LASER SAFETY

A general primer of how lasers work, what makes them potentially hazardous to a shooter and the people around him, and the potential consequences of careless or improper usage. Readers are encouraged to conduct their own research, as this is not intended to be chapter-and-verse. Some numbers and descriptions will be rough, others will merely appear so because the slide-rule geeks refuse to admit that math and science are far more mushy than they would have one know, and because said geeks are still having Sharks vs. Jets interpretive dance-offs over a great many things. Other stuff will be arbitrary for the sake of simplicity, with the desired endstate being comprehension of a principle or concept, not quotable accuracy.

References: Code of Federal Regulations 21CFR1040.10, OPNAVINST 5100.27A(B) and MCO5104.1B(C)

BLUF: By now, all should have some basic, troglodyte awareness of the safe handling of firearms. Applying the safety rules attributable to firearms to the use of lasers, be they weapon-mounted or not, will go a looooooong way to ensuring that you and those around you incur no otherwise-unwanted biological effects. TREAT LASERS LIKE THEY ARE WEAPONS.

Definitions:
LASER - an acronym that stands for Light Amplification by Stimulated Emissions of Radiation. You "common use" Scrabble aficionados can go screw yourselves, it's NOT A WORD. It's several.

MPE - Maximum Permissible Exposure - the maximum level of LASER radiation to which a person may be exposed without hazardous effect or biological changes to the eye or skin. Determined by LASER wavelength, power output, and duration of exposure.

OD - Optical Density - an energy absorbance rating used in the determination of protective eyewear appropriate for use in regard to specific LASER(s).

NOHD - Nominal Ocular Hazard Distance - described in meters, required to be listed on safety notifications affixed to any laser device Class 2 or above. Describes the distance within which the level of direct, reflected, and/or scattered radiation during normal operations exceeds the appropriate MPE. Exposure levels beyond the NOHD are below those MPE levels, ergo no safety control measures are required outside of a device NOHD. This is the single most important piece of information users should know, from a safety standpoint, about any LASER device they utilize.

Colloquially, and for the sake of you acronym-rocks out there, device NOHD + 1m may be referred to as that device's "eye-safe" distance.

NSHD - Nominal Skin Hazard Distance - distance within which direct exposure of human skin to the beam of a laser may cause a biological effect. One may surmise that said "biological effect" is NOT a positive one....which is another way of saying "you gonna get burned, sucka!"

Specular Reflection - reflection from a mirror or mirror-like surface, in which the lion's share of the energy and cohesion of reflected LASER is maintained. Smooth shiny metal (curved, angled, rounded...doesn't matter), water, the silica found in sand, glo-belts, license plates.......

Diffuse Reflection - reflection from a rough surface in which a collimated beam is scattered and emerges in many directions.

Beam Divergence - an angular measurement that describes the increase in diameter of a LASER beam as it travels from its emitter aperture. Think of this as the "cone of fire" of a LASER; if you think in the angular definition of MOA, you already get the concept.

Okey-dokey.....

The "L" in LASER stands for light. Light is part of the electromagnetic spectrum. Visible light is understood to be what humans are capable of perceiving via our unassisted eyes, and is a portion of the total light spectrum that exists within the electromagnetic spectrum. Want proof? Here: http://www.google.com/search?q=elect...w=1680&bih=867

Lo, my children, harken:

Characteristics:
"Wavelength" describes the frequency of light energy, or "color," as we call it. This measurement is described in nanometers or nm, for short.

-Humans generally see within the 400nm-700nm range.
-Below 400nm are ultraviolet (UV) wavelengths.
-Above 700 are infrared (IR) wavelengths, which go up to a frequency of about 1mm.

The human eye requires assistance to see into either the UV or IR range. This affects us in that we yammer on about image-intensification (I-square) devices used to see the IR lasers commonly used to provide active aiming and illumination capabilities to weapons.

So, lasers are light, but with certain characteristics that make them behave differently than the light you and I see on an everyday basis. Conventional light, such as from a bulb of some sort, spreads (diverges) in all directions. Lasers are focused, highly collimated beams that maintain high levels of intensity over long distances. Light as we see it is also made up from EVERY wavelength of visible light in the spectrum. Lasers are monochromatic; one frequency, one color, and not always one visible to us.

Modes:
Lasers operate in 3 modes.
-Single Pulse - energy is delivered in the form of a single pulse no more than .25 seconds in duration. This time reference will become important, later.
-Repetitive Pulse - energy delivered in multiple pulses, none of which are greater than .25sec, each.
-Continuous - energy delivered in a continuous beam.

Why the duration of .25sec? Because that's the time associated with the human "aversion response," the simplest of which is blinking the eye. If the light/laser in question is in the visible wavelengths, and of sufficient intensity, the result in an outright flinch, a physical attempt to get out of the way of the sensory impulse, with an eyeblink being merely the start of the whole thing.

If you can't SEE the energy being directed at you (UV or IR, but UV is not used for common weapon applications worth speaking of here), you will not register it, i.e., it will not necessarily hurt, and you’ll not know to flinch away from it.

So, the question becomes: "Well, if I can't see it, and it doesn't hurt, why am I still supposed to worry about it?" Good question.

BOTTOM LINE COMPONENT - Know the wavelength and operating modes of your laser.

Hazards (skin):
Pretty simple. The "R" in LASER stand for "Radiation." The primary concern is heat radiation, which, in a laser with enough power output, can burn materials. Most of the lasers we can get our hot little hands on, this is not an issue, but it is possible. The PEQ-18 IZLID/HPLP, for example, is a pretty potent system designed to point out places for planes to smack bombs into. It's got some freakin' JUICE, man. The NSHD on that bad boy is 42.3m. Inside 140' or so from the aperture, it can burn you.

That's a MIL-grade system, not common to the everyday schmo; however, there are lasers out there that can burn you: think on the order of you as a kid with a magnifying glass and an anthill. Hit YouTube and search for, say "green laser." You'll see examples of some engineering student or other egghead that got the brilliant idea to build his own laser and use to light matches, melt Army men, burn paper, etc., and he/she films it.

BOTTOM LINE COMPONENT - Don't point the things at your skin for extended periods of time.
COROLLARY - Turn the thing off when not in use. Remove the battery(ies) in cases of extended storage (think house fire).

Hazards (eyes):
Well, it turns out that the human eye itself has little in the way of tactile sensory nerves in it or on it. What pain and irritation one most often feels, such as when you get a piece of dust or an eyelash stuck on your eye, is actually that piece of flotsam/jetsam rubbing against and irritating the flesh around the eye. A blast in the eye with a laser that causes damage that hurts....that's actually GOOD news, of a sort, because it means that the damage is in the cornea and/or the lens (the pain would come from the surface of the eye being roughed up, like the surface of a golf ball, which irritates the flesh around the eye), which not only likely to heal, but to heal pretty quickly. The following is a rough rundown of what wavelengths of light, if intense enough, will cause damage to which part of the eye.

UV C & B (100-280nm and 280-320nm) Cornea
UV A (320-400nm) Cornea/Lens
Visible (400-700nm) Retina
IR A (700-1400nm) Retina
IR B (1500-1800nm) All but Retina

Meaning, that the hazard to the human eye exists between 400-1400nm, because these wavelengths, if sufficiently intense, are most likely to damage the retina, which is on the inside of the eye and therefore not going to hurt (and thereby warn you) and if damaged, will not only not heal, but the damage will go undetected unless and until retinal photos of the eye are taken, AND the damaged area may increase in area over time. Even then, we are less worried about damage to the retina as a whole, but to the macula and fovea centralis, which comprises about 3% of the area of the retina and provides us with out maximum visual acuity and color sensitivity. See the following cross-section of the eye: http://www.gloshospitals.org.uk/en/W...y---The-Facts/

If you take damage to the fovea, at some point in your life, some version of the blurry area seen in this photo is what you'll have to deal with...permanently:
http://img196.imageshack.us/img196/4...ageeffects.jpg

...because it's directly in-plane with the lens and the iris of the eye. Should be a clue as to how important it is. And, of course all of the light and laser devices generally used by shooters of one type or another use the wavelengths most likely to incur damage to the part of the eye we depend upon the most and that won't heal once damaged. Now that that is known, what needs to be considered is the intensity level of such devices and the nature of our exposure to what they throw out.

Beam Exposure and NOHD:
The NOHD of any individual system is the distance within which the human eye is subject to damage in the event of exposure to the beam. This distance is measured in terms of aperture-to-eyeball. I say again: aperture-to-eyeball. This is important because the potential for reflections MUST be accounted for in regard to safety, be they intentional or errant. For instructional purposes, we will use the NOHD of the visible laser of the Insight AN/PEQ-15 ATPIAL as evaluated by the DoN Laser Safety Review Board, which is 101m. Types of beam exposures are as follows...

-Direct or Small-Source - someone is pointing a laser directly in your eye. You are staring down the bore or a laser aperture that is emitting. If you are 101m or closer, you are at some level of risk for retinal damage. The closer you are, the more intense the beam (duh, right?), the more likely that you are taking damage AND that the damage is worse than it would be if you were further away. If you are standing at 102m, you can stare into the thing for 8 seconds, 8 hrs, 8 days, whatever, and it is unlikely to do you any harm. 101m and closer, however = bad juju. Stop it, already, and don't do it to others.

-Specular Reflection - We've all done it in some form or another: you get in your yut-yut kit , with weapon(s) and did some sort of prancing around in front of a mirror. Or in a room with a sliding glass door. Or, you've operated an ECP/VCP where there's windshields and shiny metal all over the place. Somewhere where there's smooth, polished surface(s) of some sort, where any reflection of a laser beam is likely to redirect that beam and maintain its intensity. Let's say that you are practicing weapon presentations in front of your Yeungling commemorative mirror that you've had since your halcyon college days as a fraternal brother of I Eta Pie, using your visible laser as specified above. If you are within 50.5m of that mirror, you are bouncing that laser right back at yourself. Remember the aperture-to-eyeball specification? 50.5m + 50.5m = 101m = bad juju. Keep 51m or more away from reflective surfaces. Oh, and grow up...

Yes, a reflective surface may not bounce that beam back at you, but redirect it in a completely different direction. Back to the ECP/VCP example..... YOU are 60m away from the car you're bouncing that laser off of, but one of your mates is 1m away from that car checking IDs or searching, and maybe in the line of that reflected beam. It would behoove one to be mindful of this, because you're okay due to the distance and because the laser may not even be bouncing back at you, but you're also not in this effort alone.

-Diffuse Reflections - Can be a bit fuzzy to articulate, but usually only hazardous in the presence of far more potent lasers than those mounted to individual weapons. These are reflections off of matte OR textured OR matte and textured surfaces; these not only scatter reflections also tend to outright absorb some portion of laser energy, particularly if they are black or some other dark color. BUT....there are some that would tell you that a disco ball is technically a diffuse reflective surface, even though it is made up of specular reflective surfaces. Clear as mud, right? It can apply, since that would break up a single beam in to several, somewhat less intense beams. I'm still not gonna try it....

Target-type paper, cinder blocks, Hesco barriers, bricks, asphalt, dark or textured wallpaper...perhaps you see where this is going. All of these are still reflective surfaces (our perception of color is based upon the reflection of certain light wavelengths from an object; the wavelengths absorbed do not reflect, and those that do reflect and reach the eye/brain are interpreted as color), but are generally pretty safe because they absorb a lot of energy and scatter the rest.

However, our ECP/VCP example still applies (T-wall barriers, road material, etc.), just limited to far more powerful devices, like that PEQ-18 (kind of a stupid scenario, but it's only illustrative, not realistic). Diffuse reflections from that can still carry a lot of juice simply because there's a lot of ass behind the beam to begin with. Who cares what happens to the bad guys, if they're present, but what about your pals? A bit of knowledge and some reasonable decisions go a long way.