Laser Safety For Dummies (me)

[Stiffler]

I think everyone here will agree that a high quality, high power laser, when used by a knowledgeable operator, is a safe & dramatic addition to any light show. I think everyone will also agree that this is becoming the exception, NOT the rule. I came to this forum a little over a month ago, when a google search for "kryo man" brought me here (in regards to the dangers of his laser pointers. I was performing the search because there is now a Detroit version, and he also sports high power laser pointers & pyrotechnic charges). I have since stayed because I like lasers, and this seems like a pretty cool group of people. During my time here (several hours a day), I have seen several references to safety, or the lack there of, and even some name calling. What I have not seen (here or any where else) is a comprehensive discussion about laser safety in general, and the different ways to make a show safer without loosing it's visual impact. Seriously, thanks to this forum I now know where to buy several 1000mw+ RGB laser projectors, but I still don't know what a safety lens is; this is a problem. Not that I am going to buy a bunch of Chinese lasers & crowd scan, but I'm the exception, not the rule. I am also confused about the built in safety in some software. For instance, I have seen options to have low power zones, but how does any one know for certain what is "safe"? Is there such a thing as a sensor you can stick in the audience to get laser level feedback? If another laserist scans me in the face is it ok to punch him in the eye?

Go easy on me, I'm new here.

-Eric

[chad]

Start here:

http://www.photonlexicon.com/wiki/in...itle=Main_Page

Chad

[Things]

One of the best rules when it comes to laser safety, is think, what if you were an audience member, would you feel safe with <insert laser and powers here> hitting you in the face, and if not, what can you do about it? Clearly the first option is don't allow them to hit people in the face. The other option is to research and experiment with how it can be done safely. IMO audience scanning does add a lot to a laser show, it's a whole nother thing being in the middle of a tunnel effect vs it being overhead, and it can be 100% safe if you do it properly. Using common sense is best

[Stiffler]

Thanks for the links Chad.

Hi Things,

I totally agree that being in a tunnel effect is way cooler than watching it over head, but how does one "experiment" to make sure it's safe? Is there test equipment available? Or do I just send one of my assistants into the event space, turn the power up until he goes blind, and then back it off a little?

My point is, for all of the discussion about laser safety here at PL, I have seen very little detailed (technical) discussion about how to implement it (providing me with links, while helpful & appreciated, is NOT the same as discussing it); Perhaps it's too boring a topic:-P

-Eric

[Things]

Laser safety is quite a boring topics, yes

But anyway, if you're actually looking to do serious crowd scanning, the method used to determine it's safe is done using a laser power meter, and by calculating the MPE (Maximum permissible exposure), which will vary based on scanning speed, beam size, and of course laser power.

However, as I'm not from the US I'm not 100% sure how it's calculated, so I'll leave that for a US member or someone in the know

[Jem]

Hi Eric

Take a look here, it's a very good article by Bill Benner (Pangolin Laser Systems). At the very least it'll be a start your understanding of laser show safety...

http://www.laserfx.com/BasicSafety/BBsafeScanning.html

This covers most aspects of calculating safety in a reasonably simple to understand way. You'll need the following equipment: Laser power meter, fast silicon photodiode with amplifier, oscilloscope and a scientific calculator. Another useful tool in your arsenal would be a couple of iPhone App's: Laser NOHD and Laser Safety. Both of which are written by James Stewart of LVR research in the UK.

Hope this helps a little

[buffo]

The reason you can't find a comprehensive discussion of laser safety is because it's a complicated topic with lots and lots and LOTS of information. It's not something that can be condensed to a few threads on a forum. Sorry...

ILDA has put together a great Laser Safety Officer training class that can answer a lot of your questions, but even so there is a ton of information to go over, and time is limited. Even with adequate preparation beforehand (several hours of studying), attending the class is like drinking from a fire hose. And even though the final exam is usually open-notebook, many people do not pass the first time through - even though they may have worked in the industry for years. That's how complicated the issue is.

Living in the US presents it's own challenges because our regulations are far more restrictive than other nations. Also, given our legal climate, adhering to the rules here is just as much about protecting the public as it is about protecting your business from a crippling lawsuit (frivolous or otherwise). All a plaintiff needs to prove is that you weren't following the federal regulations for a show, and they've immediately demonstrated negligence on your part. It's a very easy step from there to claiming eye damage based on the preponderance of evidence. Remember, civil suits here aren't decided "beyond a reasonable doubt", but rather on the less-stringent "preponderance of evidence" standard, and if you're already shown to be negligent, that's pretty damning evidence against you.

To answer some of your specific questions, yes, there is a meter you can purchase that will give you an irradiance measurement of the scanned beam. However, it's very expensive (mostly because it needs to be able to respond very quickly - on the order of microseconds - to scanned effects). Also, even with that measurement, you've still got some math to do to determine if an effect is eye-safe or not. And then even if you determine it is eye-safe, there are other issues you need to contend with if you actually plan to perform audience-scanning legally. These issues include proper show design, scan-fail devices, and other safety interlocks, all of which need to be approved by the CDRH.

The easier method is to use a standard power meter to measure the irradiance of a static beam and then use some clever math to calculate the exposure of a scanned beam. This simplifies things somewhat, and also allows the use of a much more affordable power meter, but it also comes with some assumptions about how the show is designed and how the audience will react.

As for a "safety lens", this is a negative power lens that is installed on the aperture of the projector which diverges the beam, making it larger than it otherwise would be as it travels away from the projector. The idea is that as you spread the beam out, the power per unit area (or irradiance) decreases. Less irradiance means less chance of exceeding the exposure level that would cause eye damage. However, merely adding a safety lens does not automatically make your projector eye-safe. It might make it "safer", but you would still need to perform the calculations to know for sure. (That being said, many hobbyists use a safety lens to increase their safety margin when doing audience-scanning in their home. We also use them at SELEM.)

ILDA has an excellent position paper on audience scanning that explains the issue in plain language and offers several good suggestions for safe audience scanning, including the use of a standard power meter for measurements that I mentioned above. I suggest you read this document carefully. Here's the link: http://www.laserist.org/files/audien...iew_latest.pdf If you follow the guidelines in this document, you should be very safe in your own home. However, always remember that you would not be legal doing these things in a commercial show.

I could go on for pages and pages and still not adequately describe all the hurdles involved with audience scanning. (There's a reason why audience-scanning is so uncommon here: it's because it is very hard to do it within the restrictions set down by the CDRH.) However, I do know that X-laser has been talking about a new product of theirs that was just approved for audience-scanning, so that is one option to look into. I also know that Pangolin's PASS system has been approved for audience-scanning, but only when it has been properly integrated into an approved projector. I think the only approved projectors right now are the one's from LSDI, which are prohibitively expensive for most hobbyists.

But as for trying to get a home-built projector certified for audience-scanning? Forget it. Not going to happen. Now, for anything you do in the privacy of your own home, there are some simple rules of thumb you can use to keep yourself relatively safe (see the ILDA document above), but obviously they can not be used for any installation that is open to the general public.

Bottom line: you've got a lot of reading to do. And once you're familiar with some of the key concepts, you'll have lots of questions. Post them here, and we'll do our best to answer them. And in the end, you will learn enough that you will be able to do safe shows for your family and friends, even if they include audience-scanning effects. But unless you want to buy an off-the-shelf solution, you're probably never going to be able to legally do audience-scanning shows for the general public.

Adam

[norty303]

However, as I'm not from the US I'm not 100% sure how it's calculated, so I'll leave that for a US member or someone in the know

I would think it's more relevant for those NOT from the US, seeing as you basically can't crowd scan in the US. MPE is the same the world over.

As Adam says, the topic is huuuuuge. I have some fairly big booklets from my one day LSO training with LVR, and that was by no means the be all and end all of the topic.

One thing I will say though, is that I learnt most of what I know BEFORE I attended the training. And I learnt it all from reading this forum.

So to say the stuff doesn't get discussed is incorrect, you just need to research it.

[WookieBoy]

Just want to +1 what Norty said above.
There's plenty of info about on the forums and elsewhere if you have a dig.
The LVR safety course was very comprehensive and covered most things (though not much help to you unless you fancy hopping across the pond for the next one!) but most of it I already knew from researching... hoewever it was good to get confirmation that what I'd found was right and corrected where my maths fell down! Plus some form of recognition that I was trying to keep safety in mind...
I'm still not going to be doing any audience scanning just yet as my kit is missing scan-fails and a few other bits to comply with what I feel are minimum safety specs for this sort of thing, but armed with this knowledge and a little more experience I may do in the future...

Just keep hunting the forum (it takes time) and asking questions... I'm doubtful you could get a Varience for aud scanning easily (if ever) in the US, but I'm assured it can be done...
Eventually...

[norty303]

As a starter, try searching for things like 'MPE calculator' or 'MPE calculation'. this will turn up tools and discussions about how you actually measure and evaluate MPE.