My google-fu was pretty good that day, as I searched for “what current would kill a human”.
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We’ve definitely seen different numbers in different sources. This makes sense to me, given the natural limitations on experimentation here… The NIH PubMed Central article is newer (2009 vs. 1966) and lists ventricular fibrillation at 500mA. I doubt that difference matters here though! I mean, I’m sure it’s important in general, but I don’t have any reason to expect that it is relevant in the context of laser cutters. If anyone here has a CO2 tube that runs as 500mA, I’m going to guess that it’s industrial… 
I do wonder whether a practical difference between LPS and the home-built Lichtenburg burners build from MOTs is that the MOT-based Lichtenburg burners can supply substantially more current?
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@dougl and @mcdanlj thanks for all the reference material. It’s always nice to see where the information comes from.
As the laser safety officer for the hospital, I am responsible for everybody’s safety. In Arizona, laser safety is regulated under the same rules and regulations that the nuclear industry is regulated under. Any safety issues or injuries are taken very seriously and can result in massive financial fines.
Our sister hospital was just audited by the state for their laser program and passed with flying colors. That program was set up by my mentor and previous laser safety officer. It was modeled after the one she set up in our hospital so I know that what we have in place will keep our patients and employees safe.
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Thanks for the information on the Lichtenberg process. I too have been thinking about building a setup but have always worried about safety. You guys have definitely made it a definite no and will leave it to others to make that style of art.
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This is another from Ohio Fatal Voltage.
One of the main issues about medicine in relation to electrical shock, is there is very little data on it, as I found out back in the 80’s.
IMHO
I purchased my machine to learn on. I had to disable the door protection to be able to work on it. I’ve made many changes to it, that’s why I bought it. Of all it’s running hours I doubt that the door has been shut for more than 10% of the time and when it’s closed, it’s still open about an inch, for air flow across the material. I also don’t button it up when I use the rotary.
As with any equipment there is inherent danger. The better you know how it works the safer you will be. Not understanding how it works is not advantageous to your own safety. It’s just as potentially bad as fear of it, which seems to be plentiful.
I’ve worked around HV for transmitters and a few Tesla coils. The insulation on the anode leads insulates it well for it’s intended voltage. All of my anode wires run right next to a metal cabinet, if they were a problem I’d hear it at the minimum. I also don’t wait for the HV to bleed off. I don’t trust it and take steps to take it ground before I meddle.
Someone mentioned being ‘bit’ by their coolant tank. It seems to happen when the coolant dielectric is becomes low and the hv arcs into the coolant. This makes the coolant and anything it’s touches ‘hot’. They are also not ‘dead’.
Don’t drive your car, shoot guns or ‘play with your laser’ and many other things if you head is somewhere else, you’ll just injure yourself or someone else. It’s the ‘or someone else’ that’s the worry.
In a factory at Honeywell I got across the 440 mains when I removed an improperly grounded machine. I pulled the Hubble connector apart I was lit up. One of my other field engineers kicked the connector out of my hand, probably saving my life. The safety team advise I should have been killed. This wasn’t from not knowing, it was the previous people who didn’t do their job. In those situations how would I know?
Maybe that’s just fate.
I respect it when it runs, you should to and you won’t have a problem.
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I can relate to you. I worked with 440 volt AC arc welders and 2000 amp arc gougers. There is no assuming around this equipment.
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Damage to biological cells… I have had about 3 laser cardiac ablation surgeries. The Wiki is interesting and at least gives you some idea of what frequencies are use… 
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Happened to me, too, so I placed a grounded rod directly in the water bucket.
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Yeah getting a shock form the cooling bucket can also be cause by a bad pump. I worked in a pet store in college and I couldn’t tell you how many time I got shocked from a bad aquarium power head pump or heater when catching fish or cleaning the tanks.
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I hope this topic isn’t too old, but the reason you don’t hear about eye injuries from K40 lasers despite their lack of interlocks is mainly due to the wavelength of the laser and optical design of the delivery system.
To the 10.6 micron wavelength, the eye is opaque. Thus, lens of the eye cannot focus 10.6 microns on the retina. However, because the 40W laser is so powerful, it could still burn the front of your eye as a collimated beam. There is where the optical design comes into play - when it emerges from the final optics, the beam is converging, and having passed through the focal range, it is then diverging again. So, the beam will be too spread out to burn you once it gets to typical distances between the laser machine and the operator.
So, to get an eye injury - or indeed a body injury, as a 40W CO2 laser can burn less sensitive parts of the body or clothing too - you’d need some special circumstances. For example, a catastrophically misaligned mirror or reflective object falling into the collimated optical path, that results in a collimated beam leaving the laser. Or attempting to process just the right shape of parabolic reflector. Or sticking your head into the machine while it is operating, a category of behavior described as “too dumb to live.”
The main hazards are probably fire then and high voltage, rather than eye injuries. I hesitate to call 10.6 um “eye safe” because at the power levels involved, nothing is, but we’re talking about burning your eye rather than blinding your retina. Neither is something you want to happen. Keep the lid down in operation.
This is distinct from diode laser cutters and solid state lasers. They are absolutely a vision hazard as they use wavelengths to which the eye is transparent and can fry the retina insidiously and painlessly.
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We intentionally don’t close old topics on Maker Forums just because they are old. New information has sometimes showed up in threads years after they started, and one of our ongoing most-referenced threads from external searches is one where the original post was imported from Google+ but the information people are searching for was written recently here. So contributing to existing threads is great! 
I saw from your Balor description that your fiber laser is 1064nm, unlike the 10.6 micron FIR CO2 lasers. Do you have information on potential vision hazards in the 1 micron range as well? For kiln work, I use green IR-absorbing goggles which should absorb in the 1 micron range, so I would assume that the cornea and lens transmit a lot at 1064nm and that the fiber lasers would also be potentially “fry the retina insidiously and painlessly”?
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Yep. Fiber lasers are mostly either 1080 nm (especially bigger CW ones) or 1064nm. It chills my blood when I see people operating fiber laser engravers unenclosed with no protective googles.
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