Safety Fence

What is a Safety Fence

A safety fence is a guard, in the formal sense of ISO 14120, whose function is to prevent a person from reaching, climbing, or crawling into a mechanical hazard zone while a machine is running. It belongs to the family of physical safeguards that also includes interlocked doors, light curtains, safety mats, and laser scanners, but it is the only one that provides a continuous, passive, always-present barrier around the perimeter of a cell. In machine safety language the fixed mesh panels are fixed guards, the access points are movable guards, and the whole assembly is referred to as perimeter guarding or a guarded enclosure.

The distinction from an ordinary industrial fence is functional, not cosmetic. A security or boundary fence is designed for deterrence, demarcation, and weather. A safety fence is designed against a specific person reaching a specific moving part, so its mesh, height, standoff, ground gap, and impact strength are all derived from a risk assessment and from the reach tables of ISO 13857. A fence that looks identical can be compliant in one geometry and non-compliant in another simply because the hazard moved closer to the mesh.

Structurally a safety fence has four building blocks: (1) infill panels, which fill the plane between posts and may be welded steel mesh, perforated or solid steel sheet, or transparent polycarbonate; (2) posts, typically square hollow section steel that carry the panels and resist impact; (3) fixings and brackets, which clamp panels to posts and bolt the posts to the floor; and (4) access elements, the sliding doors, swing gates, and lift-out panels that let people and material in, each of which must carry an interlocking device under ISO 14119 so that opening it stops the machine.

Machine guarding has a long regulatory history. In the United States, OSHA codified general machine guarding in 29 CFR 1910.212 in 1971, requiring that one or more methods of guarding protect operators from point-of-operation, nip, and rotating-part hazards, and that guards be affixed, durable, and tamper resistant. In Europe, the Machinery Directive and the harmonized EN ISO standards built a layered framework in which ISO 12100 defines risk assessment, ISO 14120 defines guards, and ISO 13857 defines the reach distances those guards must satisfy. The current edition of ISO 14120 dates to 2015 and ISO 13857 to 2019.

The scale of the category grew with industrial robotics. As articulated robots and automated cells spread through automotive, logistics, and general manufacturing, the perimeter fence became the standard means of separating people from high-speed, high-energy motion. For robot systems specifically, ISO 10218-1 and -2 and the United States consensus standard ANSI/RIA R15.06 impose cell-level guarding duties on top of the general fence standards, which is why a large share of modern safety fencing is sold and engineered as robot cell guarding.

Fence Types and Infill Panels

Safety fences are classified first by the infill that fills the panel plane, because the infill determines what the fence protects against: reach-through, ejection, spatter, light, or contamination. Choosing the wrong infill is a common error, for example using open mesh next to a welding cell where the operator outside needs protection from arc flash and spatter. The table below compares the four mainstream infill types.

Welded steel mesh is the default infill for the great majority of perimeters. Horizontal and vertical wires are resistance-welded into a grid and welded into a tubular frame, giving a rigid panel with high visibility, good airflow, and reach-through protection sized by the mesh opening. The most widespread industrial grid is a 20 x 100 mm opening formed from 3 mm wire, which blocks a hand and a grab while keeping the cell visible. Mesh panels carry the highest published impact ratings, around 2100 joules on certified post systems, because the welded grid distributes load.

Polycarbonate infill is used where the fence must also contain a liquid splash, dampen noise, or stop small ejected fragments while staying transparent. Polycarbonate panels mount on the same post systems as mesh and reach impact ratings near 1600 joules. Because they are solid, they need careful placement relative to ventilation and heat, and they are more susceptible to scratching and chemical attack than steel, so they are selected for specific containment duties rather than as a general perimeter.

Solid and perforated steel sheet infill is the choice for welding, grinding, plasma, and laser cells, where the duty is to stop spatter, sparks, grinding debris, and harmful light, and to protect personnel outside the cell from arc radiation. Perforated sheet trades some shielding for airflow and partial visibility. These panels are heavier and reduce the operator's view into the cell, so they are paired with windows of welding-grade glass or interlocked viewing doors where line-of-sight is needed.

Stainless steel mesh and frames serve food, beverage, and pharmaceutical lines where the structure must survive clean-in-place chemicals and frequent washdown without corroding or harboring bacteria. Dedicated hygienic ranges, such as a stainless line, use rounded profiles and stainless fixings so that water drains and surfaces can be cleaned. The protection principle is identical to carbon-steel mesh; the difference is corrosion resistance and cleanability rather than reach geometry.

Mesh, Height, and Reach Distances

The defining engineering content of a safety fence lives in three coupled dimensions: mesh opening, panel height, and standoff distance to the hazard. All three are derived from ISO 13857, which treats the fence as a problem of reaching over the top, reaching through the openings, and reaching under the bottom. These three values must always be solved together, because changing one shifts the others. The table below shows how mesh opening and required clearance to the hazard relate, using representative values from the standard's reach-through tables.

Reaching over the fence is governed by panel height read together with how far the fence stands from the hazard. ISO 13857 does not give a single legal height; it gives a matrix. Structures shorter than 1000 mm are not credited because they do not restrict body movement, and structures below 1400 mm should not be used without additional measures. A height of 1400 mm is the low-risk baseline. In practice machine and robot perimeters are built at 2000 mm or more so that climbing over is treated as unforeseeable misuse, and where the fence must sit close to a tall hazard, panels of 2200 to 2550 mm are used.

Reaching through the mesh is the reason mesh opening and standoff are inseparable. What governs is the narrowest dimension of the opening: for a slot, the short side. A standard 20 x 100 mm grid therefore counts as a 20 mm slot, which blocks the hand and needs about 120 mm of standoff, the figure Troax and Satech publish for this panel. Let the narrow dimension grow past 20 mm and the arm passes, so a 20 to 40 mm slot jumps to at least 850 mm of clearance. Conversely, dropping the narrow side to 12 mm or less cuts the standoff to roughly 100 mm or below, which is why fine mesh is chosen when floor space is tight and the cell must be compact.

Reaching under the fence is controlled by the ground gap below the bottom rail. The gap must be small enough that a foot or leg cannot slide toward the hazard, so makers set the bottom clearance at roughly 140 mm, within the broadly used 100 to 180 mm window, and tie the posts to the floor with a base plate. Where the floor is uneven, adjustable base plates take up the difference while preserving the maximum permitted gap. A fence that clears the ISO 13857 over and through checks can still be non-compliant if the under-gap is too large.

For robot cells, these geometric checks combine with the cell standards. ISO 10218-2 and ANSI/RIA R15.06 require that the safeguarded space account not only for the robot's reach but for the worst-case stopping distance and for any payload or tool that could be flung, which can push the standoff well beyond the basic ISO 13857 arm-reach figure. The fence height, mesh, and standoff together must contain that envelope.

Materials, Posts, and Standards

Beyond the reach geometry, a safety fence is judged by its structure: the post section that carries impact, the wire and frame that form each panel, the floor fixing, and the surface finish. Most carbon-steel systems use a square hollow post fixed to the slab with expansion anchors, panels of welded mesh in a tubular frame, and a powder-coat finish for indoor service. The table below compares published panel and post specifications from three established modular makers, with all figures taken from their public datasheets.

Posts and frames are the structural backbone. Square hollow section steel, commonly around 60 x 40 mm or 60 x 60 mm with a wall near 2 mm, carries the impact and transfers it to the floor through a base plate anchored with expansion bolts such as M10. Carbon-steel systems frequently use grades equivalent to Q235. Light systems use a 20 mm panel frame for general perimeters, while heavy-duty ranges add a 60 mm post section and reinforced frames where higher impact energy or taller panels are required.

Wire and mesh are resistance-welded grids. A representative panel welds 3 mm horizontal and vertical wires into a tubular frame; Axelent's X-Guard, for instance, combines 3 mm vertical wires with 2.5 mm horizontal wires. The mesh slot dimension drives the reach-through compliance discussed in Chapter 3, while the wire diameter and weld quality drive the impact rating. Welded mesh outperforms woven or clamped mesh under impact because the welds prevent the grid from unzipping.

Finish and corrosion matter for service life. Indoor systems are powder coated, typically in graphite or grey RAL tones such as 9011, 7037, or 9005, which suits dry factory air but not outdoor or washdown duty. Outdoor or corrosive sites use hot-dip galvanized steel, and food, pharma, or washdown lines move to stainless steel hygienic ranges. The finish is not cosmetic: a powder coat on carbon steel placed outdoors will corrode at the fixings and degrade the structural rating over time.

Standards tie the whole assembly together. ISO 14120 defines the general requirements for fixed and movable guards, including that fixed parts be removable only with a tool. ISO 13857 supplies the reach distances. ISO 14119 governs the interlocking devices on access doors. ISO 13855 positions presence-sensing equipment. For robots, ISO 10218-1 and -2 apply, and in the United States OSHA 29 CFR 1910.212 and ANSI/RIA R15.06 apply. A defensible specification cites the specific clauses, and reputable makers publish TUV test reports for impact, for example 2100 joules for mesh and 1600 joules for polycarbonate on a given post system.

Key Specification Parameters

A safety fence quote lists many dimensions, but only a handful truly drive compliance and cost. The seven parameters below are the ones to lock down before comparing makers, and each maps directly to a clause in the governing standards.

Panel height sets reach-over protection. Standard heights cluster near 1250, 2050, 2350, and 2550 mm. Heights below 1400 mm are only acceptable with additional measures, and most robot and machine perimeters use 2000 mm or more. Height is never specified alone; it is solved with the standoff distance from the hazard using the ISO 13857 reaching-over table.

Mesh opening sets reach-through protection and the minimum standoff to the hazard, governed by the opening's narrowest side. A 20 x 100 mm grid is a 20 mm slot, so it blocks the hand and needs only about 120 mm of clearance; widen the narrow side past 20 mm and the arm passes, forcing at least 850 mm. The mesh choice is therefore also a floor-space decision: a coarse-slot panel saves cost but can force a larger cell.

Wire and frame dimensions, typically 3 mm wire welded into a 19 x 19 mm to 30 x 20 mm frame, drive rigidity and impact behavior together with the post. They are the difference between a panel that deflects and recovers and one that deforms permanently under a process impact.

Post section and fixing, commonly a 60 x 40 mm or 60 x 60 mm hollow section anchored by M10 expansion bolts through an adjustable or welded base plate, determine how impact energy reaches the floor. The base plate type also accommodates uneven floors while holding the ground gap within limits.

Impact resistance is the certified energy the panel-post-fixing system absorbs without failing, with published TUV values around 2100 joules for mesh and 1600 joules for polycarbonate. The figure is only valid for the tested combination, so a panel rating must always be read with its matching post and bracket.

Ground clearance under the bottom rail is held near 140 mm, within the roughly 100 to 180 mm window, to block reaching under. It is easy to overlook on uneven floors, where an unadjusted base plate can open the gap beyond the limit.

Access and interlock provisions define the doors and gates and their safety devices. The relevant choices are sliding versus swing versus lift-out access, and the interlock type under ISO 14119, including whether guard locking is required so the gate stays shut until motion has stopped. The fence is only as safe as its weakest opening, so access hardware is a core spec, not an accessory.

One parameter often left implicit is infill type by hazard: mesh for reach protection, polycarbonate for splash and noise, solid or perforated steel for spatter and light, stainless for hygiene. Specifying the wrong infill defeats the fence even when every dimension is correct, for example open mesh beside a welding cell that needs arc-flash shielding.

Selection Decision Factors

To turn the preceding chapters into a defensible specification, follow the decision sequence below. The most common mistakes are not single wrong numbers but decisions taken out of order, such as fixing the fence layout before the risk assessment defines the hazard envelope. These eight steps can serve as a fixed RFQ template.

1. Risk assessment first: Under ISO 12100, identify the hazards inside the perimeter, the stopping distances, and any ejection or fly-off energy. For robot cells, add the ISO 10218-2 and ANSI/RIA R15.06 cell duties. Everything downstream is derived from this, so it cannot be skipped.
2. Reach geometry: Use ISO 13857 to solve panel height, mesh opening, standoff distance to the hazard, and ground gap as one coupled set. Confirm reaching over, through, and under are all blocked for the actual layout, not assumed from a default height.
3. Infill by hazard: Choose mesh for reach protection, polycarbonate for splash and noise, solid or perforated steel for spatter, sparks, and arc light, and stainless for washdown hygiene. Match the infill to the dominant hazard, not to appearance or cost alone.
4. Post system and impact rating: Select a post and fixing whose TUV-certified impact energy, paired with the chosen panel, exceeds the worst-case foreseeable impact from the risk assessment. Confirm the rating is for the exact panel-post-bracket combination quoted.
5. Access strategy: Locate doors and gates for operation and maintenance, choose sliding, swing, or lift-out, and specify the ISO 14119 interlock for each, including guard locking and presence sensing such as light curtains or safety mats where a person can pass fully inside.
6. Floor and environment: Confirm the slab and anchor type, choose adjustable base plates for uneven floors, and select finish for the environment: powder coat indoors, hot-dip galvanized outdoors, stainless for washdown. The finish protects the structural rating over the fence's life.
7. Standards documentation: Require the maker to map the design to specific clauses of ISO 14120, ISO 13857, ISO 14119, and, for robots, ISO 10218 and ANSI/RIA R15.06, plus OSHA 29 CFR 1910.212 for United States sites. A general claim of compliance is not the same as clause-level evidence.
8. Total project cost: Price the assembly, not the panel: panels, posts, brackets, doors, interlocks, base plates, anchors, and installation. A coarse mesh that saves panel cost but forces a larger cell footprint or extra interlocks can cost more than a finer mesh that compacts the cell.

One last and commonly overlooked dimension is maker serviceability and modularity: the breadth of matched door, lock, and accessory ranges, the availability of spare panels in the same finish years later, and local stock and lead time. A fence is a long-lived asset that gets reconfigured as lines change, so a system from a maker with a deep, stocked accessory range, such as Troax, Axelent, or Satech in the ISO market, or regional fabricators building to ISO 14120, is easier to extend and repair than a one-off welded enclosure.