Can 358 Security Fencing be Climbed?

358 security mesh is one of the most widely used anti-intrusion fences around high risk sites. It gets its name from the aperture size 3 by 0.5 inches (commonly written as 358) which is roughly 76 mm by 13 mm. Those tiny long rectangular gaps are not an accident. They make the mesh extremely hard to climb without tools or outside assistance. Below we explain why, how some products have been repurposed as climbing aids, and the most common and effective countermeasures, most notably double skinned systems such as Jacksons Securi mesh Plus.

Why the 358 aperture size prevents unaided climbing

The small rectangular openings of 358 mesh are deliberately too narrow for a hand or foot to get a secure hold:

• fingers cannot get a deep grip through the 13 mm side so there is no positive handhold
• toes cannot find purchase on the long 76 mm bars in the way they can on larger mesh
• the wires are close together and rigid so they will not flex to form a foothold
• the surface is relatively smooth and lacks protrusions that would allow a climber to lever themselves up

Put simply, 358 mesh denies the basic three things a climber needs: a place to wedge fingers, a place to rest a foot, and a rigid surface to push against. That makes unaided vertical ascent extremely difficult and slow, and it removes the possibility of shoulder over shoulder climbs that work on wider meshes.

Tools and improvised aids change the equation

That said, no fence is truly impregnable if someone brings tools or uses accessories that were not intended as climbing aids. A growing issue in some sectors is the repurposing of legitimate installation or maintenance fittings as footholds and handholds. For example, brackets and fixing systems designed to secure equipment to 358 mesh can, if fitted or left exposed, provide purchase points for a determined intruder. The QAB System brackets are an example of this. Devices like these fix securely to 358 mesh and LPS 1175 B3 single skin rated fences for legitimate reasons, but when they protrude they can be grabbed or stood upon.

An example of the QAB Systems Multi-purpose bracket.

Other common risk scenarios include:

• temporary items attached to the fence such as ladders, platforms, signage or cable runs creating step points
• maintenance materials left on site that can be used as leverage
• poor installation that leaves clips, bolts or bracket lips exposed
• vandalised or corroded fixings that create jagged grippable edges

So while 358 on its own resists unaided climbing, human behaviour, accessories and poor housekeeping can reduce its effectiveness.

Double skin mesh, the most common physical mitigation

A widely adopted countermeasure is to make the 358 mesh double skinned. Systems such as Jacksons Securi mesh Plus are built on that principle. Double skinned security mesh means two layers of the fine aperture mesh are secured together and often offset so the outer layer’s fixing points and any potential footholds do not line up with the inner layer. The benefits are clear:

• the number of wires stop bracket or small devices to be attached to the fence
• the cavity between layers removes the ability to compress wires and create makeshift steps
• the double layer increases the time and effort required to cut or breach the panel
• it complicates attempts to attach climbing aids because a secure load would have to span both skins

In practice, double skinned installations are costlier than single panels, but they are widely regarded as a cost effective way to raise the technical difficulty and delay of any climb or breach. For high value or high risk perimeters they are a common specification.

Best practice to keep 358 working as intended

To preserve the anti climb properties of 358 and to avoid inadvertent creation of climbing aids we recommend a few simple rules:

• design the perimeter as a system. Fence type, posts, fixings, topping, gates, lighting and CCTV should be specified together
• avoid external fixings or accessories that create step points. Where attachments are necessary use tamper resistant fittings and locate them so they do not form a climbing sequence
• use double skinned mesh where the risk assessment requires higher protection
• ensure regular inspections and prompt removal of temporary items and loose fixings
• consider anti climb toppings such as rollers or specialist spikes, but only where legal and in keeping with site requirements and safety
• combine physical measures with detection such as CCTV or motion sensors and rapid response procedures

Conclusion

Can 358 security fencing be climbed? Not easily. The defining 3 by 0.5 inch apertures make it extremely difficult to climb without tools or improvised aids. However, like any security product, its effectiveness depends on correct specification, installation and maintenance. Accessories intended for installation or maintenance have sometimes been misused as climbing aids, examples include brackets that if exposed provide purchase. The most common mitigation is a double skinned approach such as Jacksons Securi mesh Plus which significantly reduces the risk that an external fixing or bracket will become a usable foothold.