East Tennessee State University

Laser Safety Training

Laser Stands for:

  • Light
  • Amplification by the
  • Stimulated
  • Emission of
  • Radiation

Laser light:

  • The light emitted from a laser is monochromatic, that is, it is of one color/wavelength. In contrast, ordinary white light is a combination of many colors (or wavelengths) of light.
  • Lasers emit light that is highly directional, that is, laser light is emitted as a relatively narrow beam in a specific direction. Ordinary light, such as from a light bulb, is emitted in many directions away from the source.
  • The light from a laser is said to be coherent, which means that the wavelengths of the laser light are in phase in space and time. Ordinary light can be a mixture of many wavelengths.

Monochromatic, directional, coherent light waves

Many wave lengths, incoherent, multi-directional light.

Uses of Lasers:

  • Lasers are used in industry, communications, military, research and medical applications.

How a Laser Works:

  • A laser consists of an optical cavity, a pumping system, and a lasing medium
  • The optical cavity contains the media to be excited with mirrors to redirect the produced photons back along the same general path.
  • The pumping system uses various methods to raise the media to the lasing state.
  • The laser medium can be a solid (state), gas, liquid dye, or semiconductor.

Laser Media:

  1. Gas lasers
  2. Excimer lasers (a combination of the terms excited and dimers) use reactive gases mixed with inert gases.
  3. Dye lasers (complex organic dyes)
  4. Semiconductor lasers (also called diode lasers)

 There are different safety hazards associated with the various laser media.

Types of Lasers:

Lasers can be described by:

  • which part of the electromagnetic spectrum is represented:
    • Infrared
    • Visible Spectrum
    • Ultraviolet
  • the length of time the beam is active:
    • Continuous Wave
    • Pulsed
    • Ultra-short Pulsed

Electromagnetic Spectrum:

Laser wavelengths are usually in the Ultraviolet, Visible or Infrared Regions of the Electromagnetic Spectrum.

Ultraviolet (UV) radiation ranges from 200 - 400 nm.

Infrared radiation ranges from 760 - 10,000 nm.

Structure of the Eye:

The eye is a complex optical instrument consisting of several parts.

The CORNEA is exposed to the outside environment and therefore must repair itself rapidly because it is consistently faced with abrasion. It is transparent to all visible and near infrared wavelengths. The pupil is the opening that allow light into the eye. Its size is controlled by the light sensitive iris.

The RETINA is the layer of nerve cells that receives the image and sends signals to the brain. The FOVEA is the most sensitive area of the retina because it has the greatest concentration of cones. Rods and cones are the photoreceptors. The nerves leading from the rods and cones exit at the back of the eye through the OPTIC NERVE. The pigment epithelium is a layer at the back of the retina that absorbs light. The heat generated by the absorption of even environmental light in the pigment epithelium is removed by the blood flow in the choroid located just behind the retina.

Eye Hazard:

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

Wavelengths (UV) shorter than 400 nm is absorbed in the cornea. This is the same type of injury that is caused by snow blindness. This painful condition may last for several days and is very debilitating. Long term exposure to UV exposure can cause cataract formation in the lens.

Wavelengths between 300 - 400 nm are absorbed in the aqueous humor, iris, lens and vitreous humor.

Wavelengths between 400 - 1400 nm are focused into the retina.

Protection for your Eyes:

PPE is not required for Class 2 or 3A lasers unless intentional direct viewing > 0.25 seconds is necessary.

Personal Protective Equipment (PPE) for eyes exposed to Class 3B or 4 lasers is mandatory. Eyewear with side shields is best. Consider these factors when choosing eyewear.

  • Optical Density (OD) of the eyewear
  • Laser Power and/or pulse energy
  • Laser Wavelengths
  • Exposure time criteria
  • Maximum Permissible Exposure (MPE)
  • Filter characteristics, such as transient bleaching

Skin Hazards:

Ultraviolet (UV)

  • UV can cause skin injuries comparable to sun burn.
  • As with damage from the sun, there is an increased risk for developing skin cancer from UV laser exposure.

Thermal Injuries

  • High powered (Class 4) lasers, especially from the infrared (IR) and visible range of the spectrum, can burn the skin and even set clothes on fire.

Laser Safety Regulations:

  • Occupational Safety & Health Administration (OSHA)
  • American National Standards Institute (ANSI)
    • ANSI Z136.1 (2007) Safe Use of Lasers
    • ANSI Z136.2-6 Specific references

ANSI Laser Classifications:

Least Hazardous

Class 1
Class 2
Class 3A
Class 3B
Class 4

Most Hazardous

Class 1 Laser

Class I lasers are low powered devices that are considered safe from all potential hazards. Some examples of Class I lasers are: laser printers, geological survey equipment and laboratory analytical equipment. No individual, regardless of exposure conditions to the eyes or skin, would be expected to be injured by a Class I laser. No safety requirements are needed to use Class I laser devices.

Class 2 Laser

Class 2 lasers are low power visible light lasers that could possibly cause damage to a person's eyes. Some examples of Class 2 lasers use are laser pointers, aiming devices and range finding equipment. If Class 2 laser beams are viewed for long periods of time (i.e. > 15 minutes) damage to the eye could occur. The bright light of a Class 2 laser beam into your eyes will cause a normal reaction to look away or close your eyes. This is called Aversion Reaction and is expected to protect you from Class 2 laser damage to the eyes.

Class 3A Laser

Class 3A lasers are continuous wave, intermediate power devices. Some examples of Class 3A lasers are the same as Class 2 lasers with the most popular uses being laser pointers and laser scanners. Direct viewing of Class 3A laser beam could be hazardous to the eyes.

Class 3B Laser

Class 3B lasers are intermediate power devices. Some examples of Class 3B uses are spectrometry and entertainment light shows. Direct viewing of Class 3B laser beam is hazardous to the eye and diffuse reflections of the beam can also be hazardous to the eye. Do not view the Class 3B beam directly.

Class 4 Laser

Class 4 lasers are high power devices. Some examples of Class 4 laser use are surgery, research, drilling, cutting, welding and micromachining. The direct beam and diffuse reflections from Class 4 lasers are hazardous to the eyes and skin. Class 4 laser devices can also be a fire hazard depending on the reaction of the target when struck. Much greater controls are required to ensure the safe operation of this class of laser devices. Whenever occupying a laser controlled area, wear the proper eye protection. Most laser eye injuries occur from reflected beams of Class 4 laser light, so keep all reflective materials away from the beam. Do not place your hand or any other body part into the Class 4 laser beam.

Laser Safety Officer:

  • The Laser Safety Officer (LSO) is someone who has the authority to monitor and enforce the control of laser hazards and effect the knowledgeable evaluation and control of laser hazards.
  • The LSO for ETSU is Bill Hemphill with the Office of Engineering Technology.

Nominal Hazard Zones (NHZ):

  • The Nominal Hazard Zone (NHZ) is the location around the laser within which a person can be exposed to radiation in excess of the Maximum Permissible Exposure.
  • When Class 3B and 4 lasers are unenclosed the Laser Safety Officer must establish an NHZ.
  • People may be injured if they are within the perimeter of this zone while the laser is in operation.

Non Beam Hazards:

  • Electric Shock
    Use caution when working on or near the high-voltage power supplies used for high-power Class 3 and 4 lasers; there is sufficient voltage in these power supplies to injure or kill.
  • Fire
    High powered Class 4 lasers will easily ignite flammable materials (such as paper or flammable liquids). You must have a fire extinguisher if you have a class 4 laser. In some circumstances, Class 3B lasers could also ignite flammable liquids.

Control Measures:

Engineering Controls

  • Interlocks
  • Enclosed Beam

Administrative Controls

  • Standard Operating Procedures (SOPs)
  • Training
  • Warning Signs
  • Determine Nominal Hazard Zones (NHZ)

Personnel Protective Equipment (PPE)

  • Eye Protection

Warning Labels:

Only Class 1 lasers require no labels. All other lasers must be labeled at the beam's point of origin.

  • Class 2:
    "Laser Radiation - Do Not Stare into Beam."
  • Class 2M:
    "Laser Radiation - Do not Stare into Beam or View Directly with Optical Instruments."
  • Class 3A:
    "Laser Radiation - Avoid Direct Eye Exposure."
  • Class 3B:
    "Laser Radiation - Avoid Direct Exposure to Beam"
  • Class 4:
    "Laser Radiation - Avoid Eye or Skin Exposure to Direct or Scattered Radiation."

Warning Signs:

All rooms with class 3A, 3B or 4 lasers must have appropriate signs posted at all entrances. Signs must:

  • Warn of the presence of a laser hazard in the area.
  • Indicate specific laser safety policies.
  • Indicate the relative hazard such as the laser class and the location of the Nominal Hazard Zone (NHZ). The NHZ must be marked so that the boundary of the NHZ is clearly defined.
  • An audible alarm, warning light or a verbal countdown is required before activation. A visible warning light should flash when the laser is in operation and the light should be readily visible through protective eyewear.
  • Indicate precautions needed such as PPE requirements for eyewear, etc.

"Danger" indicates a very dangerous situation that could result in serious injury or death. This sign should be used for Class 3R, 3B and 4 lasers. Safety instructions may include:

  • Eyewear required
  • Invisible laser radiation
  • Knock before entering
  • Do Not Enter when Light is on
  • Restricted Area

"Caution" indicates a potentially hazardous situation which could cause a less serious injury. This sign should be used for Class 2 and 2M lasers. Safety instructions may include:

  • Eyewear required
  • Invisible laser radiation
  • Knock before entering
  • Do Not Enter when Light is on
  • Restricted Area

"Notice" does not indicate a hazardous situation. This sign should only be used to make people aware of facility policies regarding laser safety and/or to indicate that a service operation is in process. Safety instructions may include:

  • Eyewear required
  • Invisible laser radiation
  • Knock before entering
  • Do Not Enter when Light is on
  • Restricted Area

Leading Causes of Laser Accidents:

  • Unanticipated eye exposure during alignment.
  • Equipment malfunction.
  • Improper methods for handling high voltage.
  • Inadequate training.
  • Laser improperly restored following service.
  • Failure to follow Standard Operating Procedures.
  • Failure to provide non-beam hazard protection.
  • Incorrect eyewear selection and/or failure to wear eyewear.

General Laser Safety Precautions:

  • Always consult with your laser manufacturer's guidelines for laser safety.
  • Always use proper laser eye protection.
  • Operate within a controlled area or secured enclosure only, unless the beam path is totally enclosed.
  • Keep the beam path well above or below the eye level.
  • Do not look directly into a laser beam.
  • Do not point laser beam at other individuals.
  • Report all accidents or suspected eye injuries to the LSO.
  • Avoid wearing reflective objects such as jewelry.
  • Secure the laser against unauthorized use before leaving it unattended.
  • Remove all unnecessary reflective surfaces from the area of the beam path.
  • Permit only properly and authorized personnel to operate the laser.
  • Enclose the entire beam path if possible.
  • If questions or concerns check with the Laser Safety Officer.