MASSACHUSETTS INSTITUTE OF TECHNOLOGY LASER SAFETY PROGRAM

Transcription

1 MASSACHUSETTS INSTITUTE OF TECHNOLOGY RADIATION PROTECTION PROGRAM LASER SAFETY PROGRAM Eighth Edition (interim) April 2008 MIT RADIATION PROTECTION COMMITTEE

2 PREFACE: The MIT Radiation Protection Committee (RPC) is responsible for the establishment and continuing review of an adequate radiation protection program at the Institute and its offcampus sites. The Committee is also responsible for the Institute's compliance with radiation protection regulations promulgated by state, Federal, and local agencies for both ionizing and non-ionizing radiation. The MIT Radiation Protection Program (RPP) administers the radiation protection program through a variety of services provided to the MIT community. All uses of radioactive material, radiation producing equipment, RF generators, and lasers must be registered with the MIT Radiation Protection Program. Departmental, Laboratory, or Center (DLC) EHS Coordinators must contact the Radiation Protection Program to arrange laser registrations, safety inspections, and laser safety training with the responsible RPP staff member. Project Supervisors, typically members of the faculty or senior scientists, are ultimately responsible for compliance with all requirements of this laser safety program. Specific programmatic elements that the project supervisor must ensure include directing that all laser workers are trained and registered by RPP, that all laser systems are registered and inspected by RPP, and that all safety requirements, especially the use of laser protective eyewear, are followed at all times. The RPC maintains the authority for assurance of laser safety for personnel at MIT. In that capacity, the RPC may vote to revoke or modify a project s registration to use Class 3b or Class 4 lasers. Mitchell Galanek, the MIT Radiation Protection Officer, will serve as the MIT Laser Safety Officer. Please call the Radiation Protection Program at with any questions concerning the Laser Safety Program. This document is comprised of two sections the first covers specific requirements of the Laser Safety Program and the second section covers some general recommended practices and training topics

3 Please read this article first!!!!! Here is why laser safety is important! "Smart people learn from their mistakes. Wise people learn from other people's mistakes. Unknown author. (Taken from Laser Focus, August 1977) Accident Victim's View Because laser injuries to eyes are rare, workers tend to discount the importance of safety precautions. The following dramatic account by Dr. C. David Becker, a victim of such an accident earlier this year, was prepared in the hope that his experience may increase vigilance among his colleagues. The necessity for safety precautions with high power lasers was forcibly brought home to me last January when I was partially blinded by a reflection from a relatively weak neodymium- YAG laser beam. Retinal damage resulted from a 6 millijoule, 10 nanosecond pulse of invisible 1064 nanometer radiation. I was not wearing protective goggles at the time, although they were available in the laboratory. As any experienced laser researcher knows, goggles not only cause tunnel vision and become fogged, they become very uncomfortable after several hours in the laboratory. When the beam struck my eye I heard a distinct popping sound, caused by a laserinduced explosion at the back of my eyeball. My vision was obscured almost immediately by streams of blood floating in the vitreous humor, and by what appeared to be particulate matter suspended in the vitreous humor. It was like viewing the world through a round fishbowl full of glycerol into which a quart of blood and a handful of black pepper have been partially mixed. There was local pain within a few minutes of the accident, but it did not become excruciating. The most immediate response after such an accident is horror. As a Vietnam War Veteran, I have seen several terrible scenes of human carnage, but none affected me more than viewing the world through my bloodfilled eyeball. In the aftermath of the accident I went into shock, as is typical in personal injury accidents. As it turns out, my injury was severe but not nearly as bad as it might have been. I was not looking directly at the prism from which the beam had been reflected, so the retinal damage is not in the fovea. The beam struck my retina between the fovea and optic nerve, missing the optic nerve by about three millimeters. Had the focused beam struck the fovea, I would have sustained a blind spot in the center of my field of vision. Had it struck the optic nerve, I probably would have lost the sight of that eye. The beam did strike so close to the optic nerve, however, that it severed nerve-fiber bundles radiating from the optic nerve. This has resulted in a crescent-shaped blind spot many times the size of the lesion. The diagram is a Goldman-Fields scan of the damaged eye, indicating the sightless portions of my field of view four months after the accident. The small blind spot at the top exists for no discernable reason; the lateral blind spot is the optic nerve blind spot. The effect of the large blind area is much like having a finger placed over one's field of vision. Also I still have numerous floating objects in the field of view of my damaged eye, although the blood streamers have disappeared. These "floaters" are more a daily hinderance than the blind areas, because the brain tries to integrate out the blind area when the when the undamaged eye is open. There is also recurrent pain in the eye, especially when I have been reading too long or when I get tired. The moral of all this is to be careful and to wear protective goggles when using high power lasers. The temporary discomfort is far less than the permanent discomfort of eye damage. The type of reflected beam which injured me also is produced by the polarizers in q switches, by intracavity diffraction gratings, and by all beamsplitters or polarizers in optical chains.

4 Table of Contents Part One - MIT Radiation Protection Program Laser Safety Program Requirements 3 I. INTRODUCTION 5 II. Responsibilities 5 A. Radiation Protection Program B. Departments, Laboratories and Centers (DLCs) C. EHS Coordinator D. Principle Investigator/Supervisor (PI/S) E. EHS Representative: F. Laser Users III. Laser Registration 8 IV. Laser Safety Training and User Registration 9 V. Laser Incidents 9 VI. Laser Classifications 9 VII. Laser Facility - Design Requirements 11 VIII. Laser Facility - Safe Operation Requirements 13 Part Two - Laser Safety Training Supplement and Recommendations 15 IX. INTRODUCTION 15 X LASER HAZARDS 15 XI. General Hazard Controls 16 XII. Laser Classifications 17 XIII. Eye Protection and Maximum Permissible Exposures Retinal Damage 2. Lens Damage 3. Corneal Damage 4. Other Ocular Damage 5. Maximum Permissible Exposure (MPE) 6. Protective Eyewear XIV. Skin Exposure and Maximum Permissible Exposures 22 XV. General Safety Procedures 21 XVI. Recommended Laser Safety Controls 21 A. Class 1 Controls B. Class 2 Controls C. Class 1M, 2M, and 3R Controls D. Class 3b Controls E. Class 4 Controls F. General Controls for Experimental Procedures G. Controls During Beam Alignment Appendix A Registration of Laser Systems 27 Appendix B Laser Worker Registration 29 Appendix C Laser Postings 30 Appendix D MIT Policy for Laser Eye Exams 31 Appendix E Definitions 34 Appendix F Specific Precautions for Beam Alignment 36 Appendix G List of Laser Protective Eyewear Manufacturers and Vendors 39 4

5 Part One - LASER SAFETY PROGRAM REQUIREMENTS II. INTRODUCTION The safe use of laser systems depends upon the basic principles of safety, which are recognition, evaluation, and control of potential hazards. This program will review laser operations, the associated potential hazards, responsibilities of the laser user community, and the services provided by the Radiation Protection Program (RPP) to aid in the safe use of laser radiation. All persons installing, operating, using, maintaining, repairing, or servicing lasers or laser systems at MIT shall do so in accordance with the requirements set forth in the most recent published version of the publication published by ANSI entitled American National Standards for Safe Use of Lasers and known and referred to as ANSI Z Table 1. Requirements by Laser Classification (adapted from ANSI Z ) Procedural and Class Administrative Training Medical Surveillance Controls 1 Not Required Not Required Not Required 1M Not Required * Not Required * Not Required 2 Not Required Not Required Not Required 2M Not Required * Not Required * Not Required 3R Not Required Not Required Not Required 3b Required Required Suggested** 4 Required Required Suggested** * If collecting optics is used or the system is on and left unattended in a public space then these items are required. ** Anyone working with, or in the vicinity of, a Class 3b or 4 open beam laser system a baseline laser eye exam is suggested. Enclosed laser systems the baseline eye exam is not required. II. Responsibilities A. Radiation Protection Program Detailed information on the control of laser radiation hazards is available from the Radiation Protection Program, , Room N Some of the more important elements are outlined in this manual. RPP will provide services to assist the Principle Investigators/Supervisors (PI/S), DLC-EHS Coordinators, and EHS laboratory Representatives in maintaining a comprehensive laser safety program. These services include the following: 1. Collect information and maintain records in order to comply with Commonwealth of Massachusetts regulations that require registration of all Class 3b and 4 lasers. The registration of Class 3b and 4 lasers at MIT is described in Section III of this manual. 5

6 2. Classify, or verify classifications of lasers and laser systems at MIT where the classification is not provided, or where the class level may change because of the addition or deletion of engineering control measures. 3. Perform Initial hazard evaluations of laser controlled areas, including the establishment of Nominal Hazard Zones (NHZ) if necessary. 4. Recommend or approve appropriate engineering and administrative controls. 5. Approve written Standard Operating Procedures (SOPs), alignment procedures, and other procedures that may be part of the requirements for administrative and procedural control. 6. Recommend or approve protective equipment such as eyewear, clothing, barriers, screens, and others that may be required to assure personnel safety. 7. Conduct and document initial laser safety training for laser workers. 8. Coordinate and document laser eye examinations. See Appendix D for MIT s policy on laser eye exams. 9. Provide and post required laser warning signs. Approve the wording on area signs and equipment labels. 10. Investigate reports of laser accidents/incidents to discover cause of events that could be prevented in the future. Report findings to the RSC and all concerned parties. 11. RPP will approve laser installation facilities and laser equipment prior to use. This also applies to modifications of existing facilities or equipment. 12. RPP shall ensure the safety features of the laser installation facilities and laser equipment are reviewed periodically to assure proper operation. The periodicity of this review will be determined during the initial hazard evaluation performed at the time of registration, but will not exceed two years. Additionally, RPP will use the Environment, Health, and Safety Management System (EHS-MS) application of annual and biannual Inspections and Audits, and the oversight responsibilities of EHS Coordinators, Principle Investigators/Supervisors, and EHS Representatives to assure proper operations of laser or laser systems safety control features. 13. RPP will provide refresher training for all active laser users as appropriate. B. Departments, Laboratories and Centers (DLCs) The head of each DLC has final-line responsibility for EHS related compliance and good practices within his or her DLC as relates to laser safety. Each DLC is responsible for ensuring that the Environment, Health, and Safety Management System (EHS-MS) applications of PI Space Registration, Training, Inspections, and Hazard Registration/Inventory are implemented as they relate to laser safety. The DLC Head/Director supervises the activities of the EHS Coordinator(s). C. EHS Coordinator The EHS Coordinator, acting on behalf of the DLC Head/Director, provides operational day-to-day oversight of the DLC s efforts to implement the EHS-MS and meet EHS requirements for laser safety. This oversight specifically includes the following: 6

7 1. Assist RPP with gathering information to accomplish the laser registration process. Provide information relating to changes in status of registered lasers or laser systems. 2. Coordinate scheduling of visits to laboratory spaces to accomplish initial hazard evaluations, and any follow-up activities. 3. Coordinate efforts to accomplish initial training of laser users. 4. Assure the proper function of laser safety control measures are reviewed during biannual Level II audits. D. Principle Investigator/Supervisor (PI/S) The Principle Investigator/Supervisor (PI/S) of each laboratory or facility space is responsible for compliance with EHS regulations and good practices in his/her laboratory or facility space. The PI or supervisor has final-line responsibility for performing his or her responsibilities under the MIT EHS-MS and ensuring that the laboratory or facility space under his or her purview satisfies EHS requirements as they relate to laser safety. Each Project Supervisor listed on the laser registration form is responsible for the following: (They should, in most cases, use the services of the ESH Coordinator and the EHS representative to assist in accomplishing these laser safety program elements.) General Administrative Responsibility of the PI The PI or supervisor is expected to be knowledgeable of the requirements for laser safety, the potential laser hazards and associated control measures for all lasers and laser systems, education and all policies, practices and procedures pertaining to laser safety for lasers or laser systems registered in their name. The PI or supervisor is responsible for the issuance of laboratory specific instructions and training materials on laser hazards and their control to all personnel who may work with lasers that are registered and operated within the supervisor's jurisdiction. The PI or supervisor will not permit the operation of a laser unless there is adequate control of laser hazards to users, visitors, and the general public. When the supervisor knows of or suspects an accident resulting from a laser operated under his or her authority, the supervisor will immediately notify RPP at The PI or supervisor will not permit the operation of a new or modified laser under his or her authority without the approval of RPP. Specific Administrative Responsibility of the PI 7

8 1. Registration of all Class 3b and Class 4 lasers with RPP. The Project Supervisor must provide as much information as available to assist with the proper registration and evaluation of the laser system being registered. This includes updating the registration as needed. 2. Schedule a laser hazard evaluation with RPP. 3. Inform all laser workers that the laser safety training requirement must be completed prior to operating a laser system. 4. Assist in scheduling biennial laser safety refresher training for all laser users. 5. Additional training for individual laser operations and procedures as expected at the project level including experiment-specific and equipment-specific safety precautions. 6. Develop written operating and alignment procedures. These should include safety aspects for all Class 3b and Class 4 lasers. 7. Providing the necessary equipment and work environment for the safe use of the project's lasers 8. Inform the EHS coordinator and RPP of any new lasers or significant changes in the current use of lasers (including discontinuance of use).inform RPP of the intent to release or remove lasers from the premises. 9. Inform RPP of any intent to release or remove lasers from the premises. 10. Enforcement of all laser safety requirements described in this program and prescribed by RPP, with particular emphasis on facility design, wearing laser protective eyewear, and on following standard operating procedures, especially for beam alignment. E. EHS Representative The EHS Representative(s) assists the PI/S in achieving EHS requirements in the laboratory or facility space that relate to laser safety. F. Laser Users Each registered laser user is responsible for: 1. Completing the online EHS training needs assessment. 2. Attending laser safety training. 3. Complying with all requirements of the MIT Laser Safety Program. 4. Wearing appropriate laser eyewear as necessary. 5. Conducting all laser activities in accordance with the posted standard operating, and alignment procedures and accepted good safety practices. 6. Report actual or suspected over exposure to laser energy to your supervisor and RPP immediately. 8

9 III. Laser Registrations Commonwealth of Massachusetts Regulations requires that all Class 3b and Class 4 lasers be registered with the Radiation Protection Program. The Project Supervisor must complete form RP-102 and submit the form to RPP, Room N (see Appendix A). The registration shall include written Standard Operating Procedures including necessary safety requirements, for all Class 4 lasers and should accompany the registration of class 3b lasers. Alignment procedures shall also be submitted when appropriate for all class 3b and 4 lasers. Upon receipt of the completed form RP-102, and SOPs, the Radiation Protection Program will conduct a laser hazard evaluation. RPP will affix a sticker to the laser or laser system to document completion of the registration and initial hazard evaluation process. The laser registration information must be updated in a timely manner to reflect any changes, such as, moving the laser to a new lab, transferring the laser to a new group internal or outside the Institute, and disposing of a laser. RPP must inspect the laser prior to disposal to ensure the system can not be restarted and operated by untrained or unauthorized individuals. IV. Laser Safety Training and User Registration All persons working with Class 3b and Class 4 lasers are required to register with RPP and receive laser safety training. Routine laser safety training seminars are offered by RPP. Laser users may sign up for training on the EHS training website. Laser users should also check off use class 3b or 4 laser in the online EHS Training Needs Assessment procedure. A record of registered laser workers is maintained by RPP on form RP-50LASER (see Appendix B). V. Laser Incidents In the event that an individual suspects they have been exposed to in excess of the Maximum Permissible Exposure (MPE), the following steps should be taken: 1. Report to the MIT Medical Department for an eye exam. 2. Notify RPP as soon as possible (typically within 24 hours) Workday dial , and after hours dial 100 and ask for the EHS on call person. 3. Supervisor to file an online Supervisor s Injury Report ( with EHS. RPP will investigate any suspected or real exposure to laser radiation and submit a report to the Radiation Protection Committee. A copy of the report will be maintained in the laser workers' registration file. The investigation is designed to aid in preventing any future injuries with laser. There is seldom action taken against the individual injured or others involved unless there is evidence of malicious intent or reckless negligence. 9

10 VI. Laser Classifications The laser classifications listed below are those used in ANSI Z The laser will most likely have a labeled that is in compliance with the FDA s requirements (unless it has been home-built). These two classification schemes are slightly different for the low power laser but the same for higher power lasers (class 3b and 4). Refer to ANSI Z for greater details on laser classification. The labeled classification on the laser is used as the default classification for laser safety. Once a laser is onsite and a hazard evaluation has been performed by the laser safety officer the laser may be reclassified for the purposes of laser safety. See below for instructions on reclassifying a laser system. Class 1 and 1M These lasers are not considered hazardous. Any laser or laser system appropriately designed to assure that accessible laser radiation levels do not exceed the Accessible Emission Limit (AEL) for a Class 1 laser is referred to as an Exempt laser. The exemption only applies to emitted radiation hazards and not to other potential hazards (e.g., electrical). The M in class 1 M is used to indicate that the laser may exceed the class 1 AEL if magnifying optics is used, such as binoculars. Class 1 status can be achieved by completely enclosing the laser beam with light-tight interlocked shielding. However, once the interlocks are defeated the laser system reverts to the classification of the embedded laser. Class 2 and 2M Low power or low risk lasers: These lasers are only hazardous if the viewer overcomes his/her natural aversion response to bright light. Class 2 lasers emit only in the visible spectrum ( nm). The class 2M designation is the same hazard level as class 2 but is potentially hazardous when viewed with optical aids. Class 3R (formerly 3a) Medium power or moderate risk lasers: Most Class 3a lasers emit between one and five milliwatts of visible radiation. The laser light is unlikely to be hazardous except when the viewer overcomes his/her natural aversion response or when he/she uses optical instruments. Class 3b Medium power or moderate risk lasers: Class 3b lasers can cause injury to the eye from the direct beam. They are not capable of causing serious skin injury or hazardous diffuse reflection under normal use. For Continuous Wave (CW) lasers the accessible radiant power must be less than or equal to 0.5W. 10

11 Class 4 High power or high risk lasers: High-powered lasers pose the greatest risk of injury and can cause combustion of flammable materials. They can cause diffuse and specular reflections that are hazardous to the eye and may cause serious skin injury from direct exposure. For CW lasers the accessible radiant power exceeds 0.5W. LSO reclassification of class 3b or 4 lasers The LSO may reclassify a laser as needed for laser safety purposes. An example of when this may be needed is when a laser with a class 3b label is connected via a fiber optic cable to a fully enclosed system and there is no access to the laser light during normal operating conditions. If the default laser classification of 3b is used the LSO would require greater controls than is necessary under normal operating conditions of this example laser system. If the laser is reclassified as a class 1 laser for the purposes of laser safety, the controls required by the LSO will be in line with the risks. A fully enclosed laser system is a laser that is contained within a protective housing. The protective housing must be in place in order to work under these less restrictive laser facility requirements. When the protective housing is removed a temporary laser controlled area must be established (see below). Below is listed instruction for the LSO in reclassifying a laser. Note that only the LSO may reclassify a laser system. For a laser system to be considered fully enclosed and exempted from the class 3b and 4 open beam facility requirements it must meet the three following criteria. 1. The enclosed laser system must not emit light that is in excess of the AEL for a class 1 laser system. The Class1 AEL for CW visible light is 0.49 mw (Class 1 AEL = MPE x area of the limiting aperture). Refer to ANSI Z section 3.2 for a complete assessment of AELs. 2. The enclosure must be secured from unauthorized or unintentional removal. 3. The laser system must be reclassified by the LSO and labeled with the LSO laser safety classification. VII. Laser Facility - Design Requirements Class 1, 2 and 3R laser facilities The facility design requirements for a Class 1 laser with an embedded 3b or 4 laser are the same as listed below for Class 3b and 4 Laser Facility Requirements - fully enclosed laser systems. Class 2 and 3R facilities have the following requirements. The facility must have access control, such as a locked door with limited key access, card access, or combination lock. Also, all users of the system must read the operator s instructions on laser safety and proper operation. The main hazard associated with Class 2 and 3R lasers 11

12 are associated with exposure to light and overcoming the natural aversion response to bright light. Class 1 and fully enclosed Class 3b and 4 Laser Facility Requirements A fully enclosed laser system is a laser that is contained within a protective housing. The protective housing must be in place in order to work under these less restrictive laser facility requirements. When the protective housing is removed a temporary laser controlled area must be established (see below). For a laser system to be considered fully enclosed and exempted from the class 3b and 4 open beam facility requirements it must be reclassified as a class 1 laser system by the LSO. See the previous section for details on reclassifying lasers. Facility Design Requirements: Access control, such as a locked door with limited key access, card access, or combination lock. Accommodations for a temporary laser controlled area. Class 3b and 4 Laser Facility Requirements open-beam laser systems Open beam refers to laser systems that are not enclosed within a protective housing that is interlocked for laser safety purposes. Laser Facility Design Requirements: A lighted laser sign outside each entryway to the laser controlled area is required. The lighted sign must be interlocked to the laser system. 1 See detailed information regarding lighted laser signs. The room must be light tight. If the room has windows or doors with windows they must be fully blocked with permanently attached light-tight laser curtains (i.e. a barrier to the laser light) or otherwise permanently blocked. Doors must also be light tight, i.e. a strip at the bottom of the door similar to weather stripping. Facility must have access control, such as a locked door with limited key access, card access, or combination lock. 1 The Laser Safety Officer (LSO) for the Institute may grant an exemption to facilities to allow for the lighted laser sign to be administratively controlled. 12

13 Laser facilities using toxic gasses or burning/cutting must have the appropriate ventilation (such as toxic gas cabinets). If hazardous chemicals will be used a chemical fume hood must be available. The following apply only to facilities with class 4 lasers: There must be an inner barrier to the laser light such as a laser curtain around the laser table or a blocking barrier, screen, curtains, etc. at the entryway. 2 The level of laser radiation at the exterior of these barriers shall not exceed the MPE. A nondefeatable interlock or defeatable interlock may be used in place of the inner barriers. See details regarding entryway safety controls. Emergency power shutdown. A red mushroom type button must be easily accessible in an emergency. Class 4 Entryway Safety Controls (ANSI Z ) one of the three below must be used. Non-Defeatable (non-override) Area or Entryway Safety Controls Safety latches, entryway or area interlocks (e.g., electrical switches, pressure sensitive floor mats, infrared detectors) shall be used to deactivate the laser or reduce the output to levels below the MPE in the event of an unexpected entry. Defeatable Area or Entryway Safety Controls Defeatable safety latches, entryway or area interlocks shall be used if non-defeatable controls limit the intended use of the laser. These safety controls may be overridden to allow access if it is clearly evident that there is no laser hazard at the point of entry. The authorized personnel requiring entry must be adequately trained and provided with adequate personal protective equipment. Procedural Area or Entryway Safety Controls Where safety latches or interlocks are not feasible or are inappropriate, the following shall apply: a. All authorized personnel shall be adequately trained and adequate personal protective equipment shall be provided upon entry. b. A door, blocking barrier, screen, curtains, etc. shall be used to block or attenuate the 2 The LSO may grant an exemption to this requirement provided administrative and/or engineering controls are in place to ensure personnel may not be exposed above the MPE when entering the laser controlled area. 13

14 laser radiation at the entryway. The level of laser radiation at the exterior of these shall not exceed the MPE. c. At the entryway there shall be a visible or audible signal indicating that the laser is operating at class 4 levels. VIII. Laser Facility - Safe Operation Requirements Class 1 and fully enclosed Class 3b and 4 Laser Facility Requirements Laser controlled area requirements under normal operating conditions The system must not be operated without the protective housing unless a temporary laser controlled area has been established. All users of the system must read the operator s instructions on laser safety and proper operation. The room should have a posting instructing users to read the operator s instructions and call RPP if they have questions regarding the safe use of lasers. The laser system must have a label with RPP laser safety classification. Laser controlled area requirements when enclosure has been removed During service, repair or alignment a temporary laser controlled area must be established. When professional service personnel are used to service the laser system they are responsible for establishing the temporary laser controlled area. If MIT personnel will service or align the system written procedures must be reviewed by RPP prior to operating. A temporary laser controlled includes the following: A notice sign outside the temporary laser controlled area as well as the usual laser warning sign for class 3b and 4 lasers. A barrier to the laser light must be in place that will reduce the level of laser light below the MPE. Laser safety eyewear must be worn within the temporary laser controlled area while the laser is energized. Class 3b and 4 Laser Facility Requirements open-beam laser systems Class 3b and 4 Laser Controlled Area Requirements: Only individuals informed of the facility s specific laser hazards or trained in laser safety by RPP are allowed access to the laser controlled area (Class 4 only). Only individuals trained in the operation of the laser and laser safety may operate the laser system. 14

15 Appropriate protective eyewear shall be available to anyone upon entering the lasercontrolled area. Laser protective eyewear must be worn whenever a hazardous condition could exist. There shall be written standard operating procedures (SOPs) for all class 4 laser systems. Class 3b laser systems should have written SOPs. All entrances to the laser controlled area are posted with the appropriate warning sign. Path of the laser light is well defined and controlled. Hazardous beams are terminated using a beam stops made of an appropriate material. All light levels in excess of the MPE must be confined to the laser table if feasible. If this is not feasible engineering and/or administrative controls must be in place to ensure personnel are not exposed above the MPE (see entryway safety controls). Use only diffusely reflecting materials in or near the beam path. Secure the laser beam path to be above or below eye level. Facility is under the direct supervision of an individual knowledgeable in laser safety. Access is limited and requires approval to enter (i.e. knock before entering or controlled by key or card). Store lasers in a manner that prevents the unauthorized use (i.e. remove the key). 15

16 Part Two - LASER SAFETY TRAINING SUPPLEMENT AND RECCOMENDATIONS WARNING!!! DO NOT LOOK INTO LASER WITH REMAINING EYE I INTRODUCTION The acronym LASER stands for Light Amplification by Stimulated Emission of Radiation. A laser is a device, which when energized, can emit a highly collimated beam of extremely intense monochromatic electromagnetic radiation. This radiation is emitted over a wide range of the electromagnetic spectrum from the ultraviolet region through the visible to the infrared region. The range of commonly available lasers is from 200 nanometers to 10.4 micrometers. Laser radiation may be emitted as a continuous wave or in pulses. Lasers produce non-ionizing radiation, which may be a hazard to the eyes and the skin. The primary mechanism of biological damage for most lasers is thermal. It should be noted that photochemical damage may also occur when dealing with lasers operating in the ultraviolet region. The intensity of the radiation that may be emitted and the associated potential hazards depend upon the type of laser, the wavelength of the energized beam, and the proposed uses of the laser system. II LASER HAZARDS The basic hazards associated with the use of lasers are categorized as follows: Laser Hazards Eye: Corneal or retinal burns are possible from acute exposure. Location and extent of injury is dependent upon wavelength and classification of laser. Corneal opacities (cataracts) or retinal injury may be possible from chronic, as well as acute, exposures to excessive levels of laser radiation. Eye hazards are easily controlled with the use of appropriate laser safety eyewear, or other engineering safety controls. Skin: Skin burns are possible from acute exposure to high levels of laser radiation in the infrared spectral region. Erythema (sunburn), skin cancer, and accelerated skin aging are 16

17 possible effects in the ultraviolet wavelength range. Electrical Hazards The most common hazard encountered in laser use is electric shock. Potentially lethal electrical hazards may be present especially in high powered laser systems. There have been several electrocutions in the U.S. from laser-related electrical accidents. These accidents could have been prevented. Contact the MIT Safety Program if you have any questions concerning electrical safety. The following are general guidelines to prevent electrical shock: 1. Avoid wearing rings, metallic watchbands and other metallic objects. 2. When possible, only use one hand when working on a circuit. 3. Assume that all floors are conductive when working with high voltage. 4. Check that each capacitor is discharged, shorted and grounded before allowing access to the capacitor area. 5. Inspect capacitor containers for deformities or leaks. 6. Provide such safety devices as appropriate rubber gloves and insulating mats. 7. Do not work alone. 8. Specific approval is required to work on live electrical equipment. 9. The requirements of the MIT lockout/tagout program must be implemented as required. Chemical Hazards Some material used in laser systems (excimer, dye, chemical lasers) may be hazardous or toxic substances. Also, laser induced reactions may produce hazardous particles or gases around the laser system. Users should be aware of the extreme toxicity of chlorine and fluorine gases. Concentrations as low as 0.1 ppm of fluorine are considered toxic. Gases should be stored in such a way as to ensure proper ventilation to minimize any hazardous effects. Fire Hazards Solvents used in dye lasers are extremely flammable. Ignition may occur via high voltage pulses or flash lamps. Direct beams and unforeseen specular reflections of high-powered CW infrared lasers are capable of igniting flammable materials during laser operation. Other potential fire hazards are electrical components and the flammability of Class 4 laser beam enclosures. Associated Non-Beam Hazard Associated hazards can include cryogenic coolant hazards, excessive noise from high powered systems, and ionizing radiations from high power laser systems. III. General Hazard Controls 17

18 The hazard controls necessary for the safe use of laser radiation depend upon the: laser classification environment where the laser is used laser operating characteristics persons operating the laser general population within the vicinity of the laser Laser safety procedures can best be evaluated by grouping them according to the class of laser in use. Part One of this document covered the detailed control requirements for class 3b and 4 lasers. More information can be found in ANSI Z Review of repeated incidents have demonstrated that accidental eye and/or skin exposures to laser radiation, and accidents related to the ancillary hazards of a laser or laser system, are most often associated with personnel involved with the use of these systems under the following conditions: Unanticipated eye exposure during alignment (no eye protection worn) Misaligned optics Available eye protection not used Equipment malfunction Improper method of handling high voltage Intentional exposure of unprotected personnel Operator unfamiliar with laser equipment Lack of protection for ancillary hazards Improper restoration of equipment following service Inadvertent beam discharge Insertion of flammable materials into beam path VII. Laser Classifications The American National Standards Institute (ANSI) has established a laser hazard classification system in publication ANSI Z , Safe Use of Lasers. Certified laser manufactures are required to label their products as to the class type as of September 19, 1985 (21 CFR Part 1040 FDA regulation). These two classification schemes are slightly different for low power lasers. The ANSI requirements are related to laser safety and area posting requirements and the latter is the FDA s labeling requirements. Information regarding appropriate eyewear for a specific laser may be obtained from the manufacturer at time of purchase. The following table summarizes this laser classification scheme and the hazard capabilities associated with each class of laser. 18

19 Laser Hazard Classifications ANSI Z136.1 Class FDA Label Class Description 1 1 These lasers are not considered hazardous. Referred to as Exempt lasers, any laser or laser system appropriately designed to assure that accessible laser radiation levels do not exceed the Accessible Emission Limit (AEL) for a Class 1 laser. The exemption only applies to emitted radiation hazards and not to other potential hazards (e.g., electrical). Class 1 status can be achieved by completely enclosing the laser beam with light-tight interlocked shielding. However, once the interlocks are defeated the laser system reverts to the classification of the embedded laser. 1M 2 The M in class 1M is used to indicate that the laser may exceed the class 1 AEL if magnifying optics is used, such as binoculars. 2 2 Low power or low risk lasers. These lasers are only hazardous if the viewer overcomes his/her natural aversion response to bright light. Class 2 lasers emit only in the visible spectrum ( nm). 2M 2a The class 2M designation is the same hazard as class 2 but is potentially hazardous when viewed with optical aids. 3R 3a Medium power or moderate risk lasers. Most Class 3R lasers emit between one and five milliwatts of visible radiation. The laser light is unlikely to be hazardous except when the viewer overcomes his/her natural aversion response or when he/she uses optical instruments. 3b 3b Eye and skin damage will occur for direct, momentary intrabeam exposure. 4 4 Can damage the skin as well as the eye during direct, momentary intrabeam exposure or exposure to diffuse reflections. Potential fire hazard. VIII. Eye Protection and Maximum Permissible Exposures Laser irradiation of the eye may cause damage to the cornea, the lens, or the retina, depending on the wavelength of the light and the energy absorption characteristics of the ocular media (see Fig.1). Lasers cause biological damage by depositing heat energy in a small area, or by photochemical processes. Infrared, ultraviolet, and visible laser radiation are capable of causing damage to the eye. 19

20 PUPIL CORNE IRIS VITREOU LEN RETIN FOVE 1. Retinal Damage OPTIC NERVE BLOOD VESSELS Figure 1, Schematic Diagram of the Human Eye Visible and Near Infrared (Spectral Regions nm and nm) Visible and infrared A wavelengths penetrate through the cornea to be focused on a small area of the retina, the fovea centralis (see Fig. 2). This process greatly amplifies the energy density and increases the potential for damage. Lesions may form on the retina as a result of local heating of the retina subsequent to absorption of the light. 2. Lens Damage Figure 2, Ocular Absorption of Visible Light and Infrared A Ultraviolet A (Spectral Region nm) Wavelengths in this spectral region are primarily absorbed in the lens (Figure 3). Damage to this structure, either photochemical or thermal, disrupts the precise relationship between the tissue layers of the lens. This results in areas of increased light scatter - a cataract. Under normal conditions, the lens will begin to harden with age. Exposure to UV-A accelerates this process and may lead to presbyopia (the loss of the ability of the lens to accommodate or focus). Figure 3, Ocular Absorption of Ultraviolet A 20

21 3. Corneal Damage Mid Infrared and Far Infrared (Spectral Region 1.4 to 100 μm) The Cornea of the eye is opaque to infrared radiation (Figure 4). The energy in the beam is absorbed on the surface of the eye and damage results from heating of the cornea. Excessive infrared exposure causes a loss of transparency or produces a surface irregularity on the cornea. Ultraviolet B and Ultraviolet C (Spectral Region nm) The cornea of the eye is also opaque to ultraviolet radiation. As with infrared radiation, the energy of the beam is absorbed on the surface of the eye and corneal damage results (Figure 4). Excessive ultraviolet exposure results in photokeratitis (Welder's Flash), photophobia, redness, tearing, conjunctival discharge and stromal haze. There is a 6-12 hour latency period before symptoms to photochemical damage appear. Figure 4, Ocular Absorption of Infrared B, Infrared C, Ultraviolet B and Ultraviolet C 4. Other Ocular Damage There are two transition zones between corneal hazard and retinal hazard spectral regions. These are located at the bands separating UV-A and visible, and IR-A and IR-B regions. In these regions, there may be both corneal and retinal damage. An example of this hazard would be the Nd: YAG near-infrared region laser. This wavelength can be focused by the eye but not perceived by it. Damage can thus be done to the retina in the same manner as visible light even though the beam itself remains invisible. 5. Maximum Permissible Exposure (MPE) On the basis of retinal damage thresholds and concentrations of light by the lens, maximum permissible exposure limits have been recommended by the American National Standards Institute (ANSI Z ). The MPE values for visible light are based on a pupil diameter of 7 mm, which is considered to be the maximum opening of 21

22 the iris of the eye. For other wavelengths, the incident laser energy is averaged over a 1 mm diameter circle. The MPE values are below known hazardous levels. However, the MPE values may be uncomfortable to view. Thus, it is good practice to maintain exposure levels as far below the MPE values as practical. 6. Protective Eyewear ANSI Z136.1 requires that protective eyewear be available and worn whenever hazardous conditions may result from laser radiation or laser related operations. The eye may be protected against laser radiation by the use of protective eyewear that attenuates the intensity of laser light while transmitting enough ambient light for safe visibility (luminous transmission). The ideal eyewear provides maximum attenuation of the laser light while transmitting the maximum amount of ambient light. No single lens material is useful for all wavelengths or for all radiation exposures. In choosing protective eyewear, careful consideration must be given to the operating parameters, MPEs, and wavelength. The Radiation Protection Program will recommend the appropriate laser safety eyewear during the laser registration process. A list of laser safety eyewear manufacturers can be found in Appendix G. Persons working with lasers emitting in the visible region are often unwilling to wear protective eyewear during alignment procedures due to the inability to see the beam. Laser alignment goggles are available which provide acceptable protection during reduced power alignment procedures while allowing an outline of the beam to be seen. Appropriate eyewear information may be acquired for a particular laser from the manufacturer at the time of purchase. Insight as to proper and reasonable eye protection may also be obtained from the Radiation Protection Program. It is recommended that RPP evaluate all protective eyewear. It is extremely important that laser workers wear the appropriate laser safety eyewear correctly. For example, only eyewear such as goggles specifically designed to fit over prescription glasses may be worn with prescription glasses. Other protective eyewear worn over prescription glasses may not provide complete eye protection. Summary Table Spectral Region Wavelength Principal Tissue at Risk Ultraviolet C nm Cornea Ultraviolet B nm Cornea Ultraviolet A nm Lens 22

23 Visible Light nm Retina Near Infrared nm Retina Mid Infrared μm Cornea and Lens Far Infrared μm Cornea IX. Skin Exposure and Maximum Permissible Exposures Acute exposure of the skin to large amounts of energy from the laser may cause burning of the skin. These burns are similar to thermal or radiant (sun) burns. The incident radiation is converted to heat which is not dissipated rapidly enough due to poor thermal conductivity of the tissue. The resulting local temperature rise causes denaturation of tissue protein. Injury of the skin depends on the wavelength of laser light, exposure time, and degree of skin pigmentation. Skin carcinogenesis may occur at some specific ultraviolet wavelengths ( nm). XI. General Safety Procedures 1. Do not work with or near a laser unless you have been authorized to do so. 2. Do not enter a room or area where a laser is be energized unless authorized to do so. 3. Before energizing a laser, verify that prescribed safety devices for the unit are being properly employed. These may include opaque shielding, non-reflecting and/or fireresistant surfaces, goggles and/or face shields, door interlocks, and ventilation for toxic material. 4. Make sure that a pulsed laser unit cannot be energized inadvertently. Discharge capacitors and turn off power before leaving the laser unit unattended. 5. Don't stare directly into the laser beam. Use appropriate eyewear during beam alignment and laser operation. Beam alignment procedures should be performed at lowest practical power levels. 6. Control the access to the laser facility. This can be done by clearly designating those who have access to the laser room. Implement access control by locking the door and installing warning lights and signs on the outside door. 7. Never leave the laser unattended when it is in operation. 8. Remove any jewelry to avoid inadvertent reflections. XII. Recommended Laser Safety Controls A. Class 1 Controls No user safety rules are necessary. B. Class 2 Controls 1. Never permit a person continuously stare into the laser source. 2. Never point the laser at an individual's eye unless a useful purpose exists and the 23

24 exposure level and duration will not exceed the permissible limit. C. Class 1M, 2M, and 3R Controls 1. Never permit a person continuously stare into the laser source. 2. Never point the laser at an individual's eye unless a useful purpose exists and the exposure level and duration will not exceed the permissible limit. 3. Do not use with collecting optics unless it has been reviewed with regard to the increased hazard due to magnification. The M in class 1 M and 2M is used to indicate that the laser may exceed the class 1 or 2 AEL if magnifying optics is used, such as binoculars. Class 2M lasers are potentially hazardous when viewed with optical aids or if the viewer overcomes his/her natural aversion response to bright light. Class 2 and 2M lasers emit only in the visible spectrum ( nm). Class 3R (formerly 3a) laser are medium power or moderate risk lasers. Most Class 3a lasers emit between one and five milliwatts of visible radiation. The laser light is unlikely to be hazardous except when the viewer overcomes his/her natural aversion response or when he/she uses optical instruments. D. Class 3b Controls 1. Do not aim the laser at an individual's eye. 2. Permit only experienced personnel to operate the laser. 3. Enclose as much of the beam path as possible. Even a transparent enclosure will prevent individuals from placing their head or reflecting objects within the beam path. Terminations should be used at the end of the useful paths of the direct beam and any secondary beams. 4. Shutters, polarizers and optical filters should be placed at the laser exit port to reduce the beam power to the minimal useful level. 5. Control spectators. 6. A warning light or buzzer should indicate laser operation. This is especially needed if the beam is not visible, i.e., for infrared lasers. 7. Do not permit laser tracking of non-target vehicles or aircraft. 8. Operate the laser only in a restricted area - for example, in a closed room without windows. Place a warning sign on the door. 9. Place the laser beam path well above or well below the eye level of any sitting or standing observers whenever possible. The laser should be mounted firmly to assure that the beam travels only along its intended path. 10. Always use proper laser eye protection if a potential eye hazard exists for the direct beam or a specular reflection (Figure 5). 11. A key switch should be installed to minimize tampering by unauthorized 24