1. Laser safety instruction – 2009
Eric R. Eliel
Leiden University
Laser safety instruction

2. Why instruction? Awareness is all-important!
Applying safety rules is essential for the safety of you
and others!
Not caring for your own safety is one thing, being reckless with someone else’s is criminal.
Laser safety instruction
April 26, 2017

3. Optical What are the dangers? Thermal Electrical Chemical
Associated with optical beam
Optical
Thermal
Associated with apparatus
Electrical
Chemical
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April 26, 2017

4. Laser accident summary
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5. Optical damage Prime victim: the eye Laser safety instruction
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6. Laser safety instruction
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7. Eye: optical properties
Transmission of the vitreous gel + lens
Absorption (red line) by the retina
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8. Eye sensitivity vs. wavelength
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9. Looking into the sun Irradiance at earth surface: 140 mW/cm2.
When you are looking directly at the Sun, the eye collects around 4 mW.
Diameter of sun’s image on retina: 0.16 mm.
Irradiance on retina: 20 W/cm2
Damaged spot on retina from direct viewing of sun
Laser safety instruction
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10. A laser can do much more damage!
Fluorescein angiograph of rabbit retina after laser irradiation
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11. Why is laser more dangerous?
Better beam quality (better spatial coherence) yields smaller spots!
Retinal spot diameter: μm.
Irradiance at retina: 0.5x106 that at cornea.
Laser safety instruction
April 26, 2017

12. Different wavelengthsnm
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13. Laser biological hazards - Eyes
Near Ultraviolet Wavelengths (UV-A) nm
Absorbed in the lens of the eye.
Slow buildup of damage (e.g.; cataracts).
Far Ultraviolet (UVB)  nm and (UVC)  nm
Radiation is absorbed in the cornea.
Snow blindness/welder's flash) will result with high doses.
Visible (  nm) and Near Infrared (  nm)
Radiation is transmitted to the retina.
Overexposure may cause flash blindness or retinal burns and lesions.
Far Infrared (1400 nm - 1 mm)
Most of the radiation is absorbed by the cornea.
Overexposure to these wavelengths will cause corneal burns.
Laser safety instruction
April 26, 2017

14. Materials processing
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15. Laser biological hazards - Skin
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16. Laser safety standard
IEC Edition 1.2 ( ) Safety of Laser Products - Part 1:
Equipment classification, requirements and user’s guide
Objectives of standard:
To indicate safe working levels
To introduce classification system according to hazard
To lay down user and manufacturer requirements  proper precautions.
To ensure adequate warning is given of potential hazard
To reduce possibility/risk of injury
To specify user control measures.
To protect against other hazards.
Applies to LED’s and lasers in wavelength range 180 nm to 1 mm
Laser safety instruction
April 26, 2017

17. IEC 60825-1 -- Laser classes NCDH IEC Range Hazard I 1 n.a 1M II 2
< 1 µW
No hazard
n.a 1M
< 1 µW entering the pupil,
Total power < 0.5 W
No skin hazard; hazardous for eye if viewed through optical instruments; no optics
II 2
< 1 mW; 0.25 s, nm
No hazard for skin or eye: protection by the eye reflex
n.a 2M
< 1 mW/Pupil 0.25s, nm; Total power < 0.5 W
IIIa 3R
< 5 x Class 2; 0.25 s, nm < 5 x Class 1; 100s, invisible light
Hazardous for the eye, but nor for the skin
IIIb 3B
> 3R, max 0.5 W
Hazardous for both, eye and skin
IV 4
> 3B
Hazardous to eye and skin, fire hazard
Note: M-classes apply to (strongly) expanded beamdiameters
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April 26, 2017

18. Definitions - 1 About 10% of dose that has P=0.5 to yield damage
Max Permissible Exposure (MPE)*
Maximum limit to which person may be exposed without suffering adverse effects
Accessible Emission Level (AEL)
Actual exposure that person can access. AEL is the limit allowed within a laser class
Nominal Occular Hazard Distance (NOHD)
Distance at which beam irradiance (or exposure) equals MPE
Nominal Occular Hazard Area (NOHA)
Area within which beam irradiance (or exposure) equals MPE
About 10% of dose that has P=0.5 to yield damage
Calculated for fully open pupil (0.39 cm2).
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April 26, 2017

19. MPE- Continuous Wave
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20. MPE-Pulsed
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21. MPE-collimated
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22. Exposure limits
Numerical example:
A 4% reflection (glass surface!) from a 2.5 mJ laser in a 2 mm beam, gives an exposure of
(10-4 J)/( π/4 (0.2)2 cm2) = 3.2  10-3 J /cm2 ,
exceeding the threshold value on the cornea of appr J/cm2 by a factor 3.2  104.
To be adequately protected against this exposure, protection with an optical density (OD) of log(3.2  104) = 4.5 is required
Laser safety instruction
April 26, 2017

23. Common unsafe practices
• Not wearing/using appropriate protective eyewear
• Misaligned optics and upwardly directed beams
• Equipment malfunction
• Improper methods of handling high voltage
• Intentional exposure of unprotected personnel
• Lack of protection from nonbeam hazards
• Bypassing of interlocks, door and laser housing
• Insertion of reflective materials into beam paths
• Lack of pre-planning, training
• Turning on power supply accidentally
Laser safety instruction
April 26, 2017

24. Control- Class 3B & 4 lasers
1 Controlled access areas.
2 Warning signs, visible lights when in operation.
3 Protective housing and interlock systems (laser shuts off when housing is opened).
4 Removable master key switch.
5 Area interlock system and remote shut-off device.
6 Internal shutter blocking the beam when it is not required.
7 Plane of laser beam above or below seated or standing (eye)level.
8 Avoid beams out of the horizontal plane. If do, they must be clearly marked.
The lowest possible/practical power must be used during alignments.
Use a HeNe alignment laser if possible.
Use beam stops, screens and covers to terminate beams!
All optical holders should be rigidly mounted,
Don’t leave unnecessary components and tools in the laser control area.
Laser safety instruction
April 26, 2017

25. Class 3B & 4: protection
1 No unauthorized personnel in the room or area.
2 All personnel need appropriate training program.
Only authorized personnel may operate the laser.
Establish communication and mutual supervision in the lab.
4 Wear protective eyewear, with proper OD and other specs,.
5 Access by spectators or visitors must be limited and controlled by the laser user.
6 Never lower your eyes to the level of the laser beams.
7 Identify and terminating each and every stray beam.
8 Watches and reflective jewelry should be taken off.
9 Use infrared viewers or CCD camera to view the beam.
Do not align or modify the laser set up after regular working hours.
NEVER work alone in the evening, and only with explicit permission of your supervisor.
Laser safety instruction
April 26, 2017

26. Protective equipment
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27. Protective equipment
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28. Goggle specification Example: D652 L7 CE95 ZZ
Symbol
Laser type
Pulse duration (s)
No. of pulses D CW 10 1 I
Pulsed
104 - 101
100 R
Giant pulsed
109 - 107 M
Mode locked
< 109
Example: D652 L7 CE95 ZZ
Means: D indicates that they are intended for CW laser
652 indicates for 652 nm only
L7 indicates OD (transmission at 652 nm) is 107
CE95 is the European test mark
ZZ indentification of Approved Inspection Body
Laser safety instruction
April 26, 2017