1. Massachusetts Institute of Technology Laser Safety Training
William B. McCarthy, Ph.D.
Radiation Protection Office

2. Laser Safety at MIT Massachusetts State Regulations
ANSI Standard for Laser Use
MIT Radiation Protection Office
MIT Laser Safety Policies
Laser Safety Officer
Laser Safety Liaison for each department

3. MIT Radiation Protection Office and the Laser Safety Officer
Register laser systems with the State
Register laser workers
Instruct as to laser hazards and safe use of lasers
Perform hazard analysis for all Class 3b and 4 lasers
Provide safety related information to laser users such as proper eyewear
Coordinate eye exams for laser users

4. Laser Basics
Light
Amplification by
Stimulated
Emission of
Radiation

5. Laser Light vs White Light
Laser light is:
Monochromatic
Directional
Coherent
These three properties of laser light make it different than normal light.

6. Electromagnetic Spectrum
X-Rays
Cosmic
RF : AM, FM, TV MW
Power IR UV
- Rays
Visible Light

7. Laser Light Spectrum Wavelength (microns)
Wavelength (microns)
Ultraviolet Visible Near Infrared Mid Infrared Far Infrared
0.7
Photochemical Retinal Damage Not “Eye Safe” Heating Surface
Effects of the Eye
Eximer
Argon
HeNe
Ruby
GaAs
Nd:YAG
Ho:YAG
Er:YAG
CO2

8. How A Laser Works ACTIVE MEDIUM EXCITATION MECHANISM
FEEDBACK MECHANISM
ACTIVE MEDIUM
High Reflectance mirror
Output coupler mirror
EXCITATION MECHANISM

9. Types of Lasers Active Medium - Gas - Solid State - Diode - Dye
Time Duration
- Continuous Wave (> 0.25 sec)
- Pulsed (< 0.25 sec)
- Single Pulse (< 1Hz)
- Pulsed (Q-switched)

10. Laser Characteristics
Power Output (watts)
10 W to MW
Wavelength (nanometers)
200 nm to 10.6 m
Pulse Duration and Delay (nanoseconds - seconds)
1 psec to continuous
A 100 watt light bulb has 100,000 times the power of a 1 mW laser, the same laser is 10 million times brighter

11. Examples of Lasers

12. Laser Safety Terminology
MPE - Maximum Permissible Exposure - “The level of laser radiation to which a person may be exposed without hazardous effect or adverse biological changes in the eye or skin.”
NHZ - Nominal Hazard Zone - “The space within which the irradiance or radiant exposure exceeds the appropriate MPE.”

13. More Laser Terminology
O.D. - Optical Density - Approximately the order of magnitude of transmittance (). More accurately the OD is equal to log10 (1/).
Eyewear is chosen with an OD that will reduce the eye exposure to the MPE or below.
Irradiance - Watt/cm2
Radiant exposure - Joule/cm2

14. Laser Hazards
laser safety is no joke

15. Laser Hazards Primary Beam Hazards Scattered Beam Hazards
Non-Beam Hazards
Fire
Chemical
Air Contaminants
Electrical
Primary Beam
Scattered Beam

16. Specular vs Diffuse Reflections
Specular - reflection from a “shiny” object. This can be as hazardous as the primary beam.
Diffuse - reflection from a rough object. The “roughness” depends on the wavelength of the light.

17. Laser Classifications
Class 1 - No Biological effect
Class 2 - Eye hazard for chronic viewing only
Class 3a - Eye hazard for chronic viewing or use of collecting optics
Class 3b - Eye and Skin hazard for direct beam exposure
Class 4 - Eye and Skin hazard for direct beam and scattered radiation, also a fire hazard
More detail on laser classification later

18. Skin - Biological Effects
Thermal (all wavelengths)
Skin burns
surface burn from CO2 (typical thermal burn)
deep burn from YAG (very painful)
Photochemical (< 550 nm)
“tanning”
skin cancer
photosensitive reactions
(some are medication related)
Shockwave (Acoustic)

19. Degree of Bio-effect depends on:
Wavelength of the beam
Irradiance or radiant exposure on the tissue
Duration of exposure and pulse repetition characteristics
Extent of vascular flow to the area
Size of the area irradiated

20. Tissue absorption - wavelength dependence
Skin is fairly transparent to red light and near infrared. Here one can see why the CO2 laser causes a surface burn and a YAG causes a deeper burn.

21. Eye - Biological Effects
Corneal Damage
photokeratitis - welder’s flash
corneal burn
Retinal damage
blindness -
fovea/macula
retinal detachment
retinal burn
Lens
cataracts
light rays focus on the retinal back surface of the eye
fovea
optic nerve
blood supply
macula
lens
cornea
retina

22. A detailed picture of the human eye

23. Ocular transmission and retinal absorption
The highest retinal absorption is in the blue region. Blue light poses a relatively greater hazard to the retina than other visible wavelengths. Ultraviolet and mid to far infrared light is absorbed by the cornea. Near infrared is absorbed by the lens and can produce cataracts.

24. Absorption of laser light by the eye
Visible and near infrared ( um) wavelengths are focused by the cornea and lens and absorbed by the retina.
Mid and far infrared ( um) wavelengths and UV-B and C ( um) are absorbed by water on the surface of the eye.
UV-A ( um) wavelengths are absorbed in the cornea and lens structure.

25. Laser Eye Exam Baseline Incident Periodic Termination
Eye exams are required of all personnel directly involved with the use of Class 3b and 4 lasers. The eye exam is done by the MIT Medical Department.
Baseline
Incident
Periodic
Termination

26. How Do You Avoid Laser Eye Injuries?
A Multiple Choice Question
How Do You Avoid Laser Eye Injuries?
a) Always keep your eyes closed when working with lasers or
b) Wear the proper eyewear for your laser system

27. Laser Eyewear
Laser eyewear should be readily available and worn whenever a hazardous condition exists.
RPO recommends and approves the appropriate protective eyewear.
Eyewear should let as much visible light through while still blocking the laser light.
Special Alignment eyewear should be used during alignments.
Also, eyewear should fit comfortably.

28. Laser Classification Class 1 Class 2 no biological effect
less than 0.4 uW visible light
if higher class laser is fully enclosed and interlocked it can be classified as a Class 1 laser.
Class 2
visible light only
less than 1mW
hazard for chronic viewing (>0.25 sec)
aversion response adequate protection
Class 2a supermarket scanners

29. Laser classification cont.
Class 3a
visible light only (ANSI makes some exception for invisible)
1 to 5 mW
same as Class 2 except it is also a hazard with collecting optics
Class 3b
visible and invisible light
5 to 500 mW of continuous wave power
eye and skin hazard with direct beam
Class 4
greater than 500 mW
eye and skin hazard for exposure to both direct beam and scattered radiation
fire hazard

30. Laser Warning Signs CAUTION DANGER Class 2 and 3a lasers
Class 3b and 4 lasers
Laser Radiation
- Do Not Stare into Beam
2.5 mW - HeNe nm
Class 3a laser
Class 4 laser
DANGER
750 mW - Nd:YAG nm
Invisible laser beam - Avoid Eye or Skin Exposure to Direct or Scattered Radiation
MIT Radiation Protection Office

31. Laser Safety Controls Engineering Controls Administrative Controls
Procedural Controls
Use appropriate controls
Danger
Class 4
Laser

32. Engineering Controls Operation Laser beam Entry/access to laser
remote firing
key switch
Laser beam
beam stop or attenuation
beam shutters
controlled beam path
protective housing
Entry/access to laser
door interlocks
filtered windows
laser Controlled Area
warning lights
DANGER
Class 4 laser

33. Administrative Controls
Standard operating procedures
startup - shutdown - specific operations - emergencies
Administrative procedures
limitations on use of laser according to classification
training: Class 3b and 4 lasers must be operated by experienced and trained operators. Spectators are subject to entry requirements
operating manuals
eyewear labeling
Laser warning signs

34. Using Appropriate Controls
Class 1 - No warning signs are required
Class 2 - Caution signs/labels are required
Class 3a - Warning (Caution or Danger) signs/labels are required, eyewear required if laser beam can not be controlled

35. Appropriate controls cont.
Class 3b - Danger signs/labels, beam path control, and protective eyewear required, plus the following are recommended:
protective housing
key switch
area interlocks
beam stops/attenuators
activation warning system
Class 3b laser controlled area
establish Nominal Hazard Zone (NHZ)

36. Appropriate controls cont.
Class 4 - Those items recommended for Class 3b are required for Class 4 lasers. The following are recommended:
supervised by an individual knowledgeable in laser safety
require approved entry for all non-involved personnel
use diffusely reflecting materials near the beam
light tight room
remote firing or remote viewing
beam stops made of fire resistant materials
CPR training (strongly recommended)

37. Safe Work Practices Never intentionally look directly into a laser.
Do not stare at the light from a laser. Allow yourself to blink if the light is too bright.
Never direct the beam toward other people.
Remove all unnecessary reflective objects from the area near the beam path. This may include items of jewelry or tools.
Never allow a laser beam to escape from its designated area of use.
Do not enter a designated Class 3b or 4 (posted with a Danger sign) laser area without the proper eyewear.
Position the laser so that it is well above or below eye level (both standing and sitting).
When not in use a laser should be stored to prevent unauthorized use by untrained individuals.

38. Laser Accidents Electrocution at MIT
“Accident Victim's View” page 19 of the MIT Laser Safety Program manual.
Over 1/2 of the reported incidents have been with graduate students.
Visiting Professor removes his eyewear so he can see better. Retinal burn, permanent damage.
Bystander not wearing eyewear during an alignment procedure. Immediate retinal burn, lesion at edge of macula
Professor measuring output, reflected beam into his eye. Permanent damage to macula (blind spot). No eyewear.

39. Laser Warning Sign DANGER Class 4 laser
MIT Radiation Protection Office
Laser Radiation - Avoid Eye or Skin Exposure to Direct or Scattered Radiation
Type:________________________
Power:_______________________
Wavelength:___________________
Pulse:________________________