Class 4 (IV) lasers are hazardous for eye exposure. They also can burn skin and materials, mostly dark and/or lightweight materials at close range. They should be used with extreme care.
For visible-light lasers, Class 4 lasers' have an output power 500 milliwatts and above. There is no upper limit for Class 4 -- this is the most hazardous laser classification.
Class IV visible-beam lasers are high-powered. A Class IV laser can cause a significant eye injury if the beam, whether direct or reflected, enters the eye.
Even staring at the diffuse reflection of a laser "dot" on a wall or other surface, may cause an eye injury within a few feet of the dot. Do not stare at the laser "dot" when it is close to you.
To prevent eye exposure, always be aware of the beam location. Keep it away from people's eyes and heads. Watch out for reflected beams from glass and shiny surfaces.
Use of laser protective eyewear is mandatory
Avoid exposure to skin and sensitive materials. A Class IV laser can burn skin and materials, mostly dark and/or lightweight materials at close range
The Occupational Safety and Health Administration (OSHA) does not have a federal standard regulating the use of lasers.
OSAH has no specific requirements for interlocks the need following under industry “best practices.
ANSI Z136 standards are merely guidelines—and not mandatory The only regulation that enforced are FDA; all Ascent lasers are certified. We highly recommend you have the interlock on the laser room door.
Must be able to analyze laser hazards, implement control measures (proper signage, laser-safe curtains, and barriers) and continually monitor the safety program. In some cases, the LSO will have to be trained to calculate the hazard zone for one or more laser systems. Also, train other laser users as required. Online courses offered by LIA allow LSOs to train many operators at different sites without sending them to a classroom.
The ANSI Z136.1 standard indicates the following as key LSO responsibilities:
The Occupational Safety and Health Administration (OSHA) does not have a federal standard regulating the use of lasers. OSHA’s Safety and Health Topics - Laser Hazards Page does reference various internal resources such as a robotics safety directive and several interpretation letters as well as a variety of national consensus standards.
The primary consensus standard when it comes to development of a laser safety program is the American National Standards Institute (ANSI) Z136 series of laser safety standards developed by the Laser Institute of America (LIA):
Section III, Chapter 6 of OSHA’s Technical Manual (OTM), addresses laser hazards and is an excellent resource to use when developing a laser safety program. Contents of this chapter include:
LIA offers a Laser Safety Hazard Calculator Software. This software is based on Z136.1 and provides a reliable way to easily double-check laser safety calculations.
The hierarchy of hazard controls tells us eliminating the laser hazard is the first choice followed by engineering controls and then administrative controls and finally personal protective equipment... Protective eyewear is necessary only when all other controls are infeasible or not practical.
Engineering controls, such as protective housings, remote controls, or enclosed laser-beam paths, ensure protection for laser operators except when the operator is setting up, adjusting, or maintaining the beam. Control measures are discussed in Section III, Chapter 6, paragraph VI of the OTM, and section 4 of Z136.1-2014.
Laser Hazards The LIA laser safety information page states: “the human body is vulnerable to the output of certain lasers, and under certain circumstances, exposure can result in damage to the eye and skin. Research relating to injury thresholds of the eye and skin has been carried out in order to understand the biological hazards of laser radiation. It is now widely accepted that the human eye is almost always more vulnerable to injury than human skin.” The page highlights in detail laser and beam hazards.
Understanding the hazards of sunlight and conventional, man-made light sources along with research studies have permitted scientists to establish safe exposure limits for nearly all types of laser radiation. These limits are generally referred to as Maximum Permissible Exposures (MPE's) or Accessible Emission Limits (AEL) by laser safety professionals. This knowledge has led to the development of a system to classify lasers. Classes of lasers allow the use of standardized safety measures to reduce or eliminate incidents depending on the class of the laser. It is the responsibility of the manufacturer to provide the correct classification of a laser, and to equip the laser with appropriate warning labels and safety measures as prescribed by the regulations. The classifications of lasers are based on their ability to produce damage in exposed people, from class 1 (no hazard during normal use) to class 4 (severe hazard for eyes and skin). The LIA has identified four primary classes of lasers:
Class 1: safe based upon current medical knowledge. This class includes all lasers or laser systems which cannot emit levels of optical radiation above the exposure limits for the eye under any exposure conditions inherent in the design of the laser product. There may be a more hazardous laser embedded in the enclosure of a Class 1 product, but no harmful radiation can escape the enclosure.
Class 2: Must emit a visible laser beam. Because of its brightness, Class 2 laser light will be too dazzling to stare into for extended periods. Momentary viewing is not considered hazardous since the upper radiant power limit on this type of device is less than the MPE (Maximum Permissible Exposure) for momentary exposure of 0.25 seconds or less. Intentional extended viewing, however, is considered hazardous.
Class 3:Can emit any wavelength, but it cannot produce a diffuse (not mirror-like) reflection hazard unless focused or viewed for extended periods at close range. It is also not considered a fire hazard or serious skin hazard. Any continuous wave (CW) laser that is not Class 1 or Class 2 is a Class 3 device if its output power is 0.5 W or less. Since the output beam of such a laser is definitely hazardous for Intra beam viewing, control measures center on eliminating this possibility.
Class 4:Any laser that exceeds the output limits (Accessible Emission Limits, AEL's) of a Class 3 device. As would be expected, these lasers may be either a fire or skin hazard or a diffuse reflection hazard. Very stringent control measures are required for a Class 4 laser or laser system.
How does laser eyewear protect your eyes? The lens of the eyewear is a filter/absorber designed to reduce light transmittance of a specific wavelength. The lens can filter out (or absorb) a specific wavelength while maintaining adequate light transmission for other wavelengths. The absorption capability of the filtering media is called the optical density (OD). The OD is always expressed as a factor of 10. An OD of 5 means the filter has reduced the power of the beam to 1/100,000 of its original power. The required OD is the minimum OD necessary to reduce the beam to a non-hazardous level. The OD of the eyewear has to be at least equal to or greater than the required OD. The LIA offers a free online OD Calculator , which can be used to calculate the OD recommended for use with a given laser system and power.
When choosing appropriate eyewear, time is also a consideration. How long will the eyewear protect your eye before the beam goes through? How long will you have to react if you are hit with a direct beam? Per Z136.1, protective eyewear must exhibit a damage threshold for specified exposure time, and the eyewear must be used such that the damage threshold is not exceeded.