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Department of Physics

Department of Physics. Safe use of Class 3B and 4 Lasers October 12th 2011 Duncan McCallum Health and Safety Coordinator. Introduction. Introduction to Safe use of Class 3B and 4 Lasers In the Physics department Departmental Laser safety officer Prof A.P. Monkman

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Department of Physics

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  1. Department of Physics Safe use of Class 3B and 4 Lasers October 12th 2011 Duncan McCallum Health and Safety Coordinator

  2. Introduction • Introduction to Safe use of Class 3B and 4 Lasers In the Physics department • Departmental Laser safety officer Prof A.P. Monkman • Health and safety co-ordinator Duncan McCallum

  3. Class 3B and 4 Laser • Class 3B and 4 Laser use in Physics • These lasers present a high level of Hazard • Potential of injury to eyes and skin • Eye Damage is usually irreversible

  4. Health and Safety • Failure to follow the Universities policies can result in serious consequences in terms of :- • Personal injury to oneself and others • Legal liability for individuals and for the university • In serious cases prosecution by the HSE

  5. LASER • LASERstands for: • Light • Amplification by the • Stimulated • Emission of • Radiation

  6. Lasers Description • Lasers can be described by: • which part of the electromagnetic spectrum is represented: • Infrared • Visible Spectrum • Ultraviolet • the length of time the beam is active: • Continuous Wave • Pulsed • Ultra-short Pulsed

  7. Laser Light Laser light • is monochromatic, unlike ordinary light which is made of a spectrum of many wavelengths. Because the light is all of the same wavelength, the light waves are said to be synchronous. • is directional and focused so that it does not spread out from the point of origin. Asynchronous, multi-directional light. Synchronous,monochromatic, directionallight waves

  8. LASER BASICS -DESIGN - Lasing Medium (gas, liquid, solid, semiconductor) • - Excitation Mechanism (power supply, flashlamp, laser) • uses various methods to raise the media to the lasing state. - Feedback Mechanism (mirrors) - Output Coupler (semi-transparent mirror) Lasing medium Feedback mechanism Output coupler Excitation mechanism

  9. Laser Media • Solid state lasers • Gas lasers • Excimer lasers (a combination of the terms excited and dimers) use reactive gases mixed with inert gases. • Dye lasers (complex organic dyes) • Semiconductor lasers (also called diode lasers) There are different safety hazards associated with the various laser media.

  10. Electromagnetic Spectrum Laser wavelengths are usually in the Ultraviolet, Visible or Infrared Regions of the Electromagnetic Spectrum.

  11. Common Ultraviolet Lasers Ionizing Radiation x-rays Ultra- Ultra- Ultra- Radio Electric Radar gamma rays Infrared violet violet violet waves waves Wavelength (cm) -12 -10 -8 -6 -4 -2 0 2 4 6 8 10 10 10 10 10 10 10 10 10 10 10 Ultraviolet (UV) radiation ranges from 200-400 nm.

  12. Common Infrared Lasers Ionizing Radiation x-rays Ultra- Radio Electric Radar gamma rays Infrared Infrared Infrared violet waves waves Wavelength (cm) -12 -10 -8 -6 -4 -2 0 2 4 6 8 10 10 10 10 10 10 10 10 10 10 10 Infrared radiation ranges from 760-10,000 nm.

  13. Common Visible Light Lasers The wavelength range for light that is visible to the eye ranges from400-760 nm.

  14. Leading Causes of Laser Accidents • Unanticipated eye exposure during alignment • Available eye protection not used • Equipment malfunction • Improper methods for handling high voltage(This type of injury has resulted in death.) • Inadequate training • Failure to follow SOP • Failure to provide non-beam hazard protection. • Equipment improperly restored following service • Incorrect eyewear selection and/or eyewear failure

  15. BEAM RELATED EFFECTS Eye related Eye damage caused by the laser is usually permanent Skin related Most skin damage caused by the laser is temporary

  16. EYE RELATED - Injury can result from exposure to: - direct beam - specular reflection - diffuse beam (tissue reflection) - Damage dependent on: - intensity - lens of eye can focus beam onto the retina (dye laser) - Wavelength - absorbed by different parts of the eye (CO2 - cornea, sclera) - duration - fraction of second, before you can blink

  17. Eye damage • UV - Cornea + lens • VIS - Retina • IR - Cornea

  18. Retinal Hazard Region The wavelength range of light that can enter the eye is 400 to 1400 nm, though the range that we can actually see is only 400 – 760 nm. The eye can focus a collimated beam of light to a spot 20 microns in diameter on the retina (called the focal point). This focusing ability places the retina at risk when exposed to laser light in the wavelength range that will penetrate to the retina, because even fairly low wattage laser light can impact the retina with 100,000 times the radiant power that entered the eye. Because of this optical gain, laser light in the 400 – 1400 nm is referred to as the Retinal Hazard Region. This is important to remember when working with infrared lasers, because the retina can be injured even though the laser is invisible.

  19. Focusing places the retina at risk

  20. Biological Hazards - Retina • Thermal damage (a thermal burn) to the retina occurs in the Retinal Hazard Region (from 400 nm – 1400 nm). • Photochemical damage is severe at shorter visible wavelengths (violet & blue) and is cumulative over a working day. • Acoustic shock from exposure to high energy pulsed lasers induce shock waves that cause tissue rupture and results in physical tissue damage.

  21. Biological Hazards – Cornea & Lens • Ultraviolet and far-infrared laser radiation is absorbed at the cornea or lens • Inflammation injury to the cornea is caused by ultraviolet (UV) wavelengths (200-400 nm). This is the same type of injury that is caused by snow blindness. • Chronic exposure can cause cataract formation in the lens of the eye. At high intensities, immediate thermal burns occur, while lower exposures may lead to the development of cataracts over a period of years. Cornea Lens

  22. Examples of EYE Damage Retinal injury from a dye laser Corneal injury from CO2 laser

  23. Protect Your Eyes! In a fraction of a second, your vision can go dark.

  24. Types of Reflections • Types of Reflections • Specular reflection is a reflection from a mirror-like surface. A laser beam will retain all of its original power when reflected in this manner. Note that surfaces which appear dull to the eye may be specular reflectors of IR wavelengths. • Diffuse reflection is a reflection from a dull surface.Note that surfaces that appear shiny to the eye may be diffuse reflectors of UV wavelengths. • Diffuse laser light reflection from a high powered laser can result in an eye injury

  25. Specular Reflection Specular Reflection • Specular reflection is a reflection from a mirror-like surface. A laser beam will retain all of its original power when reflected in this manner. • Note that surfaces which appear dull to the eye may be specular reflectors of IR wavelengths.

  26. Diffuse Reflection Diffuse Reflection • Diffuse reflection is a reflection from a dull surface. • Note that surfaces that appear shiny to the eye may be diffuse reflectors of UV wavelengths.

  27. Biological Hazards - Skin • Ultraviolet (UV) • UV can cause skin injuries comparable to sun burn. • As with damage from the sun, there is an increased risk for developing skin cancer from UV laser exposure. • Thermal Injuries • High powered (Class 4) lasers, especially from the infrared (IR) and visible range of the spectrum, can burn the skin and even set clothes on fire.

  28. Non-Beam Hazards Non-beam hazards refer to anything other than the laser itself that can create a hazard. This type of hazard includes: • Electrical Hazards • Fire Hazards • Laser Generated Air Contaminants (LGAC) • Compressed Gases • Chemical Hazards • Collateral and Plasma Radiation • Noise

  29. Non-Beam Hazards – Electric Shock and Fire • Electric ShockUse caution when working on or near the high-voltage power supplies used for high-power Class 3 and 4 lasers; there is sufficient voltage in these power supplies to injure or kill. • FireHigh powered Class 4 lasers will easily ignite flammable materials (such as paper or flammable liquids).. In some circumstances, Class 3B lasers could also ignite flammable liquids.

  30. Collateral & Plasma Radiation • Collateral radiation refers to radiation that is not associated with the primary laser beam. This collateral radiation may be produced by power supplies, discharge lamps and plasma tubes. This radiation can be any type of EM radiation, from x-rays to radio waves. • High powered lasers can also produce Plasma Radiation from the interaction of the laser beam with the target material, especially when these lasers are used to weld metals. Plasma radiation maycontain enough UV and/or blue light torequire additional protective measures.

  31. Laser Generated Air Contaminants (LGAC) Air contaminated due to interaction of laser beam with target material can result in the production of toxic chemicals. To prevent personnel from inhaling the LGAC and to prevent the release of LGAC to the environment, exhaust ventilation with special filters may be needed.

  32. Laser Operator Responsibilities • Following laboratory administrative, alignment and standard operating procedures while operating lasers. • Keep the Principal Investigator/Supervisor fully informed of any departure from established safety procedures. This includes notification of an exposure incident. • Attending the Departments Laser Safety Training program or viewing the on-line Laser Safety power point training

  33. PPE for Eyes • Personnel Protective Equipment (PPE) for eyes exposed to Class 3B or 4 lasers is mandatory. Eyewear with side protection is best. Consider these factors when selecting eyewear: • Optical Density (OD) of the eyewear • Laser Power and/or pulse energy • Laser Wavelength(s) • Exposure time criteria • Maximum Permissible Exposure (MPE) • Filter characteristics, such as transient bleaching

  34. MPE • Maximum Permissible exposure • This is the level of laser radiation that a persons eye or skin may be exposed to without suffering adverse effects. • The level is determined by the wavelength, duration of exposure ,the size and divergence of the source

  35. N.O.H.D. • The Nominal Ocular Hazard Distance • (NOHD), is the minimum distance from the laser emitter along its optical axis at which no hazard exists to the human eye. An observer at this point or further away would have no adverse eye effects.

  36. Accessible Emission • Accessible Emission • This is the level of laser radiation that a person will be exposed to at the closest accessible point of the laser

  37. EN207 L Number • EN207 L Number • These numbers are used by laser safety goggle manufactures to specify the level of protection they afford. • The numbers define the minimum optical density and the maximum energy or power density that the goggle can withstand • On log scale so L2 10x L1 • Can also have a prefix specific to type of laser output referring to pulse lengths

  38. Laser classification • Divided into the following classes Class 1 Class 2 Class 2M Class 3R Class 3B Class 4

  39. Class 1 • 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. [Comment: This class may include lasers of a higher class whose beams are confined within a suitable enclosure so that access to laser radiation is physically prevented.]

  40. Class 1M • Class 1M • 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.

  41. Class 2 • Class 2 • A Class 2 laser emits in the visible region. It is presumed that the human blink reflex will be sufficient to prevent damaging exposure, although prolonged viewing may be dangerous.

  42. Class 2M • Class 2M • A Class 2M laser emits in the visible region in the form of a large diameter or divergent beam. It is presumed that the human blink reflex will be sufficient to prevent damaging exposure, but if the beam is focused down, damaging levels of radiation may be reached and may lead to a reclassification of the laser.

  43. Class 3R • Class 3R • 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.

  44. Class 3B • A Class 3B laser produces light of an intensity such that the MPE for eye exposure may be exceeded and direct viewing of the beam is potentially serious. • CW emission from such lasers at wavelengths above 315nm must not exceed 0.5 watts.

  45. Class 4 • Class 4 lasers are of high power (typically up to 500 mW or more if cw, or 10 J cm-2 if pulsed). • 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.

  46. Laser Safety Department has strict policy which must be compiled with Usage of class 3B and class 4 lasers will be monitored by the Laser SafetySubcommittee via periodic inspections. An internal prohibition notice will be served on any person or Group found to be using lasers in an unsafe manner. The prohibition notice will only be lifted once the control measures described in this document have been fully implemented

  47. Signage • Warning sign on the door of the laser laboratory • Should have emergency contacts • All laser users should be named • Laboratory should have door interlocked illuminated sign • First aid advice specific to laser accidents should be displayed in the Laboratory

  48. Engineering Controls • Engineering controls are measures that are incorporated into the laser system and are designed to prevent injury to personnel. Engineered safety controls are preferable to PPE or Administrative controls. • Examples include • Protective housings • Interlocks on Removable protective housings • Service access panels • Key control master switch (Class 3B & 4) • Viewing Windows, Display Screens, Collecting Optics • Beam path enclosures • Remote interlock connectors (Class 3B & 4) • Beam Stop or attenuator (Class 3B & 4)

  49. Physics Laser safety policy Laser safety policy • This document contains • 1. Laser worker registration form, This should be completed by any person whose work involves a class 3b or 4 laser. • 2. Laser registration form, A separate laser registration form is required for each class 3B or class 4 laser. • 3. Laser controlled area registration form, Only one laser controlled area registration form is required for each area but the form should be reviewed and updated if necessary whenever a new laser is put into use. • 4. Pro-forma risk assessment, A risk assessment is required for each experiment making use of class 3B or class 4 lasers it is recommended that separate assessments are carried out for the alignment and normal use stages of the experiment. Unmodified copies of the generic risk assessment are not acceptable • 5. Pro-forma safe method of work. Each authorised user should sign a copy of the safe method of work

  50. Laser worker registration form, All persons who intend to work with lasers of Class 3B or above must register as laser workers and sign the declaration that they have read and understood the Local Rules and the University Health and Safety Manual Section L1

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