Laser Safety Training

 

red laser picture

 

This class is required for Class 3B, 3R and 4 laser users and recommended for all laser users.To be authorized to work with Class 3B, 3R or 4 lasers you must complete this online tutorial and receive specific training on the systems you will use.  At the end of the tutorial you will take a quiz and send an acknowledgement of completion to Environmental Health and Safety (EH&S).  

Training on the specific laser systems you will use must be conducted by the responsible Principal Investigator (PI) or supervisor. The documentation of the specific training is kept on file in the lab on the Laser Specific Training Documentation Form.

Are you ready to begin training?  Get comfortable, this class can take 1-4 hours, depending on your knowledge level.  Take it at your own pace and enjoy!

 

Calvin dreaming

 

Use the Laser Safety Training navigation box on the left side of the page to move between sections.

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Definition and Properties of Laser Light

 

The word "LASER" has become a household word, but it didn't start out as a word.  It is actually an acronym for:

 

 Lightdr. evil quote

 Amplification by the

 Stimulated

 Emission of

 Radiation

 


Properties

 

First, let's discuss the properties of laser light and then we will go into how is is created. Laser light is monochromatic, directional, and coherent.

 

 

Monochromatic

prism

The light emitted from a laser is monochromatic, that is, it is of one wavelength (color).  In contrast, ordinary white light is a combination of many different wavelengths (colors).

Directional

green laser

Lasers emit light that is highly directional.  Laser light is emitted as a relatively narrow beam in a specific direction.  Ordinary light, such as coming from the sun, a light bulb, or a candle, is emitted in many directions away from the source.

 

sun through clouds

 

 

Coherent

coherent

 

The light from a laser is said to be coherent, which means the wavelengths of the laser light are in phase in space and time.

 


 

Goldfinger

These three properties of laser light are what make it more of a hazard than ordinary light.  Laser light can deposit a great deal of energy within a very small area - as James Bond nearly found out in Goldfinger!

Next section

How a Laser Works

 

 laser table

 


   

The Electromagnetic Spectrum and Quantum Energy

 

 The electromagnetic spectrum consists of the complete range of frequencies from radio waves to gamma rays.  All electromagnetic radiation consists of photons which are individual quantum packets of energy.  For example, a household light bulb emits about 1,000,000,000,000,000,000,000 photons of light per second!  In this course we will only concern ourselves with the portion of the electromagnetic spectrum where lasers operate - infared, visible, and ultraviolet radiation.

 

Name Wavelength
Ultaviolet 100 nm - 400 nm
Visible 400 nm - 750 nm
Near Infrared 750 nm - 3000 nm
Far Infrared 3000 nm - 1 mm

Einstein

Einstein was awarded the Nobel Prize for his discovery and interpretation of the formula - E=mc2 - right?  Wrong.

 

He won the Nobel Prize for his explanation of the phenomena referred to as the photoelectric effect.  When light (electomagnetic energy) is shined on a metal surface in a vacuum, it may free electrons from that surface.  These electrons can be detected as a current flowing in the vacuum to an electrode.  The light was not always strong enough to cause this effect, however.  When the scientists made the light brighter, no increase in electrons was seen.  Only when they changed the color of the light (the wavelength) did they see a change in photoemission of electrons.   This was explained by Einstein using a theory that light consists of photons, each with discrete quantum of energy proportional to their wavelength.  For an electron to be freed from the metal surface it would need a photon with enough energy to overcome the energy that bound it to the atom.  So, making the light brighter would supply more photons, but none would have the energy to free the electron.  Light with a shorter wavelength consisted of higher energy photons that could supply the needed energy to free the electron.  Now, you ask, "What the heck does this idea of quantum energy have to do with a laser?".  Well, with this background under our belts we will continue.


 Laser Components

laser schematic

The Lasing Medium

green lasing medium

A substance that when excited by energy emits light in all directions.   The substance can be a gas, liquid, or semi-conducting material.

  

The Excitation Mechanism or Energy Pump

 

electric excitation

The excitation mechanism of a laser is the source of energy used to excite the lasing medium.  Excitation mechanisms typically used are: electricity from a power supply, flash tubes, lamps, or the energy from another laser.

  

The Optical Cavity

 

 

The optical cavity is used to reflect light from the lasing medium back into itself.  It typically consists of two mirrors, one at each end of the lasing medium.  As the light is bounced between the two mirrors, it increases in strength, resulting in amplification of the energy from the excitation mechanism in the form of light.  The output coupler of a laser is usually a partially transparent mirror on one end of the lasing medium that allows some of the light to leave the optical cavity to be used for the production of the laser beam.


How it Works

 The lasing medium will normally emit photons in specific spectral lines when excited by an energy source.  The wavelength is determined by the different quantum levels, or energy states, of the material.  Normally, most atoms in a medium are in the ground state.  Some small percentage will exist at higher energies as well.  Normally, these higher energy states are unstable and the electrons will release this excess energy as photons almost immediately and return to the ground state.   In some materials, specifically those chosen as lasing medium, a metastable state is possible where the atom or molecule will remain at an excited state for some time.

Energy is supplied to the laser medium by the energy pumping system.   This energy is stored in the form of electrons trapped in the metastable energy levels.  Pumping must produce a population inversion (i.e., more atoms in the metastable state than the ground state) before laser action can take place.

 

When population inversion is achieved, the spontaneous decay of a few electrons from the metastable energy level to a lower energy level starts a chain reaction.  The photons emitted spontaneously will hit (without being absorbed)other atoms and stimulate their electrons to make the transition from the metastable energy level to lower energy levels - emitting photons of precisely the same wavelength, phase, and direction.

 

This action occurs in the optical cavity.  When the photons that decay in the direction of the mirrors (most are lost - lasers are not as efficient as one would believe) reach the end of the laser material, they are reflected back into the material where the chain reaction continues and the number of photons increase.  When the photons arrive at the partially-reflecting mirror, only a portion will be reflected back into the cavity and the rest will emerge as a laser beam.

Now that we know the basics, lets discuss the Types and Classifications of lasers.

<<Previous section            Next section>>                                                      

Laser Types and Classification


 

Types of Lasers

laser picture green laser laser components


There are many types of lasers available for research, medical, industrial, and commercial uses.  Lasers are often described by the kind of lasing medium they use - solid state, gas, excimer, dye, or semiconductor.

Solid state lasers have lasing material distributed in a solid matrix, e.g., the ruby or neodymium-YAG (yttrium aluminum garnet) lasers. The neodymium-YAG laser emits infrared light at 1.064 micrometers.

Gas lasers (helium and helium-neon, HeNe, are the most common gas lasers) have a primary output of a visible red light. CO2 lasers emit energy in the far-infrared, 10.6 micrometers, and are used for cutting hard materials.

Excimer lasers (the name is derived from the terms excited and dimers) use reactive gases such as chlorine and fluorine mixed with inert gases such as argon, krypton, or xenon. When electrically stimulated, a pseudomolecule or dimer is produced and when lased, produces light in the ultraviolet range.

Dye lasers use complex organic dyes like rhodamine 6G in liquid solution or suspension as lasing media. They are tunable over a broad range of wavelengths.

Semiconductor lasers, sometimes called diode lasers, are not solid-state lasers. These electronic devices are generally very small and use low power. They may be built into larger arrays, e.g., the writing source in some laser printers or compact disk players.

 


 

Spaceship shooting laser

Lasers are also characterized by the duration of laser emission - continuous wave or pulsed laser. A Q-Switched laser is a pulsed laser which contains a shutter-like device that does not allow emission of laser light until opened. Energy is built-up in a Q-Switched laser and released by opening the device to produce a single, intense laser pulse.


Classification of Lasers

 

A classification label will be found on the laser housing. This label provides important information on the hazard of the laser.

 

danger sign  caution sign

Lasers have been classified with respect to their hazards based on power, wavelength, and pulse duration. These definitions are wordy and cumbersome to read out of context, but when given the specifications of a laser or laser system are not difficult to apply.

Classes of Lasers (adopted from ANSI Z-136.1-2007)

 

Class 1

Class 1M  

  Class 2  

     

class 2 sign

Cla


Class 2M

 Same criteria for classification as Class 2 but where beam may be hazardous for viewing with magnification. 

 Class 3R  
 

laser 3 caution laser 3 danger

 

Class 3b


 Class 3b laser sign

  Class 4

   

class 4 danger

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Laser Hazards-General

Improperly used laser devices are potentially dangerous.  Effects can range from mild skin burns to irreversible injury to the skin and eye.  The biological damage caused by lasers is produced through thermal, acoustical and photochemical processes.

Thermal effects are caused by a rise in temperature following absorption of laser energy.  The severity of the damage is dependent upon several factors, including exposure duration, wavelength of the beam, energy of the beam, and the area and type of tissue exposed to the beam.

Acoustical effects result from a mechanical shockwave, propogated through tissue, ultimately damaging the tissue.  This happens when the laser beam causes localized vaporization of tissue, causing the shockwave analogous to ripples in water from throwing a rock into a pond.

Beam exposure may also cause photochemical effects when photons interact with tissue cells.  A change in cell chemistry may result in damage or change to tissue.  Photochemical effects depend greatly on wavelength.  Table 1 summarizes the probable biological effects of exposure of eyes and skin to different wavelengths.

  Summary of Laser Biological Effects

 

Photobiological Spectral Domain

Eye

Skin

Ultraviolet C

(200 nm - 280 nm)

Photokeratitis

Erythema (sunburn)

Skin Cancer

Accelerated skin aging

Ultraviolet B

(280 nm - 315 nm)

Photokeratitis

Increased pigmentation

Ultraviolet A

(315 nm - 400 nm)

Photochemical cataract

Pigment darkening

Skin burn

Visible

(400 nm - 780 nm)

Photochemical and thermal retinal injury

Pigment darkening

Photosenstive reactions

Skin burn

Infrared A

(780 nm - 1400 nm)

Cataract and retinal burn

Skin burn

Infrared B

(1.4mm - 3.0 mm)

Corneal burn, aqueous flare, cataract

Skin burn

Infrared C

(3.0 mm - 1000 mm)

Corneal burn only

Skin burn

Types of Beam Exposures 

Exposure to the laser beam is not limited to direct beam exposure.  Particularly for high powered lasers, exposure to beam reflections may be just as damaging as exposure to the primary beam.

Intrabeam exposure means that the eye or skin is exposed directly to all or part of the laser beam.  The eye or skin is exposed to the full irradiance or radiant exposure possible.

Specular reflections from mirror surfaces can be nearly as harmful as exposure to the direct beam, particularly if the surface is flat.  Curved mirror-like surfaces will widen the beam such that while the exposed eye or skin does not absorb the full impact of the beam, there is a larger area for possible exposure.

A diffuse surface is a surface that will reflect the laser beam in many directions.  Mirror-like surfaces that are not completely flat, such as jewelry or metal tools, may cause diffuse reflections of the beam.  These reflections do not carry the full power or energy of the primary beam, but may still be harmful, particularly for high powered lasers.  Diffuse reflections from Class 4 lasers are capable of initiating fires.

Whether a surface is a diffuse reflector or a specular reflector will depend upon the wavelength of the beam.  A surface that would be a diffuse reflector for a visible laser may be a specular reflector for an infrared laser beam.            

   Next section>>

Laser Biological Hazards-Eyes

Light causes biological damage through both temperature effects due to absorbed energy and through photochemical reactions.  The chief mode of damage depends on the wavelength of the light and on the tissue being exposed.  For control of hazards from lasers, the damage is believed to be due principally to temperature effects, and the critical organs are the eye and the skin.

 


 

The Eye

the eye

 

The structure of the eye is shown below.  The optical components of the eye - those components that act together to focus an image of an object on the retina - are the cornea, aqueous humor, lens, and vitreous humor.  The components of the eye most susceptible to laser damage are the cornea, retina, and lens.  The active components of the eye are described in more detail below.

 

eye schematic

 


Components

Cornea

 

cornea

Pupil - Iris - Sclera

 

pupil-iris-sclera

 

Retina

retina

 

roda and cones

Lens

 

lens

 


 

Light Induced Biological Damage

Laser irradiation of the eye may cause damage to the cornea, lens, or retina, depending on the wavelength of the light and the energy absorption characteristics of the ocular tissues.

 

radiation penetrating eye

The potential location of injury in the eye is directly related to the wavelength of the laser radiation. For laser radiation entering the eye:


NOTE: Laser retinal injury can be severe because of the focal magnification (optical gain) of the eye which is approximately 100,000 times. This means that an irradiance of 1 mW/cm2 entering the eye will be effectively increased to 100 W/cm2 when it reaches the retina.

More Notes on Ocular Laser Damage

blinking eye

0.25 seconds is considered the amount of time it takes a person to blink or avert their eyes.

The first rule of laser safety is: NEVER UNDER ANY CIRCUMSTANCES LOOK INTO ANY LASER BEAM!  If you can prevent the laser beam and beam reflections from entering the eye, you can prevent a painful and possibly blinding injury. 

 

<<Previous section        Next section>>

Laser Biological Hazards-Skin

Skin is the largest organ of the body and, as such, is at the greatest risk for coming in contact with the laser beam.  The most likely skin surfaces to be exposed to the beam are the hands, head, or arms.


Lasers can harm the skin via photochemical or thermal burns.  Depending on the wavelength, the beam may penetrate both the epidermis and the dermis.  The epidermis is the outermost living layer of skin.  Far and Mid-ultraviolet (the actinic UV) are absorbed by the epidermis.  A sunburn (reddening and blistering) may result from short-term exposure to the beam.  UV exposure is also associated with an increased risk of developing skin cancer and premature aging (wrinkles, etc) of the skin.



Skin Components


 


skin schematic




How Does Laser Light Affect the Skin?


Laser effects on tissue depend on - the power density of the incident beam, absorption of tissues at the incident wavelength, time beam is held on tissue, and the effects of blood circulation and heat conduction in the effected area.


wavelength vs. penetration


As indicated by the illustration above, different wavelengths of light penetrate the skin in different ways. At approximately 750 nm, absorption to the subcutis occurs.


Tissue Damage from a CO2 Laser


 


hot dog


250 Watt Laser Moving at 1 Inch per Second


chicken with laser burns


250 Watt Laser in Single Pulses


Immediate Effects


As shown above, the immediate effect of exposure to laser light above the biological damage threshold is normally burning of the tissue.  Injury to the skin can result either from thermal injury following temperature elevation in skin tissues or from a photochemical effect (e.g., "sunburn") from excessive levels of actinic ultraviolet radiation.


Some individuals are photosensitive or may be taking prescription drugs that induce photosensitivity.  Particular attention must be given to the effect of these (prescribed) drugs, including some antibiotics and fungicides, on the individual taking the medication and working with or around lasers.
 


Delayed Effects


The possibility of adverse effects from repeated or chronic laser irradiation to the skin has been suggested, although it is normally discounted.  Only optical radiation in the ultraviolet region of the spectrum has been shown to cause long-term, delayed effects.  These effects are: accelerated skin aging and skin cancer.  At present, laser safety standards for exposure of the skin attempt to take these adverse effects into account.


<<Previous section        Next section>>

Non-Beam Laser Hazards

As shown previously, an exposure to laser light can be hazardous to both the eye and skin.  There are other hazards related to the operation of a laser besides exposure to the beam or its reflection.  Many of these non-beam-related hazards can be far more dangerous than the beam itself. This section will discuss these "non-beam hazards". 

 


 

electrocution

Electrical Hazard

    
With the use of large power supplies and repetitively pulsed lasers, there is a great potential for electric shock.  Shocks usually happen when a person is working on equipment that is not properly grounded or has a large capacitor bank that was not discharged.  Most injuries to personnel involving lasers are of this type. For this reason, the "buddy" system should always be observed when performing maintenance on high voltage equipment.  According to the ANSI Z136.1, the following potential problems have frequently been identified during laser facility audits:
       

 

lab explosion

Explosion Hazard

With the use of high-pressure arc lamps, filament lamps, and capacitor banks in laser equipment, there is a potential for explosion hazards.  These items should be enclosed in housings that can withstand the high pressure resulting from exploding components.

In addition, explosions can be caused by the beam from a Class 4 laser hitting a gas cylinder , regluator, or delivery hose.   

poison gas

Compressed Gases

Many lasers are used that incorporate hazardous gases such as chlorine, fluorine, hydrogen chloride, and hydrogen fluoride.  Referring again to ANSI Z136.1, there are typical safety problems that arise in the use of compressed gasses. These include:
    

 

laser dyes

Laser Dyes and Solvents

Dyes are used in some lasers as a lasing medium.  These dyes are complex organic compounds that are mixed in solution with certain solvents.  Some dyes are highly toxic or carcinogenic, and great care must be taken when handling them, preparing solutions, and operating lasers that contain these dyes.  A Material Safety Data Sheet must be made available to anyone working with these dyes.
    

noise

Noise

Some lasers, such as the Excimer, create an intensity of noise that may require controls to be instituted.  The Health and Safety Office should be consulted if there are concerns about noise.

    

fire

Fire Hazards

There is a great potential for a fire hazard to exist with the use of Class IV lasers.  Fires can occur when a Class IV laser is enclosed in a material that is exposed to irradiances greater than 10 W/cm2 or beam powers exceeding 0.5 W.  Fire resistant materials should be used in this situation.
    
Barriers such as black photographic cloth are used in a wide variety of applications for the purpose of containing the beam.  These materials should not be used as the primary barrier for a high-powered Class IV system. Beams of sufficient energy will burn this material quickly, causing smoke, fire, and breach of the barrier.  The use of beam blocks and beam stops is highly encouraged in this situation.

Laser Generated Air Contaminants

This is a term used to refer to the “cloud” of contaminants created when there is an interaction between the beam and the target matter.  These air contaminants are mostly associated with Class 3B and 4 lasers, and range from metallic fumes and dust, chemical fumes, and aerosols containing biological contaminants. 

Some examples include:

  •  polycyclic aromatic hydrocarbons from mode burns on poly (methyl methacrylate) type polymers;
  • hydrogen cyanide and benzene from cutting of aromatic polyamide fibers;
  • fused silica from cutting quartz;
  • heavy metals from etching;
  • benzene from cutting polyvinyl chloride; and
  • cyanide, formaldehyde and synthetic and natural fibers associated with other processes.

Special optical materials used for far infrared windows and lenses have been the source of potentially hazardous levels of airborne contaminants.  For example, calcium telluride and zinc telluride will burn in the presence of oxygen when beam irradiance limits are exceeded.  Exposure to cadmium oxide, tellurium and tellurium hexafluoride should also be controlled.

Exposure to these contaminants must be controlled to reduce exposure below acceptable OSHA permissible exposure limits.  The material safety data sheet (MSDS) may be consulted to determine exposure information and permissible exposure limits.  In general, there are three major control measures available:  exhaust ventilation, respiratory protection, and isolation of the process.

Whenever possible, recirculation of plume should be avoided.  Exhaust ventilation, including use of fume hoods should be used to control airborne contaminants. 

Respiratory protection may be used to control brief exposures, or as an interim control measure until other administrative or engineering controls are implemented.  Use of respirators must comply with the University Policy on Respiratory Protection.  Contact the Laser Safety Officer at 737-7080 if a respirator is needed. 

The laser process may be isolated by physical barriers, master-slave manipulators, or remote control apparatus.  This is particularly useful for laser welding or cutting of targets such as plastics, biological material, coated metals, and composite substrates.

 

radiation

X-Ray Radiation Hazards

X-rays may be generated by electronic components of the laser system(e.g., high-voltage vacuum tubes and from laser-metal induced plasmas).
    

radio tower

Radio-Frequency Radiation Hazards

Some lasers contain RF excited components, such as plasma tubes and Q-switches.
    

Other Potential Hazards

<<Previous section        Next section>>

Laser Control Measures--General Concepts

Individuals who operate lasers should follow the guidelines in this section to protect both themselves and others in the area.  Supervisors and operators should be properly trained before working with or around Class 2, 3, and 4 lasers

Features of a laser device, such as power output, beam diameter, pulse length, wavelength, beam path, beam divergence, and exposure duration determine the capability for injuring personnel.  The potential for injury from use of a laser is determined by its classification, therefore, the control measures are also determined by laser class. 

Concepts such are the maximum permissible exposure (MPE), accessible emission level (AEL) and  nominal hazard zone (NHZ) are important for the laser operator to use and understand.

Maximum Permissible Exposure (MPE)

MPE is the maximum level of laser radiation to which a person may be exposed without hazardous effects or biological changes in the eye or skin.  The MPE is determined by the wavelength of of laser, the energy involved, and the duration of the exposure.  The ANSI 136.1 standard tables 5, 6, and 7 (See Appendix A) summarize the MPE for particular wavelengths and exposure durations.  

MPE is a necessary parameter in determining the appropriate optical density and the nominal hazard zone.

Optical Density (OD)

http://www.takegreatpictures.com/app/webroot/content/2010_images/2007/01/08/humor_shots_2.jpg

The OD (absorbance) is used in the determination of the appropriate eye protection.  OD is a logarithmic function defined by:

Where H0 is the anticipated worst case exposure conditions (in joules/cm2 or watts/cm2) and the MPE is expressed in the same units as H0.  The OD values for various lasers, computed for various appropriate exposure times, are listed below.  Keep in mind that these values are for intrabeam viewing (worst case) only.  Viewing Class 4 diffuse reflections (such as alignment tasks) requires, in general, less OD.  These should be determined for each situation and would be dependent upon the laser parameters and viewing distance.

The table belowprovides a summary of optical density needed for particular lasers, based on the worst case exposure duration:

 

 Optical Densities for Protective Eyewear for Various Laser Types

Laser Type/ Power

Wavelength

(mm)

OD

0.25 seconds

OD

10 seconds

OD for

600 seconds

OD for

30,000 seconds

XeCl

50 watts

0.308a

---

6.2

8.0

9.7

XeFl

50 watts

0.351a

---

4.8

6.6

8.3

Argon

1.0 watt

0.514

3.0

3.4

5.2

6.4

Krypton

1.0 watt

0.530

3.0

3.4

5.2

6.4

Krypton

1.0 watt

0.568

3.0

3.4

4.9

6.1

HeNe

0.005 watt

0.633

0.7

1.1

1.7

2.9

Krypton

1.0 watt

0.647

3.0

3.4

3.9

5.0

GaAs

50 mW

0.840c

---

1.8

2.3

3.7

Nd:YAG

100 watt

1.064a

---

4.7

5.2

5.2

Nd:YAG

(Q-switch)b

1.064a

---

4.5

5.0

5.4

Nd:YAGc

50 watts

1.33a

---

4.4

4.9

4.9

CO2

1000 watts

10.6a

---

6.2

8.0

9.7

a Repetitively pulsed at 11 Hertz, 12 ns pulses, 20mJ/pulse

b OD for UV and FIR beams computed using 1 mm limiting aperture which presents a “worst case scenario.  All visible/NIR computation assume 7 mm limiting aperture.

c Nd:YAG operating at a less common 1.33 mm wavelength.

NOTE:  All OD values determined using MPE criteria of ANSI Z-136.1

Nominal Hazard Zone (NHZ)

The NHZ relates to the space within which the level of direct, reflected, or scattered radiation during normal operation exceeds the appropriate MPE.  Exposure levels beyond the NHZ are below the appropriate MPE level, thus no control measures are needed outside the NHZ.  The NHZ may be calculated using the following formula:

Where ø is the emergent beam divergence measured in radians;  Φ is the radiant power (total radiant power for continuous wave lasers or average radiant power of a pulsed laser) measured in watts; and a is the diameter of the emergent laser beam, in centimeters.

nominal hazard zone diagram

 <<Previous section       

                                                                                             Next section>>

Control Measures by Laser Classification

Potential hazards exist to all individuals working near a laser system.  Such individuals should be warned of the existence and location of lasers, and of the meaning of the warning labels for all classes of lasers. 

Particular attention should be given to the environment where the laser is used.  This factor should be considered together with the class and application of the laser for determining the control measures to be applied.  Basic elements to be considered are:

Control measures may be broken down to two types: administrative controls, such as training, signage, procedures, etc., and engineering controls, such as key controls, interlocks, beam housings, shutters, etc. Engineering controls are design features or devices applied to a laser system and are considered the most effective of the two types of controls.

The following are general considerations for work with lasers, per laser hazard class. The table below provides a summary of these control measures.

Class 1

Many Class 1 lasers have higher class lasers enclosed within a protective housing.  If the Class 1 laser has an enclosed Class 3b or 4 laser, interlocks should be provided on any removable parts of the housing, or the laser should have a service access panel that is either interlocked or requires a tool for removal.  If the protective housing is removed, control measures appropriate for the enclosed laser class should be followed. 

All Class 1 lasers must be labeled.

 

Class 2

Class 2 lasers must be labeled. 

The laser beam should not be purposefully directed toward the eye of any person.  Alignment of the laser optical systems (mirrors, lenses, beam deflectors, etc.) should be performed in such a manner that the primary beam, or specular reflection of the primary beam, does not expose the eye to a level above the MPE for direct irradiation of the eye.

The work area should be posted with a warning label or sign cautioning users to avoid staring into the beam or directing the beam toward the eye of individuals.

If the MPE is exceeded, design viewing portals and/or display screens to reduce exposure to acceptable levels.

If the Class 2 laser has an enclosed Class 3b or 4 laser, interlocks should be provided on any removable parts of the housing, or the laser should have a service access panel that is either interlocked or requires a tool for removal.  If the protective housing is removed, control measures appropriate for the enclosed laser class should be followed. 

 

Class 3a (3R)

Class 3a lasers must be labeled accordingly.  The work area should be posted with a warning label or sign cautioning users to avoid staring into the beam or directing the beam toward the eye of individuals.

Removable parts of the housing and service access panels should have interlocks to prevent accidental exposure.  A permanent beam stop or attenuator may also be used.

If the MPE is exceeded, design viewing portals and/or display screens to reduce exposure to acceptable levels.  Alignment procedures should be designed to ensure the MPE is not exceeded.

 

Class 3b

Class 3b lasers and laser systems must be labeled accordingly.  These lasers are used in areas where entry by unauthorized individuals can be controlled.  If an individual who has not been trained in laser safety must enter the area, the laser operator or supervisor should first instruct the individual as to safety requirements and must provide protective eyewear, if required.

If the entire beam is not enclosed or if a limited open beam exists, the laser operator, supervisor or laser safety officer should determine a Nominal Hazard Zone (NHZ).  An alarm, warning light or verbal countdown should be used during use or start up of the laser.

The controlled area should

·       have limited access to spectators,

·       have beam stops to terminate potentially dangerous laser beams,

·       be designed to reduce diffuse and specular reflections,

·       have eye protection for all personnel,

·       not have a laser beam at eye level,

·       have restrictions on windows and doorways to reduce exposure to levels below the MPE, and

·       require storage or disabling of the laser when it is not being used.

If the MPE is exceeded, design viewing portals and/or display screens to reduce exposure to acceptable levels.  Alignment procedures and collecting optics should be designed to ensure the MPE is not exceeded.

Only authorized, trained individuals should service the laser.  Approved, written standard operating, maintenance and service procedures should be developed and followed.

 

Class 4

In addition to the control measures described for Class 3b, Class 4 lasers should be operated by trained individuals in areas dedicated to their use.  Failsafe interlocks should be used to prevent unexpected entry into the controlled area, and access should be limited by the laser operator to persons who have been instructed as to the safety procedures and who are wearing proper laser protection eyewear when the laser is capable of emission.

Laser operators are responsible for providing information and safety protection to untrained personnel who may enter the laser controlled areas as visitors.

The laser area should be

The beam path must be free of specularly reflective surfaces and combustible objects and the beam terminated in a non-combustible, non-reflective barrier or beam stop.

 

Control Measures for the Four Laser Classes

Control Measures

Classification

Engineering Controls 

1 

1M

2 

2M

3R 

3B 

4 

Protective Housing

X

X

X

X

X

X

X

Without protective housing

Laser Safety Officer establishes alternative controls

Interlocks on protective housing

à 

à

à 

à 

à 

X

X

Service Access Panel

à 

à

à 

à 

à 

X

X

Key Control

--

--

--

--

--

· 

X

Viewing Portals

Assure viewing limited < MPE

Collecting Optics

             

Totally Open Beam Path

--

--

--

--

--

X
NHZ

X
NHZ

Limited Open Beam Path

--

--

--

--

--

X
NHZ

X
NHZ

Enclosed Beam Path

None required if protective housing and interlocks in place

Remote Interlock Connector

--

--

--

--

--

· 

X

Beam Stop or Attenuator

--

--

--

--

--

· 

X

Activation Warning Systems

--

--

--

--

--

· 

X

Indoor Laser Controlled Area

--

--

--

--

--

--

X

Class 3B Indoor Laser Controlled Area
--
--
--
--
--
X
--
Class 4 Laser Controlled Area
--
--
--
--
--
--
--
Outdoor Control Measures
--
--
--
--
--
--
--
Laser in Navigable Airspace

X

·
NHZ

X
NHZ

·
NHZ

X
NHZ

X
MPE

X
MPE

Temporary Laser Controlled Area

à
MPE

à
MPE

à
MPE

à
MPE

à
MPE

--

--

Controled Operation

--

--

--

--

--

--

· 

Equipment Labels

X

X

X

X

X

X

X

Laser Area Warning Signs

--

--

--

X

·

X

X


Administrative and Procedural Controls 

Standard Operating Procedure

--

--

--

--

--

· 

X

Output Emission Limitations

--

--

--

--

--

LSO Determines

Education and Training

--

· 

· 

· 

· 

X

X

Authorized Personnel

--

*

--

*

--

X 

X

Alignment Procedures

à

à

à

à

à

X

X

Protective Equipment

--

*

--

*

--

·

X

Spectator

--

*

--

*

--

·

X

Service Personnel

à

à

à

à

à

X

X

Demonstration with Public

--

*

X

*

X

X

X

Laser Fiber Optic Systems

MPE

MPE

MPE

MPE

MPE

X

X

Laser Robotic Installation

--

--

--

--

--

X
NHZ

X
NHZ

Protective Eyewear

--

--

--

--

--

·
MPE

X
MPE

Window Protection

--

--

--

--

--

X

X
NHZ

Protective Barriers and Curtains

--

--

--

--

--

· 

· 

Skin Protection

--

--

--

--

--

X

X
MPE

Warning Signs and Labels

--

--

·

·

·

X
NHZ

X
NHZ

Skin Protection

--

 

--

--

--

X
MPE

X
MPE

LEGEND 

X = shall       · = should      -- = no requirement    NHZ = NHZ analysis required

à = shall if enclosed Class 3b or 4            MPE = shall if MPE is exceeded

                 

<<Previous section        Next section>>

Warning Signs and Labels

 All Class 2, 3 and 4 laser equipment must be labeled indicating hazard classification, output power/energy, and lasing material or wavelength with words and symbols as indicated below:

caution class 2

caution class 3

danger class 3R

danger class 3

danger class 4

 

Labels and warning signs should be displayed conspicuously in areas where they would best serve to warn individuals of potential safety hazards.  Normally, signs are posted at entryways to laser controlled areas and labels are affixed to the laser in a conspicuous location.

<<Previous section       

                                                                                   Next section>>

Protective Equipment

Enclosure of the laser equipment or beam path is the preferred method of control, since the enclosure will isolate or minimize the hazard.  When engineering controls do not provide adequate means to prevent access to direct or reflected beams at levels above the MPE, it may be necessary to use personal protective equipment.  Note that use of personal protective equipment may have serious limitations when used as the only control measure with higher power Class 4 lasers or laser systems.  The protective equipment may not adequately reduce or eliminate the hazard and may be damaged by the incident laser radiation.

 Protective Eyewear

safety goggles

Protective eyewear is necessary for Class 3 and 4 laser use where irradiation of the eye is possible.  Such eye protection should be used only at the wavelength and energy/power for which it is intended.  Eye protection may include goggles, face shields, spectacles or prescription eyewear using special filter materials or reflective coatings (or a combination of both) to reduce exposure below the MPE.  Eye protection may also be necessary to protect against physical or chemical hazards.

The following factors should be considered in selecting the appropriate laser protective eyewear:

 

Laser Eye Protection Selection Process

1.   Determine the wavelength of the laser Eye protection is wavelength-specific.  Eyewear that provides protection for CO2 lasers will not necessarily protect against Nd:YAG lasers.

2.   Determine the maximum anticipated viewing duration. Viewing duration usually fall into one of three categories:

a)     Unintentional, accidental exposure to visible lasers(400-700 nm), use 0.25 seconds

b)     Unintentional, accidental viewing of near infrared (700-1000 nm) beams, use 10 seconds

c)     For all other lasers, use 600 seconds or laser on time, up to 8 hours.

3.   Determine the maximum irradiance or radiant exposure to which the eye may be exposed.  Consider the following:

a)     If the emergent beam is not focused down to a smaller spot and is greater than 7 mm in diameter, the emergent beam radiant exposure/irradiance may be considered the maximum intensity that could enter the eye. 

b)     If the beam is focused after emerging from the laser or if the beam diameter is less than 7 mm, assume that all of the laser energy/power could enter the eye.  In this case, use the columns titled Maximum Output Power/Energy in the table below.

4.   Determine the optical density needed.

5.   Select the type of eye protection needed.  Laser eye protection is available in the form of glasses and goggles.  The lens may be made out of glass or crystalline filter material or plastic.  Generally, glass or crystalline lenses are recommended for harsh environments, such as areas where solvents and corrosives are used.

6.   Test the eye protection.  Always check the integrity of the lens before use.  At very high beam intensities, filter materials become bleached out or otherwise damaged.  A continuous wave power exceeding 10 W can fracture glass and burn through plastics.

 

  

Selecting Laser Eye Protection for Intrabeam Viewing for 400 - 1400 nm Wavelengths

Q-Switched
(1 ns - 0.1 ms)
Non-Q-Switched
(0.4 ms - 10 ms)

CW Momentary View (0.25 s to 10 s)

CW Starting (more than 3 hours)

Attenuation Factor

Max Output Energy (J)

Max Beam Radiant Exposure (j/cm^2)
Max Laser Output Energy (J)
Max Beam Radiant Exposure (J/cm^2)
Max Power Output (W)
Max Beam Irradiance (W/cm^2)
Max Power Output (W)
Max Beam Irradiance (W/cm^2)
10
20
100
200
na
na
na
na
100,000,000
1
2
10
20
na
na
na
na
10,000,000
10^-1
2x10^-1
1
2
na
na
na
na
1,000,000

10^-2

2x10^-2
10^-1
2x10^-1
na
na
10^-1
2x10^-1
100,000
10^-3
2x10^-3
10^-2
2x10^-2
10
20
10^-2
2x10^-2
10,000
10^-4
2x10^-4
10^-3
2x10^-3
1
2
10^-3
2x10^-3
1,000
10^-5
2x10^-5
10^-4
2x10^-4
10^-1
2x10^-1
10^-4
2x10^-4
100
10^-6
2x10^-6
10^-5
2x10^-5
10^-2
2x10^-2
10^-5
2x10^-5
10

 

Other Protective Equipment

It is important that protective equipment such as beam stops, shields, safety interlocks, and warning lights and horns be maintained in proper operating condition and be utilized whenever indicated to prevent harmful exposure to laser radiation. 

 

Special Controls for UltraViolet and Infrared Lasers

Since infrared (IR) and ultraviolet (UV) wavelengths are normally invisible, particular care must be taken when using these types of lasers.  In addition to the recommended control measures that apply for each laser classification, the following should also be employed:

Infrared

1.  The collimated beam from a Class 3 laser should be terminated by a highly absorbent backstop wherever practicable.  Many surfaces which appear dull visually can act as reflectors of IR.

2.  The beam from a Class 4 laser should be terminated in a fire resistant material wherever practicable.  Periodic inspection of the absorbent material is required since many materials degrade with use.

3.  Areas that are exposed to reflections from Class 3 or 4 lasers, at levels above the MPE, should be protected by appropriately screening the beam or target area with IR absorbent material.  This material should be fire-resistant for use with Class 4 lasers.

UV

1.  Exposure to UV should be minimized by using shield material which attenuates the radiation to levels below the appropriate MPE for the specific wavelength.

2.  Special attention should be given to the possibility of producing undesirable reactions in the presence of UV, for example, ozone formation. 

  <<Previous section                                                                          Next section>>

Laser Safety at Oregon State University

Introduction 

Most lasers used at Oregon State University are capable of causing eye injury to anyone who looks directly into the beam or its reflections from a specular (mirror-like) surface.  In addition, diffuse reflections of a high-power laser beam can produce permanent eye damage.  High-power laser beams can burn exposed skin, ignite flammable materials, and heat materials that release hazardous fumes, gases, debris, or radiation.  Equipment and optical apparatus required to produce and control laser energy may also introduce additional hazards associated with high voltage, high pressure, cryogenics, noise, other forms of radiation, flammable materials, and toxic fluids.  Thus, each proposed experiment or operation involving a laser must be evaluated to determine the hazards involved and the appropriate safety measures and controls required.


Laser Safety Program

The Laser Safety Program is administered by Environmental Health & Safety (EH&S).  The Laser Safety Officer for Oregon State University recommends that individuals using lasers set up and operate laser facilities to meet the laser safety guidelines established by the American National Standards Institute (ANSI) standard ANSI Z136.1-2007, American National Standard for the Safe Use of Lasers.

The Laser Safety Program applies to individuals who operate or work in proximity to Class 3b or Class 4 lasers.


Hazard Classification 

Commercial lasers are classified and certified by the manufacturer.  When a commercial laser is modified or when a new laser is constructed in the laboratory, it is the responsibility of the principal investigator to classify and label the laser per the ANSI Standard.  EH&S can assist in determining the appropriate classification.  


Medical Surveillance

Some individuals who operate or work in close proximity to particular Class 3B or Class 4 lasers or laser systems may receive a pre-assignment and a post-assignment eye examination performed by a consulting ophthalmologist.  Results of the examinations are maintained by the Occupational Health in Student Health Services at the Plageman Building.   Contact the Laser Safety Officer for more information.


Training

Individuals who work with or in close proximity to Class 3b or Class 4 lasers must complete laser safety training provided by EH&S.  Training is recommended for users of Class 2, Class 3a and Class 3R users. This training includes:

 


Roles and Responsibilities 

Department

Supervisors/Principal Investigators

Purchasing Office

EH&S

Individual


References

Contact the Laser Safety Officer at 541-737-7082 for more information. 

The following resources and training aids are available through EH&S:

  • ANSI Standard Z136.1-2007, American National Standard for the Safe Use of Lasers, 2007
  • OSHA Technical Manual, Section III, Chapter 6, Laser Hazards
  • DVD: Mastering Light: An Introduction to Laser Safety and Hazards, Laser Institute of America
  • Interactive training, LIMITS: Laser Safety in Medicine, Austrian Research Centers/Laser Institute of America, 2001
  • Sliney, David and Wolbarsht, Safety with Lasers and Other Optical Sources, A Comprehensive Handbook, Plenum Press, 1977
  • Marshall, Wesley and Sliney, David, Laser Safety Guide, Laser Institute of America, 2000
  • Sliney, David, editor, LIA Guide for the Selection of Laser Eye Protection, 2000
  • Hitchcock, Timothy, editor, LIA Guide to Non-beam Hazards Associated with Laser Use, Laser Institute of America, 1999
  • Trokel, Stephen L., M.D., editor, LIA Guide to Medical Laser Safety, Laser Institute of America, 1997 

<<Previous section        Next section>>

Laser Safety Training completion

Contact Radiation Safety if you are unable to access the Laser Safety Quiz.


On successful completion of the quiz, must complete and submit the Laser Safety Acknowledgemnt form by email.


You will also need to receive specific training from your Program Director on the laser systems that you will use.


Laser Safety Quiz