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Safeguarding

Light Curtain Safety Distance

A light curtain has to sit far enough from the hazard that the machine can stop before a person reaches it. ISO 13855 calls that the separation distance.

This page calculates one case only: a vertical curtain, approached straight on, with a person reaching through the beams, and a detection capability of 40 mm or less. The formula is S = (K × T) + C. T is the machine stopping time plus the curtain response time. C is 8 × (d − 14) millimetres, and not below 0. K starts at 2,000 mm/s. If S is above 500 mm, calculate again with K = 1,600 mm/s. If that second result is 500 mm or below, use 500 mm. When the first result stays on K = 2,000 mm/s, S is at least 100 mm.

ISO 13855:2024 also covers reaching over, under, and around, coarser detection, and supplemental distances this page does not calculate. A full assessment can require a longer distance than the number here. This result is for planning only. A qualified safety assessment is required before anyone specifies or installs a curtain, a fence, or a robot cell. Innovation Peer does not perform that assessment.

Every number in the fields is an example input. Replace it with a figure from your plant. Nothing you type is saved.

Formula

  • S = (K × T) + C
  • T = machine stopping time + curtain response time
  • C = 8 × (d − 14), and C is at least 0, when d is 40 mm or less
  • K = 2,000 mm/s, or 1,600 mm/s when the first S is above 500 mm

Worked example

  1. Example inputs: machine stopping time 300 ms, light curtain response 15 ms, detection capability 30 mm, and 0 mm of extra distance.
  2. T = (300 + 15) ÷ 1,000 = 0.32 s.
  3. C = 8 × (30 − 14) = 128 mm.
  4. First pass, K = 2,000 mm/s: S = 2,000 × 0.32 + 128 = 758 mm. That is above 500 mm, so the approach speed steps down.
  5. Second pass, K = 1,600 mm/s: S = 1,600 × 0.32 + 128 = 632 mm. That stays above 500 mm.
  6. Planning separation distance: 632 mm, rounded up to the next millimetre.

Calculator

The fields open on the worked example. Change a number and the result updates.

Example inputs. Replace them with your figures.

The time from the stop command until the hazard has ceased. Example input.

From the device data sheet. Example input.

This planner accepts 40 mm or less.

Example input. Leave at 0 unless a safety engineer has given you a supplement.

Related calculators

Questions

Can I install a curtain at this distance?

No. The number is a planning estimate of one formula in ISO 13855, for a straight-on approach through a curtain with detection capability of 40 mm or less. It leaves out reaching over, under, or around, coarser beams, and supplemental distances in ISO 13855:2024. A qualified safety assessment is required.

What do S, K, T, and C mean?

S is the separation distance in millimetres. K is the approach speed from the standard, 2,000 or 1,600 millimetres per second. T is stopping time plus curtain response time, in seconds. C is the extra distance from the detection capability. d is that detection capability in millimetres.

Free Automation Project Review

If you are still choosing between a fence, a curtain, and a collaborative application, the distance is only one input. A free project review can help you describe the task a safety assessor will need. It is not a risk assessment and not a safeguarding design.

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