Download Laser Safety

Laser Safety
Aletta Karsten
National Laser Centre, CSIR, P.O. Box 395, Pretoria, South Africa
[email protected]
Outline
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Laser wavelengths
•
International standards
•
Eye and skin injuries
•
Laser accidents
•
Protection
•
MPE
•
SA regulations
© CSIR 2012
Wavelength Classification
• UVC: 100 nm to 280 nm (Actinic UV)
• UVB: 280 nm to 315 nm (Actinic UV)
• UVA: 315 nm to 400 nm (Near UV)
• Visible Light: 400 nm to 780 nm
• IRA: 780 nm to 1 400 nm (Near IR)
• IRB: 1 400 nm to 3 000nm (Mid IR)
• IRC: 3 000 nm to 1 mm (Far IR)
Typical wavelengths used in Raman
Spectroscopy
• Ultra-violet: 244 nm, 257 nm, 325 nm, 364 nm
• Visible: 457 nm, 473 nm, 488 nm, 514 nm, 532 nm, 633
nm, 660 nm
• Near infra-red: 785 nm, 830 nm, 980 nm, 1064 nm
Diffuse vs Specular Reflection
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Specular reflection
– Mirror like
– Surface roughness less than laser wavelength
Diffuse reflection
– Surface irregularities are randomly orientated
– Size of surface irregularities are greater than the laser wavelength
Laser Hazard Classification: ANSI Z136.1-2007
• Class 1
– A class 1 laser is safe under all conditions of normal
use. The maximum permissible exposure (MPE)
cannot be exceeded.
• Class 1M
– A Class 1M laser is safe for all conditions of use
except when using magnifying optics such as
microscopes and telescopes. Class 1M lasers
produce large-diameter beams, or beams that are
divergent.
Laser Hazard Classification: ANSI Z136.1-2007
• Class 2
– A Class 2 laser is safe because the blink reflex will limit
the exposure. It only applies to visible-light lasers (400–
700 nm). Class-2 lasers are limited to 1 mW continuous
wave. Many laser pointers are class 2.
• Class 2M
– A Class 2M laser is safe because of the blink reflex if
not viewed through optical instruments. As with class
1M, this applies to laser beams with a large diameter or
large divergence, for which the amount of light passing
through the pupil cannot exceed the limits for class 2.
Laser Hazard Classification: ANSI Z136.1-2007
• Class 3R
– A Class 3R laser is considered safe if handled
carefully, with restricted beam viewing. With a class
3R laser, the MPE can be exceeded, but with a low
risk of injury. Visible continuous lasers in Class 3R are
limited to 5 mW.
• Class 3B
– A Class 3B laser is hazardous if the eye is exposed
directly, but diffuse reflections such as from paper or
other matte surfaces are not harmful. lasers. Class-3B
lasers must be equipped with a key switch and a
safety interlock.
Laser Hazard Classification: ANSI Z136.1-2007
• Class 4
– Class 4 lasers include all lasers with beam power
greater than class 3B.
– By definition, a class 4 laser can burn the skin, in
addition to potentially devastating and permanent eye
damage as a result of direct or diffuse beam viewing.
– These lasers may ignite combustible materials, and
thus may represent a fire risk. Class 4 lasers must be
equipped with a key switch and a safety interlock.
– Many industrial, scientific, and medical lasers are in
this category.
Laser Hazard Classification: ANSI Z136.1-2000
• Class 1 (Exempt)
– Do not produce damaging radiation levels
• Class 2 (Low power)
– Only visible lasers (400 – 700 nm)
– Aversion response protects the eye
– Upper limit for CW is 1 mW
Laser Hazard Classification: ANSI Z136.1-2000
Class 3 (Medium power)
– Divided into two subclasses: 3a, 3b
– Hazardous under direct viewing and specular
reflection viewing
– Upper limit for CW is 0.5 W
Class 4 (High power)
– Hazard to eye and skin from direct viewing and
diffuse reflection
– Fire hazard
– May produce laser generated air contaminants
(LGAC)
– May produce hazardous plasma radiation
Skin Injury
• Thermal skin burns
– Rare – high exposure, several J/cm²
– Most common from CO2 exposure
• Ultraviolet ‘Sunburn’
– Erythema (reddening) from UV-B and UV-C
• UV Radiation delayed effects
– Skin cancer
– Accelerated skin aging
The Human Eye
Laser Absorption in the Eye (Visible)
Laser Absorption in the Eye (Non Visible)
Symptoms of Laser Eye Injuries
• CO2 laser: Burning pain at site of injury
• Visible laser: Bright colour flash and after-image the
colour of complementary colour
• Q-switched Nd:YAG: Very dangerous –
– Invisible beam but focused on retina which lacks
sensory nerves
– Considerable damage before visual disorientation.
May
hear a ‘pop’ sound when laser beam hits
retina
Corneal Injury
• Photochemical injury
– UV radiation
– Peak @270 nm
• Thermal injury
– IR-B and IR-C
Retinal Injury
• Thermal burns
– From brief (normally pulsed) intense exposure
from 400 – 1 400 nm laser radiation
• Photo retinitis
– Photochemical injury from lengthy (>10 s), intense
exposure from 400 – 500 nm light
– Delayed appearance (24 - 48 h)
• Eclipse retinitis
Retinal Image Size
• Minimal image diameter – 10 to 20 μm
• Optical gain in visible region ~ 100 000
– 1 mW/cm2 cornea = 100 W/cm2 on retina
• Rapid eye movement
– Welding arc create 180 μm spot if image = 10 μm
Laser Accidents
• Times when accidents happen
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During alignment
Under stress or pressure
When tired
Failure to pay attention
• Reasons
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Failure to wear eyewear
Equipment malfunction
Improper restoration after servicing
Lack of pre-planning and controls
Laser Injuries
• Skin
• Eye
– >70% of all reported injuries
– 90% of severe injuries caused
– by:
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•
•
•
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Nd:YAG
Ar
Dye
Ruby
HeNe
– CO2 lasers: 56%
– Nd:YAG lasers: 14.7%
Eye Protection
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Wavelength compatibility
Attenuation at wavelength
Visual transmittance
Comfort and fit
Training
Inspection
Storage
Optical Density (OD)
• OD of a filter describes the ability of the filter to attenuate
optical radiation
(Incident intensity)
• OD = log10------------------------(Intensity with filter)
OD Table
OD
1
2
3
4
5
6
Attenuation
10
100
1 000
10 000
100 000
1 000 000
Eye Protection
• Laser eyewear is not for direct viewing of laser beam
• Eyewear must be marked with the OD at specific
wavelength for use
• Glass or plastic
Laser Safety Glasses
Laser Accidents: Eyewear Problems
• Eyewear not worn
• Improper eyewear
– Wrong eyewear or OD range
• Improper fit
Maximum Permissible Exposure (MPE)
• Level of laser radiation to which a person may be
exposed without hazardous effects on skin or eye
• MPE for eye and skin differ
• MPE for eye normally lower than for skin
• Depends on wavelength, exposure duration and other
factors
MPE for UV
Wavelength
(µm)
0.180 to 0.302
0.315 to 0.400
0.315 to 0.400
Exposure
Duration, t ,(s )
10-9 to 3 x 104
10-9 to 10
10 to 3 x 104
MPE
(J.cm-2)
3 x 10-3
0.56 t0.25
1
(W.cm-2)
MPE for Visible and Near IR
Wavelength
(µm)
Exposure
Duration, t , (s )
0.400 to 0.700
0.400 to 0.700
0.400 to 0.500
10-9 to 18 X 10-6
18 X 10-6 to 10
100 to 3 x 104
0.500 to 0.700
0.700 to 1.050
10 to 3 x 104
18 X 10-6 to 10
0.700 to 1.050
10 to 3 x 104
1.050 to 1.400
50 x 10-6 to 10
1.050 to1.400
10 to 3 x 104
MPE
(J.cm-2)
(W.cm-2 )
5.0 x 10-7
1.8 t0.75 x 10-3
CB x 10-4
1 x 10-3
1.8 C A t0.75 x 10-3
CA x 10-3
9.0 CC t0.75 x 10-3
5.0 CC x 10-3
Laser Rangefinder Comparison
Laser energy = 100 mJ, diameter = 30 mm, divergence = 0.5 mrad
Laser
Nd:YAG Er:Glass
CO2
Wavelength (mm)
1.064
1.54
10.6
Pulse length (ns)
15
15
75
5x10-6
1
1x10-2
Class
3b
1
3a
OD Required
3.4
0
0.15
3 000
0
39
MPE (J/cm2)
NOHD (m)
Laser Safety in South Africa
• Governed by Department of Health (DoH), Directorate:
Radiation Control
• Requirements for the Safe Use of Laser Products
• Bases on American ANSI Z136.1 –1993 standard
• Apply to Class 3b and Class 4 lasers, wavelengths from
180 nm to 1 mm
• All Class 3b and Class 4 lasers must be registered with
DoH
• Companies/Organisations using lasers:
– Must have a LSO
– Must provide laser safety training to personnel
working with, or around lasers
– Do baseline eye examinations
Laser Safety Signs: I (Entrance)
DANGER
Laser hazard
Laser Safety Signs: II
Laser Safety Signs: III
Good Practice Guidelines
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Enclose as much of the beam as possible
Don’t direct beam towards doors/windows
Don’t locate beam at eye level
Use beam stops
Use surfaces that scatter laser radiation
Locate laser controls
Ensure warning lights are visible through protective
filters
• View application remotely (e.g. CCTV)
Keep in Mind
– Laser vendor is usually not the best laser safety
advisor
– Don’t wear ties around Class 4 open beam
– Laser light may be reflected off jewellery (e.g.
watches and rings)
– All interlocks can be defeated
– The most important administrative laser safety control
is training
THANK YOU