Under what condition may fencing be reduced to 5 feet tall?

Fencing regulations typically require specific heights to ensure safety and security for CNG facilities. The correct answer indicates that a fence may be reduced to a height of 5 feet if it is topped with at least three strands of barbed wire. This requirement is rooted in the understanding that barbed wire significantly enhances the barrier's deterrent effect, making it more difficult for unauthorized individuals to climb over the fence. The addition of barbed wire serves as a physical and psychological deterrent, providing extra security while allowing for a reduced height under specific regulations.

The other choices might suggest additional safety measures or enhancements, but they do not meet the regulatory stipulations that allow for the reduction in height of fencing in the presence of effective deterrent features, like barbed wire. The emphasis is on creating a robust security perimeter while balancing practical considerations such as height limitations.