What to specify after NPSA dropped MFES ratings (height, toppings, and tested standards)

What counts as an anti scale fence (and what doesn’t)

An anti scale fence is a perimeter barrier engineered to delay or deter climbing by removing practical hand/foot purchase and by reducing quick defeat routes (climb, cut, lift, burrow, or exploit the gate). Modern authoritative guidance treats the fence as one layer in a system—selection should follow an Operational Requirements / risk-led process rather than “pick a tall fence and hope.”

Anti-scale vs. “security fence”

A common mistake is assuming “anti-scale” is purely about height. NPSA frames a “Security Fence” as a continuous barrier offering climb resistance and forced-entry resistance, with design choices linked to threat, standards, and performance ratings—tested to recognized standards and at independent test houses.

The 5 ways attackers actually defeat fences

If your spec only addresses climbing, you’ll still lose at the weak points. NPSA explicitly lists common attack methods such as climbing, burrowing underneath, passing items through/over, vehicle force entry, and exploiting access points (gates) via deception, sabotage, or forced entry.

What authoritative guidance says makes a fence “hard to scale”

1) Small apertures remove toe/finger holds

DoD’s UFC guidance explains why welded wire mesh is commonly used for higher deterrence: openings are relatively small to prevent toe or finger holds, and it can provide greater deterrence than chain link for climbing and cutting. UFC also gives clear numeric limits for welded wire mesh: maximum opening dimension 2 inches (51 mm) and minimum thickness 9 gauge (3.76 mm), and it points to ASTM F2453/F2453M for material requirements.

2) Height and topping are part of the design—not an afterthought

NPSA provides concrete recommendations that often show up in real projects:

• For basic to moderate security fencing, minimum 2.4 m panels, and where appropriate an anti-climb topping (e.g., barbed tape coil) starting at a minimum height.

• For higher security requirements, minimum 3.0 m panels with larger topping requirements.

NPSA also explicitly notes it does not recommend chain link fence fabric for these security fence applications, which is a key reason “anti-scale fence vs chain link” keeps trending.

3) “Under” and “around” are where many fences fail

Anti-scale performance collapses if an intruder can:

• burrow or erode a gap under the fence, or

• use nearby landscaping/site furniture as a ladder.

NPSA flags both burrowing/erosion and plant growth near the perimeter as issues that can create access points or provide climbing aids and concealment that undermines detection.

How to specify an anti scale fence like a professional buyer

Step 1: Write a threat-led requirement (don’t start with product names)

Good specs start with “what the fence must do”:

• Deter casual intrusion?

• Delay a prepared attacker long enough for response?

• Support detection (fence-mounted sensors/PIDS) and surveillance?

Both NPSA and the Government of Canada’s security fencing guide emphasize starting from a structured threat/risk process (Operational Requirements / Threat and Risk Assessment), then selecting measures that match the threat and how the site operates.

Step 2: Require independent testing to a recognized standard

NPSA is explicit: perimeter fences and gates should be tested to a recognized standard, at an independent test house, achieving a performance rating aligned to the chosen standard.

For forced-entry resistance ratings, a widely used route in the UK market is LPCB LPS 1175, where ratings are described in terms of attack toolset and time available, and the scheme includes ratings A1 to H20 (formerly SR1–SR8).

Step 3: Lock down the geometry that makes scaling hard

If you want “anti-scale” to be more than marketing, specify the geometry:

• Aperture/opening small enough to deny toe/finger holds (UFC’s welded mesh limit: ≤ 51 mm).

• Wire diameter/thickness that resists cutting and deformation (UFC baseline: ≥ 3.76 mm / 9 gauge).

• Panel height tied to your threat level (NPSA examples: 2.4 m or 3.0 m+ depending on requirement).

For material definition, reference ASTM F2453/F2453M when using welded wire mesh fabric so coating types and the fabric category are clearly defined rather than vaguely described as “heavy duty.”

Step 4: Design the weakest points first: gates and fixings

An anti scale fence is only as good as:

• gate frames, hinges, latch hardware

• panel-to-post brackets

• exposed bolts that can be removed from the public side

A USACE design guide warns that bolts/nuts used for security fencing can be easily removed and recommends spot welding gate hinge pins and bolts attaching fence fabric to posts for physical security.

Installation details that decide whether it works in real life

Put “tamper opportunity” on the secure side

Where possible:

• keep fixings on the protected side,

• use anti-tamper hardware,

• avoid exposed clamp heads that can be attacked with common tools.

If your fence is rated, install it exactly as the rated configuration requires—changing brackets, spacing, or toppings can quietly invalidate the performance you think you bought.

Control the ground interface

Treat the bottom of the fence as a security requirement:

• prevent lift-to-create-gap,

• mitigate burrowing,

• account for topography and groundwater, especially for temporary solutions.

Manage the “climb assists”

Your anti scale fence can be defeated by your own site:

• trees near the line,

• stacked pallets,

• dumpsters,

• low walls or equipment that provides a first step.

NPSA explicitly calls out vegetation/plant growth near perimeter lines as something that can provide climbing aids or concealment that undermines detection.

Copy-paste RFQ checklist for an anti scale fence

Minimum performance language

• Provide an anti scale fence system (panels + posts + gates + toppings where specified) tested to a recognized forced-entry standard at an independent test house, with a performance rating appropriate to the threat.

• Panels to use welded wire mesh meeting ASTM F2453/F2453M (where applicable).

• Mesh geometry consistent with climb resistance (example benchmark from UFC welded mesh: ≤ 51 mm opening, ≥ 3.76 mm wire).

• Heights per requirement (example benchmarks: 2.4 m minimum for security fence, 3.0 m+ for higher security, per NPSA guidance).

• Gate and fixing security: include anti-tamper measures; consider spot welding of vulnerable fasteners where appropriate.

Optional upgrades (choose based on threat)

• Anti-climb toppings configured to your safety/regulatory constraints.

• Multiple fence layers / zoning inside the compound for defense-in-depth.

• Integration with detection (PIDS) and visual surveillance systems.

Common buyer questions

“Is a taller fence automatically anti-scale?”

No. Height helps, but anti-scale comes from denying grips, preventing bypass at the bottom, and securing gates/fixings—exactly the attack paths NPSA lists (climb, burrow, exploit access points).

“Can chain link be ‘anti-scale’ if we add toppings?”

NPSA explicitly does not recommend chain link fabric for security fencing, and guidance like UFC highlights welded mesh as more deterrent to climbing/cutting due to small openings that deny toe/finger holds.

“What should I do first if I’m confused by standards and ratings?”

Start with a threat-led Operational Requirements / risk assessment, then specify independently tested performance to a recognized standard and build your design around the known attack methods (climb/burrow/gate).