Scanning Audiences at Laser Shows: Theory and Practice ... and a Proposal

1. Scanning Audiences at Laser Shows:Theory and Practice ... and a Proposal Patrick Murphy, ILDA Executive Director Greg Makhov, ILDA Safety Committee Chair

2. What is Audience Scanning?

3. “Creating beautiful mid-air beam patterns which surround and envelop the audience,for entertainment and display purposes”

4. 3 important points • Scans are not intended to enter the eye • An undesired consequence • “Audience scanning” means deliberate exposure only • Does NOT include accidental exposures from non-audience scanning shows • Visible, continuous-wave lasers only • Never use pulsed lasers (ex: Q-switched) • Only CW lasers discussed in this paper International Laser Display Association

5. How many peoplehave been exposed?

6. Conservative estimate • Number of people exposed to direct laser beams: • 100 clubs with 100 people nightly: 10,000/day • 3,650,000 people experience this yearly • 109,500,000 people over the past 30 years • Number of exposures per show: • Beam crosses the eye an average of 20 times per show • Typical 5 pulses each crossing • 100 pulses per show International Laser Display Association

7. 109,500,000 people x 100 pulses per show = 10,950,000,000 pulsesover 30 years

8. What laser power have these110 million peoplebeen exposed to?

9. Typical raw laser power • 500 milliwattsto 5 watts raw power(at laser, before projector optics and scanner) • As much as 20 watts raw power for larger shows International Laser Display Association

10. What is the irradianceat the audience? • Exact irradiance unknown • Estimates from laser show and safety experts • Greg Makhov, John O’Hagan, James Stewart • Most shows are above the MPEat the point of closest audience access • Many shows are far above the MPE • 10, 50, 100 ... even 300 times the MPE International Laser Display Association

11. A typical show • 3 watt laser • After optics and scanners, about 1 watt output toward audience • 1 milliradian divergence • Closest audience access 25 meters International Laser Display Association

12. A typical show, cont. • Static irradiance: 162 mW/cm2 • 65x the ¼ second MPE • Well-designed scanning effects, no static beams • Dwell time is 1 msec or less, so single pulse MPE applies • Because of scanning, hazard is reduced 4x • 16x the single pulse MPE International Laser Display Association

13. Where are the injuriesfrom 11 billion pulses,most over the MPE?

14. “Close to zero” injuries

15. “Close to zero” injuries • 1996 studyby independent research firm • Presented at ILSC 1997 • Looked worldwide • Found 5 reported accidents over 20 years • Article notes “there may be underreporting” • If 9 out of 10 injuries are not reported,this is 25 injuries per decade (2.5 per year) "Is Deliberate Audience Scanning Unsafe?", Patrick Murphy, Pangolin Laser SystemsProceedings of the 1997 International Laser Safety Conference, Vol. 3, pp. 493-502.

16. “Close to zero” injuries • Google Scholar • 2007 article on injuries at a show caused by a pulsed YAG laser • “To our knowledge, only one case of eye injury during a laser show has been reported previously.” • “The lesions resolved within 3 months” Retinal Laser Injury During A Laser ShowShneck, Marina MD; Levy, Jaime MD; Klemperer, Itamar MD; Lifshitz, Tova MDDepartment of Ophthalmology, Soroka University Medical Center, Ben-Gurion University of the NegevRetinal Cases & Brief Reports: Volume 1(3) Summer 2007, pp 178-181

17. “Close to zero” injuries • Google search • No reports found of incidents of audience members at shows with CW lasers • (Again, we are not including the July 2009 Tomorrowland incident at this time) • Not even informal complaints on blogs or forums International Laser Display Association

18. “Close to zero” injuries • Rockwell Laser Industries database of over 1600 incident cases • Only two cases involving deliberate audience scanning with CW lasers: • One case of “eye irritation” following a laser show, 1980 • One case of retinal scotomaproduced while watching a laser show (beam hit into eye), 1997 International Laser Display Association

19. Recent incidents • July 2008, Aquamarine Festival, near Moscow • 35+ persons injured by pulsed laser • Due to rain forcing audience into a tent, the laser was irresponsibly and illegally aimed down into audience instead of up into the sky • Wrong type of laser; pulsed lasers should never be used for audience scanning • Because of illegal use, these injuries do not apply to statistics about continuous-wave lasers used for audience scanning International Laser Display Association

20. Recent incidents • July 2009, Tomorrowland Festival, Belgium • 2 persons (out of 90,000) had eye injuries • Laser show irradiance was calculated to be close to or at MPE: 50 mW/cm² closest to audience (5x MPE), 10 mW/cm² at 20 meters into crowd (same as MPE) • Many high-powered laser pointers in use in crowd • Conclusion: Legal and safety authorities agreed injuries were due to crowd laser pointers International Laser Display Association

21. Summary • Based on 1996 study finding 5 incidents over 20 years • 2.5 reported injuries per decade • Estimating 90% underreporting: • 25 estimated injuries per decade, worldwide

22. How does this compare? Lasers U.S. amusement park rides 2.5 reported injuries per decade Due to underreporting, could be 25 injuries per decade Worldwide • 72,000 reported injuries per decade • 44 deaths • Just one country International Laser Display Association

23. Important caveats • Not saying there aren’t changes to retina • It is unknown whether shows cause laboratory-detectable changes • Further research would be very helpful • Not saying the MPEs are wrong • We believe in and support the MPE levels International Laser Display Association

24. Our conclusion • We are saying that, after 30 years and 11 billion pulses, most over the MPE, there are practically no complaints, injury claims, proven injuries, lawsuits, etc. from audience members, from CW shows. • If there were, these shows would not be occurring • Clients were very skittish after press reports of July 2008 injuries caused by pulsed laser International Laser Display Association

25. Why are there essentiallyno reported injuries?

26. Reasons for essentially no injuries • MPEs have a built-in safety factor • Does not explain shows which are well over 10 times the MPE International Laser Display Association

27. Reasons for essentially no injuries • Lasers are relatively far from audience members • Gives time for beam to diverge • Audience is not always looking at the laser beams • Audience rarely focuses vision directly on the laser projector output (scanners) • Taking in entire scene International Laser Display Association

28. Reasons for essentially no injuries • Multiple pulses are safer than previously thought • Effect of multiple pulses not n-1/4 • See papers presented earlier at ILSC 2009 International Laser Display Association

29. Reasons for essentially no injuries • Pupil is smaller than 7 mm • Laser shows are usually presented with stage lights, etc., so 5 mm is more realistic • At 5 mm: • 50% less light enters the eye • Pulse width is decreased by 30% International Laser Display Association

30. Reasons for essentially no injuries • 0.25 second aversion response prevents serious damage from scanning failure • Small likelihood of hitting a pupil • Randomly positioned static beamhas a 1/25,000 chance of being on a pupil International Laser Display Association

31. Reasons for essentially no injuries • Avoidance response beforebeam crosses the eye • Move head • Look down or to the side • Blink or close eyes • View show while blocking beam emission point • Put up a hand in front of the projector output • Stay behind the head of the person in front of them International Laser Display Association

32. Reasons for essentially no injuries • Audience is spread out • Those closest to the laser receive the maximum exposure • Those farther back have a lower exposure,due to: • Increased divergence • Increased linear velocity of the scanned beam International Laser Display Association

33. Is it possible to create shows which are below the MPE?

34. Before:Very hard to measure exposure • Requires a detector watching the entire show • Only measures that one spot • To calculate additional locations, requires re-running entire show • Practically impossible to determine maximum exposure International Laser Display Association

35. After:Analyze scan characteristics... • Angular velocity of scanners • From 10 radians/sec to 100 radians/sec • Distance from projector to audience • From 1 meter to 10,000 meters • Angular velocity * distance = linear velocity • From 10 meters/sec to 10,000,000 meters/sec • Assume 1 mraddivergence (tight for a laser projector) • Beam diameter/linear velocity = pulse duration • From 2 milliseconds to 10 microseconds • Within range of Thermal MPE for 10 sec to 18 μsec • MPE for pulse is therefore 1.8 x t3/4 x 10-3 J/cm2 International Laser Display Association

36. ... compare to MPEs ... International Laser Display Association

37. ... express scanning factor as a multiple of the static beam • Conclusion: Scanning the beam allows an increase of 4 times to 10 times the exposure, compared with a static beam. International Laser Display Association

38. Easy, safe measurement technique • Show measurement is vastly simplified: • Put out a static beam • Measure at point of closest audience access • Adjust power and/or divergence so the irradiance is 10 mW/cm2 (this is the MPE for a 1 msec exposure) • Requires a show with smooth, constantly moving scans • Recommended to use scan-fail safeguard or similar velocity-monitoring circuit International Laser Display Association

39. Problem:MPE-level shows are not impressive

40. MPE shows are dim & fuzzy • Shows done at the MPE are • Low power: Dim • High divergence: Fat, fuzzy beams • Require almost total darkness to be effective • Similar to turning down the volume at a disco or rock concert, to background listening levels International Laser Display Association

41. No longer an impressive show • Forcing MPE-only shows would be unacceptable to many clients and laser show producers • For 30 years, they’ve presented shows that are 10, 50, 100 times the MPE, with no injury reports • Want shows to be visually impressive, not wimpy International Laser Display Association

42. Solution lies inrisk analysisand management

43. Risks in everyday life • People accept risk in their everyday life (driving to work) and in their leisure activities • Playing sports • Going hiking • Riding bicycles • These activities can and do cause injuries • Cuts (leaving visible scars) • Bruises • Broken bones International Laser Display Association

44. Injuries and life • Minor injuries (cuts, scrapes, bruises) are an unfortunate but inescapable consequence of leading an active, interesting life • NOT saying it is OK to cause injuries • Should minimize or eliminate if possible • But people routinely choose to participate in activities which eventually will lead to a cut, scrape, bruise (or worse) International Laser Display Association

45. Risk acceptance • People make individual risk/reward calculations, based on factors including... • ... enjoyment of the activity • ... chance of injury (bowling vs. tackle football) • People manage their risk • Having control over risk exposure International Laser Display Association

46. Risk management • Goal is to manage and minimize the risk • Tackle football: Wear helmets and padding • Hiking: Carry first aid gear, GPS • Bicycling: Wear helmet, use lights at night International Laser Display Association

47. Risk management • Goal is NOT to eliminate or water-downthe activity to bland nothingness • Only allow touch football • No hiking except on marked paths • All bicycles to have outboard training wheels International Laser Display Association

48. Risks at discos,nightclubs and concerts • Loud sound systems. One evening too close to the speakers can cause permanent hearing damage • Audiences like loud music (rightly or wrongly) • Note that there is not a movement to turn down sound to OSHA-approved levels • Widespread alcohol consumption • Often to excess • Smoking in many countries • Illegal drugs at some concerts, raves International Laser Display Association

49. Risks at discos,nightclubs and concerts • Patrons can control risks • Bring earplugs • Stand farther from speakers • Drink in moderation, or non-alcohol drinks • Despite the risks – or maybe BECAUSE of some of the risks – these remain popular • A disco with moderate, OSHA-approved sound levels, that serves only soft drinks, will have very few patrons International Laser Display Association

50. Risks at discos, nightclubs and concerts • Patrons can control risks • Bring earplugs • Stand farther from speakers • Drink in moderation, or non-alcohol drinks • Despite the risks – or maybe BECAUSE of some of the risks – these remain popular • A disco with moderate, OSHA-approved sound levels, that serves only soft drinks, will have very few patrons International Laser Display Association