Laser Safety Training:Online Segment Radiological and Environmental Management Purdue University with information from ANSI Z136.1 - 2007
Module 1 Fundamentals of Laser Theory and Operation Laser Definition Laser Components Laser Characteristics
What is a laser? • LASER: an acronym for Light Amplification by the Stimulated Emission of Radiation • Laser System: a laser and its associated electrical, mechanical, and optical components. • UV lamps, light boxes are NOT lasers
Laser Components • Optical Cavity: resonator that provides the necessary geometry Resonator encapsulated by a fully-reflective mirror on one end and a partially-reflective mirror on the other.
Laser Components (2) • Lasing Medium: causes amplification of a certain incident light at a particular wavelength. • Solid-state • Gas • Dye • Semi-conductor Atoms at “ground-state” awaiting stimulus from energy source.
Laser Components (3) • Pumping System: imparts energy to the atoms or molecules of the laser medium. • Optical pumping • Collision pumping • Chemical pumping Energy delivered to medium, causing excitation of atoms and the release of photons.
Q-Switch • Provides laser pulses of an extremely short time duration.
Monochromatic: either a single wavelength or a relatively small range of wavelengths. Laser Characteristics VS.
Monochromatic: either a single wavelength or a relatively small range of wavelengths. Directional: “parallel light beam” - small divergence over distance, unless purposely diverged (e.g. diffusing lenses). Laser Characteristics2 VS.
Monochromatic: either a single wavelength or a relatively small range of wavelengths. Directional: “parallel light beam” - small divergence over distance, unless purposely diverged (e.g. diffusing lenses). Coherent: a “fixed phase” relationship exists within the wavelength – in step. Laser Characteristics3 VS.
Module 2 Bioeffects of Laser Radiation on the Eye and Skin Criteria for Eye and Skin Exposure Eye Tissues Mechanisms of Eye Injury Eye Hazard vs. Wavelength Special Considerations for Ocular Exposure Mechanisms of Dermal Injury
Criteria for Exposures of Eye and Skin • Maximum Permissible Exposure (MPE) limits are below known hazardous levels. • Exposures at the MPE limit may be uncomfortable. • MPEs are normalized relative to the limiting aperture area – we assume the limiting aperture area is 7mm for the pupil size of a dark-adapted eye in most cases. • Irradiance is affected by the Radiant Exposure and the Exposure Duration ANSI Z136.1-2007 Section 8: Criteria for Exposures of Eye and Skin
Eye Tissues - Macula Macula: devoid of blood vessels; area of eye most responsible for color vision. Fovea: center of macula; area of eye of clearest vision/focusing.
Eye Tissues – Optic Nerve Optic Nerve: transmits electrical impulses from the retina to the brain; fibers enter eye at the Optic Disk.
Eye Tissues – Retina Retina: innermost coat of outside of eye, responsible for vision.
Eye Tissues – Vitreous Body Vitreous Body: transparent, colorless, gelatinous material which fills the eyeball chamber.
Eye Tissues – Lens Lens: focuses light onto the retina.
Eye Tissues - Pupil Pupil: opening in the center of the iris; pupil size determines amount of light entering eye.
Eye Tissues - Iris Iris: pigmented muscle that dilates and constricts, depending on ambient light.
Eye Tissues - Cornea Cornea: transparent, layered window of eye; provides 2/3 of eye’s focusing power.
Mechanisms of Eye Injury • Thermal • Potential effects: charring, edema, hemorrhage • Photochemical (blue light and UV) • Potential effects: production of toxins and biochemical changes which may cause inflammation, lesions and lens opacities • Photoacoustic (short intense pulses) • Potential effects: explosive forces due to expanding gases ANSI Z136.1-2007 Section 8: Criteria for Exposures of Eye and Skin
Eye Hazard vs. Wavelength TARGET: Cornea Far IR (IRC): 3000 nm – 1 mm Mid IR (IRB): 1400 nm – 3000 nm Mid UV (UVB): 280 nm – 315 nm Far UV (UVC): 100 nm – 280 nm EFFECT: Mid IR and Far IR: Thermal Mid UV and Far UV: Acute inflammation and conjunctivitis, fluorescence of lens, corneal and lenticular opacities (“clouding”) cataractogenesis (peaks at 300 nm) ANSI Z136.1-2007 Section 8: Criteria for Exposures of Eye and Skin
Eye Hazard vs. Wavelength (Retina) TARGET: Retina Near IR (IRA) : 700 nm – 1400 nm Visible Light: 400 nm – 700 nm EFFECT: Thermal burns, hemorrhage, scotoma (“blind spot”), photoretinitis (“blue light damage”) ANSI Z136.1-2007 Section 8: Criteria for Exposures of Eye and Skin
Eye Hazard vs. Wavelength (Lens) TARGET: Lens Near UV (UVA): 315 nm – 400 nm EFFECT: Development of cataracts ANSI Z136.1-2007 Section 8: Criteria for Exposures of Eye and Skin
Special Considerations for Ocular Exposures • Lower MPE limits may be required when normal protective mechanisms such as eye movement and pupil constriction are hindered. Inform your LPI if you think that you have a condition that may impact your susceptibility to the laser beam. • For example, individuals who have had pupil dilation performed will not have the natural defenses of the constricting iris which could limit that amount of radiation entering their eye. • Also, advanced age of an individual may reduce the ability of the iris to contract. ANSI Z136.1-2007 Section 8: Criteria for Exposures of Eye and Skin
Thermal (from direct beam or specular reflection) for Near UV, Visible, and IR wavelengths Potential effects: mild reddening (erythema) to blistering Severity is dependent upon exposure dose rate, exposure dose, and conduction of heat away from the site of absorption Mechanisms of Dermal Injury2
Mechanisms of Dermal Injury • Photochemical (from scatter of beam, specular or diffuse reflection) for Mid UV and Far UV wavelengths • Potential effects: erythema to blistering, possibly carcinogenic • Effects are dependent upon wavelength and exposure dose
Module 3 Significance of Specular and Diffuse Reflections Specular Reflection Diffuse Reflection Specular vs. Diffuse Reflection Important Notes
Specular Reflection • Mirror-like Reflection • Reflected wavelength is near same shape and intensity as direct beam • Obeys the Law of Reflection: Angle of Reflection = Angle of Incidence • Occurs when wavelength of laser beam is greater than the irregularities of the surface the beam hits
Diffuse Reflection • Reflected wavelength is blurred and weaker than direct beam • Obeys Lambert’s Law or the Cosine Law of Reflection • Occurs when wavelength of laser beam is smaller than the irregularities of the surface the beam hits
Diffuse Specular vs. Diffuse Reflection • Specular
Important Notes • Avoid having objects that may produce a specular reflection in or near laser beam (e.g. jewelry, tools, etc.), unless deliberately used as part of laser system (e.g. mirrors) • Surfaces that appear dull and pitted to our eyes may be a specular surface to beams of larger wavelengths
Module 4 Non-Beam Hazards of Lasers General Information Physical Agents Chemical Agents Biological Agents Human Use
General Information • Include physical, chemical, and biological agents, as well as human use issues. • May occur when: • material is exposed to a laser beam. • laser-related materials are released into the atmosphere. • Individuals contact system components. • Written SOPs shall address non-beam hazards, as well as beam hazards. ANSI Z136.1-2007 Section 7: Non-Beam Hazards
Physical Agents • Electrical Hazards • Potential Hazards • Shock: risk from contact with energized electrical conductors, power supplies, and other devices operating at potentials or 50 volts and above. (note: 600 volts and higher are considered to be High Voltage) • Resistive Heating: routinely check equipment for decay. • Electric Spark Ignition of Flammable Materials: malfunction can lead to fire; sparks may be ignition source. • Potential effects: “tingle”, startle, serious injury, death. • Electrical Hazard Control Measures: comply with OSHA, NFPA 70, and state and local regulations. Must have: • Fire extinguishers designed for electrical fires. • Panic Button or Emergency Shutdown Switch. ANSI Z136.1-2007 Section 7: Non-Beam Hazards
Physical Agents (2) • Collateral and Plasma Radiation • Ionizing Radiation: x-rays from electronic components of laser system (e.g. voltages exceeding 15 kV) and laser-metal induced plasmas. • Non-Ionizing Radiation: • UV and Visible: suitably shielded so as not to exceed limits specified by the ACGIH TLVs. • Electromagnetic Fields (EMF): MPEs set by IEEE C95 • Plasma: UV and blue light ANSI Z136.1-2007 Section 7: Non-Beam Hazards
Physical Agents (3) • Fire Hazards • Use flame retardant materials wherever possible. • Possible affected material: beam enclosures, barriers, unprotected wire insulation, and plastic tubing. • Obtain appropriate fire protection information from manufacturer. • Explosion Hazards • Possible causes: component (high-pressure arc lamps, filament lamps, and capacitor banks) disintegration, laser target and elements of the optical train may shatter, chemical laser reactants or other laser gases, ignition of dust collected in ventilation systems serving laser processes. • Required preventative measures: proper and timely maintenance of system, protective housing enclosure surrounding internal components, enclosure (or equivalent protection) of laser target and susceptible elements of optical train. ANSI Z136.1-2007 Section 7: Non-Beam Hazards
Physical Agents (4) • Mechanical Hazards Associated with Robotics • Potential hazards: damage to protective housing and beam delivery system, misalignment of beam, pinning/pinching of personnel. • Protective measures: may include surface interlock mats, interlocked light curtains, non-rigid walls and barriers. • Consult REM for further information. • Noise: • Certain lasers (e.g. pulsed excimers), and/or work environment may require noise control. • Consult REM for further information. ANSI Z136.1-2007 Section 7: Non-Beam Hazards
Chemical Agents • Laser Generated Air Contaminants (LGACs) • Primary Factors: target material, cover gas, and the beam irradiance. • Lower limit of occurrence appears at an irradiance level of approximately 107 W/cm2. • Possible carcinogenic toxic, and noxious airborne contaminants (list in Appendix F, ANSI Z136.1 – 2007). • LSO must ensure industrial hygiene characterizations of exposure to LGACs are conducted properly and refer to Material Safety Data Sheets (MSDSs) supplied by the manufacturer. • If necessary, LSO may require additional control methods. ANSI Z136.1-2007 Section 7: Non-Beam Hazards
Chemical Agents (2) • Compressed Gases • E.g.: chlorine, fluorine, hydrogen chloride, hydrogen fluoride. • All compressed gases with a Hazardous Material Information System (HMIS) or NFPA Diamond with a health, flammability, or reactivity rating of 3 or 4 shall be properly contained (i.e in an approved and appropriately exhausted gas cabinet that is alarmed with sensors to indicate potential leakage conditions). • SOPs shall be developed for safely handling compressed gases. • Sample of associated safety problems: • Free-standing cylinder not isolated from personnel. • Failure to protect open cylinders (i.e. regulator disconnected) from atmosphere and contaminants. • No remote shutoff valve or provisions for purging gas before disconnect or reconnect. • Labeled hazardous gas cylinders not maintained in appropriate exhausted enclosures. • Gases of different hazards (toxic, corrosive, flammable, oxidizer, inert, high pressure, and cryogenic) not stored separately in accordance with OSHA and Compressed Gas Association requirements. ANSI Z136.1-2007 Section 7: Non-Beam Hazards
Chemical Agents (3) • Laser Dyes and Solvents • Fluorescent compounds which, when in solution with certain solvents, form a lasing medium for dye lasers. • Some are highly toxic or carcinogenic. • Dye handling must employ special care (see Purdue University Chemical Hygiene Plan) • Dye lasers containing 100 ml or greater of flammable liquids shall be in conformance with NFPA 30 and 45, and the NEC Article 500. • All dyes shall be prepared in a laboratory fume hood. • Dye pumps and reservoirs should be placed in secondary containment vessels to minimize leakage and spills in conformance with NFPA 115. • Assist Gases • May be used to produce an inert atmosphere, remove material from beam-interaction site, and minimize deposition on components. • May appear in some types of LGACs and spectral distribution of plasma radiation. ANSI Z136.1-2007 Section 7: Non-Beam Hazards
Chemical Agents (4) • Control Measures: Engineering controls preferred • Exhaust Ventilation • avoid recirculation of LGACs. • use enclosing hoods, if possible. • designed in accordance with ACGIH and ANSI Z9.2. • Respiratory Protection • for brief exposures or interim control measure. • If used, must comply with 29 CFR 1910.134 (OSHA). • Process Isolation • physical barriers, master-slave manipulators, or remote control apparatus. • certain applications (e.g. biomedical applications) require disinfection/sterilization of equipment after use. • Sensors and Alarms • Shall be installed in hazardous gas cabinets and other locations as appropriate (including exhaust ventilation ducts). • Should be used for toxic and corrosive chemical agents (e.g. halogens), and be able to detect the hazardous gas in a mixture of emitted gases. • Must be properly shielded to minimize susceptibility to electromagnetic interference (EMI). ANSI Z136.1-2007 Section 7: Non-Beam Hazards
Biological Agents • LGACs: may be generated when a high-powered lasers interacts with biological tissue. • Infectious Materials: may survive beam irradiation and become airborne. • Consult ANSI Z136.3, Appendix F. ANSI Z136.1-2007 Section 7: Non-Beam Hazards
Human Factors • Ergonomics • E.g.: workstation layout, worker-machine interface, handling techniques, area illumination, visual distractions. • Limited Work Space • There must be sufficient room for personnel to turn around an maneuver freely, without trip/fall hazards (e.g. wires or cables on floor). • Work Patterns • Unusual or long hours may affect worker alertness. ANSI Z136.1-2007 Section 7: Non-Beam Hazards
Human Factors (2) • Disposal • Laser Disposal: donation, remove all means or activation and disposed, destruction • Laser Waste Disposal: waste disposal shall conform with Purdue University disposal requirements (see REM’s Hazardous Material Management webpage) • Chillers • May be employed to reduce heat load produced by lasers. • Chiller types: conductivity-cooled, air-cooled, or cooled with a closed loop chiller. • If using chilled water, filter the incoming water to ensure that minerals and particulate matter are removed to minimize damage to equipment. ANSI Z136.1-2007 Section 7: Non-Beam Hazards
Module 5 Laser and Laser System Classifications
Laser Classifications • Class 1: exempt from control measures or other surveillance, considered incapable of producing damaging radiation levels during operation. Former Class IIa lasers are considered to be in this category. • Class 1M: exempt from any control measures other than to prevent potentially hazardous optically aided viewing, considered incapable of producing hazardous exposure conditions during normal operation unless the beam is viewed with an optical instrument. ANSI Z136.1-2007 Section 1: General
Laser Classifications(2) Both Class 2 and Class 2M laser emit only in the visible spectrum (400 – 700 nm wavelengths). In the visible spectrum, the human aversion response (a reflex action of blinking and looking away from a strong optical stimulus) occurs when the eye becomes exposed; the response time occurs within 0.25 seconds. • Class 2 lasers are considered harmless for accidental viewing based on the power level and protection of the human aversion response. • Class 2M lasers are considered potentially hazardous if viewed with certain optical aids. For instance, a focusing lens may produce a magnified intensity to which the eye could be exposed. The Laser Safety Officer should evaluate a Class 2M laser or laser system to determine what hazard controls may be necessary for the safe use of the laser. ANSI Z136.1-2007 Section 1: General