Some factoids based on this history that only a few people on PL know. This is a rant, I don't have time this morning to type out a proper paper.
1. Laser safety will always rely on a trained operator following procedures. No combination of MPE Meters, Inclinometers, Scanfail, or Cameras with AI is going to replace a human operator. Many years ago the US FDA hired a team of scientists to follow a "Typical" laser show operator around and they made measurements and came up with a system that worked, placing the burden of safety on a trained operator who faced inspection and loss of business if he failed to follow the rules. This worked. The three meter and two meter rules worked, and audience scanning was a difficult burden to prove, but allowed if you could do the math. If you followed the rules, you followed a quality control worksheet for each show and documented your work each night at each site. I know, I've done it.
2. Factoid, the above mentioned procedure is based on medical instrument quality control procedures for a reason. Most of you are unwilling to relinquish your "precious" audience scanning, so now we have a conundrum. An MPE meter will not fully solve the current problem. 10X MPE and the "Simple Method" is set up to ignore cumulative exposure. Its set up so you can scan all night at low power. The past MPE meters were set up to do both a instantaneous and cumulative exposure, allowing brighter effects for short periods of time. The cumulative effects were measured assuming the same show plays again and again, with no human intervention. You had to set through your whole show a few times holding the MPE meter where a typical audience member was. Now you cant, because you play the effects live. In the past it was assumed the whole audience stayed for the whole show and left. For the most part they did, because only a few events per year could afford lasers.
There is no changing the bio-physics, so you have to assume the projector is in a club situation. Cumulative MPE matters.
3. Shows back then were designed so that high power effects were above the "Zero Line" aka "X Axis" and audience scanning was done by adjusting the zero line to be just above the audience's heads. Audience scanning effects were all that was allowed below the zero line. This made calculating and measuring cumulative exposure easy, and show design easy. Any part of the show done live had to be above the zero line, and the rest was synced to the music, created off-line, and relied on the computer or ADAT tape playing exactly the same thing every time to the same music. A scan fail monitor looked at the position signals from the scanner.
So when I took my show on tape to CANADA for a LFX conference, to compete in the awards, all I had to do was ensure the cool stuff was below the line and full power was above the line. I knew the left and right audience scanning scan heads were about 250 mW at full RGB White and mirrored on the X axis. I knew the distance to the audience and the fact that the fiber fed heads were adjusted for a given divergence. A power meter was used to ensure prior to the show the power to each scan head was correct. We had a informal standard set up by the conference organizers, and keeping with the regulatory QC scheme, we followed it. Safety people monitored the audience to ensure no one crossed forward of the minimum distance and no one stood up on a table or chair.
Back then I could call Tarm or Lobo and order a show designed to fit a similar scheme, the ADAT Tape came with a minimum audience distance printed on the tape and a maximum power, assuming a non Q-switched, ion laser type beam with a known power.
A full time safety person was required besides the show operator.
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Fast forward to Today. The most common situation is: We have no control of where the audience is. We do not have a canned, pre-calculated show. We have operators pressing keys to interpret the music live. For the most part, We do not have trained operators following QC procedures. We do not have professionals, we have DJs who have the cash to buy a off the shelf box. If you do cumulative exposure, at some point during the night effects will have to go above the zero line or you shut the laser off. Thus effects have to be weak.
So unless you can institute rules and enforcement, Pandora is out of the box. A MPE meter would help, but there are less then five people in the industry who look at PL who are qualified with the EE Degree and have the experience to design one. Three of them lurk and do not post here ever. It would be something like PASS, integrated in the projector. How you mandate PASS worldwide, I have no idea. How you mandate that PASS or similar systems stay calibrated, without regulatory checks I have no idea.
You need enforceable calibration and frequent re-checking of the calibration. That calibration and stability is not achievable to levels that would make a engineer, lawyer or regulator happy, for 300$ or less. In 1990s Dollars, a MPE meter that would satisfy a court challenge was 3000$. It was not in mass production however. Cost today would be less, but how do you insure the yearly calibration and have it do self checks? It has to be built to medical instrument, five sigma reliability.
The Unsung Hero of all this Past History is Greg Makhov, who will not post here. He simply does not have the time to handle major clients such as Disney, be ILDA Safety Chair, and have a family. Most full time, professionals don't have time for forums. We prefer email and phone for simple, direct, fast communications. I have no family, so I can somewhat lurk on PL. Anyone designing a MPE meter would have to work with Greg, as he knows the details inside out.
We already have enough quality control issues with mass produced projectors, achieving the level of quality control needed..... I'm out of time, I will finish this post later.
About trained operators. Example follows:
I have to go be acting LSO on a project right now, My task today will be to insure a 30 Joule pulse every ten minutes does not harm 20 students and staff working in a lab. It is akin to herding cats. Until the laser is installed and tuned, not all of the safety gear can not be installed, and the beam must fire across the room for profiling. Operation of the high energy experiment in the huge room must continue, it is too expensive to shut down during the laser install. The safety briefing was brutal, procedures for entry into the controlled space were applied, and involved ZERO tolerance for human behavior. Think military firing range style controls and procedures. I have two people assisting me part time, to ensure compliant behavior and that I don't miss a procedure. People who cross into the controlled space without permission run a serious risk of being kicked out of grad school. I can't do that level of enforcement in a night club. We're working on a Sunday for a reason, but four of the twenty people still showed up yesterday at random times. One did not follow procedure, entered the area not wearing goggles, but we caught him before he got into the "HOT" area. He came in to ask about the required goggles. We said OD seven at least five times in the briefing. Humans are Humans. (In his defense, he needed a pair that would fit over his glasses, unforeseen problem.)
People are un-predictable, so there must be a penalty for not following the rules, and there must be inspection. Self compliance worked in the old days when there were few shows.
Some how, some way, we have "lucked out" and there are few reported incidents. But diode power is climbing.... The other user of lasers in public, the theatre industry, now uses the laser show industry as a example of "high risk".
BTW, there is no self developing film material sensitive enough to emulate the human eyeball. I've tried...... We use a similar material to calibrate our instruments. It has to be a photodiode.
End RANTEX. (Rant Exercise)
Steve
Last edited by mixedgas; 02-02-2014 at 06:01.
Qui habet Christos, habet Vitam!
I should have rented the space under my name for advertising.
When I still could have...
Originally Posted by Stiffler
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As you say, safety devices are lagging dangerously behind the availaibility of strong diodes. Most of those people aren't scientists, or even bench test engineers. So they obviously need meters equivalent to the kind of domestic mains line tester or cheap multimeter.
