New Laser MPE Limits published

[JStewart]

For anyone interested in laser MPE, I’ve posted some details up on our website regarding the newly published exposure limits.

http://www.lvroptical.com/blog_MPE_limits.htm

The new limits will appear in the next editions of the IEC and ANSI laser standards, (which are in a very advanced stage of development), as will be the case with worker exposure limits published in the Artificial Optical Radiation Directive in Europe.

Until then, keep with the existing limits. But as a heads up, newer limits are on the way!

James

[White-Light]

Hi James,

In terms of mw cm2 what effect do the new limits have?

[JStewart]

The MPE for a 0.25s accidental exposure is 2.5mW/cm^2 , which is the same as 25W/m^2

This side of the pond, which includes IEC and ICNIRP, we express the area in m instead of cm, but both are the same. There is just a multiplication or division factor of 10,000 if you want to go from one to the other.

The limits published by ICNIRP are international, so these end up being used worldwide in safety standards and legislation etc.

So the increases and decreases I summarise in the text are equally valid for whatever your units of choice are.

James

[White-Light]

Just been looking again as I misread it 1st time around. Has it actually changed the MPE limit when using the simple method?

Thanks James.

[sbk]

Interesting reading, thanks. Should not change lots since most of us already used the single pulse method anyway...

By the way, which component should I use to measure the pulse length of scanned effect? A fast silicon photosensor should do the job, but I'm not sure how fast should it be. I found one with rising/falling time in the 10th nanoseconds, but propagation delay is still 5 us?! Is it fast enough to have a sub-microsecond resolution on the scope?

[norty303]

Is it not the case that even if you have a single pulse in the us range, your exposure timeframe should still be based on the lowest of your scanfail response time (typically 1 to 20ms) or blink reflex (250ms)?
Otherwise you are still waaaay in excess of MPE in the event of a fault condition.
i.e. nothing will really change with regard to how we currently crowd scan.

Or am I missing something significant here James?

[Laser Electronics Ltd]

Hi James
Give me a call, to discuss this.
Could you tell me where the HSG 95/PM 19, data was implemented, and sanctioned.

[JStewart]

The main point of me posting this news and putting a little piece about it up on our website is that, rather than people hearing rumours of changes, getting excited or dismayed etc., I could spell it out from the outset. And also give people a bit of an insight as to where/how the limits are agreed, and also how they then end up being used as the exposure limits in safety standards/permitted workplace exposures etc.

Not sure I understand your question Clive. HS(G)95 and its predecessor PM19 always referred to ICNIRP data. Nothing has changed with the current version of HS(G)95.

As you know HS(G)95 is shortly to be reviewed by a group that PLASA has gathered together. If it’s decided to keep exposure limit references in the document, I’m sure they will end up being the limits that are mandated through the AORD and published in the most recent IEC laser safety standards. i.e. by the time a revised HS(G)95 is agreed, the 2013 ICNIRP laser exposure limits will be the accepted norm.

Adam, you are right in that the effectiveness of your scan-fail monitor/termination system is usually the most limiting factor in an assessment. The new way that Cp is considered supports the argument for being able to consider single pulses, especially at the shorter durations, when there is an increased chance of more pulses occurring; then of course the average MPE could still come into play if the pulses occur too frequently.

You are right though, nothing will really change with how people crowd scan – most people that do it will do so without even attempting to get anywhere near the exposure limits! – ignoring the need the alter the irradiance of the beam, or having a decent scanner health monitor in place.

Something like a Thorlabs PDA100A/DET100A type detector is a convenient little package that has the silicon diode and amplifier self-contained and can be hooked up to a scope to see the pulses. A DSO with a bandwidth of several MHz will keep you from having nyquist issues.

James

[Laser Electronics Ltd]

James
The current implemented HSG guidelines for laser displays within the UK are HSG95, and as such exposure levels or safe practice hasn't been proven or disassociated.
I was hoping you might call me regarding this.
Let me throw a new concept in the discussion, We have multiple suppliers of lasers that are being used, that have no inbuilt safety, Ir or Uv filtering.
People harvest components and make them freely available, building a light source without the ramifications of what they sell or hire, having no implementation of the original design, leaving people exposed to serious levels of radiation.
Would it not be prudent to ask Casio or one of the other commercial suppliers to get involved on the revision of the crowd scanning debate.
Casio produce a laser based video projector that people harvest components from, Mitsubishi, Coherent are also providers of such components.
Let's get some big boys on board and the HSE.

[The_Doctor]

James
The current implemented HSG guidelines for laser displays within the UK are HSG95, and as such exposure levels or safe practice hasn't been proven or disassociated.
I was hoping you might call me regarding this.
Let me throw a new concept in the discussion, We have multiple suppliers of lasers that are being used, that have no inbuilt safety, Ir or Uv filtering.
People harvest components and make them freely available, building a light source without the ramifications of what they sell or hire, having no implementation of the original design, leaving people exposed to serious levels of radiation.
Would it not be prudent to ask Casio or one of the other commercial suppliers to get involved on the revision of the crowd scanning debate.
Casio produce a laser based video projector that people harvest components from, Mitsubishi, Coherent are also providers of such components.
Let's get some big boys on board and the HSE.

Where exactly is this going? This talk of 'the big boys' bothers me. Is this really about safety? Or is it the beginnings of an attempt to stitch up the budding industry for the well-established few to deprive fun and possible earnings for many?

Those are deliberately loaded and provocative words to make the point, but this is actually an innocent question. I really don't know what you're implying. I hope it is based strictly on safety. Because if it isn't it is very similar to the half-baked attempt to legislate to prevent legal highs. While that fantasy about 'cream supplies' when it's obvious to all who know, that the meaning is laughing gas, is a thing I find disgusting, as I think it better to say it like it is and not hide what is basically drug-dealing in a cloak of 'barely legal' convenience, if the 'big boys' close it like a cartel, it is very likely that similar venal deceits will be put into the public domain in order to sell various laser parts to what is in many ways a related market! The desire to share a collective and fun experience. In many cases the venues are literally the same. Raves. My outlandish metaphors are soundly based in a real condition.

In all cases where a limited few have mounted what is effectively a protection racket, the danger is driven underground where it usually thrives. In the case of lasers that might be harder to do but only because they are so intensely visible!

When I read the HSE guidelines I remember something I liked. Was a long time ago now, I don;t do shows so it's not something I keep close tabs on, so my memory is vague..Anyway, there was a description that showed you could make sensible estimates of safe limits based on CW power, scan speed, distance from scanner, dwell time, etc, and that so long as you made an honest attempt to stay on the safe side of a limit you were likely ok. If the estimation were vague, you'd end up being that much further away on the safe side so long as you made an honest effort to judge it well. Once you end up demanding expensive metering and expensive fast digital storage oscilloscopes you get specsmanship, people edging for stronger power than in other shows, people competing to push the envelope. By demanding what appears to be more rigor there is a risk of people getting closer to real danger while believing that their expensive instrumentation will protect them from both lasers and the law.

It's a lot easier to plot a course that cannot produce a dangerous pulse to an eye than it is to measure one if you're trying for all the 'safe' power you can get within the law. The more people try the harder that will get.

Now that was a vague and overlong post, but I think it makes the point well enough: More people are getting into this. So make it possible for them to be safe with the limits they have, and don't risk forcing them to hide from you when experimenting with weird and risky toys. To do anything else is effectively making things more limited and riskier under the guise of making things more safe. It sounds to me like the big boys in the show industry getting scared that legislation might kill their joy because of all the reckless newbs butting in. But you can't put the genie back, you can't watch in every dark hall where it strays over the ropes, and the best thing you can do is keep things as simple as possible, measurable with the cheapest and most widely available means as possible, so that the newbs will be able to correct each other. That way you won't have to worry so much yourself.