The basis for the classifications in this document are:
1. The ANSI Z-136.1 and ANSI Z-136.2 Standards of the American National Standards Institute (ANSI).
2. The U.S. Federal Laser Product Performance Standard (FLPPS): Title 21 of the Code of Federal Regulations; Part 1000;
The intent of laser hazard classification is to provide warning to users by identifying the potential hazards associated with the corresponding levels of accessible laser radiation through the use of labels and instruction. It also serves as a basis for defining appropriate control measures and medical surveillance.
Lasers and laser systems received from manufacturers shall be classified and appropriately labeled by the manufacturer. However, the classification may change whenever the laser or laser system is modified to accomplish a given task.
Also, the Laser Safety Officer (LSO) shall effect the classification designation in cases where the laser or laser system classification is not provided or where the class level may change because of alterations to the laser or laser system.
It should be mentioned that the U.S. Federal Government does not “approve” laser systems. The manufacturer of the laser system first classifies the laser and then certifies that it meets all performance requirements of the Federal Laser Product Performance Standard (FLPPS).
Therefore, all lasers and laser systems that are manufactured by a company, or purchased by a company and relabeled and placed into commerce, or incorporated into a system and placed into commerce, shall be classified in accordance with the FLPPS. The classification shall be confirmed by the LSO at the laser installation.
B. Laser Hazard Classes:
Virtually all of the U.S. and international standards divide all lasers into four major hazard categories called the laser hazard classifications.
The basis of the classification scheme is the ability of the primary or reflected primary beam to cause biological damage to the eye or skin during intended use. The criteria is established relative to the Maximum Permissible Exposure (MPE) levels that are accessible during operation of the laser.
Lasers and laser systems are assigned one of four broad Classes (I to IV) and Optical Fiber Communications Systems (OFCS) are assigned one of four service groups (SG1, SG2, SG3a, SG3b) depending on the potential for causing biological damage.
The laser hazard classes are given as:
CLASS I: cannot emit laser radiation at known hazard levels (typically CW: 0.4 µwatts at visible wavelengths). Users of a Class I laser products are generally exempt from radiation hazard controls during operation and maintenance (but not necessarily during service).
Since lasers are not classified on beam access during service, most all Class I industrial lasers will consist of a higher class (high power) laser enclosed in a properly interlocked and labeled protective enclosure. In some cases, the enclosure may be a room (walk-in protective housing) which requires a means to prevent operation when operators are inside the room.
CLASS II: low power visible lasers which emit above Class I levels but emitting a radiant power not above 1 mW. The concept is that the human aversion reaction to bright light will protect a person.
NOTE: Class IIA is a special designation that is based upon a 1000 second exposure and applies only to lasers that are “not intended for viewing” such as a supermarket laser scanner. The upper power limit of Class IIA is 4.0 µW. These are products whose emission does not exceed the Class I limit for an emission duration of 1000 seconds.
CLASS IIIA: intermediate power lasers (CW: 1-5 mW). Only hazardous for intrabeam viewing. Some limited controls are usually recommended.
NOTE: There are different labeling requirements for Class IIIA lasers with a beam irradiance that does not exceed 2.5 mW/cm(2) (Caution logotype) and those where the beam irradiance does exceed 2.5 mW/cm(2) (Danger logotype).
CLASS IIIB: moderate power lasers (CW: 5-500 mW, pulsed: 10 J/cm(2) – or the diffuse reflection limit, which ever is lower). In general, Class IIIB lasers will not be a fire hazard nor are not generally capable of producing a hazardous diffuse reflection except for conditions of intentional staring done at distances close to the diffuser. Specific controls are recommended.
CLASS IV: High power lasers (cw: 500 mW) are hazardous to view under any condition (directly or diffusely scattered) and are a potential fire hazard and a skin hazard. Significant controls are required of Class IV laser facilities.
EMBEDDED LASER: A Class II, Class III, or Class IV laser or laser system contained in a protective housing and operated in a lower classification (Class I, Class II or Class III). Specific control measures may be required to maintain the lower classification.
C. Optical Fiber Communication Systems (OFCS):
Optical Fiber Communication Systems (OFCS) and the associated optical test sets use semiconductor lasers or LED transmitters that emit energy at wavelengths typically greater than 700 nm into the lightguide fiber optic cables.
All OFCS are designed to operate with the beam totally enclosed within the fiber optic and associated equipment and, therefore, are always considered as Class I in normal operation. The only risk for exposure would occur during installation and service when lightguide cables are disconnected or during an infrequent accidental cable break.
Optical Fiber Communication Systems (OFCS) are assigned into one of four service group designations: SG1, SG2, SG3a, SG3b, depending on the potential for an accessible beam to cause biological damage. The service group designations relate to the potential for ocular hazards to occur only during accessible beam conditions. This would normally occur only during periods of service to a OFCS. Such designations apply only during periods of service in one of the following four service groups (SG):
SERVICE GROUP 1: An OFCS that is SG1 has a total output power that is less than the Accessible Emission Limit (AEL) for Class I and there is no risk of exceeding the Maximum Permissible Exposure (MPE) when viewing the end of a fiber with a microscope, an eye loupe or with the unaided eye.
SERVICE GROUP 2: An OFCS is SG2 only if wavelengths between 400 and 700 nm are emitted and is potentially hazardous if viewed for more than 0.25 s. (Note: at present, there are virtually no OFCS that operate in this wavelength range.)
SERVICE GROUP 3A: A SG 3A OFCS is not hazardous when viewed with the unaided eye and is hazardous only when viewed with a microscope or an eye-loupe. SERVICE GROUP 3B: OFCS which meet none of the above criteria are designated as SG 3B.
NOTE: OFCS where the total power is at or above 0.5W do not meet the criteria for optical fiber service group designation. In this case, the OFCS are treated as a standard laser system.
D. Laser Classification Measurements:
The measurement and test parameters for purposes of laser classification are outlined in detail in 21 CFR Part 1040. For convenience, they are summarized below:
Tests on lasers and laser systems, for purposes of classification, shall be made during operation, maintenance or service as appropriate:
Under those conditions and procedures which maximize the accessible emission levels, including start-up, stabilized emission, and shut-down of the laser or laser system;
With all controls and adjustments listed in the operation, maintenance, and service instruction adjusted in combination to result in the maximum accessible emission level of radiation; and, . For the case of laser diodes, with the device biased to operate at the output power levels specified in the data sheet for the intended use.
At points in space to which human access is possible in the configuration which is necessary to determine compliance with each requirement, e.g., if operation may require removal of portions of the protective housing e.g., disconnection of an optical connector for OFCS, and defeat of safety interlocks, measurements shall be made at accessible points with the measuring instrument detector positioned and so oriented with respect to the laser or laser system as to result in the maximum detection of radiation by the instrument.
Accessible emission levels of laser and collateral radiation shall be based upon the following measurements (or their equivalent) as appropriate:
For laser products intended to be used in a locale where the emitted laser radiation is unlikely to be viewed with optical instruments, the radiant power (W) or radiant energy (J) detectable through a circular aperture stop having a diameter of 7 millimeters and within a circular solid angle of acceptance of 10(-3) steradians with collimating optics of 5 diopters or less (i.e., a maximum distance of 20 cm). A 50 millimeter diameter aperture stop with the same collimating optics and acceptance angle shall be used for all other laser products. For scanned laser radiation, the direction of the solid angle of acceptance shall change as needed to maximize detectable radiation, with an angular speed of up to 5 radians/second. A 50 millimeter diameter aperture stop with the same collimating optics and acceptance angle stated above shall be used for all other laser products.
The irradiance (W/cm(2)) or radiant exposure (J/cm(2)) equivalent to the radiant power (W) or radiant energy (J) detectable through a circular aperture stop having a diameter of 7 millimeters and, for irradiance, within a circular solid angle of acceptance of 10(-3) steradian with collimating optics of 5 diopters or less, divided by the area of the aperture stop (cm(2)).
The radiance (W/cm(2) sr) equivalent to the radiant power (W) or radiant energy (J) detectable through a circular aperture stop having a diameter of 7 millimeters and within a circular solid angle of acceptance of 10(-5) steradians with collimating optics of 5 diopters or less, divided by that solid angle (sr) and by the area of the aperture stop (cm(2)).
For diode lasers coupled to an optical fiber, the radiant power (W) or radiant energy (J) detectable through a circular aperture stop having a diameter of 7 mm can be calculated from the output power measured at the connector (closed system) and the numerical aperture (for a multimode fiber) or the mode-field diameter (for a single mode fiber). This procedure, described in ANSI Z- 136.2, provides a conservative estimate, i.e., yields values slightly in excess of the corresponding measured values.
Guidelines for Laser Safety and Hazard Assessment
Source: Occupational Safety & Health Administration, Guidelines for Laser Safety and Hazard Assessment PUB 8-1.7 (tablular data and equation illustrations have been omitted).