From the first lasers in 1964, it was clear that this light source had a power not only to do the required job, but that could also be dangerous if operated improperly. Laser safety is the safe design, use and implementation of lasers to minimize the risk of laser accidents, especially those involving eye injuries. Since even relatively small amounts of laser light can lead to permanent eye injuries, the sale and usage of lasers is typically subject to government regulations. Laser are now divided into Class 1, Class 1M, Class 2, Class 2M, Class 3R(3A), Class 3B, Class 4. In the USA it is considered that Class 1 to Class 3R(3A) lasers are safe for consumers, while the EU requires lasers to be Class 1, Class 2, Class 1M, Class 2M for consumers products. It is suggested to people working with class 3B and class 4 lasers to protect their eyes with safety goggles, which are designed to absorb light of a particular wavelength.
The main characteristics and requirements for the classification system as specified by the IEC 60825-1 standard are listed, along with typical required warning labels. Additionally, class 2 and higher must have the triangular warning label shown here and other labels are required in specific cases indicating laser emission, laser apertures, skin hazards, and invisible wavelengths.
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Classification: IEC60825-1 Standard
The classification of a laser is based on the concept of accessible emission limits (AEL) that are defined for each laser class. This is usually a maximum power (in W) or energy (in J) that can be emitted in a specified wavelength range and exposure time that passes through a specified aperture stop at a specified distance. Below, the main characteristics and requirements for the classification system as specified by the IEC 60825-1 standard are listed, along with typical required warning labels. Additionally, classes 2 and higher must have the triangular warning label shown here and other labels are required in specific cases indicating laser emission, laser apertures, skin hazards, and invisible wavelengths.
Class 1 (Output Power <0.39mW)
A Class 1 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). To verify compliance, the standard specifies the aperture and distance corresponding to the naked eye. For example, a high-power laser with a very large beam or highly divergent beam may be classified as Class 1 if the power that passes through the apertures defined in the standard is less than the AEL for Class 1. Often, devices such as optical drives will be considered class 1 if they fully contain the beam of a more powerful laser, such that no light escapes under normal use.
Class 1M (for Divergent Laser, Output Power <0.39mW through Dia.7mm Aperture @10cm Distance)
A Class 1M laser is safe for all conditions of use except when passed through magnifying optics such as microscopes and telescopes. Class 1M lasers produce large-diameter beams, or beams that are divergent. The MPE for a Class 1M laser cannot normally be exceeded unless focusing or imaging optics are used to narrow the beam. A laser can be classified as Class 1M if the power that can pass through the pupil of the naked eye is less than the AEL for Class 1.
Class 2 (Output Power <1mW)
A Class 2 laser is considered to be safe but may cause eyes uncomfortable if stare into laser light long time. Class-2 lasers are limited to 1 mW continuous wave, or more if the emission time is less than 0.25 seconds.
Class 2M (for Divergent Laser, Output Power <1mW through Dia.7mm Aperture @10cm Distance)
A Class 2M laser is safe because of the blink reflex if not viewed through optical instruments. As with class 1M, this applies to laser beams with a large diameter or large divergence, for which the amount of light passing through the pupil cannot exceed the limits for class 2.
Class 3R(3A) (Output Power <5mW)
A Class 3R laser is considered safe if handled carefully, with restricted beam viewing. With a class 3R laser, the MPE can be exceeded, but with a low risk of injury. Visible continuous lasers in Class 3R are limited to 5mW. For other wavelengths and for pulsed lasers, other limits apply.
Class 3B (Output Power <0.5W)
A Class 3B 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 AEL for continuous lasers in the wavelength range from 315 nm to far infrared is 0.5 W. For pulsed lasers between 400 and 700 nm, the limit is 30mJ. Class-3B lasers must be equipped with a key switch and a safety interlock. Class 3B lasers are used inside CD and DVD writers, although the writer unit itself is class 1 because the laser light cannot leave the unit.
Class 4 is the highest and most dangerous class of laser, including all lasers that exceed the Class 3B AEL. By definition, a class 4 laser can burn the skin, or cause devastating and permanent eye damage as a result of direct, diffuse or indirect beam viewing. These lasers may ignite combustible materials, and thus may represent a fire risk. Class 4 lasers must be equipped with a key switch and a safety interlock. Most industrial, scientific, military, and medical lasers are in this category. Medical lasers can have divergent emissions and require awareness of nominal ocular hazard distance (NOHD) and nominal ocular hazard area (NOHA).
More laser safety introduction: https://en.wikipedia.org/wiki/Laser_safety
IEC60825-1 : 2014 official link: https://webstore.iec.ch/publication/3587