Laser Standards and Classifications

Among the most often asked questions in the laser industry is that of the differences between the various laser standards and classifications. In an effort to provide some clarity on the subject, the following is presented:

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 lasersor 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 lasersare 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.

⁽¹⁾ Note that the ANSI Z136.1 (2000) Standard is under revision and is [proposing the adoption of the IEC Standard’s Classification Scheme described below.

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⁾

Class I laser product means any laser product that does not permit human access during the operation to levels of laser radiation in excess of the accessible emission limits as defined in Table I of 21 CFR Subchapter J Part 1040.10. Class I levels of laser radiation are not considered to be hazardous.
Class II laser product means any laser product that permits human access during operation to levels of visible laser radiation in excess of the accessible emission limits contained in Table II-A of 21 CFR Subchapter J Part 1040.10, but does not permit human access during operation to levels of laser radiation in excess of the accessible emission limits contained in Table II of 21 CFR Subchapter J Part 1040.10. Class II levels of laser radiation are considered to be a chronic viewing hazard.
Class IIIa laser product means any laser product that permits human access during operation to levels of visible laser radiation in excess of the accessible emission limits contained in Table II of 21 CFR Subchapter J Part 1040.10, but does not permit human access during operation to levels of laser radiation in excess of the accessible emission limits contained in Table III-A of 21 CFR Subchapter J Part 1040.10. Class IIIa levels of laser radiation are considered to be, depending upon the irradiance, either an acute intrabeam viewing hazard or chronic viewing hazard, and an acute viewing hazard if viewed directly with optical instruments.
Class IIIb laser product means any laser product that permits human access during operation to levels of laser radiation in excess of the accessible emission limits of Table III-A, but does not permit human access during operation to levels of laser radiation in excess of the accessible emission limits contained in Table III-B of 21 CFR Subchapter J Part 1040.10. Class IIIb levels of laser radiation are considered to be an acute hazard to the skin and eyes from direct radiation. Class IIIb laser products may have removable panels that, when displaced, permit access to levels of laser radiation ranging from Class II to Class IV.
Class IV laser product means any laser that permits human access during operation to levels of laser radiation in excess of the accessible emission limits contained in Table III-B of 21 CFR Subchapter J Part 1040.10. Class IV levels of laser radiation are considered to be an acute hazard to the skin and eyes from direct and scattered radiation. Class IV laser products may have removable panels that, when displaced, permit access to levels of laser radiation ranging from Class II to Class IV.

⁽²⁾ Note that the FDA/CDRH LPP Standard is under revision and is [proposing the adoption of the IEC Standard’s Classification Scheme described below.

OSHA

Within the Department of Labor is the Occupational Safety and Health Administration (OSHA), which is responsible for assuring a safe work place. At the present time, OSHA does not have a comprehensive laser safety standard. Instead, the OSHA policy has been to rely on ANSI Z136.1, the generally accepted industry laser standard, and FDA/CDRH laser manufacturer requirements.

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 “M” Classes **

As discussed below in the M Classes Table, a laser product is classified as the "non-M" class when both Conditions 1 and 2 are satisfied, i.e. the measured power is below the AEL (and therefore below the MPE for the eye) even when the measurement requirements reflect the possible use of optical instruments. If one of the power values measured according to Condition 1 or Condition 2 is larger than the AEL, the product can no longer be in that "non-M" category, i.e. it can not be Class 1 or Class 2. It can however be in the Class-M category when the power or energy measured with a 7 mm aperture at a distance of 10 cm from the apparent source is below the AEL. The measurement condition of 7 mm aperture at a distance of 10 cm from the apparent source ensures that the exposure of the naked eye to radiation from a Class-M product is below the MPE for the eye, i.e. as long as no optical instrument is used, Class 1M is as safe as Class 1 (and Class 2 as safe as Class 2M).

As the MPE can potentially be exceeded considerably for the Classes 1M and 2M when exposure occurs with optical instruments, the maximum power or energy collected with optical instruments (i.e. the power or energy as measured under Condition 1 and 2) is limited to the AEL of Class 3B. Consequently in terms of the power of a product when measured with a large aperture (5 cm at 2 m) or at close distance (7 mm at 14 mm), this power can be larger for a Class 1M or Class 2M laser product as the power which is allowed for Class 3R, for instance, for a HeNe laser product (632.8 nm) with a 10 mW collimated beam with a diameter of 4 cm (1/e points) at the exit aperture and 5 cm at a distance of 2 m from the laser, the power measured through a 7 mm pupil will be about 0.3 mW, hence the product would be assigned Class 1M (the AEL for Class 1M is 0.39 mW for a point source), however, when measured with a 5 cm aperture. all of the 10 mW would be collected and the measured power would exceed the AEL for Class 3R. The product is to be classified as Class 1M, as this is the smallest AEL which is not exceeded. The irradiance is at least a factor of 3 below the MPE for 0.25 second exposure duration and is also below the MPE for an exposure duration longer than 10 seconds.

The concept outlined here facilitates a practical risk management and also makes the setting of restrictions on the use of a given category of products simpler and more flexible. For instance when the exposure with optical instruments is unlikely, the use of Class 1M and Class 2M will represent a correspondingly small risk for injury. For the practical use of the Class-M category in terms of user controls and restrictions it is important to define which one of the two measurement conditions was not fulfilled, i.e. if the AEL was exceeded for measurement Condition 1, user controls should be considered when it is anticipated that exposure through telescopes can occur. Generally, collimated laser beams with a large diameter fall in that category and an example could be the use of a range finder on a military training ground where it is “reasonably foreseeable” that exposure with large binoculars occurs.

By way of comparison, the use of a Class 1M laser speed meter when used for traffic control, where exposure with binoculars is unlikely, might be acceptable in terms of associated risk, i.e. probability for injury. On the other hand, when a product is assigned to the Class-M category because it failed Condition 2, it is usually safe to be exposed to radiation from the product through binoculars or telescopes, while an exposure with an eye loupe or magnifier would increase the hazard. An example for the general category of products which could fail Condition 2 are LED and various fiber optic based laser sources.

^** The “M” Classes portion is an excerpt from Review of Current Topics in Laser Safety By Karl Schulmeister, Austrian Research Centers Seibersdorf

Comparison of Classifications

The following charts have been created to illustrate the various similarities and differences between the classification criteria of the different laser standards.

Class	IEC 60825 (Amend. 2)	U.S. FDA/CDRH	ANSI-Z136.1 (2000)
Class 1	Any laser or laser system containing a laser that cannot emit laser radiation at levels that are known to cause eye or skin injury during normal operation. This does not apply to service periods requiring access to Class 1 enclosures containing higher class lasers.
Class 1M	Not known to cause eye or skin damage unless collecting optics are used.	N/A	N/A
Class 2a	N/A	Visible lasers that are not intended for viewing and cannot produce any known eye or skin injury during operation based on a maximum exposure time of 1000 seconds.	N/A
Class 2	Visible lasers considered incapable of emitting laser radiation at levels that are known to cause skin or eye injury within the time period of the human eye aversion response (0.25 seconds).
Class 2M	Not known to cause eye or skin damage within the aversion response time unless collecting optics are used.	N/A	N/A
Class 3a	N/A	Lasers similar to Class 2 with the exception that collecting optics cannot be used to directly view the beam Visible Only	Lasers similar to Class 2 with the exception that collecting optics cannot be used to directly view the beam
Class 3R	Replaces Class 3a and has different limits. Up to 5 times the Class 2 limit for visible and 5 times the Class 1 limits for some invisible.	N/A	N/A
Class 3b	Medium powered lasers (visible or invisible regions) that present a potential eye hazard for intrabeam (direct) or specular (mirror-like) conditions. Class 3b lasers do not present a diffuse (scatter) hazard or significant skin hazard except for higher powered 3b lasers operating at certain wavelength regions.
Class 4	High powered lasers (visible or invisible) considered to present potential acute hazard to the eye and skin for both direct (intrabeam) and scatter (diffused) conditions. Also have potential hazard considerations for fire (ignition) and byproduct emissions from target or process materials.

Overview of Laser Safety Classes*

Class	Type of lasers	Meaning	Relationship to MPE	Hazard Area	Typical AEL for CW Lasers
Class 1	Very low power lasers or encapsulated lasers	Safe	MPEs are not exceeded, even for long exposure duration (either 100 seconds or 30000 seconds), even with the use of optical instruments	No hazard area (NOHA)	40 µW for blue
Class 1M	Very low power lasers; either collimated with large beam diameter or highly divergent	Safe for the naked eye, potentially hazardous when optical instruments** are used	MPEs are not exceeded for the naked eye, even for long exposure durations, but maybe exceeded with the use of optical instruments**	No hazard area for the naked eye, but hazard area for the use of optical instruments** (extended NOHA)	Same as Class 1, distinction with measurement requirements
Class 2	Visible low power lasers	Safe for unintended exposure, prolonged staring should be avoided	Blink reflex limits exposure duration to nominally 0.25 seconds. MPE for 0.25 seconds not exceeded, even with the use of optical instruments.	No hazard area when based on unintended exposure (0.25 seconds exposure duration)	1 mW
Class 2M	Visible low power lasers; either collimated with large beam diameter or highly divergent	Same as Class 2, but potentially hazardous when optical instruments** are used	MPE for 0.25 seconds not exceeded for the naked eye, but maybe exceeded with the use of optical instruments**	No hazard area for the naked eye when based on accidental exposure (0.25 seconds exposure duration), but hazard area for the use of optical instruments** (extended NOHA)	Same as Class 2, distinction with measurement requirements
Class 3R	Low power lasers	Safe when handled carefully. Only small hazard potential for accidental exposure	MPE with naked eye and optical instruments may be exceeded up to 5 times	5 times the limit of Class 1 in UV and IR, and 5 times the limit for Class 2 in visible, i.e. 5 mW	5 times the limit of Class 1 in UV and IR, and 5 times the limit for Class 2 in visible, i.e. 5 mW
Class 3B	Medium power lasers	Hazardous when eye is exposed. Wear Eye Protection within NOHA. Usually no hazard to the skin. Diffuse reflections usually safe	Ocular MPE with naked eye and optical instruments may be exceeded more than 5 times. Skin MPE usually not exceeded.	Hazard area for the eye (NOHA), no hazard area for the skin	500 mW
Class 4	High power lasers	Hazardous to eye and skin, also diffuse reflection may be hazardous. Protect Eye and skin. Fire hazard.	Ocular and skin MPE exceeded, diffuse reflections exceed ocular MPE	Hazard area for the eye and skin, hazard area for diffuse reflections	No limit

**Note for optical instruments: two classes of optical instruments are accounted for: such that increase hazard of well collimated beam with large diameter, i.e. telescopes and binoculars, and such that increase hazard of highly divergent beams (such as from fibers or LEDs), i.e. eye loupes and magnifiers. Generally only one of the group of optical instrument for a given laser product leads to an increase in the hazard. Therefore, at the discretion of the manufacturer, a specific wording can be added to the warning label. See sections on optical instruments and warning labels below.

* Chart Courtesy of David Sliney

Note: The above table discusses the classification scheme and concept of the new (2001) edition of IEC 60825-1 and compares it to the previous scheme in terms of AEL values and definition of the classes. However, additionally to some changes of the class definitions and classification scheme, also the measurement requirements for assessing the class, i.e. the aperture diameter and distance, are somewhat different in the new edition in comparison with the previous version. Therefore, if in above table it says “unchanged”, this means that the concept, definition and AEL of the class is unchanged, but it does not mean that a specific laser product, which was classified as for instance Class 4 because the emission as measured with the previous requirements was slightly above the AEL for Class 3B, might not be classified as Class 3B following the measurement requirements of the new edition of the standard.

Summary of Concept of Subclasses "M"

	Time Base	Class		Class -M
AEL for Class 1, 1M	100 seconds or 30000 seconds	Generally safe, even for intentional exposure, for the naked eye and with optical instruments		Safe even for intentional exposure of the naked eye, potentially hazardous for exposure with optical instruments of either category 1 or 2
AEL for Class 2, 2M	0.25 seconds	Safe for accidental exposure, for the naked eye and with optical instruments		Safe for accidental exposure, potentially hazardous for exposure with optical instruments of either category 1 or 2
Measurement Conditions* (measured power < AEL)		Condition 1	Condition 2
	To account for possible use of	Binoculars, telescopes	Eye loupes, magnifiers	Unaided eye
	Usually limiting condition for	Large diameter well collimated beams	Divergent beams	-
	Aperture diameter	50 mm	7 mm	7 mm
	Distance	2 m	14 mm	10 cm

b* simplified presentation, strictly only applicable for point sources and for wavelengths in the retinal hazard region. The 2 m measurement distance is measured from the physical product while 14 mm and 10 cm distance are measured from the position of the apparent source. For other wavelengths and extended sources the measurement requirements differ and are not discussed here.