Laser Safety FAQs

Do all lasers at Yale have to be registered with the Office of Environmental Health and Safety?

No. Only lasers that are Class 3B or Class 4 have to be registered with Environmental Health and Safety. This requirement also includes embedded Class 3B or 4 lasers such as laser cutters/engravers and certain microscopy units. If you are unsure if your unit needs to be registered, contact the Laser Safety Officer at lasersafety@yale.edu.

What is the difference between a Class 3B laser and a Class 4 laser?

Laser classes are based on the output power of the laser. Lasers that have output powers between 5 mW and 500 mW are considered to be Class 3B. Lasers with output powers greater than 500 mW are considered to be Class 4.

What are the hazards associated with each laser class?

Lasers in classes 1, 1M, 2, 2M, and 3R are not generally considered to be hazardous when used as intended and the laser light is not intentionally directed into the eye. The eye is protected from unintentional exposures by the aversion response (the body’s natural response of looking away from bright light) and blinking.

Class 3B lasers are of high enough power that the aversion response is not effective to prevent injury. Lasers in this class can cause eye injury if the direct beam or a specular reflection enters the eye.

Class 4 lasers can be hazardous if the eye is exposed to the direct beam or specular or diffuse reflections. Lasers in this class can also be a fire hazard and create laser generated air contaminants when interacting with certain materials.

When is laser safety training required?

Laser Safety Awareness Training and Laser Safety Training Part II On-the-Job Training Checklist are required for anyone who is working with Class 3B or 4 lasers or who will be in the lab while Class 3B or 4 lasers are operating. Departments with laser cutters\engravers have specialized trainings for their facilities.

When is laser light capable of causing injury?

Laser light is capable of causing eye or skin injury if it is greater than the maximum permissible exposure (MPE) for that laser. Maximum permissible exposure is the level of radiation to which an unprotected person may be exposed without adverse biological changes in the eye or skin. The MPE is calculated for each laser and is dependent on the wavelength or the beam and the exposure duration. To get this value for your laser, contact the Laser Safety Officer at lasersafety@yale.edu.

What personal protective equipment is needed when working with lasers?

The most important laser protective equipment needed is laser protective eyewear. Laser protective eyewear must be worn at all times when working with Class 3B and 4 lasers. If UV lasers are used, lab coats or long sleeves are recommended to protect the skin. When working with high-powered lasers that can cause fires, a flame-resistant lab coat should be considered.

How does laser protective eyewear (LPE) differ from regular safety glasses?

LPE contains layers of attenuating filter material that reduces the level of laser light reaching the eye. LPE has a specific wavelength range (or multiple ranges) that it can attenuate and a limit to how much attenuation occurs (optical density(OD)). The optical density is a measure of the attenuation needed to reduce the level of laser light reaching the eye to below the maximum permissible exposure (MPE). To find the necessary OD value for your laser, contact the Laser Safety Officer at lasersafety@yale.edu.

What does OD stand for?

The optical density is a measure of the attenuation needed to reduce the level of laser light reaching the eye to below the maximum permissible exposure (MPE).

The following is an example of how the Optical Density value translates into the percentage of laser light reaching the eye.

  • OD of 0 = 100% of light reaches the eye
  • OD of 1 = 10%
  • OD of 2 = 1%
  • OD of 3 = 0.1%
  • OD of 4 = 0.01%
  • OD of 5 = 0.001%
Can the same pair of laser protective eyewear be worn for any laser?

This depends on the characteristics of the lasers being used. Laser protective eyewear is designed to protect certain wavelength ranges with a specific optical density (OD). An example of coverage for a pair of eyewear is: 190-534nm OD 6.5+, 910-1070 OD 6+. This would provide protection for any laser that fell in those wavelength ranges and required an OD of less than 6.5 or 6, respectively. Contact the Laser Safety Officer at lasersafety@yale.edu to confirm that the laser protective eyewear being used is appropriate for your laser(s).