KNOW WHAT YOUR DEALING WITH:
THIS IS SHORT BECAUSE I HAVE TO GET TO WORK!
WITH CLASS IV LASERS, NOT ONLY IS THE DIRECT BEAM A HAZARD, THE BACKSCATTER FROM EVEN A DIFFUSE SURFACE HIT BY THE LASER CAN BE POWERFUL ENOUGH TO CAUSE DAMAGE TO THE EYE. THIS CAN BE TRUE AT CLASS III AS WELL
WHEN IS THE BACKSCATTER NOT DANGEROUS? IT IS ENTIRELY DIFFERENT FOR EACH SITUATION. MEASUREMENTS AND CALCULATIONS HAVE TO BE MADE. THERE IS NO HARD AND FAST RULE TO SAY A 1 WATT 445 nM LASER SCATTERED OFF A MATERIAL AT A GIVEN DISTANCE IS SAFE. YOU HAVE TO KNOW THE POWER OF THE LASER AND THE CHARACTERISTICS OF THE LASER AND THE SCATTERING SURFACE.
A QUICK ANSWER FOR THE 1 WATT 445 nM POINTER? SOME METERS/YARDS AWAY. WHY AM I SAYING METERS? I JUST BUILT IN A GENEROUS SAFETY FACTOR FOR MY OWN MENTAL HEALTH REASONS.
INVERSE SQUARE LAW APPLIES TO THE SCATTER FOR MOST MATERIALS, AND THUS DISTANCE IS MAJOR FACTOR IN THE SITUATION. BUT SOME MATERIALS, GLASS AND CERAMICS AND SOME TRANSPARENT PLASTICS, FOR EXAMPLE, CAN BE RETROREFLECTORS
WHILE THIS MAINLY APPLIES IN DOORS, IT IS A FOOLISH THING TO AIM A CLASS III OR IV LASER OUTDOORS NEAR OTHER PEOPLE, BECAUSE OF BACKSCATTER!
DANGER, DO NOT DO THIS TEST, THIS JUST A EXAMPLE OF WHY YOU NEED TO EVALUATE EACH SITUATION YOU USE A HIGH POWERED LASER IN!
[/COLOR]
DO NOT AIM THE LASER AT A BICYCLE REFLECTOR , REFLECTIVE TAPE< OR CAR TAIL LIGHT FOR EXAMPLE, A SOMEWHAT DIFFUSE BEAM WILL COME RIGHT BACK AT YOU, BUT IT MAY NOT BE DIFFUSE ENOUGH TO PROTECT YOUR EYES. MOST BICYCLE REFLECTORS AND MANY CAR TAIL LIGHTS ARE
"RETROREFLECTORS" BY DESIGN, THE OPTICS DESIGNED TO REVERSE THE COURSE OF THE LIGHT RIGHT BACK DOWN THE PATH OF WHICH IT CAME. SOME OF THEM ARE BETTER THEN OTHERS, AND THE BIKE ONES WITH THOUSANDS OF MOLDED PRISMS CAN BE VERY GOOD AT REVERSING A LASER BEAM.
SILLY EXAMPLE: IF DARTH VADER MOUNTED A HIGH QUALITY RETRO-REFLECTOR ON A SERVO DRIVEN TURRET ON THE DEATH STAR, LUKE WOULD NOT HAVE MADE IT TO THE SEQUEL.
YOU GET THE IDEA!
NOT ONLY CAN RETROREFLCTORS DO THIS, UNDER CERTAIN CONDITIONS, THINGS LIKE GLASS RODS AND GLASSES OF WATER AND PLASTIC BOTTLES CAN REFLECT ENOUGH ENERGY TO CAUSE A PROBLEM!
(Steve said DO NOT DO THIS. SO I"M GONNA DO IT!, THAT GIVES ME NIGHTMARES. OK, IF YOU MUST, DO IT WITH A 1 mW HENE, BUT NOT MORE THEN CLASS II OR CLASS IIIA LASER, IE NOT MORE THEN 5 mW, EXPECT TO BE BLASTED IN THE EYE IF YOU DONT SET THE LASER ON A TABLE AND HOLD THE RETROREFLECTOR INTO THE BEAM, USING A WOOD STICK PAINTED BLACK WHICH REMOVES YOU FROM THE TARGET AREA, MAKE SURE YOU HAVE TOTAL CONTROL OF ENTRY TO THE ROOM AND THAT NO ONE ELSE IS AROUND THE LASER. GET USED TO PLANNING YOUR EXPERIMENT!)
SOME OTHER THINGS I've SEEN THIS MORNING THAT NEED TOUCHED ON:
Nominal Ocular Hazard Distance (NOHD):
The calculated distance in which it is possible to exceed the Maximum Permitted Exposure.
Maximum Permitted Exposure (MPE)
Maximum permissible exposure (MPE), is the level of laser radiation to which a person may be exposed without hazardous effects or biological changes in the eye. MPE levels are determined as a function of laser wavelength, exposure time and pulse repetition. The MPE is usually expressed either in terms of radiant exposure in J/cm2 or as irradiance in W/cm2 for a given wavelength and exposure duration.
Note, these are calculated numbers. IF I have my seven watt argon outdoors, the NOHD is upward of eight miles. Does that mean I can safely stand at 8.1 miles and view the beam head on? ABSOLUTELY NOT!
If I accidently illuminate a aircraft at distance farther the the MPE, its good odds that the pilots vision will be OK, but that does NOT mean it will NOT Disorient him or Flashblind Him.
Does that mean I can use a 20 watt ion laser turned down to 7 watts and be just as safe, NO! The longer 20 watt ion cavity has less divergence, because it has a longer resonator, and this less divergence. SO the NOHD is father for the better beam quality laser.
DO I CALCULATE THE MPE AND BASK IN THE LASER LIGHT AT THE MPE?
NO, INTENSE LIGHT EXPOSURE IS CUMULATIVE, TIME MATTERS!
IS it ok to spend 10x as long illuminated at 1/10 the MPE, Close, but not quite. You can still experience long term biological effects with short wavelengths etc.
It would take me a full day to research and post VERIFIED, VALID, examples, pictures and drawings, and laser safety fills whole books, like this one:
http://www.army.mil/usapa/med/DR_pubs/dr_a/pdf/tbmed524.pdf
HEADS UP FOLKS, PHYSICS IS COMPLEX, AND CAN BITE YOU. (BUT USED WITH CAUTION, AND PREPAREDNESS, IT CAN BE FUN)
KNOW YOUR TARGET !!! TEST AT VERY LOW POWERS.
(This is why lab lasers and industrial/medical lasers tend to have power controls and aiming beams.)
ONE OTHER THING, QUALITY CONTROL, JUST BECAUSE A EXPERIMENT WAS SAFE FOR YOU, DOES NOT MEAN THE MATERIALS AND GEAR ARE SAFE FOR THE NEXT GUY, PRODUCT VARIATIONS DO HAPPEN, AND NOT EVERYONE MAKING GOGGLES FOR EXAMPLE, ARE LEGIT OR TRAINED ENOUGH TO DO IT RIGHT! QUALITY CONTROL REQUIRES THINKING, PLANNING AHEAD, PAPERWORK, AND MEASUREMENTS, AS WELL AS SOME ONE ELSE CHECKING YOUR WORK BEFORE YOU RUN THE EVENT!
THE POINT OF THIS POST IS SO YOU CAN BE SAFE AND UNDERSTAND WHY CLASS IV LIGHT SOURCES DO NOT BELONG IN UNEDUCATED HANDS AND DO NOT BELONG IN UNCONTROLLED CONDITIONS!
DISClAIMER: I'M NOT A SPECIALIST IN LASER SAFETY, MOST PLACES WHERE I WORK WITH HIGH POWER LASERS, I'M DEPENDENT UPON THE WORK OF LASER SAFETY SPECIALISTS, WHO ARE EITHER ON SITE OR HAVE PROVIDED GUIDELINES. AND AT MANY OF THOSE PLACES, A SPECIALIST COMES AND CHECKS WHAT I"M DOING PERIODICALLY, TO MAKE SURE I'M FOLLOWING THE GUIDELINES AND NOT MISSING A DETAIL.
IF I even think I have to, I DO THE MATH! DON'T ASSUME ANYTHING!
Steve (WHO IS NOW LATE FOR WORK)
THIS IS SHORT BECAUSE I HAVE TO GET TO WORK!
WITH CLASS IV LASERS, NOT ONLY IS THE DIRECT BEAM A HAZARD, THE BACKSCATTER FROM EVEN A DIFFUSE SURFACE HIT BY THE LASER CAN BE POWERFUL ENOUGH TO CAUSE DAMAGE TO THE EYE. THIS CAN BE TRUE AT CLASS III AS WELL
WHEN IS THE BACKSCATTER NOT DANGEROUS? IT IS ENTIRELY DIFFERENT FOR EACH SITUATION. MEASUREMENTS AND CALCULATIONS HAVE TO BE MADE. THERE IS NO HARD AND FAST RULE TO SAY A 1 WATT 445 nM LASER SCATTERED OFF A MATERIAL AT A GIVEN DISTANCE IS SAFE. YOU HAVE TO KNOW THE POWER OF THE LASER AND THE CHARACTERISTICS OF THE LASER AND THE SCATTERING SURFACE.
A QUICK ANSWER FOR THE 1 WATT 445 nM POINTER? SOME METERS/YARDS AWAY. WHY AM I SAYING METERS? I JUST BUILT IN A GENEROUS SAFETY FACTOR FOR MY OWN MENTAL HEALTH REASONS.
INVERSE SQUARE LAW APPLIES TO THE SCATTER FOR MOST MATERIALS, AND THUS DISTANCE IS MAJOR FACTOR IN THE SITUATION. BUT SOME MATERIALS, GLASS AND CERAMICS AND SOME TRANSPARENT PLASTICS, FOR EXAMPLE, CAN BE RETROREFLECTORS
WHILE THIS MAINLY APPLIES IN DOORS, IT IS A FOOLISH THING TO AIM A CLASS III OR IV LASER OUTDOORS NEAR OTHER PEOPLE, BECAUSE OF BACKSCATTER!
DANGER, DO NOT DO THIS TEST, THIS JUST A EXAMPLE OF WHY YOU NEED TO EVALUATE EACH SITUATION YOU USE A HIGH POWERED LASER IN!
[/COLOR]
DO NOT AIM THE LASER AT A BICYCLE REFLECTOR , REFLECTIVE TAPE< OR CAR TAIL LIGHT FOR EXAMPLE, A SOMEWHAT DIFFUSE BEAM WILL COME RIGHT BACK AT YOU, BUT IT MAY NOT BE DIFFUSE ENOUGH TO PROTECT YOUR EYES. MOST BICYCLE REFLECTORS AND MANY CAR TAIL LIGHTS ARE
"RETROREFLECTORS" BY DESIGN, THE OPTICS DESIGNED TO REVERSE THE COURSE OF THE LIGHT RIGHT BACK DOWN THE PATH OF WHICH IT CAME. SOME OF THEM ARE BETTER THEN OTHERS, AND THE BIKE ONES WITH THOUSANDS OF MOLDED PRISMS CAN BE VERY GOOD AT REVERSING A LASER BEAM.
SILLY EXAMPLE: IF DARTH VADER MOUNTED A HIGH QUALITY RETRO-REFLECTOR ON A SERVO DRIVEN TURRET ON THE DEATH STAR, LUKE WOULD NOT HAVE MADE IT TO THE SEQUEL.
YOU GET THE IDEA!
NOT ONLY CAN RETROREFLCTORS DO THIS, UNDER CERTAIN CONDITIONS, THINGS LIKE GLASS RODS AND GLASSES OF WATER AND PLASTIC BOTTLES CAN REFLECT ENOUGH ENERGY TO CAUSE A PROBLEM!
(Steve said DO NOT DO THIS. SO I"M GONNA DO IT!, THAT GIVES ME NIGHTMARES. OK, IF YOU MUST, DO IT WITH A 1 mW HENE, BUT NOT MORE THEN CLASS II OR CLASS IIIA LASER, IE NOT MORE THEN 5 mW, EXPECT TO BE BLASTED IN THE EYE IF YOU DONT SET THE LASER ON A TABLE AND HOLD THE RETROREFLECTOR INTO THE BEAM, USING A WOOD STICK PAINTED BLACK WHICH REMOVES YOU FROM THE TARGET AREA, MAKE SURE YOU HAVE TOTAL CONTROL OF ENTRY TO THE ROOM AND THAT NO ONE ELSE IS AROUND THE LASER. GET USED TO PLANNING YOUR EXPERIMENT!)
SOME OTHER THINGS I've SEEN THIS MORNING THAT NEED TOUCHED ON:
Nominal Ocular Hazard Distance (NOHD):
The calculated distance in which it is possible to exceed the Maximum Permitted Exposure.
Maximum Permitted Exposure (MPE)
Maximum permissible exposure (MPE), is the level of laser radiation to which a person may be exposed without hazardous effects or biological changes in the eye. MPE levels are determined as a function of laser wavelength, exposure time and pulse repetition. The MPE is usually expressed either in terms of radiant exposure in J/cm2 or as irradiance in W/cm2 for a given wavelength and exposure duration.
Note, these are calculated numbers. IF I have my seven watt argon outdoors, the NOHD is upward of eight miles. Does that mean I can safely stand at 8.1 miles and view the beam head on? ABSOLUTELY NOT!
If I accidently illuminate a aircraft at distance farther the the MPE, its good odds that the pilots vision will be OK, but that does NOT mean it will NOT Disorient him or Flashblind Him.
Does that mean I can use a 20 watt ion laser turned down to 7 watts and be just as safe, NO! The longer 20 watt ion cavity has less divergence, because it has a longer resonator, and this less divergence. SO the NOHD is father for the better beam quality laser.
DO I CALCULATE THE MPE AND BASK IN THE LASER LIGHT AT THE MPE?
NO, INTENSE LIGHT EXPOSURE IS CUMULATIVE, TIME MATTERS!
IS it ok to spend 10x as long illuminated at 1/10 the MPE, Close, but not quite. You can still experience long term biological effects with short wavelengths etc.
It would take me a full day to research and post VERIFIED, VALID, examples, pictures and drawings, and laser safety fills whole books, like this one:
http://www.army.mil/usapa/med/DR_pubs/dr_a/pdf/tbmed524.pdf
HEADS UP FOLKS, PHYSICS IS COMPLEX, AND CAN BITE YOU. (BUT USED WITH CAUTION, AND PREPAREDNESS, IT CAN BE FUN)
KNOW YOUR TARGET !!! TEST AT VERY LOW POWERS.
(This is why lab lasers and industrial/medical lasers tend to have power controls and aiming beams.)
ONE OTHER THING, QUALITY CONTROL, JUST BECAUSE A EXPERIMENT WAS SAFE FOR YOU, DOES NOT MEAN THE MATERIALS AND GEAR ARE SAFE FOR THE NEXT GUY, PRODUCT VARIATIONS DO HAPPEN, AND NOT EVERYONE MAKING GOGGLES FOR EXAMPLE, ARE LEGIT OR TRAINED ENOUGH TO DO IT RIGHT! QUALITY CONTROL REQUIRES THINKING, PLANNING AHEAD, PAPERWORK, AND MEASUREMENTS, AS WELL AS SOME ONE ELSE CHECKING YOUR WORK BEFORE YOU RUN THE EVENT!
THE POINT OF THIS POST IS SO YOU CAN BE SAFE AND UNDERSTAND WHY CLASS IV LIGHT SOURCES DO NOT BELONG IN UNEDUCATED HANDS AND DO NOT BELONG IN UNCONTROLLED CONDITIONS!
DISClAIMER: I'M NOT A SPECIALIST IN LASER SAFETY, MOST PLACES WHERE I WORK WITH HIGH POWER LASERS, I'M DEPENDENT UPON THE WORK OF LASER SAFETY SPECIALISTS, WHO ARE EITHER ON SITE OR HAVE PROVIDED GUIDELINES. AND AT MANY OF THOSE PLACES, A SPECIALIST COMES AND CHECKS WHAT I"M DOING PERIODICALLY, TO MAKE SURE I'M FOLLOWING THE GUIDELINES AND NOT MISSING A DETAIL.
IF I even think I have to, I DO THE MATH! DON'T ASSUME ANYTHING!
Steve (WHO IS NOW LATE FOR WORK)
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