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NAVY ENGINEERING BULLETIN MARCH 2003 57 Focus on Laser Safety in the RAN How do we use lasers in defence? Lasers are already commonplace in defence forces around the world, and their numbers and uses are increasing. Their military applications are numerous and can range from optical communications to highenergy weapons. Accurate range finding is currently the most common use, and it is a capability that we implement on many RAN platforms (ANZAC 9LV, FFG EOTS, and MHC EOSS). We also use hand held laser thermometers in damage control to determine the temperature of objects from a safe distance, without having to touch the potentially hot surface. We use a system known as Laser Airborne Depth Sounder (LADS) to perform ocean depth surveying using lasers operated on board an aircraft. RAN ships have even used laser designators to guide beam-riding missiles. These applications are only the beginning. As the technology matures we will begin to see laser systems used for hard and soft kill point defence systems, low power line of sight communications with very high bandwidth, LIDARs that construct real-time threedimensional images of distant targets, one day we may even have to learn ceremonial light-sabre drill. LEUT CHRIS DAVIDSON NAOS What are the dangers? Apart from the obvious danger involved with an inbound laser guided missile, there are other risks to personnel involved with the use of lasers. Laser radiation is non-ionising (ie, will not result in radiation sickness or genetic abnormalities), but it can burn flesh, and eyes are especially susceptible. Even a 100 mW laser is powerful enough to blind you permanently. A person can happily stare at a 100 W light globe because it emits noncollimated light. That means that the power is dissipated in every direction, so only a tiny fraction of the total power emitted enters the eye of any single observer. Laser light on the other hand is highly collimated (every ray has approximately the same direction of travel). So if a laser beam is pointed at an observer, the full power of the laser is concentrated onto the small spot on the skin where the laser beam strikes. What makes the eye even more susceptible to damage than skin is the ‘Spot Size effect’. This refers to wavelengths in the optical hazard region (not only visible wavelengths from 0.4 – 0.7 micrometres, but also the near infra-red from 0.7 – 1.4 micrometres), which are bought into sharp focus onto the retina of the eye. This concentrates the full energy of the laser beam onto an even smaller spot, superheating that point on the retina. Depending on the wavelength, and duration of exposure to the laser, the resultant super-heating can cause damage ranging from temporary dazzle to blind spots to total blindness. Eyes can be put in further danger if magnifying optics such as binoculars are used. Binoculars have a much larger aperture than the eye, so they have the ability to collect a lot more laser radiation from beams with a large diameter, and focus this radiation into the eye. What is being done about laser safety in the RAN? The Defence Laser Safety Committee (LSC) is a tri-service
58 NAVY ENGINEERING BULLETIN MARCH 2003 organisation put together by the Defence Safety Management Agency (DSMA). The LSC promulgate defence laser safety procedures in Ref A in order to minimise the likelihood of Defence personnel being injured by laser radiation. Subject matter experts from ADFA and DSTO ensure that the LSC keep abreast of developments in laser technology, laser safety and laser incidents. Navy, Army and Air Force all have their own Service Laser Authority (SLA) each of whom is a member of the LSC. The RAN SLA is located in the Naval Acoustic and Optronic Systems (NAOS) section headed by DDNAOS and is part of the Navy ISREW Systems Group in the Navy C4ISREW Directorate of the Navy Systems Branch. DDNAOS sponsors a DI(N) (Ref B) which is a tailored, Navy-specific version of Ref A. This DI(N) details the responsibilities of laser safety in the RAN and the process by which laser safety measures are put in place. The basic elements of the laser safety process are: i. Laser Safety Paper (LSP); ii. Range Safety Paper (RSP); iii. Laser Safe To Fire Zones (LSTFZ); and iv. equipment specific Standard Operating Procedures (SOP). When a new laser system is being procured for Navy, the project authority is to either produce a LSP, or if the laser class is below Class 3B (See the accompanying laser classification diagram), simply produce proof that the laser classification is in accordance with Ref C. Assuming the laser is Class 3B or higher, the LSP contains the laser properties, hazard distance calculations, built in/recommended safety precautions and any compatibility problems with other systems/equipment. Basically the LSP should ensure that all pertinent safety aspects associated with the laser system have been considered and that personnel and materiel are not endangered by the use of the laser device. It also acts as a foundation for the development of the RSP, LSTFZ and SOPs. A LSP template and examples are available from the NAOS section. When the NAOS section receives a LSP, they either validate or return the LSP to the project with corrections to be made. Once DDNAOS has signed off on a LSP and the LSC have given final approval, the RSP is produced by FIST, LSTFZ produced by both DNWS and FIST and SOPs are developed by Ships/Establishments that use the laser system. The LSP is a good starting point for Ships/Establishments writing SOPs. NAOS section provides assistance to all these agencies in laser matters. If a laser system is modified, the through-life support agency of the system makes DNC4ISREW aware of the modification details. The RAN SLA then assess whether the LSP needs updating. If so the above process is repeated. EOTS Laser Upgrade An example of a laser system that is being modified is the FFG EOTS Ranger 600 Laser Range Finder. It was found that the laser optics could not meet specified mean time between failures, which was resulting in more frequent maintenance. The contractor has found that they can fix this problem by reducing the power in the laser to a point where specified range performance is still met, and the optics are put under less stress. Reducing the power of the laser has a useful knock-on affect in the form of reduced laser safety restrictions. The reduction in power has resulted in the Ranger 600 being reclassified from laser Class 3B to Class 3A. Although Class 3A lasers do not strictly need a LSP, the NAOS section is producing a LSP anyway to help with the production of new LSTFZs and SOPs. To give an idea of the relaxed safety restrictions, the current Class 3B EOTS laser has an ocular hazard distance of 348 yd’s for an observer looking through standard 7x50 bridge binoculars (Ref D). The new Class 3A laser will reduce the 7x50 ocular hazard distance to around 22 yd’s. The EOTS lasers are currently being upgraded during their
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