, primarily the velocity of the vehicle at the moment of impact. The amount of kinetic energy posed by a vehicle changes as the square of its velocity. For example, a vehicle moving at 50 mph has 25 times as much kinetic energy as it would at 10 mph. Thus, an armored car weighing 30 times as much as a Toyota Corolla and moving at 10 mph would have less hitting power than the Toyota moving at 60 mph!

Upon designing a way to slow down vehicle approach, take precautions to stop the attacking car from making a "corner cutting shot" at a barricade. Often, only a light post defines a turning point and a speeding car can take it out and not even hesitate. Knolls and other impediments should be considered.

Failing to understand this and not using the proper equipment to counter the threat may lead to a false sense of security.

Overcoming Common Design Deficiencies

Because of the relationship of velocity to the total kinetic energy possessed by the vehicle, every effort must be made by the security engineer to force a vehicle to slow down before it reaches the barricade. As mentioned, straight lines make for faster and easier approaches for vehicles, so it's best to create curves on access roads to your facility as a natural impediment to speeding cars or trucks.

The most frequently used technique is to require a sharp turn immediately in front of the barrier. When vehicle speed is reduced by 50 percent, the "hitting power" is reduced by four times. If the speed is reduced by 2/3rds, the force of impact will be reduced by nine times.

Another common planning deficiency occurs when designers choose non-certified barriers or barricades. Certified equipment has been tested and proven to work under extreme conditions, giving planners the confidence they can rely upon. Testing is normally by an independent testing company or government agency, such as the Department of State (DOS) and military. Comprehensive reports of test results are issued and are available from the testing agency or manufacturer.

A Variety of Barriers and Bollards to Meet Any Circumstance

Today's barriers and bollards are capable of stopping and destroying a truck weighing up to 65,000 pounds and traveling at 50 mph. Such barricades can be raised or lowered at will to stop traffic or let it through. In an emergency, the thick steel plates or bollards pop out of the ground within 1.5 seconds.

At the other extreme, a mobile barrier can be light enough to be towed by a golf cart and set up in only 10 minutes. Nonetheless, it will stop a 5,000-pound vehicle going 50 mph.

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