Lasers have been classified by wavelength and maximum output power into four classes and a few subclasses since the early 1970s. The classifications categorize lasers according to their ability to produce damage in exposed people, from class 1 (no hazard during normal use) to class 4 (severe hazard for eyes and skin). These classes are I, II IIa, IIIa, IIIb and IV for the U.S., and 1, 1M, 2,2M, 3R, 3B and 4 for Europe.
Laser Standards and Recommendations
The Federal Food and Drug Administration (FDA) Center for Devices and Radiological Health (CDRH) has the responsibility for implementing and enforcing the laws and regulations which apply to radiation- producing electronic products and medical devices.
Medical devices, including laser systems for medical applications, require clearance by the FDA in order to be introduced commercially in the US. The clearance can follow the review of a premarket notification under section 510(k) of the Federal Food, Drug and Cosmetic Act (FFDCA) for a device that is substantially equivalent to a device that was in commercial distribution in the US prior to May 1976 or to previously cleared devices. Clearances are device specific and for indications claimed in the cleared labeling.
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 in determining appropriate optical density and the nominal hazard zone.
CDRH The Center for Devices and Radiological Health
IEC The International Electrotechnical Commission
ANSI The American National Standards Institute
Some states currently require registration of medical lasers. The regulations cover use of class IIIB and IV medical lasers and require following specific guidelines for use.
Overview of Laser Classifications
The Food and Drug Administration (FDA) recognizes four major hazard classes (I to IV) of lasers, including three subclasses (IIa, IIIa, and IIIb). The higher the class, the more powerful the laser and the potential to pose serious danger if used improperly. The labeling for Classes II–IV must include a warning symbol that states the class and the output power of the product. IEC equivalent classes are included for products labeled under the classification system of the International Electrotechnical Commission.
The Center for Devices and Radiological Health (CDRH)
The Center for Devices and Radiological Health (CDRH) is a regulatory bureau within the U.S. Federal Food and Drug Administration (FDA) of the Department of Health and Human Services. CDRH has been chartered by Congress to standardize the performance safety of manufactured laser products.
All laser products that have been manufactured and entered into commerce, after August 2, 1976, must comply with these regulations. The regulation is known as the Federal Laser Product Performance Standard (FLPPS), and is identified as 21CFR subchapter parts 1040.10 and 1040.11. The FLPPS assigns lasers into one of four broad hazards in a manner similar to the ANSI Z136.1 (2000) Standard – Classes I, II, IIIa, IIIb and IV) depending on the potential for causing biological damage.(2)
There are laws, regulations, and standards that require engineering controls and risk communication to aid in the management of the biological hazards associated with each laser class. However, no controls are completely effective if lasers are improperly used.
Lasers and Laser Systems – “Exempt Lasers”
These lasers are exempt from the requirements of most corporate Laser Safety Programs. Class 1 laser cannot, under normal operating conditions, produce damaging radiation levels. All Class 1 lasers must be labeled.
CD/ DVD players
Lasers and Laser Systems – “Low Power Visible Lasers”
Output: 1 milliwatt (mW) of continuous wave
Wavelength: 400–700 nanometers (nm) (visible)
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. Eye protection is usually afforded by aversion response and blink reflex (0.25 seconds). However, a class 2 laser beam could be hazardous if one were to intentionally expose the eye for longer than 0.25 seconds. 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.
Example: barcode scanners
Lasers and Laser Systems – “Medium Power”
Output: 1–5 mW of continuous wave
Wavelength: Infrared spectrum (non-visible)
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. Do not view the direct or reflected beam. 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.
Lasers and Laser Systems – “Medium Power”
Output: 5 – 500mW of continuous wave
Wavelength: Infrared spectrum (non-visible)
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.
An alarm, warning light or verbal countdown should be used during use or startup 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.
Lasers and Laser Systems
Output: 500mW and greater, continuous wave
Wavelength: Infrared spectrum (non-visible)
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.
Used to cut, coagulate and evaporate tissues.
The biological effect is photochemical not thermal, unlike surgical lasers
Used for the stimulation of cell function, provides effective dosage levels in the deep tissues
The International Electrotechnical Commission (IEC)
The International Electrotechnical Commission (IEC) is a global organization that prepares and publishes international standards for all electrical, electronic and related technologies. The IEC document 60825-1 is the primary standard that outlines the safety of laser products. Classification is based on calculations and determined by the AEL as with the ANSI standard, but the IEC standard also incorporates viewing conditions:
Class 1 lasers are very low risk and “safe under reasonably foreseeable use”, including the use of optical instruments for intrabeam viewing.
Class 1M lasers have wavelengths between 302.5 nm and 4000 nm, and are safe except when used with optical aids (e.g. binoculars).
Class 2 lasers do not permit human access to exposure levels beyond the Class 2 AEL for wavelengths between 400 nm and 700 nm. Any emissions outside this wavelength region must be below the Class 1 AEL.
Class 2M lasers have wavelengths between 400 nm and 700 nm, and are potentially hazardous when viewed with an optical instrument. Any emissions outside this wavelength region must be below the Class 1M AEL.
Class 3R lasers range from 302.5 nm and 106 nm, and is potentially hazardous but the risk is lower than that of Class 3B lasers. The accessible emission limit is within 5 times the Class 2 AEL for wavelengths between 400 nm and 700 nm, and within 5 times the Class 1 AEL for wavelengths outside this region.
Class 3B lasers are normally hazardous under direct beam viewing conditions, but are normally safe when viewing diffuse reflections.
Class 4 lasers are hazardous under both intrabeam and diffuse reflection viewing conditions. They may cause also skin injuries and are potential fire hazards.
The American National Standards Institute (ANSI)
The American National Standards Institute (ANSI) is an organization for which expert volunteers participate on committees to set industry consensus standards in various fields. The ANSI Z136 Committee has published or has under development seven standards specific to the laser field. The current version of the main ANSI Z136.1 Standard (Z136.1-2000) assigns lasers into one of four broad hazard Classes (1, 2, 3a, 3b and 4) depending on the potential for causing biological damage. Classification is determined by calculations based on exposure time, laser wavelength and average power for CW or repetitively-pulsed lasers and total energy per pulse for pulsed lasers. (1) These calculations are used to determine a factor defined as the Accessible Emission Limit, or AEL which is the mathematical product of the Maximum Permissible Exposure limit (MPE) given in the Standard and an area factor computed from the defined term called the Limiting Aperture (LA). That is: AEL = MPE x Area of LA. Limiting Apertures are dependent on factors such as laser wavelength and are based on physical factors such as the fully dilated pupil size (7mm) and beam “hotspots” (1mm). For most all exposures to the skin and IR exposures to the eye lasting greater 10 seconds, the involuntary movement of the eyes and the body as well as heat conduction will average an irradiance profile over an area of about 10 mm2, even if the irradiated body part is kept intentionally still. This equates to a size of about 3.5 mm. Especially in the near-infrared, radiation is penetrating relatively deep into skin and due to scattering, the irradiance profile is averaged over corresponding dimensions. For wavelengths larger than 0.1 mm, an aperture size of 11 mm is specified, as smaller apertures would lead to inaccurate measurements due to diffraction effects.
Each laser class is based on these AEL thresholds:
Class 1 lasers or systems cannot emit accessible laser radiation in excess of the applicable Class 1 AEL for any exposure times within the maximum duration inherent in the design or intended use of the laser. Class 1 lasers are exempt from all beam-hazard control measures.
Class 2 lasers are CW and repetitively pulsed lasers with wavelengths between 0.4 µm and 0.7 µm that can emit energy in excess of the Class 1 AEL, but do not exceed the Class 1 AEL for an emission duration less than 0.25 seconds and have an average radiant power of 1mW or less.
Class 3a lasers have an accessible output between 1 and 5 times the Class 1 AEL for wavelengths shorter than 0.4 µm or longer than 0.7 µm, or less than 5 times the Class 2 AEL for wavelengths between 0.4 µm and 0.7 µm.
Class 3b lasers cannot emit an average radiant power greater than 0.5 Watts for an exposure time equal to or greater than 0.25 seconds or 0.125 Joules for an exposure time less than 0.25 seconds for wavelengths between 0.18 µm and 0.4 µm, or between 1.4 µm and 1 mm. In addition, lasers between 0.4 µm and 1.4 µm exceeding the Class 3a AEL cannot emit an average radiant power greater than 0.5 Watts for exposures equal to or greater than 0.25 seconds, or a radiant energy greater than 0.03 Joules per pulse.
Class 4 lasers and laser systems exceed the Class 3b AEL.