Judy Donnelly

1
Laser Safety Seminar PHO K105 Fall, 2006
Judy Donnelly Three Rivers
Community College
donnellyjj_at_sbcglobal.net www.lasertechonline.org
2
TOPICS (Modules) for Laser Safety Laser
Basics Laser Hazards Laser Hazard
Classifications Control Measures Common Causes of
Accidents General Laser Safety Guidelines
3
CHARACTERISTICS OF LASER LIGHT
The word LASER is an acronym
4
CHARACTERISTICS of LASER LIGHT (Details in later
courses!)

• Monochromatic- single color
• Coherent- waves are in phase
• Highly Directional- resulting in very
  concentrated light energy (high irradiance)
• These characteristics describe the unique nature
  of laser light. Because of these characteristics,
  lasers have unique hazards.
• You can be burned by a 60 Watt light bulb, but a
  60 Watt laser can cut through wood!

5
COMPARE LIGHT FROM A LASER AND A FLASHLIGHT

• Monochromatic
• laser is single color flashlight has rainbow
  spectrum
• Coherent
• Laser Speckle- due to wave interference
• Highly Directional
• Flashlight beam spreads much more than lasers
• Define Irradiance Power/area laser is lower
  power but much smaller area

6
What is Irradiance?
Irradiance depends on both laser power and on the
area being irradiated. It is a concept of central
importance in laser safety. The symbol for
irradiance is E, and the units are usually
mW/cm2.
Some books use I for irradiance.
7
EXAMPLE CALCULATION of IRRADIANCE
A 5 mWatt laser makes a 2 mm by 3 mm spot on a
wall. Find the irradiance. Power 5 mWatt Area
0.2 cm x 0.3 cm 0.06 cm2 Irradiance
Power/Area 5 mWatt / 0.06 cm2
83 mWatt / cm2
8
Laser Safety Standards The primary laser safety
standard in use today is the ANSI Z-136.5 The
standard can be obtained from the Laser Institute
of America in Orlando, FL. It provides guidance
for the safe use of lasers and laser systems by
defining control measures for each of the four
broad laser classifications.
www.laserinstitute.org
9

• Laser Safety Standards
• Several organizations oversee standards for laser
  safety
• ANSI American National Standards Institute
• Reference for laser users
• CDRH Center for Devices and Radiological Health
• Product safety standards for laser manufacturers
• OSHA Occupational Safety and Health
  Administration
• Enforces regulations in the workplace
• IEC International Electrotechnical Commission
• International standards organization, with 60
  member countries

10
Laser Eye Hazards
The eye is the part of the body most vulnerable
to laser hazards. Changes to the eye can occur at
much lower laser power levels than changes to the
skin. And, eye injuries are generally far more
serious (life altering) than injuries to the
skin.
fovea
iris
11
Parts of the Eye
The cornea is the outermost, transparent layer.
It covers the front of the eye. The cornea can
withstand dust, sand, and other assaults from the
environment. Thats partly because corneal cells
replace themselves in about 48 hours. Thus, mild
injuries to the cornea are healed quickly. The
aqueous humor is a liquid (mostly water) between
the cornea and the lens. The water in the aqueous
humor absorbs heat, so it protects the internal
portion of the eye from thermal (heat) radiation.
The index of refraction is approximately 1.33,
same as water. The lens of the eye is a flexible
tissue that changes shape. In conjunction with
the cornea, the lens focuses light on the back of
the eye. When the lens changes shape, its focal
length changes. This lets the eye focus on both
near and far objects. The iris controls the
amount of light that enters the eye. The iris is
the pigmented or colored part of the eye. It
responds to light intensity by adjusting its
size. The change in iris size adjusts pupil size
and controls the amount of light admitted to the
eye.
12
Parts of the Eye - Continued
The pupil is the opening in the center of the
iris through which light passes. The size of a
pupil changes from about 2 mm to 7 mm, according
to the brightness of light in the environment.
The darker the environment, the larger the pupil.
A fully dilated pupil (expanded to admit the
greatest amount of light) is considered to be
about 7 mm. The vitreous humor is a colorless
gel that fills the large area at the center of
the eyeball. The vitreous humor helps to maintain
the shape of the eye. The retina is the
light-sensitive layer located at the back of the
eye. The retina contains two types of
photoreceptor (light-receiving) cells  rods and
cones. These cells convert the optical image
produced by the lens into electrical signals. The
signals then are transmitted to the brain. The
fovea is the most sensitive, central part of the
retina. Its the area responsible for the most
detailed vision. A foveal lesion caused by laser
radiation is a worst-case scenario for vision.
The optic nerve carries electrical impulses
from the retina to the brain.
13
Absorption of Light by the Eye
Lens
Retina
Cornea
Mid and Far IR(1400 nm-1 mm) Mid UV (180 nm-315
nm)
Laser Wavelength Region IR-C 1 mm to 1400
nmIR-B 3000 nm to 1400 nmIR-A 1400 nm to
700 nmVisible light 700 nm to 400 nm UV-A
400 nm to 315 nmUV-B 315 nm to 280 nmUV-C
280 nm to 100 nm
Near UV (315 nm-400 nm)
Visible and Near IR (400 nm-1400 nm)
14
Irradiance at the Retina
Example A laser pointer produces a 2-mW beam. The
beam enters the eye and is focused by the cornea
and lens to a spot on the retina 16 um in
diameter. Find The irradiance on the retina,
assuming that all of the 2 mW of power is focused
on the retina. Solution Area of spot A
?d2/4 ?(1.6 x 10-3cm)2/4 2 x
10-6 cm2 Irradiance E P/A 2 mW/2 x
10-6 cm2 1000 W/cm2
Rule of thumb The optics of the eye increase
irradiance by a factor of 100,000!
15
Example of retinal damage due to laser exposure
16
Not all viewing conditions are the same
Whether a reflection is specular or diffuse for a
given surface depends on the laser wavelength.
Smooth is relative to the laser wavelength.
Diffuse reflection
17

• LASER SKIN HAZARDS
• Thermal hazards (skin burns) from high level of
  optical radiation
• Photochemical hazards (accelerated aging and risk
  of skin cancer) due to ultraviolet radiation

18

• NONBEAM HAZARDS
• There are several nonbeam potential hazards
  associated with the use of lasers and laser
  systems.
• Fire hazard
• Explosion hazard
• Electrical hazard
• Chemical hazard
• Laser generated air contaminants (LGAC)
• Other hazards
• Although loss of sight may be life altering,
  electrocution is the hazard most likely to end
  life!

19

• NONBEAM HAZARDS
• FIRE HAZARD
• Class 4 laser systems represent a fire hazard.
  Enclosure of Class 4 laser beams can result in
  potential fire hazards if enclosure materials are
  likely to be exposed to irradiances exceeding
  10 W/cm2 or beam powers exceeding 0.5 W. The use
  of flame-retardant materials is advisable and
  necessary.
• Fires have occurred in medical facilities where
  oxygen provides an explosive environment.

20

• NONBEAM HAZARDS
• EXPLOSION HAZARD
• High-pressure arc lamps, filament lamps, and
  capacitor banks in laser equipment shall be
  enclosed in housings that can withstand the
  maximum explosive pressure resulting from
  component disintegration. The laser target and
  elements of the optical train that may shatter
  during laser operation shall also be enclosed or
  equivalently protected to prevent injury to
  operators and observers. Explosive reactions of
  chemical laser reactants or other laser gases may
  be a concern in some cases.

21

• NONBEAM HAZARDS
• ELECTRICAL HAZARD
• The use of lasers or laser systems can present an
  electric shock hazard. This may occur from
  contact with exposed utility power use, device
  control, and power-supply conductors operating at
  potentials of 50 volts and above. These exposures
  can occur during laser setup or installation,
  maintenance, and service, where equipment
  protective covers are often removed to allow
  access to active components as required for those
  activities. Those exposed can be equipment
  installers, users, technicians, and uninformed
  members of the public, such as passersby.

22

• NONBEAM HAZARDS
• ELECTRICAL HAZARD
• The following potential problems have frequently
  been identified during laser facility audits.
• Uncovered electrical terminals
• Improperly insulated electrical terminals
• Hidden power-up warning lights
• Lack of personnel trained in current
  cardiopulmonary resuscitation practices, or lack
  of refresher training
• Buddy system not being practiced during
  maintenance and service
• Non-earth-grounded or improperly grounded laser
  equipment
• Non-adherence to the OSHA lock-out standard (29
  CFR 1910.147)
• Excessive wires and cables on floor that create
  fall or slip hazards

23

• NONBEAM HAZARDS
• CHEMICAL HAZARDS
• Dye lasers use a complex fluorescent organic
  compound that, when in solution with certain
  solvents, forms a lasing medium for dye lasers.
  Certain dyes are highly toxic or carcinogenic.
  Since these dyes frequently have to be changed,
  special care must be taken when handling,
  preparing solutions, and operating dye lasers.
• In many applications, semiconductor and solid
  state lasers are replacing more dangerous dye
  lasers.

24

• NONBEAM HAZARDS
• LASER GENERATED AIR CONTAMINANTS
• LGAC result from the interaction of high-energy
  laser radiation, assist gases used in material
  processing, and the material itself. In addition
  to molten and evaporated materials liberated from
  the processed surface, new noxious and toxic
  compounds may be formed in some processes
  including metal oxide fumes, cyanide, and
  formaldehyde. When lasers are used in a medical
  setting, particles of biological origin such as
  bacteria may be released into the air. Air
  filters and/or ventilation systems are usually
  required.

25

• NONBEAM HAZARDS
• OTHER HAZARDS
• Compressed gases
• Cryogenic liquids

26
Laser Hazard Classifications The most important
criterion you will use in applying laser safety
control measures is the hazard classification
designated by manufacturers on the equipment
labels. Certain controls are required for each
class (except Class 1). This means that
manufacturers and users of lasers must follow
guidelines for safe use depending on the
classification of the laser. NOTE These
standards are being revised, harmonized, to be
in alignment with IEC standards. CDRH allows
manufacturers to follow the IEC classification
now, which helps international marketing efforts.
ANSI has not yet converted to IEC standards.
27

• Laser Hazard Classifications
• Class 1 Cannot, under normal operating
  conditions, emit a hazardous level of optical
  radiation.
• Included in this category is laboratory equipment
  using lasers with all beam paths and reflections
  enclosed. These are called embedded lasers.
• Examples
• very low powered lasers (lt 0.4 microwatts)
• CD players, laser printers
• Class 1M (NEW!) Eye safe unless focused by a
  optics

28

• Laser Hazard Classifications
• Class 2 low-power visible laser of more than 0.4
  microwatts but less than1 milliwatt. The eye is
  protected by the blink reflex.
• That is, the laser does not have enough output
  power to injure a person accidentally, but may
  injure the eye when stared at for a long period.
• A caution label is required.
• Examples
• Many low power HeNe lasers, especially in school
  labs
• Lasers used for alignment procedures
• Bar Code scanners
• Class 2M (NEW!) Visible output, less than 1 mW,
  eye safe unless focused by a optics

29

• Laser Hazard Classifications
• Class 3a lasersrated in power from 1 milliwatt
  to 5 milliwatts
• Will not normally injure a person when viewed
  briefly with the unaided eye but may cause injury
  when viewed with a focusing device such as a lens
  or telescope.
• A danger or caution sign must label the device,
  depending on its irradiance.
• Examples
• many red laser pointers
• some HeNe lab lasers

IEC Class 3R is similar.
30
Laser Hazard Classifications (continued) Class
3b lasers from 5 milliwatts to 500 milliwatts can
produce eye injury when viewed without eye
protection. This class of laser requires a
danger label and could have dangerous specular
reflections. Eye protection is required.

• EXAMPLES in the TRCC lab
• 12 mW HeNe
• 50 mW HeCd

31
Laser Hazard Classifications (continued) Class
4 lasers above 500 milliwatts in power can injure
you if viewed directly or by viewing either the
specular and diffuse reflections of the beam.
These lasers can also present a fire hazard. A
danger sign will label this laser. Eye and skin
protection are required.
The laser engraving station is Class 1, with an
embedded Class 4.
32

• MAXIMUM PERMISSIBLE EXPOSURE (MPE)
• Maximum permissible exposure (MPE) limits
  indicate the greatest exposure that most
  individuals can tolerate without sustaining
  injury. MPE depends on
• Wavelength
• Output Energy and Power
• Size of the Irradiated Area
• Duration of Exposure
• Pulse Repetition Rate
• MPE is usually expressed in terms of the
  allowable exposure time (in seconds) for a given
  irradiance (in watts/cm2) at a particular
  wavelength. MPEs are useful for determining
  optical densities for eyewear, filters or
  windows.

33
MPE for Selected Lasers and Exposure Times
(Calculated from ANSI Z136.1-1993)
a - Operating at less common 1.33 mmb - Pulsed
operation at 11 Hz, 12-ns pulse, 20-mJ/pulsec -
When repeated exposure levels are anticipated the
MPE level must be reduced by a factor of 2.5.
34

• MAXIMUM PERMISSIBLE EXPOSURE (MPE)
• 0.25 second the human aversion response time
  (blink reflex)
• only applies to visible light!
• 10 seconds average time for eye movement
• 600 seconds average time for laser alignment
  procedure
• 30000 seconds an 8 hour work day

35
Calculations of Irradiance and MPE Does the
irradiance from a 3mW laser pointer (650 nm)
exceed the MPE for 0.25 seconds if it enters (and
fully fills) a 7mm fully dilated pupil? E P/A
3 mW / (p)(0.35 cm)2 7.8 x 10-3
W/cm2 According to the MPE table, the MPE for a
laser operating at 650 mW is 2.5 x 10-3 W/cm2.
The MPE is exceed by more than a factor of 3.
36
Nominal Hazard Zone (NHZ) This zone describes the
region within which the level of direct,
reflected, or scattered (diffuse) laser radiation
is above the allowable MPE. The distance depends
on whether or not the beam is direct, focused, or
diffused, as well as the power and MPE.
LASER
f0
NHZ
d
NHZ illustrated for a focused laser beam
37
Nominal Hazard Zone (NHZ)
38
Nominal Hazard Zone (NHZ)
39
Control Measures for Class 3b and Class 4 Lasers
Engineering Administrative PPE
Protective housing and service panelInterlocks
on the protective housingDoor interlocks and
remote-control connectorBeam attenuators and
beam shutters Key switch or padlockFiltered
viewing optics and windowsEmission delay
Warning lights, emission indicatorsBeam
enclosure Controlled beam pathLaser controlled
areaBeam stopsRemote firing and/or monitoring
THE LASER SAFETY OFFICER (LSO) IS RESPONSIBLE FOR
MAKING SURE CONTROL MEASURES ARE IN PLACE
40
Choosing laser eyewear Optical Density

• The ability of a material to absorb light is
  sometimesexpressed in terms of optical density.
• Optical density is a logarithmic quantity.
• In terms of optical density (OD), transmittance
  is

41
Optical Density
Example Laser goggles with OD 2 at a
particular wavelength have a transmittance of
The goggles transmit 1 of the incident light at
thespecific rated wavelength.
42
Optical Density
T 10-OD
43
Choosing the Optical Density for laser glasses
To determine the required OD for safety glasses,
comparethe irradiation incident on the eye(Eo)
to the MPE (what is allowed to be transmitted to
the eye) and take the log of the ratio.
44
Optical Density- choosing laser safety eyewear
Example The expected exposure from a high powered
HeNe laser is 50 mW/cm2 for a momentary (0.25
second) exposure. What is the appropriate OD for
protective eyewear? Solution Refer to the MPE
table for the appropriate Maximum Permissible
Exposure MPE 2.5 mW/cm2 for HeNe, 633 nm, 0.25
second exposure
The glasses need an OD of at least 1.3
45
Laser safety eyewear is required when class 3b
and 4 lasers are in use. It is important to wear
safety eyewear all the time whenusing class 3b
and 4 lasers. If the eyewear prevents seeing
the beam during alignment, the OD is too high.
A lower OD should bespecified, lessening the
temptation to remove the eyewear to see the beam.
46
(Source Fundamental of Photonics, CORD
Communications)
47

• SAFETY RULES FOR LAB LASERS
• Avoid looking directly into any laser beam or at
  its reflection.Be aware of the beams location.
• Only trained qualified personnel should work with
  lasers
• Dont let friends and visitors to the lab play
  with the lasers
• Keep room lights on whenever possible
• Remove all watches, jewelry and unnecessary
  specular (shiny) reflecting surfaces from the
  work area.
• Dont bend down below beam height
• Use beam blocks
• Wear laser safety eyewear
• Report accidents immediately.
• In the case of eye exposure consult an
  opthalmologist.

48
CAROL DIDNT USE HER SAFETY EYEWEAR..
..NOW SHE DOESNT NEED IT.
Sign seen in high school science lab.