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In the USA, lasers are regulated by the FDA according to the Code of Federal Regulations (21CFR1040.10). Lasers are classified for safety purposes based on their potential for causing injury to humans' eyes and skin. For visible-beam consumer lasers, there are four main classes.
A Class I laser is safe under all conditions of normal use. This means the maximum permissible exposure (MPE) cannot be exceeded when viewing a laser with the naked eye or with the aid of typical magnifying optics (e.g. telescope or microscope). It is important to realize that certain lasers classified as Class 1 may still pose a hazard when viewed with a telescope or microscope of sufficiently large aperture
A Class II laser is considered to be safe because the blink reflex (glare aversion response to bright lights) will limit the exposure to no more than 0.25 seconds. It only applies to visible-light lasers (400-700 nm). Class II lasers are limited to 1 mW continuous wave, or more if the emission time is less than 0.25 seconds or if the light is not spatially coherent. Intentional suppression of the blink reflex could lead to eye injury.
A Class IIIa laser is considered safe if handled carefully, with restricted beam viewing. With a class IIIa laser, the maximum permissible exposure (MPE) can be exceeded, but with a low risk of injury. Visible continuous lasers in Class IIIa are limited to 5 mW. For other wavelengths and for pulsed lasers, other limits apply.
A Class IIIb laser is hazardous if the eye is exposed directly, but diffuse reflections such as those from paper or other matte surfaces are not harmful. The accessible emission limits (AEL) for continuous lasers in the wavelength range from 315 nm to far infrared is 500 mW. For pulsed lasers between 400 and 700 nm, the limit is 30 mJ. Class IIIb lasers must be equipped with a key switch and a safety interlock.
Class IV is the highest class of laser, including all lasers that exceed the Class IIIb AEL. By definition, a class IV laser can burn the skin, or cause devastating and permanent eye damage as a result of direct, diffuse or indirect beam viewing. These hazards may also apply to indirect or non-specular reflections of the beam, even from apparently matte surfaces-meaning that great care must be taken to control the beam path. Class IV lasers must be equipped with a key switch and a safety interlock. Most industrial, scientific, military, and medical lasers are in this category.
Any laser product which during operation does not permit human access to laser radiation in excess of the Accessible Emission Limit (AEL) of Class 1 for applicable wavelengths and emission durations. Laser products that are safe during use, including long-term direct intrabeam viewing, even when exposure occurs while using telescopic optics. Class 1 also includes high power lasers that are fully enclosed so that no potentially hazardous radiation is accessible during use (embedded laser product). Intrabeam viewing of Class 1 laser products which emit visible radiant energy may still produce dazzling visual effects, particularly in low ambient light.
Any laser product in the wavelength range from 400 nm to 700 nm which during operation does not permit human access to laser radiation in excess of the AEL of Class 2 for applicable wavelengths and emission durations. The output of a Class 2M laser product is potentially hazardous when viewed using telescopic optics such as a telescope or a binocular. Laser products that emit visible laser beams and are safe for short time exposure only for the naked (unaided) eye. The MPE can be exceeded and eye injury may occur following exposure with telescopic optics such as binoculars for a collimated beam with a diameter larger than the measurement diameter specified for Condition 3 (see Table 10).
Any laser product in the wavelength range from 400 nm to 700 nm which during operation does not permit human access to laser radiation in excess of the AEL of Class 2 for applicable wavelengths and emission durations Laser products that emit visible radiation in the wavelength range from 400 nm to 700 nm that are safe for momentary exposures but can be hazardous for deliberate staring into the beam. The time base of 0.25 s is inherent in the definition of the class and presumption is that there is very low risk of injury for momentary exposures that are somewhat longer. The following factors contribute to precluding injury under reasonably foreseeable conditions:
- unintentional exposures would rarely reflect worst-case conditions, for example, of beam alignment with the pupil for a stabilised head, worst-case accommodation;
- the inherent safety margin in the MPE upon which the AEL is based;
- natural aversion behaviour for exposure to bright light.
However, dazzle, flash-blindness and afterimages may be caused by a beam from a Class 2 laser product, particularly under low ambient light conditions. This may have indirect general safety implications resulting from temporary disturbance of vision or from startle reactions. Such visual disturbances could be of particular concern if experienced while performing safety-critical operations such as working with machines or at height, with high voltages or driving.
Users are instructed by labelling not to stare into the beam, i.e. to perform active protective reactions by moving the head or closing the eyes and to avoid continued intentional intrabeam viewing.
Any laser product in the wavelength range from 400 nm to 700 nm which during operation does not permit human access to laser radiation in excess of the AEL of Class 2 for applicable wavelengths and emission durations. The output of a Class 2M laser product is potentially hazardous when viewed using telescopic optics such as a telescope or a binocular. Laser products that emit visible laser beams and are safe for short time exposure only for the naked (unaided) eye. The MPE can be exceeded and eye injury may occur following exposure with telescopic optics such as binoculars for a collimated beam with a diameter larger than the measurement diameter specified for Condition 3 (see Table 10).
Any laser product which during operation permits human access to laser radiation in excess of the AEL of Class 1 and Class 2 as applicable, but which does not permit human access to laser radiation in excess of the AEL of Class 3R for any emission duration and wavelength. Laser products that emit radiation that can exceed the MPE under direct intrabeam viewing, but the risk of injury in most cases is relatively low. The AEL for Class 3R is limited to 5 times he AEL of Class 2 (visible laser radiation) or 5 times the AEL of Class 1 (for non-visible laser radiation). Because of the lower risk, fewer manufacturing requirements and control measures for the user (depending on national regulations) apply than for Class 3B. While Class 3R laser products are not considered intrinsically safe, the risk is limited because
- unintentional exposures would rarely reflect worst-case conditions of (e.g.) beam alignment with a large pupil and worst-case accommodation with the entire beam energy entering the eye.
- of the inherent reduction factor (safety margin) in the MPE.
- of natural aversion behaviour for exposure to bright light for the case of visible radiation and by the response to heating of the cornea for far infrared radiation.
The risk of injury increases with exposure duration, and exposure may be hazardous for ocular exposure under worst-case conditions or for intentional direct intrabeam viewing
Any laser product which during operation permits human access to laser radiation in excess of the AEL of Class 1, Class 2, and Class 3R as applicable, but which does not permit human access to laser radiation in excess of the AEL of Class 3B for any emission duration and wavelength. Laser products that are normally hazardous when intrabeam ocular exposure occurs (i.e. within the Nominal Hazzard Zone) including accidental short time exposure. Viewing diffuse reflections is normally safe. Class 3B lasers which approach the AEL for Class 3B may produce minor skin injuries or even pose a risk of igniting flammable materials. However, this is only likely if the beam has a small diameter or is focussed.
Any laser product which permits human access to laser radiation (accessible emission, see 3.2) in excess of the AEL of Class 3B. Laser products for which intrabeam viewing and skin exposure is hazardous and for which the viewing of diffuse reflections may be hazardous. These lasers also often represent a fire hazard.
Maximum accessible emission permitted within a particular class. The IEC uses a comprehensive table of values to determine the AEL for each safety class. These tables consider exposure time, power, wavelength, peak power, and other variables to enable the user to accurately determine the safety risk in a variety of situations.
Two measurement conditions are specified for the determination of the accessible emission. Condition 1 is applied for wavelengths where aided viewing of collimated beams with telescopic optics may increase the hazard. Condition 3 applies to the unaided eye. For power and energy measurement of scanned laser radiation, only Condition 3 shall be used. For classification of laser products intended for use exclusively indoors and where intrabeam viewing with telescopic optics such as binoculars is not reasonably foreseeable, it is not required to apply Condition 1
| Condition 1 applied to collimated beam where e.g. telescope or binoculars may increase the hazard * | Condition 3 applied to determine irradiation relevant for the unaided eye, for low power magnifiers and for scanning beams | |||
| Wavelength nm | Aperture stop mm | Distance mm | Aperture stop/limiting aperture mm | Distance mm |
| >=400 to 1400 | 50 | 2000 | 7 | 100 |
Measurement condition 3 is one of the major differences between the FDA and IEC safety standards. This condition permits a variety of laser products with diverging optics (like line lenses) to be classified in a lower safety class than would be allowed according to FDA standards, as it only takes into account the amount of optical power that can pass through a 7mm aperture at a 10cm distance.