Control Considerations for Safe Laser Alignment Deana Luke ESH&Q Manager National Renewable Energy Laboratory deana.luke@nrel.gov DOE LSO Workshop May 8, 2018
Risk of Alignment Tasks 60-70% of laser accidents in research occur during alignment Common scenario: unanticipated reflection from an optic while not wearing protective eyewear Consequences vs. Likelihood may result in Moderate to High Risk NREL 2
NREL 3
Elimination and Substitution Can you use another light source in process instead of laser (e.g. LED)? Low power alignment laser (Class 3R or lower) NREL 4
Engineering Controls Fully enclosed Class 1 systems Remote viewing with cameras Inexpensive cameras NREL 5
Engineering Controls Fully enclosed Class 1 systems Motorize movement of optics Remote operation NREL 6
Engineering Controls Fully enclosed Class 1 systems More examples Motorized translation stages Remote operation NREL 7
Externally controlled rotation stages And translation stages With easy access switches and controls.
Engineering Controls Fully enclosed Class 1 systems Reduce power below Class 3B using neutral density filters Control optical filters remotely NREL 9
Administrative Controls & Work Practices Written alignment procedures Safe Operating Procedure Safe Work Permit Beam path diagram Training Hands-on Mentoring Laser Alignment Practice Lab NREL 10
Example Laser Alignment Hands-on Practical Students complete 2 required exercises and at least 1 additional exercise based on the operator s scope of work. Exercise 1: Laser Hazards & Controls* Exercise 2: 2-Iris Alignment* Exercise 3: Power Attenuation Exercise 4: Co-Alignment of Two Beams Exercise 5: Retroreflector Safety & Lessons Learned Exercise 6: Periscope Safety & Use Exercise 7: Alignment Through a Monochromator Exercise 8: Aligning IR Beams Exercise 9: Motorized Remote Alignment *Required, at minimum NREL 11
Administrative Controls & Work Practices Non-reflective tools Matte black Reduce reflections Beam display/locating devices Reduce power as low as possible Use beam blocks or shutter at source Use beam blocks, shields or barriers to block stray beams Place beam blocks behind optics in case beam misses mirrors Align through irises Fix optics to optical tables NREL 12
Administrative Controls & Work Practice Locate and control stray beams before moving on to next optical component Recheck for stray beams if changing beam size Beam blocks to terminate beam Use signage and lights to communicate hazard NREL 13
PPE - Laser Eye Protection Full Protection LEP or Reduced OD Alignment Eyewear?? It s a Balancing Act: Alignment eyewear counterintuitive given elevated risk Full protection OD decreased beam viewing, user may remove eyewear Improper use of LEP is primary hazard for alignment tasks NREL 14
PPE - Laser Protective Eyewear What does ANSI Say? ANSI Z136.1 2014 Section 4.4.4.2.5 Use full protection for routine operations & most alignment procedures Protect against direct beam or specular reflections LSO must evaluate & authorize alignment eyewear option Only use alignment eyewear for visible beams NREL 15
PPE - Laser Protective Eyewear What does ANSI Say? Calculate OD for both point source intrabeam and diffuse viewing At a minimum LEP must meet minimum OD requirement for viewing diffuse reflection at distance of 20 cm. Notify user that they are not protected from intrabeam exposure, MPE exceeded NREL 16
Alignment Eyewear Prudent Practices Minimum OD s for diffuse reflection viewing are liberal Much lower than OD s for intrabeam viewing and specular reflections MPE values exceeded if accidental exposures occur to direct beam or specular reflections More conservative approach: Specify OD that will protect user to Class 3R or Class 2 conditions NREL 17
Alignment Eyewear Prudent Practices Don t forget about Visible Light Transmission (% VLT) Select one wavelength for bulk of alignment tasks limit use of broad spectrum LEP Increase vigilance with administrative controls and safe alignment procedures Adhere to good practices for wearing laser eyewear Inspect, no scratches on reflective coatings, saturable absorption, proper fit NREL 18
PPE - Skin Protection Alignment tasks Potential increased exposure: Longer exposure times Open beam Close proximity to laser beam Recommended PPE: Lab coats, gloves, tightly-woven flame-retardant fabrics UV skin exposures Evaluate against MPEs for skin Skin covers, and/or sun screen creams may be recommended NREL 19
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