ISO 13855 safety distance calculator
Authoritative & engineer-ready. Compute the minimum separation distance S between a hazardous motion and a protective device (e.g., safety light curtain), using ISO 13855: S = K × T + C. Includes worked examples, a printable record table, and a commissioning checklist.
Calculator
Pick the conservative value applicable to your risk scenario.
For finger protection, d=14 mm is common.
Optional margin for repeatability, mounting tolerances, etc.
Measured with a stop-time meter (include worst-case).
From datasheet; add cable/IO latency if specified.
Using K=2000 mm/s, T=0.230 s (from 200+20+10+0 ms), C=0 mm (from resolution d=14 mm), extra=0 mm, floor ≥100 mm applied.
Formula & constants (ISO 13855)
| Term | Meaning | Typical value / rule |
|---|---|---|
| S | Required safety distance | S = K × T + C |
| K | Approach speed | Hand/arm: 2000 mm/s; Whole-body: 1600 mm/s |
| T | Total response time | T = (Tstop + TESPE + Tlogic + Tother) / 1000 s |
| C | Additional distance | For light curtains: C = 8 × (d − 14) mm when d > 14 mm; otherwise 0. Add Cextra if needed. |
| Floor | Minimum distance | Common engineering practice uses S ≥ 100 mm (selectable in the calculator). |
Worked examples
Example A — Finger protection, press brake
K=2000 mm/s, d=14 mm ⇒ C=0; Tstop=180 ms, TESPE=18 ms, Tlogic=10 ms. No extra margin.
T = (180+18+10)/1000 = 0.208 s
S = 2000 × 0.208 + 0 = 416 mm → apply floor ≥100 mm ⇒ 416 mmExample B — Hand protection, conveyor line
K=2000 mm/s, d=30 mm ⇒ C=8×(30−14)=128 mm; Tstop=220 ms, TESPE=20 ms, Tlogic=10 ms, margin 20 mm.
T = (220+20+10)/1000 = 0.250 s
Base: S = 2000 × 0.250 + 128 = 628 mm
Add margin 20 mm ⇒ 648 mmExample C — Whole-body approach, robot cell
K=1600 mm/s (body), d=40 mm ⇒ C=8×(40−14)=208 mm; Ttotal=300 ms.
T = 0.300 s
S = 1600 × 0.300 + 208 = 688 mmPrintable record (copy to CSV)
Machine/Line,Device,Location,Approach(K mm/s),Resolution d (mm),Tstop (ms),TESPE (ms),Tlogic (ms),Tother (ms),Cextra (mm),S (mm),Date,By,Notes
,,,,,,,,,,,,
Commissioning & periodic verification
- Stop-time measured with a calibrated meter; worst-case recorded.
- Resolution d and protective height documented; device type (Type 4/PL e) verified.
- Reset is edge/two-stage; no auto-restart.
- EDM feedback from K1/K2 present; reset blocked on welded contactors.
- Mounting tolerances reviewed; added margin (Cextra) justified.
- Signage, cleaning plan, and inspection intervals defined.
FAQ
Why 2000 mm/s vs 1600 mm/s?
ISO 13855 defines approach speeds for different body parts. Use 2000 mm/s for hand/arm, and 1600 mm/s for whole-body approach to a hazard.
What if my ESPE datasheet includes cable delay?
Add any listed delays to TESPE or Tother. The total response time T must represent the worst case.
Do I always need an extra margin?
It is prudent to include a small allowance for mounting tolerances, sensor aging, or repeatability. Document the rationale in the record sheet.