I spent most of last week at The International Laser Safety Conference (ILSC) which was held in Orlando, FL. It was probably one of the best laser safety conferences I’ve attended and I’ve been to a lot of them dating back to 1997. This was one of the largest ILSC’s I can remember and to put it bluntly – it was great! Congratulations to LIA for running a very successful event.
During the conference CLSO Jamie King of Lawrence Livermore National Lab was the recipient of the R. James Rockwell Jr. Educational Achievement Award. Congratulations to Jamie as this award is well deserved. For several years Jamie has been discussing the possible need for a Class 5 laser and most recently in his presentation this year at ILSC entitled “Beyond Class 4, Laser Safety Controls for Very High-Power Lasers”. Also worth reading is his paper from ILSC 2013 which can be seen by clicking on this link: https://e-reports-ext.llnl.gov/pdf/710233.pdf. Let’s take a look at the current classification scheme.
Class 1
A Class 1 laser is incapable of causing an injury during normal use. Lasers can be Class 1 because they are very low power or because the beam is fully enclosed. The operators of Class 1 lasers do not need to take any precautions to protect themselves from laser hazards. The Class 1 limits for visible lasers under the ANSI Standard vary with laser wavelength. Visible lasers with wavelengths longer than 500 nm have a class 1 limit of 0.4 mW. The Class 1 limit for visible lasers with wavelengths shorter than 450 nm is 40 mW. Power limits have been increased from earlier versions of the ANSI Standard because we now know that they had been set lower than necessary for safety. The CDRH Class 1 limit is 0.4 microwatts for the entire visible. The power limits have not yet been changed since it took effect in 1976. Class 1 limits under the IEC 60825-1 Standard agree with the ANSI Standard for the visible and near infrared, but they may be slightly different in the UV or far IR
Class 2
Class 2 lasers must be visible. The natural aversion response to bright light will cause a person to blink before a Class 2 laser can produce an eye injury. The average time for a human aversion response to bright light is 190 ms. The maximum aversion time is always less than 0.25 s. The only protection you need from a Class 2 laser is to know not to overcome the aversion response and stare directly into the beam. This has been done, and people have burned their retinas doing it.
Class 3R
Class 3R lasers are “Marginally Unsafe.” This means that the aversion response is not adequate protection for a direct exposure of the eye to the laser beam, but the actual hazard level is low, and minimum precautions will result in safe use. The CDRH Standard (FLPPS) allows only visible lasers in Class IIIa. The CW power is limited to 5 mW. If the laser has a small beam so that more than 1 mW can enter the pupil of the eye, it carries a DANGER label. If the beam is expanded to be large enough that only 1 mW can pass through the pupil, the laser carries a CAUTION label. (This category of expanded beam laser is in Class 2M in the new classification scheme.) The ANSI Standard has the same limits for visible Class 3R lasers as the old ANSI Class 3a and CDRH IIIa. It also allows invisible lasers in this class. An invisible laser with 1 to 5 times the Class 1 limit is a Class 3R invisible laser under the ANSI Standard. The only precautions required for safe use of a Class 3R laser are that the laser user must recognize the level of hazard and avoid direct eye exposure.
Class 3B
Class 3B lasers are hazardous for direct eye exposure to the laser beam, but diffuse reflections are not usually hazardous (unless the laser is near the class limit and the diffuse reflection is viewed from a close distance). The maximum average power for a CW or repetitive pulse class 3B laser is 0.5 W. The maximum pulse energy for a single pulse Class 3B laser in the visible and near IR varies with the wavelength. For visible lasers the maximum pulse energy is 30 mJ. It increases to 150 mJ per pulse in the wavelength range of 1050-1400 nm. For the ultraviolet and the far IR the limit is 125 mJ. Class 3B lasers operating near the upper power or energy limit of the class may produce minor skin hazards. However, this is not usually a real concern. Most Class 3B lasers do not produce diffuse reflection hazards. However, single pulse visible or near IR Class 3B lasers with ultrashort pulses can produce diffuse reflection hazards of more than a meter. Your laser safety officer will perform a hazard analysis.
Class 4
Class 4 lasers are powerful enough that even the diffuse reflection is a hazard. The lower power limit for CW and repetitive pulsed Class 4 lasers is an average power of 0.5 W. The lower limit for single pulse Class 4 lasers varies from 0.03 J for visible wavelengths to 0.15 J for some near infrared wavelengths. Class 4 lasers require the application of the most stringent control measures.
Class 1M & 2M
Class 1M and Class 2M lasers have the same hazards as Class 1 and Class 2 lasers when viewed with the unaided eye. If these lasers are viewed with magnifying or collecting optics, more light enters the eye and the hazard is greater. These lasers can be viewed safely using optical instruments only if appropriate laser safety eyewear or filters are used. Previous versions on the IEC 60825 Standard included some diverging laser beams in M classes. This applied to the diverging beams from optical fibers. The 2014 version of this standard does not include diverging beams in M classes. It is in agreement with the ANSI Standard, which never included diverging beams.
Below is a more simplified graphic for the different laser classes.
So – is there a need for a Class 5 laser? This is certainly a topic worth discussing in the laser safety community.