EN ISO 13855:2024: changes to the positioning of safeguards

Why the new EN ISO 13855:2024 is an important revision

The 2024 revision replaces the 2010 edition and brings the standard into line with the state of the art. The most visible change is its wider scope: the new version goes beyond traditional photoelectric light curtains and pressure-sensitive mats to address modern protective devices, mobile applications, two- and three-dimensional detection zones, vision-based systems and cases where a person’s approach to the hazard zone is neither straight nor predictable.

From a practical point of view, this review mainly affects automatic machines with access protected by ESPE, packaging lines, robotic cells, end-of-line system, shuttles, mobile trolleys, AGV/AMR, systems with laser scanners, muting zones, interlocked guards, two-hand controls, single-actuation controls and manual reset or enabling devices.

The real novelty is not only the presence of new formulas. The novelty is the change of approach: it is necessary to demonstrate that the distance chosen is consistent with the risk, with the safety function, with the overall response time and with the real way in which a person can approach the danger.

scope: what falls in and what remains excluded

EN ISO 13855:2024 addresses the positioning of safeguards in relation to the approach of the human body, or parts of it, towards a hazard zone. The standard no longer considers only the approach speed of parts of the body, but the way a person may reach an area in which the risk must be reduced before contact or access occurs.

The standard covers the positioning of ESPE detection zones, AOPD, two- or three-dimensional AOPDDR, vision-based protective devices, pressure-sensitive mats and floors, two-hand controls, single controls and interlocked guards; the widening of the application landscape is important because it moves the attention from a single category of device to the function carried out by the device in the safety system.

Some cases remain outside such as devices that can be moved manually without tools closer to danger, risks from emissions or expulsions of material, radiation, electric arcs, heat, noise, fumes and gases, risks due to mechanical failure or falling under gravity. Distances calculated according to the standard also do not apply to devices used solely for presence sensing, when the function is not to stop or reduce the risk before the person reaches the hazard zone.

From the concept of minimum distance to separation distance

One of the most important terminological changes is the transition from the concept of “minimum distance” to the concept of “separation distance”, indicated with S. The difference is not only linguistic. “minimum distance” could be read as a minimum geometric distance; “separation distance” better describes the technical function: to maintain a sufficient separation between person and danger until the attainment of the expected risk reduction.

S = (K × T) + C

The basic formula remains the same S depends on the approaching speed K, the total time T and the reach distance associated with the protection device, now referred to as DDS. However, the new setting also requires additional Z factors to be considered when the application makes them necessary.

In practice, it is no longer enough to take the stop time of the machine, apply a generic K factor and sum a table value. It is necessary to determine what safety function is, when the risk reduction is reached, which part of the body can be involved, which device detects access, which path the person can perform and which uncertainties must be considered.

The method of calculation: more risks, more paths, more real conditions

Chapter 4 has been rewritten to make the working method clearer. The starting point remains the identification of hazards and the assessment of risks. If there is a C-type standard applicable to the machine, this must be considered first: EN ISO 13855 intervenes to calculate, verify or support the positioning of the protective media when the C-type standard refers to this criterion or does not provide a sufficient specific distance.

The methodology requires considering the real path with which the person can reach the danger: direct, indirect, orthogonal, parallel approach, through openings, above, below, around obstacles or through a combination of protections. This is a significant change for complex machines, because it requires analyzing not only “straight-line distance”, but the shortest actual and reasonably foreseeable route.

Another operating point is the need to use the most conservative value between the applicable ones. If the risk can be achieved in different ways, the designer should consider the case requiring a greater separation distance or take additional physical measures to exclude certain paths. The standard therefore makes the relationship between calculation, layout and guard design more explicit.

Response time T: from stop measure to reduction of expected risk

EN ISO 13855:2024 definitively abandons the simplified idea of “stop time” as the only parameter. The central parameter is the overall system response time T: the time between activation of the detection or control function and the time when the expected risk reduction is achieved. This does not always coincide with the complete stop of the machine, but if it is not possible to accurately demonstrate when the risk is reduced, the prudent criterion remains to consider the complete stop.

Time T must include every relevant contribution: the protective device response time, SRP/CS or SCS logic, outputs, energy dissipation, mechanical response, inertia and, where necessary, tolerance factors associated with degradation or variability in machine performance. This is particularly important for pneumatic, hydraulic and servo-driven machinery, machines with variable-speed drives, and applications with controlled stops.

For a manufacturer it means that the value used in the calculation cannot be a generic data taken from the catalog. It must be demonstrated through calculation, measurement or combination of the two, considering the worst credible conditions.

Additional factors Z and application uncertainties

The new edition of the standard gives much more weight to the additional factors Z; these factors serve to incorporate in the calculation the uncertainties and conditions of application that can reduce the effective safety distance.

Among the factors to consider include general device measuring errors, machine position uncertainty, person position uncertainty, reflection-related errors, insufficient ground clearance for vehicles or mobile machines and reduction of braking torque over time. If a protected area is managed by laser scanner, vision, AOPDDR or localization systems, the designer must ask how precise the measure is, how stable the position of danger is, how reliable the detection of the person and what tolerances must be added.

Dynamic separation: the key innovation for mobile machines and flexible systems

Dynamic separation is one of the most important technical changes in EN ISO 13855:2024. The standard distinguishes between static and dynamic separation. Static separation is calculated with reference to the furthest boundary of the hazard zone, regardless of the actual position of the hazard when the safety function is activated. Dynamic separation considers the actual position of the hazard and the distance it may travel during time T.

This is essential for mobile machines, shuttles, industrial vehicles, automatic axes, robots and flexible systems. If the danger moves towards the person, the distance must take into account not only the movement of the person towards danger, but also the movement of danger to the person.

For applications where the direction of a person’s approach is not known, the standard introduces the SM contribution, i.e. the displacement of the machine or hazardous part during the overall response time. If acceleration and deceleration are known, they can be used in the calculation; if deceleration is not known, the approach becomes prudent and an unfavorable value must be assumed. If SM is determined by measurement, it is necessary to add an application tolerance and validate the result.

Two-handed controls and single controls

EN ISO 13855:2024 devotes more attention to manually actuated control devices. For two-hand controls, it is necessary to distinguish whether or not the device prevents the encroachment, i.e. the advancement of the body or the limbs towards danger during actuation. If the two-hand control does not prevent approaching, the calculation must include an associated reaching distance. If the encroachment is eliminated by design, shielding, orientation or protection, the contribution can be reduced according to the criteria of the standard.

The most obvious novelty is the introduction of specific requirements for single control devices. A single hand-operated control or foot pedal cannot be treated as if it had the same level of segregation of a two-hand control. The standard considers the distance between actuator and hazard zone and introduces dedicated criteria for manual controls and pedals. The technical message is clear: if the operator can control the movement and at the same time reach the hazard zone, the position of the command becomes part of the protection measure.

This applies for example to jog, hold-to-run commands, manual feeding, cycle activation, functional resets or tool controls. In these cases the designer must verify that the command cannot be operated by a position from which it is possible to reach the danger before the risk reduction.

Reappeared interlocked and guard locking

The standard considers that a guard can open partially before the interlocking device activates the safety function. In that short interval, the person can already create a sufficient opening to introduce finger, hand, arm or body.

For interlocked guards without locking, separation must be determined by considering the distance between the edge of the opening and the hazard zone, the speed of approach and the distance of reaching through the opening, to be evaluated in relation to EN ISO 13857. It is then necessary to consider size, shape and position of the real opening before the activation of the interlock.

For guard locking guards, if the time of release of the locking is less than the total time T, the distance must however prevent access to the hazard zone before reaching the reduction of the expected risk. The locking is therefore not a “shortcut”: it is effective only if the release time, the distance and the safety function are consistent.

Technical details of changes relevant to the chapter

Below is a technical reading of the changes to be considered in the design, validation and document update. The values and formulas shown are indicative to guide technical work; the final design calculation must always be carried out on the official text of the standard and on the actual configuration of the machine.

Reasoned application examples

Example 1 – Laser scanner on mobile shuttle or AMR in production area

Scenario: a mobile shuttle transports semi-finished products on an automated line. The protection is entrusted to a laser scanner with dynamic fields that vary according to speed. With 2010 logic, attention could focus on a fairly static stop distance. With 2024 the reasoning must be more complete.

The machine moves, so the danger is not fixed. It is necessary to consider the current position of the shuttle, its speed, the real deceleration, the response time of the laser scanner, the safety logic, the drive and the mechanical part. If the direction of approach of the person is not known, it is necessary to consider the SM contribution: the shuttle continues to travel a certain distance during the T time. Z factors must also be evaluated: laser scanner uncertainty, position accuracy, reflections, ground clearance and decay of braking capacity.

Technical conclusions: it is not enough to declare “the scanner field = stop distance + margin”. It requires a validation of dynamic separation under the worst credible conditions, with evidence in the technical file and consistent tests with speed, load, floor, slopes, wear and environmental conditions.

Example 2 – Packaging line with vertical photoelectric barrier and external reset

Scenario: a packaging line is protected by a vertical photoelectric barrier. Within the protected area there are multiple access points and a reset/manual enable device is installed close to the edge of the protection. The new EN ISO 13855:2024 requires not only to look at the distance between barrier and hazardous moving part.

It should be checked whether the operator can reach the danger above, below or through the detection zone. If access is possible by circumventing an obstacle, it should be considered the shortest real path. If a SRMCD can be reached within the protected space, the reset must be treated as a safety-related element: its position must prevent actuation from a hazardous or obscured position.

Technical conclusions: the layout must demonstrate both the S distance to the dangerous area and the impossibility to act reset/start/enable from the inside of the protected space or from a location from which you do not see the affected area. In many cases the correct modification is not “increasing the barrier”, but repositioning resets, integrating fixed guards, eliminating indirect paths and validating the real T time.

Example 3 – Interlocked repair on tool zone with partial opening

Scenario: a machine has an interlocked guard without guard locking. The sensor is mounted in such a way that the guard can open a few centimeters before the safety function is activated. With the new EN ISO 13855:2024 this condition must be explicitly assessed.

The designer must calculate the real opening available before the implementation of the interlock. If the opening allows the introduction of fingers or hands, it is necessary to determine the distance to reach through the guard according to EN ISO 13857 and to verify that the hazard zone is not reachable before the reduction of the risk. If the guard is operated by a rotary cam, the width of the guard, the thickness and angle of implementation become relevant technical parameters.

Technical conclusion: the positioning of the sensor and the mechanics of the guard become part of the safety calculation. A seemingly “mechanical” choice can turn into a non-conformity if it allows access to danger before the safety function has effect.

Checklist for designers and manufacturers

1. Check if the machine is covered by a type C standard and if it sends back to EN ISO 13855:2024.
2. Identify any hazard zone and any reasonably foreseeable route to the area.
3. Define whether separation is static or dynamic.
4. Classify the approach: orthogonal, parallel, angled or indirect.
5. Establish which part of the body should be detected or kept out of the hazard zone.
6. Calculate S with K, T, DDS and Z, documenting the hypotheses.
7. Measure or calculate T under the worst credible conditions, not in ideal conditions.
8. Evaluate measuring uncertainties, reflections, machine/personal position and brake decay.
9. Check access above, below, through and around the protections.
10. Check the reset location, start, enable, unblock guards and other SRMCDs.
11. For mobile or SSC systems, validate the dynamic separation and sampling of the system.
12. For interlocked guards, consider opening before implementation and possible time to release the guard locking.
13. Update instructions for use, technical file, safety schemes, stop tests and validation of the Performance Level/SIL where applicable.

Frequently avoided errors

How Waves Engineering supports manufacturers and supplements

Waves Engineering supports machinery manufacturers, integrators and industrial companies in verifying safety distances under EN ISO 13855:2024. The work covers both technical and documentary aspects: layout analysis, hazard-zone identification, verification of safeguards, calculation or measurement of response times, assessment of access paths and updating of the technical file.

The service is particularly useful when designing new machines, changing an existing line, replacing barriers or laser scanners, introducing robots, shuttles, AGV/AMR or systems with speed and separation control. In these cases the risk is not only wrong: the risk is to build an apparently correct but not demonstrable protective measure according to the state of the art.

An early assessment helps reduce rework, issues during acceptance testing, CE-marking problems and difficulties with the end customer, HSE team or inspection bodies.

4. Suggested internal links

• Risk assessment according to EN ISO 12100
• Performance Level calculation EN ISO 13849-1
• Technical Paper Machine according to Machinery Regulation
• CE marking machines and automatic lines
• Check safety control systems PLC and safety functions
• Safety packaging lines and end-of-line system
• Substantial modification of a machine

FAQ

EN ISO 13855:2024 replaces EN ISO 13855:2010?

Yes, the new 2024 edition replaces the previous EN ISO 13855:2010. However, national adoption and any citation in the EU Official Journal must be checked for the purposes of the presumption of conformity.

Does the safety distance always change?

No. It changes when the new method leads to consider previously unvalued factors: real direction of approach, uncertainties, dynamic hazards, SRMCD, interlocked guards, single commands or unfinished response times.

Is time T equal to time of arrest?

Not necessarily. T is the total time until the expected risk reduction is achieved. It can coincide with the complete stop, but it can also be different if the risk reduction is demonstrable before the complete stop.

Does the standard apply to laser scanners?

Yes, the standard also treats AOPDDR, including devices with two-dimensional and three-dimensional detection zones, and provides criteria for parallel, dynamic, mobile approach and additional factors.

Does the standard apply to resets?

Yes, when a reset or other manual control is safety-related and its actuation can immediately increase the risk, it should be evaluated as SRMCD and positioned in a manner consistent with the standard.

Interlocked guards now require a distance calculation?

In several cases, yes. If the guard can open before the interlocking activates the safety function, it is necessary to check that the hazard zone is not reachable before the reduction of the expected risk.

Is EN ISO 13855:2024 enough to declare a machine compliant?

No. It is a standard of type B1: it supports the positioning of protection devices, but it must be integrated with risk analysis, type C standards, device standards and requirements of the applicable legislative framework.