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Protection Distance Calculator (NOHD)

Estimate Nominal Ocular Hazard Distance against current laser safety references

Input Parameters

NIR laser - MPE: 10.0 mW/cm²

Continuous output (welding, cutting)

Typical: 5-15 mrad for industrial lasers

Enter parameters and click Calculate to see safety zones

Laser Safety Standards Comparison

International MPE and classification guidelines

StandardRegionMPE BasisKey Differences
GB/T 7247.1-2024ChinaCorneal exposureMore conservative for UV, stricter training requirements
ANSI Z136.1USACorneal + retinalStandard reference, widely adopted, detailed NHZ calculations
IEC 60825-1InternationalHarmonized EUProduct classification focus, CE marking requirement
ISO 11553InternationalMachine safetyCovers laser processing machines specifically

Note: MPE methods are broadly aligned across major references, but local rules, laser configuration, and machine design still govern the final safety plan. This calculator uses conservative planning values rather than a release approval.

Understanding NOHD (Nominal Ocular Hazard Distance)

NOHD is the distance beyond which the laser exposure is below the Maximum Permissible Exposure (MPE) for eye safety. This planning estimate is compared against GB/T 7247.1-2024, ANSI Z136.1-2022, and ISO 11553-1:2020 reference concepts. Final hazard zoning still depends on the full machine and facility controls. Use the GB 7247 laser safety planning map to connect this distance estimate to product classification, enclosure, PPE, and workplace checks.

Safety Zone Marking

  • Controlled zone (inside the calculated NOHD): Treat as a controlled-access area with barriers, eyewear, and written controls.
  • Review zone (outside NOHD but near the work area): Check reflections, service access, warning signs, and supervision.
  • Release zone: Mark only after enclosure, beam path, and site procedures have been reviewed.

Laser Classification System

  • Class 1: Product classification used when accessible emission is controlled within the applicable limit.
  • Class 2: Visible-laser classification with assumptions that must be checked against the standard.
  • Class 3R: Direct viewing may be hazardous; use the product documentation and standard basis.
  • Class 3B: Direct viewing is hazardous and requires controlled-use planning.
  • Class 4: High-hazard classification requiring enclosure, access, fire, skin, and reflection controls.

Wavelength-Specific Hazards

UV Lasers (200-400nm):

  • Absorbed by cornea and lens - cataract risk
  • Skin damage (sunburn-like) possible
  • Lower MPE due to photochemical damage

Visible Lasers (400-700nm):

  • Focused on retina - burn risk
  • Do not use blink-response assumptions as the primary control for welding work.
  • Green (532nm) most visible, appears brighter than same power red

Near-IR Lasers (700-1400nm):

  • Invisible near-IR sources can create retinal hazard without a visible warning cue.
  • Aversion-response assumptions should not be used as the primary control.
  • Verify wavelength, power, beam delivery, and eyewear documentation for the actual source.

Far-IR Lasers (1400nm+):

  • Absorbed by cornea and water in eye (CO₂ at 10.6μm)
  • Lower retinal risk but corneal burn possible
  • Higher MPE than visible/near-IR

Factors Affecting NOHD

  • Laser Power: Higher delivered power normally increases the calculated hazard distance.
  • Beam Divergence: Divergence changes how quickly irradiance falls with distance.
  • Wavelength: Different wavelengths use different exposure-limit bases.
  • Exposure Duration: Exposure time changes the applicable MPE basis.
  • Beam Quality (M²): Beam delivery and focus behavior should be verified on the actual optics.

Eye Protection Selection

Optical Density (OD) indicates the attenuation factor: OD 5 = 10⁵ = 100,000× reduction.

Verify eyewear documentation covers:

  • Specific wavelength with an approximately 50 nm tolerance band
  • Correct OD rating for maximum laser power
  • Continuous wave or pulsed operation
  • Sufficient Visible Light Transmission (VLT) for task visibility

Safety Planning Note:
Do not rely solely on calculations. Review multiple safety barriers: beam enclosure, interlocks, warning labels, training, and supervision. NOHD calculations assume direct beam exposure - scatter and reflections can extend hazard zones.

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