Approach
How quickly could a person reach the danger?
The positioning method accounts for defined approach behaviour. The exact method depends on the safeguard type and how access can occur.
Safeguard positioning and stopping behaviour
ISO 13855:2024 safeguard positioning and separation distances.
A practical guide for engineers deciding where interlocking guards, light curtains, scanners, pressure-sensitive equipment and safety-related manual controls should sit in relation to a hazard.
Understanding the standard
What is ISO 13855?
ISO 13855:2024 specifies requirements for positioning and dimensioning safeguards in relation to the approach of the human body or its parts toward a hazard. In practical terms, it connects the safeguard location with approach assumptions, the safety system’s response and the machine’s stopping behaviour.
Response
How long does the safety function take to respond?
Device detection, signal processing and other safety-system response times contribute to the total time used for positioning decisions.
Stopping
How long before the hazardous condition is gone?
A stop command is not the same as an immediate safe state. Actual machine stopping performance is part of the separation-distance assessment.
Where engineers use it
Safeguards covered by ISO 13855:2024
The 2024 edition covers several safeguard families. Each has different geometry, detection behaviour and ways a person may approach or remain within the safeguarded space.
Interlocking guards
Positioning has to account for access through a movable guard and the time required for the safety system and machine to reach the defined condition.
See ISO 14119 interlocking guidanceLight curtains and light grids
The detection zone must be positioned so the protective function acts before the approaching person can reach the hazard.
Laser scanners and other ESPE
Detection-field dimensions, approach direction, response time and the possibility of stepping into or remaining in the protected area all matter.
Pressure-sensitive mats and floors
The sensing area and its position are assessed against the approach path and the time required to remove the hazardous condition.
Two-hand control devices
Positioning helps prevent a person from releasing the controls and reaching the hazard before the protective objective is achieved.
Safety-related manual controls
The 2024 edition also addresses the positioning of specified safety-related manual control devices from within the safeguarded space.
A practical engineering workflow
Separation distance is measured, calculated and then verified.
A catalogue dimension cannot replace machine data. Build the decision from the actual hazard, safeguard and stopping performance.
01 — Define
Identify the hazardous condition
Locate the danger points and define what condition must be removed or controlled before access.
02 — Measure
Establish stopping performance
Use suitable measurement and include the relevant response of the protective equipment and control system.
03 — Position
Apply the relevant methodology
Select the provisions for the safeguard type, approach direction and foreseeable access route.
04 — Validate
Confirm the installed result
Verify dimensions, response, stopping behaviour and potential routes around, over, under or behind the safeguard.
Common layout failures
Why a correct drawing can become an incorrect installation
Safeguard positioning is vulnerable to small late-stage changes. A relocated sensor, added conveyor, slower stop or altered access route can change the engineering basis.
Using estimated stopping time
Assuming the machine stops “quickly” can understate the separation required. Actual stopping performance should be established and rechecked where conditions can change.
Measuring to the wrong reference point
The useful measurement is between the relevant safeguard position and the nearest hazard that the person could reach—not a convenient machine frame or drawing datum.
Ignoring alternative approach paths
People may reach around a fence end, step over a scanner field, enter through a conveyor opening or remain inside a cell after another access point closes.
Treating modifications as cosmetic
Tooling, speed, braking, control logic, floor level and device replacement can affect the original positioning assessment.
Do not confuse the two
ISO 13855 and ISO 13857 answer different distance questions.
ISO 13855: approach and stopping
Used to position safeguards so their protective action occurs before an approaching person can reach the hazard, considering response and stopping behaviour.
View ISO 13855:2024 at ISOISO 13857: reaching through space
Provides safety-distance values intended to prevent upper or lower limbs reaching a hazard over, under or through protective structures.
Read our ISO 13857 guideFrequently asked questions
ISO 13855 questions from machine projects
What is a separation distance?
It is the positioning distance used so a safeguard’s protective action can occur before an approaching person reaches the hazard, based on the applicable methodology and the complete response and stopping behaviour.
Does ISO 13855 give one distance for every light curtain?
No. The result depends on the safeguard, approach, response time, stopping performance and other factors defined by the standard. It must be determined for the application.
Does ISO 13855 apply to interlocked gates?
Yes. The 2024 edition includes positioning requirements for interlocking guards. ISO 14119 separately addresses the associated interlocking devices.
Should stopping time be measured again?
Rechecking is prudent after changes that can affect stopping or response, and as part of the inspection and validation approach established for the machine.
Can physical fencing and electro-sensitive protection be combined?
Yes. Many systems combine perimeter guarding with gates, light curtains or scanners at controlled openings. The interfaces and complete safety functions should be assessed together.
Practical information only. This page does not replace ISO 13855:2024, stopping-time measurement, a machine-specific risk assessment, competent engineering advice or applicable legal requirements.
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