Alignment Procedures for Class 4 Lasers
1. Exclude unnecessary personnel from the laser area during alignment.
2. Whenever possible, use low power visible lasers for path simulation of higher- power visible or invisible lasers.
3. Wear laser protective eyewear during alignment. Use special alignment eyewear when circumstances (e.g. wavelength, power, etc.) permit their use.
4. When aligning invisible (e.g. UV, IR) beams, use beam display devices such as image converter viewers or phosphor cards to locate beams.
5. Perform alignment tasks using high-power lasers at the lowest possible power level.
6. Use a shutter or beam block to block high power beams at their source except when actually needed during the alignment process.
7. Use a laser rated beam block to terminate high –powered beams downstream of the optics being aligned.
8. Use beam blocks and/or laser protective barriers in conditions where alignment beams could stray into areas with uninvolved personnel.
9. Place beam blocks behind optics (e.g.: turning mirrors) to terminate beams that might miss mirrors during alignment.
10. Locate and block all stray reflections before proceeding to the next optical component or section.
11. Be sure all beams and reflections are properly terminated before high-power operation.
12. Post appropriate warning signs during alignment procedure where lasers are normally Class 1 (enclosed).
13. Alignments should be done only by those who have received laser safety training.
Class 4: eye hazards if beams are viewed directly or specular reflections and sometimes even from diffuse reflections are viewed. Also skin burns from direct beam exposure. .
Laser Exposure Limits
Maximum Permissible Exposure (MPE) is defined as the level of laser radiation to which a person may be exposed without hazardous effect or adverse biological changes in the eye or skin. The MPE of a specific laser is determined based on the wavelength and exposure duration.
Nominal Hazard Zone (NHZ) is the space within which level of the direct, reflected, or scattered radiation during normal operation exceeds the applicable MPE. Exposure levels beyond the boundary of the NHZ are below the appropriate MPE level.
Non Beam Hazards - Electrical
Lasers may contain high voltage power supplies and large capacitors or capacitor banks that store large amounts of charge. In general, systems that permit access to components with large charges must be interlocked; however, during maintenance and alignment procedures such components often become exposed or accessible. The proper high voltage electrical safety precautions should be utilized in these situations.
As a reminder, the following electrical safety precautions should be followed to help prevent electrical injury when working around laser equipment:
Use one hand when working around power supplies, capacitors or other electrical equipment.
Avoid wearing metallic items.
Never handle electrical equipment when hands are wet or when standing on wet ground.
With high voltages, regard all floors as conductive and grounded for high voltages unless they are covered with well-maintained dry rubber matting of a type suitable for electrical work.
Be familiar with the following rescue procedures for application to apparent victims of electrocution:
Kill the circuit.
Remove the victim with a non-conductor if he is still in contact with an energized circuit.
Initiate artificial mouth-to-mouth resuscitation immediately (or the technique of heart-lung resuscitation if known) and continue until relieved by a physician.
One of the major sources of chemical hazards from lasers is from the organic dyes used in dye lasers.
Other chemical hazards include toxic gases from exciplex lasers, coolant such as liquid nitrogen, and gases that are formed by the interaction of the laser light with target materials.
Class 4 lasers represent a fire hazard. Depending on the construction material, beam enclosures, barriers and beam stops are potentially flammable if exposed to high beam irradiance (>10 W/cm2) or beam powers in excess of 0.5 W for more than a few seconds.
To prevent fire hazard:
Beam enclosures should be constructed of flammable resistant materials. Electrical circuitry shall be evaluated for the potential to cause fire.
Non Beam Hazards - Explosion
High-pressure arc lamps, filament lamps, and capacitors may explode violently if they fail during operation.
Laser targets and some optical components also may shatter if heat can not be dissipated quickly enough.
Care must be used to provide adequate mechanical shielding when exposing brittle materials to high intensity lasers.
Control Measures - Engineering
Engineering controls are design features or devices that are applied to a laser or its environment for the purpose of reducing laser hazards. Engineering controls are considered to be the most effective types of control:
Beam stop or attenuator
Activation warning systems: audible sound, warning light
Laser safety eyewear is required for class 4 lasers.
The amount of attenuation is measured by optical density (OD). For instance, OD 5 means that the incident beam is attenuated by a factor of 100,000. The greater the OD, the greater the attenuation.
Eyewear is very wavelength dependent. Safety eyewear for one type of laser will not work for another type of laser. Eyewear stamped OD 5 for 488 & 514 nm [Argon] may be OD 0 for 633 nm [HeNe].
All laser safety eyewear should be stamped with the OD at a particular wavelength.
Designation of protective clothing for UV lasers should be considered, even if not class 3b or 4.
Fire resistant material should be considered when class 4 lasers are being used.
Remote firing and monitoring should also be considered as a method of skin protection
Common Causes of Laser Accidents
According to ANSI(American National Standard) Z136.1-2000. Ninety five percentage of laser accidents occurs due to the following:
Unanticipated eye exposure during alignment
Misaligned optics and upwardly directed beams
Available laser eye protection not used
And the rest are:
Improper methods of handling high voltage
Intentional exposure of protected personnel
Operators unfamiliar with laser equipment
Lack of protection for ancillary hazards
Improper restoration of equipment
Eyewear worn not appropriate for laser in use
Unanticipated eye/skin exposure during laser usage
Inhalation of laser-generated air contaminants and/or viewing laser-generated plasma
Ignition of fires of both a facility or personal nature
Eye or skin injury or photochemical origin
Failure to follow standard operating procedures (SOP)
General Laser Safety Precautions
Always consult with your laser manufacturer's guidelines for laser safety Always use proper laser eye protection.
Operate within a controlled area or secured enclosure only, unless the beam path is totally enclosed.
Keep the beam path well above or below the eye level.
Remove all unnecessary reflective surfaces from the area of the beam path.
Permit only properly trained & authorized personnel to operate the laser.
Enclose the entire beam path if possible
Use the entire beam path if possible
Use remote viewing methods where feasible (e.g. video monitoring) to accomplish any necessary view of the beam
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