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

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Scanning Audiences at Laser ShowsTheory and
Practice ... and a Proposal

• Patrick Murphy, ILDA Executive Director
• Greg Makhov, ILDA Safety Committee Chair

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What is Audience Scanning?
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Creating beautiful mid-air beam patterns which
surround and envelop the audience,for
entertainment and display purposes
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(No Transcript)
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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

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Audience scanning is widespread outside the
United States
50,000 spectators 2006 Asian Games Khalifa
Stadium Doha, Qatar
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How many peoplehave been exposed?
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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

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109,500,000 people x 100 pulses per show
10,950,000,000 pulsesover 30 years
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What laser power have these110 million
peoplebeen exposed to?
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Typical raw laser power

• 500 milliwatts to 5 watts raw power(at laser,
  before projector optics and scanner)
• As much as 20 watts raw power for larger shows

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What is the irradianceat the audience?

• Exact irradiance unknown
• Estimates from laser show and safety experts
• Greg Makhov, John OHagan, 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

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Typical show

• 3 watt laser
• After optics and scanners, about 1 watt output
  toward audience
• 1 milliradian divergence
• Closest audience access 25 meters

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Typical show, cont.

• Static irradiance 162 µW/cm2
• (65x the static MPE)
• Well-designed scanning effects, no static beams
• Reduced hazard 4x
• Single pulse MPE applies 16x single pulse MPE
• Performers located closer, at 10 meters
• 75 times the single pulse MPE

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Where are the injuriesfrom 11 billion
pulses,most over the MPE?
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Close to zero injuries

• 1996 study by 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.
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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
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Close to zero injuries

• Google search
• No reports found of incidents of audience members
  at shows with CW lasers
• Not even informal complaints on blogs or forums

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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 scotoma produced while
  watching a laser show (beam hit into eye), 1997

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Worst case findings

• 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

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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

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Important caveats

• Not saying there arent changes to retina
• It is unknown whether shows cause
  laboratory-detectable changes
• Not saying the MPEs are wrong
• We believe in and support the MPE levels

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Our conclusion

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

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Why are there essentiallyno reported injuries?
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Reasons for essentially no injuries

• MPEs have a built-in safety factor
• Does not explain shows which are well over 10
  times the MPE

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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

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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

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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

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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

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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

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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

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

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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 mrad divergence (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

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... compare to MPEs ...
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... 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.

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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

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ProblemMPE-level shows are not impressive
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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

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No longer an impressive show

• Forcing MPE-only shows would be unacceptable to
  many clients and laser show producers
• For 30 years, theyve presented shows that are
  10, 50, 100 times the MPE, with no injury reports
• Want shows to be visually impressive, not wimpy

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Solution lies inrisk analysisand management
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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

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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)

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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

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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

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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

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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

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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

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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

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Putting it all together...
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The good and badof audience scanning

• Audience scanning -- good

• Audience scanning - bad

• Excellent safety record, despite many shows
  exceeding MPE
• New technique for accurately setting show
  irradiance
• 4x the static MPE
• Very popular, especially in discos, nightclubs,
  rock concerts

• Too many shows exceeding the MPE by far too much
• Too many laser show producers setting light
  levels by eye
• No idea of the exposure levels
• MPE shows are dim, fuzzy
• Unacceptable in higher risk environments such as
  discos, nightclubs, concerts

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Patron-managed risk at laser shows

• Take conscious or subconscious avoidance actions
  before the beam crosses the eye
• Look away
• Blink
• Dont look directly at the projector
• Hold up a hand
• Stay behind another persons head
• Turn around
• Move away from the laser-scanned area

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A practical proposal to increase audience
scanning safety
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Requirements forall audience scanning shows

• CW lasers only
• Operator must measure static beam so as to know
  irradiance no more guessing
• Well-designed, smooth scan patterns with no hot
  spots
• Effective scan-fail circuit
• Laser show operator continuously monitoring the
  show (or equivalent automated detection system)

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Level 1 showBelow MPE (similar to current
regulations)

• Laser power at point of closest audience access
  is below the MPE
• Set beam irradiance to 10 mW/cm2
• This is the MPE for 1 millisecond pulses
• No signage or other warning needed

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Level 2 ShowWith greater power, comes greater
responsibility

• Show is allowed to exceed the MPE by a factor of
  10
• Measure the static beam set irradiance to 100
  mW/cm2
• When scanning, this is 10x the MPE for 1
  millisecond pulses
• Signage and caution announcements required
• Caution Extra-bright laser lights in use. Avoid
  looking directly into beams
• Similar to signs at amusement parks such as Do
  not ride if you are pregnant or have heart
  problems.

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How does this improve safety?

• All audience scanning shows must be measured. NO
  EXCEPTIONS.
• No audience scanning above 10x the MPE.
• This eliminates the very high powered shows at
  50, 100, 300 times the MPE
• Audience at Level 2 shows have additional safety
  information
• Avoid looking directly into laser beam

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Who will use these levels?

• Level 1 shows will be for cautious clients
• Corporate shows, family-audience shows, major
  theme parks
• Level 2 shows will be used where patrons accept
  or even welcome some risks
• Discos, nightclubs, rock concerts

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Use by private sector

• Guidelines used by venue owners, show producers
  in areas where laser laws or enforcement is weak.
• They decide whether shows they present are Level
  1 or Level 2
• Guidelines championed within the laser show
  industry (ILDA)

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Regulatory enforcement

• Regulators could informally permit Level 2 shows,
  if comfortable with professionalism, safety
  measures of laser show producer
• Similar to police enforcement of speed limitsno
  tickets until you are 10 mph over the 60 mph
  speed limit

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Work in standards committees

• Seek discussion, improvement and acceptance by
  standards bodies
• IEC 60825-3, Guidance for laser displays and
  shows
• ANSI Z136.10, Safe Use of Lasers in
  Entertainment, Displays and Exhibitions

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Conclusion

• Audience scanning with visible CW lasers appears
  to be causing essentially no claimed or proven
  injuries
• There are mechanisms which are reducing the
  exposure on the retina
• For improved safety, we want to eliminate shows
  which are significantly over the MPE
• In return, we ask for shows at a reasonable
  brightness level

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Questions?
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(No Transcript)
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(Note Leftover slides are after this point. The
leftover slides did not make it into the main
presentation given at ILSC 2009. This is usually
due to time constraints, but may also be an
unfinished thought or line of reasoning.)
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Changes vs. injuries
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Changes vs. injuries

• Changes Lesion or other visible change to the
  structure of the eye, which is observable under
  laboratory conditions
• Injury A change which the person notices, either
• Under special conditions such as a uniform blue
  sky, or
• As they go about their daily routine

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Changes vs. injuries

• Changes? Unknown whether audience scanning causes
  visible lesions on the eye
• No studies
• Injuries? What is known after 100,000,000 people
  and 11 billion pulses
• Worst case, 25 claimed injuries per decade
• Despite most shows being above the MPE, and many
  being far above the MPE

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Future studies

• Would welcome future studies. For example
• Recruit university students who already go to
  discos which use lasers. Record their eyes using
  SDOCT or similar detailed techniques. Let them go
  to the laser disco as they would normally. After
  returning
• Survey students about their exposure how many
  times did the laser enter their eye, was it
  uncomfortable, etc.
• Examine eyes at 1 hour, 24 hours, etc. for
  changes.

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To make a show below the MPE

• Design show with smooth, always-moving beam
  effects
• No static beams or hot spots
• Before show, set beam irradiance to the MPE limit
  for 1 millisecond pulses (10 mW/cm2)
• For details, see Makhovs 2005 paper in
  Proceedings of the ILSC

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Makhovs analysis oflaser scan patterns

• Pulses (eye crossings) in a show are from 2
  milliseconds to 10 microseconds
• Within range of thermal MPE
• Safest to use MPE for 1 millisecond (10 mW/cm2)
• This is four times the static MPE

Makhov, Greg. Proceedings of the 2005
International Laser Safety Conference, Vol. 7