Laser Classifications

The ANSI Standard Laser Hazard Classifications are used to signify the level of hazard inherent in a laser system and the extent of safety controls required. These range from Class 1 lasers (which are inherently safe for direct beam viewing under most circumstances) to Class 4 laser (which require the most strict controls).

The pertinent parameters are:

• laser output energy or power
• radiation wavelengths
• exposure duration
• cross-sectional area of the laser beam at the point of interest

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 a laser, the energy involved, and the duration of the exposure. MPE is a necessary parameter in determining the appropriate optical density and the nominal hazard zone.

The laser classifications are described below:

Class 1-Exempt Lasers

All Class 1 lasers must be labeled.
Class 1 laser cannot, under normal operating conditions, produce damaging radiation levels. These lasers are exempt from the requirements of most corporate Laser Safety Programs. A laser printer is an example of a Class 1 laser.

Class 2-Low Power Visible Lasers

Class 2 lasers must be labeled.
Class 2 lasers are low power lasers or laser system in the visible range (400 - 700 nm wavelength) that may be viewed directly under carefully controlled exposure conditions.
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. A continuous wave (cw) HeNe laser above Class 1, but not exceeding 1 mW radiant power is an example of a Class 2 laser.

Class 3-Medium Power Lasers and Laser Systems

Class 3 lasers are medium power lasers or laser systems that require control measures to prevent viewing of the direct beam. Control measures emphasize preventing exposure of the eye to the primary or specularly reflected beam.

Class 3a denotes lasers or laser systems that normally would not produce a hazard if viewed for only momentary periods with the unaided eye. They may present a hazard if viewed using collecting optics.

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. Visible CW HeNe lasers above 1 mW, but not exceeding 5 mW radiant power, are examples of this class.

Class 3b denotes lasers or laser systems that can produce a hazard if viewed directly. This includes intrabeam viewing or specular reflections. Except for the higher power Class 3b lasers, this class laser will not produce diffuse reflections.

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. Visible CW HeNe lasers above 5 mW, but not exceeding 500 mW radiant power, are examples of this class.

Class 4-High Power Lasers and Laser Systems

Class 4 Lasers are high power lasers or laser systems that can produce a hazard not only from direct or specular reflections, but also from a diffuse reflection. In addition, such lasers may produce fire and skin hazards. Class 4 lasers include all lasers in excess of Class 3 limitations.

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:

• restricted to authorized personnel only
• designed to allow for rapid emergency egress
• equipped with a device that allows for deactivation of the laser or reduction of the output to below the MPE
• designed to fulfill Class 3b controlled area requirements
• designed with entry safe controls
• designed such that the laser may be monitored and fired from a remote location
• (for pulsed systems) have interlocks designed to prevent firing of the laser by dumping the stored energy into a dummy load
• (for continuous wave systems) have interlocks designed to turn off the power supply or interrupt the beam by means of shutters.

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.