{"id":32074,"date":"2026-08-20T07:00:55","date_gmt":"2026-08-20T05:00:55","guid":{"rendered":"https:\/\/www.accessafe.eu\/?p=32074"},"modified":"2026-07-24T11:35:08","modified_gmt":"2026-07-24T09:35:08","slug":"en-iso-13855-2024-safety-distances-stopping-time","status":"publish","type":"post","link":"https:\/\/www.accessafe.eu\/en\/en-iso-13855-2024-safety-distances-stopping-time\/","title":{"rendered":"Stopping time changes everything: what EN ISO 13855:2024 introduces into the calculation of Safety Distances"},"content":{"rendered":"\t\t
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Stopping time changes everything<\/h1>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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What EN ISO 13855:2024 introduces into the calculation of Safety Distances<\/h2>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t
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The Safety Distance depends on what actually happens<\/h2>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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The Safety Distance is calculated, verified, documented. Then the machine undergoes a maintenance operation. Or a component wears out. Or the control software is updated. The stopping time changes. The distance calculated at commissioning may no longer be valid.<\/p>\n

EN ISO 13855:2024<\/strong>, which defines the criteria for positioning safeguards with respect to the approach of the human body to hazard zones, does not only change the calculation formula. It changes the way stopping time is conceived and managed, requiring its assessment and control across the entire machine lifecycle.<\/p>\n

The standard applies to safety light curtains, laser scanners, pressure-sensitive mats, two-hand control devices and interlocked guards<\/strong>: all safeguards that act before the operator can reach the hazard zone.<\/p>\n\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t

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The formula and the parameter that governs everything<\/h2>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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The separation distance is defined by the formula:<\/p>\n\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t

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S = (K \u00d7 T) + DDS + Z<\/p>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t

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S is the Safety Distance. K is the approach speed. T is the overall response time of the system. DDS is the reaching distance associated with the protective device. Z gathers the correction factors specific to the scenario.<\/p>\n

The significant change is not in the structure of the formula. It is in the parameter T: EN ISO 13855:2024<\/strong> requires a systemic reading of the entire functional safety chain. T is not the response time of the individual sensor. It is the overall time that elapses between the detection of the hazardous condition and the machine reaching the safe state.<\/p>\n

Every link in the chain, detection, signal processing, mechanical action, contributes to the value of T. If one of these links changes, T changes. And with T, S changes.<\/p>\n\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t

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Contextual distances: the direction of approach changes everything<\/h2>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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The standard abandons the idea that the Safety Distance is a single, invariable value.<\/p>\n

EN ISO 13855:2024<\/strong> distinguishes scenarios in which the direction of approach to the hazard zone is known from those in which it is not predictable. The standard recognises that approach is not a uniform event: it varies with the geometry of the installation and the operating modes.<\/p>\n

In open areas, robot cells or installations with multiple access points, the direction of approach is not controlled. The Safety Distance must be dimensioned for the most critical case.<\/p>\n

The Safety Distance<\/strong> is no longer a geometric parameter derived from an ideal situation: it must be consistent with the real configuration of the machine-operator system<\/strong>.<\/p>\n\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t

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From point-based systems to protection volumes<\/h2>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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Modern electro-sensitive protective equipment<\/strong> (ESPE) no longer detects a point or a line: it detects a volume<\/strong>.<\/p>\n

3D laser scanners, integrated vision systems and advanced area sensors work on three-dimensional protective fields with dynamic triggering logic.<\/p>\n

EN ISO 13855:2024 incorporates this conceptual evolution<\/strong>: the shift from logic based on a detection point or line to logic based on a dynamic safety volume.<\/p>\n

In this context, distance is no longer just a geometric parameter. It must be assessed with respect to the real shape of the protective field and its triggering logic. A 3D field that adapts to the operator’s posture requires a different calculation approach from a single-beam light curtain.<\/p>\n\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t

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The response time also includes the operator<\/h2>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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The standard updates the criteria for two-hand control devices and single control devices, and for the position of interlocked guards. It also specifies the requirements for the positioning of safety-related manual control devices (SRMCD).<\/p>\n

The central element is not only the revision of the calculation criteria. It is the recognition of the variability of human behaviour.<\/p>\n

In real conditions, the operator’s intervention time is not constant: workstation ergonomics, operating frequency, fatigue, machine layout and production context directly affect the response of the human-machine system.<\/p>\n

This leads to a more realistic modelling of the overall response time, which must include not only the technical system but also the human component.<\/p>\n\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t

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The protected space as a dynamic relationship<\/h2>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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EN ISO 13855:2024<\/strong> introduces a more rigorous definition of the concepts of protected space and access to hazard zones<\/strong>.<\/p>\n

The focus shifts from physical distance alone to the relationship between available space, possibility of access and the state of the safety function. Concepts such as whole body access, reachability from different positions and the relationship between the hazard zone and the dynamic state of the system are clarified.<\/p>\n

This approach reduces the interpretative ambiguities present in previous versions and reinforces a systemic view of machine safety: safety is not a property of the individual device, but a relationship between the installation, the operator and the operating conditions.<\/p>\n\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t

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\n\t\t\t\t\tFurther reading<\/span>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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Stopping time is not a fixed value<\/h2>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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This is the point that EN ISO 13855:2024 places at the centre.<\/p>\n

The parameter T is the central element of the model.
The Safety Distance<\/strong> depends directly on the time needed for:<\/p>\n\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t

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