This calculator determines the required safety distances EN ISO 13857 (reaching over, around and through hazard zones) sets for the design of protective structures.
Safety distances under EN ISO 13857: guards, openings and reaching zones
How tall does a safety fence need to be? How far may a grille stand from the hazard point if the mesh size is 20 mm? And from what opening size does not just a finger but the whole arm fit through? EN ISO 13857 answers these questions not with a formula but with tables: it specifies the safety distances that must be maintained so that hazard zones cannot be reached with the upper and lower limbs.
The calculator below outputs the table values for the four practically relevant cases – reaching over protective structures, reaching through openings with the upper and with the lower limbs, and reaching around obstacles – together with a highlighted table extract and a print-ready calculation sheet.
The difference from EN ISO 13855
Both standards determine safety distances, but for different reasons. EN ISO 13855 calculates with time: it ensures that a hazardous movement has stopped before the hand reaches it. EN ISO 13857 calculates with the body: it ensures that the hazard point cannot be reached by design at all – regardless of whether the machine is running or stopped. For fixed guards, EN ISO 13857 is therefore authoritative; for non-contact safeguards, EN ISO 13855 is. On many machines the two interlock: a light curtain that can be reached over is correctly positioned according to 13855 and yet ineffective.
Reaching over protective structures
The most common application is the safety fence. Three dimensions determine the result: the height of the hazard zone above the reference plane (a), the height of the protective structure (b), and the horizontal distance between the two (c). The standard distinguishes between low and high risk: at low risk, a hazard zone from a height of 2500 mm is considered unreachable; at high risk, only from 2700 mm.
Two rules are regularly overlooked here. First, protective structures below 1000 mm in height are not included in the tables at all, because they do not sufficiently restrict body movement – below 1400 mm they should not be used without additional measures. Second, table values must not be interpolated: if a value falls between two table values, the value that gives the higher safety must be chosen.
The reference plane is the most common mistake
a and b are measured from the plane on which people can actually stand. An operating platform, a step, a stored pallet, or a fixed access point next to the fence shifts this plane upwards – turning a 2000 mm high fence into, in effect, a 1200 mm high one. In modification assessments, this is, from experience, the most common finding.
Reaching through openings
For grilles, perforated sheets, expanded metal and slots, the following applies: the opening width e, as the smallest dimension of the opening, is decisive, and the shape also plays a role. A slot 25 mm wide requires an 850 mm distance, whereas a square of the same width requires only 120 mm – because the arm can be guided within the slot. However, if the slot is no longer than 65 mm, 200 mm is sufficient. Above an opening width of 120 mm, the table no longer applies; the distances for reaching over then apply instead.
For low-level openings, the standard contains a separate table for the lower limbs – from the tip of the toe to the leg. It applies only as long as access by the whole body is excluded: slots above 180 mm and square or circular openings above 240 mm allow the whole body through and require an access guard. Both tables must always be checked for the same opening – the larger distance is decisive.
Reaching around obstacles
If arm movement is restricted by the structure, the required distance decreases: from 850 mm with free movement to 550 mm if the arm is supported up to the elbow, to 230 mm up to the wrist, and to 130 mm up to the root of the finger. However, these reduced values only apply if the restriction is permanent and cannot be bypassed – an edge that can be bypassed through a different body posture does not restrict anything.
Frequently asked questions
Which edition of EN ISO 13857 applies?
Currently applicable is EN ISO 13857:2019 (in Austria ÖNORM EN ISO 13857, in Germany DIN EN ISO 13857:2020-04). ISO reviewed this edition in March 2025 as part of its systematic review and explicitly confirmed it – a newer version is currently neither published nor in preparation. Compared with the 2008 edition, the standard was mainly revised editorially and aligned with ISO 12100; the table values are unchanged. New is the provision on whole-body access.
Do the values also apply to children?
The values output by the calculator apply to persons aged 14 and over. If access by children from age 3 is possible – for example at publicly accessible installations – the standard contains its own, significantly stricter values for the upper limbs.
May table values be interpolated?
No. If a or b falls between two table values, the value giving the higher safety must be used. The calculator applies this rule automatically and indicates which table row and column were used.
What applies for irregular openings?
The opening width must be determined as the smallest dimension of the cross-section. If different shape assumptions lead to different results, the least favourable one is decisive – that is, the one with the greatest safety distance.
Support with implementation
Whether a safety fence is sufficient, whether a guard has the correct mesh size, or whether a new conformity assessment is due after a modification, is decided in the risk assessment. 4S – Safety Services prepares risk assessments under the Machinery Directive or, from 20 January 2027, the Machinery Regulation (EU) 2023/1230, supports CE conformity, carries out validation after measures have been implemented, and prepares the technical documentation. For the transition to the Machinery Regulation (EU) 2023/1230, we offer the MVO Readiness Check as a one-day on-site analysis.
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4S – Sascha Steinkrauß Safety Services e.U., 1230 Vienna · 4S@4S.at · +43 664 9123780
Note: The calculator reproduces table values from EN ISO 13857 and replaces neither the risk assessment nor case-by-case verification. Only the wording of the standard is authoritative.
See also: Calculate safety distance under EN ISO 13855 – for light curtains, laser scanners and two-hand control devices.
Are you delivering machinery into German-speaking markets (Germany, Austria, Switzerland)? 4S can also act as your German-speaking point of contact on site and support the entire project from a safety-engineering perspective. Technical documents are prepared directly in German or English; a Spanish or Swedish version is translated on request.