Laser Safety

Laser Safety

Aletta Karsten

National Laser Centre, CSIR, P.O. Box 395, Pretoria, South Africa

[email protected]

Outline

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

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.

Class 2

A Class 2 laser is safe because the blink reflex will limit the exposure. It only applies to visible-light lasers (400700 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.


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.


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.



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


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/cm

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 m

Optical gain in visible region ~ 100 000

1 mW/cm2 cornea = 100 W/cm2 on retina

Rapid eye movement

Welding arc create 180 m spot if image = 10 m

Laser Accidents

Times when accidents happen During alignment

Under stress or pressure

When tired

Failure to pay attention

Reasons Failure to wear eyewear

Equipment malfunction

Improper restoration after servicing

Lack of pre-planning and controls

Laser Injuries

Eye

>70% of all reported injuries

90% of severe injuries caused

by:

Nd:YAG

Ar

Dye

Ruby

HeNe

Skin

CO2 lasers: 56%

Nd:YAG lasers: 14.7%

Eye Protection

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

Attenuation

10

100

1 000

10 000

100 000

1 000 000

OD

1

2

3

4

5

6

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

(J.cm-2) (W.cm-2)

0.180 to 0.302 10-9 to 3 x 104 3 x 10-3

0.315 to 0.400 10-9 to 10 0.56 t0.25

0.315 to 0.400 10 to 3 x 104 1

Wavelength

(m)

Exposure

Duration, t ,(s )

MPE

MPE for Visible and Near IR

(J.cm-2) (W.cm-2)

0.400 to 0.700 10-9 to 18 X 10-6 5.0 x 10-7

0.400 to 0.700 18 X 10-6 to 10 1.8 t0.75 x 10-3

0.400 to 0.500 100 to 3 x 104 CB x 10-4

0.500 to 0.700 10 to 3 x 104 1 x 10-3

0.700 to 1.050 18 X 10-6 to 10 1.8 C A t0.75 x 10-3

0.700 to 1.050 10 to 3 x 104 CA x 10-3

1.050 to 1.400 50 x 10-6 to 10 9.0 CC t0.75 x 10-3

1.050 to1.400 10 to 3 x 104 5.0 CC x 10-3

Wavelength

(m)

Exposure

Duration, t , (s )

MPE

Laser Rangefinder Comparison

Laser Nd:YAG Er:Glass CO2

Wavelength (mm) 1.064 1.54 10.6

Pulse length (ns) 15 15 75

MPE (J/cm2) 5x10-6 1 1x10-2

Class 3b 1 3a

OD Required 3.4 0 0.15

NOHD (m) 3 000 0 39

Laser energy = 100 mJ, diameter = 30 mm, divergence = 0.5 mrad

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

Enclose as much of the beam as possible

Dont direct beam towards doors/windows

Dont 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

Dont 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

Laser Safety

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