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Thread: crowd scanning advice (UK)

  1. #1
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    Default crowd scanning advice (UK)

    (I was recommended to post here from somebody at LPF, so what follows is my original post from LPF).

    I volunteer on my University's 'Entertainments Crew' who handle the sound & light in the Students' Union for discos/bands/club nights etc. The first week of the new academic year (late September) always has special events where we get to spend a bit of cash hiring in equipment & effects we don't own.

    We've hired scanning lasers before but always aimed them above the crowd as none of us had done enough research into the safety of aiming them at the crowd. Well this September I want to do some crowd scanning & as it was my idea I've been put in charge of determining the safety of such an effect, what scanners will be suitable, where we will be able to rig the scanners, etc.

    I've read through HS(G)95 & the summary document published by Terralec & I'm starting to find out how restrictive the recommendations are. HS(G)95 doesn't contain any example distances for scanners, but the Terralec document gives the following table of 'hazard distances' (which I presume means that within that distance MPE is exceeded) for a scanner drawing a stationary circular tunnel (I doubt a moving tunnel will increase the distances that much), with a spread of 50 degrees, a scan rate of 20Hz & presuming a divergence of 2 mradians;

    10mW : 5m
    30mW : 9m
    50mW : 11m
    100mW : 16m
    250mW : 26m
    450mW : 35m

    In addition to that, HS(G)95 recommends that you keep a 3m vertical distance between anywhere the audience can access (eg the dance floor) & any beams that exceed MPE.

    I haven't heard back from the guy in charge with accurate dimensions of the venue, but from my guesstimates it's about 30 feet tall (about 9.1m). From the numbers provided by Terralec that means we'll struggle to use anything more than about 15-20mW for audience scanning.

    Does this seem about right, or am I doing something wrong? Even if we only use green for audience scanning & keep the hazer on full all night, is the audience really going to see an impressive effect when 2x piddly 20mW scanners open up on them?

    I know there are plenty of small clubs in the UK that rake the audience with 100mW+ Chinese scanners from barely 6 feet away with no consideration to safety & they never get into trouble, but I don't plan on being such an idiot & getting all of the responsible laserists bad press!

  2. #2
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    Default

    Those numbers looks safe to me, and are way below most of the audiance scannings shows in the netherlands.

    You can also take a look at the mpe calculator i made:

    http://www.photonlexicon.com/forums/...Mpe+calculator

  3. #3
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    Hello again 'lost eden'

    Try dropping Lasermad or Gashead a PM and see what they might be able to do you for your budget.
    Frikkin Lasers
    http://www.frikkinlasers.co.uk

    You are using Bonetti's defense against me, ah?

    I thought it fitting, considering the rocky terrain.

  4. #4
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    Adam

    What do you know that i dont mmmmm ?

    Pauil
    In the beginning there was none. Then came the light - #1 UKLEM - 2007
    BUY UK LEGAL LASER POINTER :: NEW - Blue 460nm Laser Pointers

  5. #5
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    I've been participating in a thread with the OP on a different (sound related) forum where their location is listed as Fife (of course the event could be elsewhere, we never got that far). I suggested perhaps hitting up someone who does lasers properly to see what might be able to be done 'in budget' and then a good amount of the worry and hassle goes away, plus they'll get some 'proper' control rather than DMX.
    Frikkin Lasers
    http://www.frikkinlasers.co.uk

    You are using Bonetti's defense against me, ah?

    I thought it fitting, considering the rocky terrain.

  6. #6
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    CJD

    Looks like your in St Andrews , Gashead , nigel is in fife , he may pop in here or PM him.

    Personally I rarely do audiance scanning , due to the paper trail required to cover your buttocks successfully , id seriously consider not doing it or your university should have a trained experienced designated "laser Safety Officer" , working together you may be able to acheive the paper trail required.

    Everything you do in terms of laser power readings requires a recently calibrated , normally expensive (2k plus) power meter to prove your calculations which your physics dept may have available , so liase.

    I you would liek any buildings lasered to advertise events though ..gimme a call

    Paul
    In the beginning there was none. Then came the light - #1 UKLEM - 2007
    BUY UK LEGAL LASER POINTER :: NEW - Blue 460nm Laser Pointers

  7. #7
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    Yep I am indeed in St Andrews & that's where the events will be taking place.

    The more I (re)read the paperwork & advice I'm getting on forums (here & elsewhere) the more I'm beginning to think that audience scanning is going to be out of the question. From the vague numbers I've gotten from the Terralec document & from playing about with McCarrots MPE calculator (from...LPF I think?) it looks like we would need something probably no more than 10-15mW if we mounted them in the top front corners of the main part of the venue, maybe pushing 20-25mW if we mounted them at the back of the stage area (& ignored the dangers of the stage where the crew operate being completely above MPE...).

    So I started looking about for green scanners with diodes that weak, which also have enough information to fill in MPE calculations & which also have a keyswitch (which is 'recommended' by HS(G)95) & not to my surprise, I couldn't find anything suitable.

    I'm going to keep doing some more research, but it's beginning to look as though if we want lasers we should just stick to fingers above the crowd's heads at 3m. Of course this still means that we technically need to find a scanner with a keyswitch, which the 0.5W blue Vayron we hired last time didn't...

  8. #8
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    You will see lots of audiance scanning laser shows around , most are completely ignoring the rules , those who arent are increasing their divergence substanially 7-9 mR but your entering a world of custom equipment and optics , those doing laser shows commercially ( such as roger waters recent tour with audiance scanning ) are incrasing divergence and paying extensive amounts to " laser Safety officer " to sign off effects and events and create a paper trail to prove they are doing everything as safely as feasibly possible

    Paul
    In the beginning there was none. Then came the light - #1 UKLEM - 2007
    BUY UK LEGAL LASER POINTER :: NEW - Blue 460nm Laser Pointers

  9. #9
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    gashead is offline Admin Verified: Best Accent Ever(Tm)
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    Gidday,

    PM replied to from cjdavies.

    No reply?!

  10. #10
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    Sorry for going AWOL. The powers-that-be (in other words the guys in charge of the hires budget) have decided to cut back a lot, sinking more money into the acts than the tech. The budget won't stretch to getting a pro laserist in & we've given up entirely on being able to crowd scan on our own without breaking regulations. The most we'll do is hire 2x naff green scanners & have them doing fingers at 3m off the ground.

    Thanks for all your input though, if we get the opportunity to use lasers in the future for a big event I know where to come for advice!

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