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Machinery Safety Distance & Light Curtain Sizer

Ensure machine movement comes to a complete standstill before an operator can reach the hazardous point of operation. This tool calculates the statutory minimum safety distance S = (K × T) + C under BS EN ISO 13855:2010, factoring in optical beam resolution, stopping times, and brake wear.

Statutory ISO 13855 Rule: Hand approach speed is initially evaluated at K = 2000 mm/s. If the calculated distance exceeds 500 mm, K = 1600 mm/s may be used, provided the final distance does not fall below 500 mm.

1. Safeguard Type & Approach ModeSafeguarding Mechanism

Optical Beam Resolution (d)Manufacturer stated optical pitch / detection capability.

2. Machine & Safeguard Stopping Time (T)Safeguard & Safety Controller Response Time (t1)Output Signal Switching Device (OSSD) + safety relay de-energise time (ms).Machine Mechanical Braking / Stopping Time (t2)Time from trip signal until hazardous motion has completely ceased (ms).Brake Wear & Aging Safety FactorAccounts for mechanical friction brake pad wear and valve lag.

Safety Distance Evaluation

Minimum Safety Distance (S)CALCULATING...

Effective Approach Speed (K)-

Total Design Stopping Time (T)-

Penetration Factor (C)-

Formula Breakdown-

Evaluating ISO 13855 safety distance...

Hazard Point-Optical Sensing Plane

0 mm (Danger)500 mm (Speed Knee)1000+ mm

Show Full Mathematical Derivation (AM2 Working Standard)

BS 7671:2018+A4:2026

AM2 PORTFOLIO & DESIGN AUDIT FORMATTRANSPARENT FIRST-PRINCIPLES MATHS

Worked Example & Engineering Rationale

Scenario: A hydraulic press is safeguarded by an optical light curtain with 14 mm finger resolution.

Controller Response (t1): 20 ms.
Hydraulic Valve & Ram Stopping Time (t2): 140 ms with a +10% brake wear factor: 140 × 1.10 = 154 ms.
Total Stopping Time (T): 20 ms + 154 ms = 174 ms (0.174 s).
Penetration Factor (C): For 14 mm resolution, C = 8 × (14 - 14) = 0 mm.
Initial Calculation at K = 2000 mm/s: S = (2000 × 0.174) + 0 = 348 mm.
ISO 13855 Rule Check: Since 348 mm ≤ 500 mm, K cannot be lowered to 1600 mm/s. The light curtain must be positioned at an exact physical distance of ≥ 348 mm from the pinch point.

Optical Reset & Continuous Presence: If an operator can step entirely between the light curtain detection plane and the hazard zone, optical trip alone is insufficient. Secondary horizontal safeguarding beams, safety laser scanners, or a manual latching reset button outside the danger zone are mandatory.

Statutory Standards: BS EN ISO 13855:2010 Section 6.2 • BS EN ISO 13857:2019 Table 2 • BS EN 60204-1:2018