To inform those that may encounter lasers, they are classified according to their potential to cause biological damage. 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.
In addition to these general parameters, lasers are classified in accordance with the accessible emission limit (AEL), which is the maximum accessible level of laser radiation permitted within a particular laser class. . Safety thresholds for lasers are expressed in terms of maximum permissible exposure (MPE). The higher the classification numbers the greater potential risk the laser or laser system presents. Two bodies are involved in laser hazard classification. The Center for Devices and Radiological Health (CDRH) a part of the Food & Drug Administration and The American National Standards Institute Z136.1 Safe Use of Laser Standard. Of these two it is the CDRH that laser manufacturers need to satisfy for there are minor differences between the two. Laser or laser system in use at LBNL are classified per CDRH criteria. The classifications are as follows:
This class is eye-safe under all operating conditions. A Class 1 laser is safe for use under all reasonably anticipated conditions of use; in other words, it is not expected that the MPE can be exceeded.
Class 1 Product
This is a laser product or device which may include lasers of a higher class whose beams are confined within a suitable enclosure so that access to laser radiation is physically prevented. Such products do not require a laser warning label on the exterior, think of a laser printer.
This class is safe for viewing directly with the naked eye, but may be hazardous to view with the aid of optical instruments. In general, the use of magnifying glasses increases the hazard from a widely diverging beam (e.g. LEDs and bare laser diodes), and binoculars or telescopes increase the hazard from a wide, collimated beam (such as those used in open-beam telecommunications systems).
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 down the beam. If the beam is refocused, the hazard of Class 1M lasers may be increased and the product class may be changed.
A Class 2 laser emits in the visible region (400-700nm). It is presumed that the natural aversion response to the very bright light will be sufficient to prevent damaging exposure, although prolonged viewing may be dangerous.
These are visible lasers. This class is safe for accidental viewing with the naked eye, as long as the natural aversion response is not overcome as with Class 2, but may be hazardous (even for accidental viewing) when viewed with the aid of optical instruments, as with class 1M.
Classes 1M and 2M broadly replace the old class 3A under IEC and EN classification. Prior to the 2001 amendment there were also lasers, which were, Class 3B but were eye-safe when viewed without optical instruments. These lasers are Class 1M or 2M under the current Classification system.
Class 3R (replacement for Class 3A)
A Class 3R laser is a continuous wave laser, which may produce up to five times the emission limit for Class 1, or Class 2 lasers. Although the MPE can be exceeded, the risk of injury is low. The laser can produce no more than 5 mW in the visible region.
Visible class 3R is similar to class IIIA in the US regulations.
A Class 3B laser produces light of intensity such that the MPE for eye exposure may be exceeded and direct viewing of the beam is potentially serious. Diffuse radiation (i.e., that which is scattered from a diffusing surface) should not be hazardous. CW emission from such lasers at wavelengths above 315nm must not exceed 0.5 watts. For pulse laser system to be Class 3B their output cannot exceed 125 mJ in less than 0.25 seconds.
This is the highest class of laser radiation. These are hazardous to view at all times, may cause devastating and permanent eye damage, may have sufficient energy to ignite materials, and may cause significant skin damage. Exposure of the eye or skin to both the direct laser beam and to scattered beams, even those produced by reflection from diffusing surfaces, must be avoided at all times. In addition, they may pose a fire risk and may generate hazardous fumes. Class 4 output levels for CW start at 500 mW and for pulse systems they CAN producer over 125mJ in less than 0.25 seconds.
The origin of Class 1M, 2M, 3R
In 2001 the standard governing the safety of laser products in Europe (EN) and Internationally (IEC), was substantially revised and the Classification system was overhauled. This resulted in the introduction of three new laser classes (1M, 2M and 3R) and the abolition of Class 3A. Below is a brief description of each of the current laser classes.
The 60825-1 standards apply equally to lasers and LEDs. In most places we have used the word “laser”, but “LED” can replace it. Generally speaking LEDs would be in the lower Classes (1, 1M, 2, 2M, 3R), but very exceptionally may be Class 3B. At the time of writing we are not aware of any Class 4 LEDs*.
The phrase “eye-safe” is used below. Please note that “eye-safe” is applicable to the whole optical spectrum from 180nm to 1mm wavelength, not just in the retinal hazard range of 400nm to 1400nm. Outside the retinal hazard range there is potentially a hazard to the cornea. A wavelength outside the retinal hazard range is therefore not automatically eye-safe!
|CW||Continuous Wave – i.e. not pulsed|
|Diffuse reflection||The reflection of radiation from a matt surface such as a wall|
|Extended source||Having an apparent source size with angular subtense of greater than 1.5 mradian|
|Optical instruments||Binoculars, telescopes, microscopes, magnifying glasses (but not prescription glasses)|
|Point source||Having an apparent source size with angular subtense of less than 1.5 mradian|
Note: For a product to be classified correctly, it must be tested at the maximum output accessible under reasonably foreseeable single-fault conditions (e.g. in the drive circuitry). A non-M class product must pass both Condition 1 and Condition 2 of Table 10 in IEC/EN 60825-1, and an M-class product (which by definition has failed either Condition 1 or 2) must pass the irradiance condition in the same table.