What is ISO 13855?
ISO 13855 is the international standard for positioning safety devices based on the approach of a human body or body part. It provides calculation rules and guidelines for the minimum distance between a detection system (such as a light curtain) and the hazard zone.
The standard ensures that a machine comes to a complete stop fast enough before an operator actually reaches the hazard.
🎯 What is ISO 13855 used for?
| Application | Example |
|---|---|
| Positioning of light curtains | Calculating distance to the hazard based on the machine’s stopping time and reaction time |
| Layout of safety mats | Determining the necessary overlap with walkways and stop zones |
| Distance from area scanner | Placing it so that detection occurs before any risky interaction |
| Validation of existing installations | Checking whether distances still meet the standard after modification or MOC |
📐 Key variables
| Parameter | Meaning |
|---|---|
S |
Minimum distance between detection point and hazard zone (mm) |
K |
Approach speed of body part (mm/s), default = 1600 mm/s |
T |
Total stopping and reaction time of the system (sec) |
C |
Correction factor (e.g. +120 mm for light curtains with resolution >40 mm) |
Basic formula:
S = (K × T) + C
For example: A machine has a stop/reaction time of 0.3 sec and uses a light curtain with coarse resolution:
S = (1600 × 0.3) + 120 = 600 mm
So the light curtain must be placed at least 60 cm before the hazard zone.
📏 Table: typical K values
| Approach type | K (mm/s) |
|---|---|
| Arm or hand | 1600 mm/s (default) |
| Whole person (walking) | 2000 mm/s |
| Foot or leg (mats) | 1600 mm/s |
🛠️ Application examples
| Application | Distance per ISO 13855 |
|---|---|
| Light curtain with 30 mm resolution | S = (1600 × T) + 8 mm |
| Light curtain with 50 mm resolution | S = (1600 × T) + 120 mm |
| Safety mat | Edge of the mat must be at least 1600 × T mm from the hazard |
| Horizontal light curtain | Additional correction factor (e.g. +850 mm) due to the possibility of bending |
Note: pay attention to C values and always use the current version of the standard.
✅ Best practices
- Measure and document T (stop/reaction time) with suitable measuring equipment
- Take account of delays in safety relays or Safety PLC
- Allow sufficient margin in positioning (safety > efficiency)
- Annually verify that the layout still complies (wear, maintenance, reconfiguration)
- Add the measurement report and calculation method to your safety dossier and CE marking
📌 In summary
ISO 13855 provides objective formulas for the safe positioning of detection devices around machines. Indispensable for anyone working with light curtains, scanners and safety mats under the Machinery Directive.