Laser Safety Officer Refresher

  • Posted on Sep 22, 2020

If you have already received training or high level education regarding lasers/optics/physics/electricity & magnetism, then much if this will be information that you already know.  The purpose is to make sure that all of the relevant information is fresh in your mind.  If this information is new to you, that is just as well because it will be a comprehensive guide for you to effectively do your job as an LSO.

  1. Laser Fundamentals
    • L.A.S.E.R is an acronym for Light Amplification by Stimulated Emission of Radiation.
    • Most lasers have three fundamental components: 
      • Optical Cavity – contains the standing wave that created the coherent laser beam
      • Pump – external energy source, light/electricity
      • Gain Medium – solid, liquid, gas, or semiconductor whose electrons are excited to the point that they emit photons
        • Solid State Lasers are usually ruby or neodymium-YAG 
        • Gas Lasers are usually HeNe or CO2
        • Liquid Dye Lasers use tunable organic rhodamine 6G
        • Semiconductor Lasers create a population inversion in a P-doped & N-doped semiconductor material
    • Common Laser Wavelengths:
      • N2 – 337 nm (ultraviolet)
      • Ar – 488 nm (blue)
      • Nd YAG – 532 & 1064 nm (green & shortwave infrared)
      • HeNe – 632 nm (red)
      • CO2 – 10.6 μm (longwave infrared)
  1. Laser Hazards
    • Ensure that lasers containing hazardous materials and gasses are properly ventilated.  Any process that may produce hazardous gasses (cutting, welding, etc.) should also be properly ventilated.  Refer to the ACGIH Threshold Limit Values and OSHA Permissible Exposure Limits.
    • Laser welders and cutters should also be contained in enclosures that can withstand high pressures and flying debris from the laser process. 
    • RF & UV radiation from pump lamps and discharge tubes should be shielded.
    • Ensure that all laser equipment is installed with the proper electrical connections.  Refer to the NEC and the specific laser product manual. 
    • Class IV & IIIB lasers pose a fire hazard.  Ensure that the enclosure material can withstand the irradiance from the laser source and are non-flammable
  1. Biological Effects
    • The most common workplace injury around lasers is retinal damage.  The beam is focused to a small point on the eye and causes burns, irritation, permanent damage, and even blindness. 
    • Lasers can also burn the skin.  The most dangerous lasers are UV and IR lasers because the operator cannot see the beam visually.  This often leads to the placement of skin tissue in the beam path, resulting in thermal radiation absorption and burns. 
    • Even pulsed lasers can cause damage, because the burns are additive with each pulse incident on the skin. 
    • UV sources cause photochemical reactions, over a long period of time (10 seconds), similar to a sunburn.  They can also cause DNA damage, resulting in skin cancer
  1. Classifications
    • Laser hazard classifications identify the dangers associated with a specific type of laser at a specific power level.
    • All lasers must have their classification displayed on a label on the laser.
    • Classifications establish a laser’s Accessible Emission Limit (AEL) and Maximum Permissible Exposure (MPE).  They are defined by their ability to cause biological damage.
    • There are four main classifications:
      • Class I – Unable to emit hazardous radiation (<0.4 μW).
      • Class I.A – Not intended for viewing, 1000 second exposure limit (<4 mW).
      • Class II – Low power visible laser (<1 mW).  Human aversion response will protect the operator.
      • Class IIIA – Intermediate power lasers (<5 mW).  Hazardous if directly viewed. 
      • Class IIIB – Moderate power lasers (<500 mW).  Not fire hazards and not capable of producing damaging diffuse reflections. 
      • Class IV – High power lasers (>500 mW).  These are the most dangerous.  They can cause burns to skin and damage to the eyes, even if viewed off of a diffuse reflection. 
    • Classification of new or modified laser product is required by the manufacturer and the label must be found on just one location of the warning label. Class 1 lasers are exempt from the label requirement. 
    • Optical fiber communication systems, in which the beam is completely enclosed by the fiber and housing, are considered Class 1 regardless of their internal laser radiation power level.  These systems can still be dangerous if the fiber breaks or is disconnected and light is allowed to radiate in an uncontrolled manner. 
  1. Regulations & Guidelines 
    • OSHA has standards for personal protective equipment (PPE).  This is the employer’s responsibility to provide appropriate PPE to employees. Laser safety goggles are meant for specific wavelengths and power ratings, so one set of goggles will not protect the worker from all potential laser hazards.  It is the job of the LSO to determine the correct goggles for each laser. 
    • Some states have their own specific laser safety regulatory bodies and agencies.  Many of these are primarily concerned with registration and licensing of lasers and operators. 
    • FDA Center for Devices and Radiological Health Performance Requirements within the Department of Health and Human Services standardizes the manufacture of lasers.  This regulatory body enforces compliance with medical device legislation. 
    • The American National Standard Institute has no requirements, but serves as a guide for both manufacturers and consumers. 
    • These aforementioned regulatory bodies provide exposure limits for medical and industrial lasers:
      • FDA – linearly additive biological effects for visible light 10 seconds to 100,000 seconds.  This is a limit of 3.85 mJ of cumulative radiant energy exposure.  This standard also assumes a 7 mm aperture of the human eye.  
      • ANSI – defines long term exposure limits & Accessible Exposure Limit of 0.385 μW with a 7 mm pupil aperture.  
      • Refer to the OSHA Technical Manual for a more detailed description of exposure limits.  Exposure limits specific to different laser types are also included.
    • A space is considered to be in Nominal Hazard Zone (NHZ) of a laser when the Maximum Permissible Exposure limits are exceeded.  This is specific to the laser classification and the type of beam being emitted (free space, incident, diffuse, etc.)
    • An NHZ evaluation must be done for each laser to determine the space which requires laser controls. All of the beam characteristics are required to carry out the NHZ calculation. 
    • Refer to the OSHA Technical Manual for a more detailed example of one of these calculations. 
    • Optical Density is a logarithmic function that determines how much light is absorbed by a given blocking medium.  Laser goggles are often labeled with an OD rating.  The OD number is the number of orders of magnitude of light that a given medium blocks.  For example, a pair of goggles with a rating of OD 1 transmits 1/10th of the light, OD 2 transmits 1/100th of the light, and so on.
  1. Control Measures
    • The four main types of laser controls are engineering, PPE, administrative, and special controls.  Some of these include interlocking doors, keys, enclosures, etc.
    • Service and maintenance are part of these control measures, ensuring that the laser systems are kept in good working order so that they can be operated without incident or malfunction that may cause a safety hazard.
    • Laser Safety Officers are elected by the employer to ensure that all of the lasers are properly controlled and that all of the operators are trained and performing their functions safely. 
    • Beam paths controlled in the following ways:
      • Totally Enclosed Beam Paths – high power lasers are embedded in an enclosure that does not allow the laser to fire if opened or damaged.  The beam is not accessible during operation or maintenance.  This can be accomplished with interlocks on the enclosure.  These types of control measures allow the system to be considered a Class 1 laser.  Fiber optic communication devices are an example of this. 
      • Limited Open Beam Path – the laser and associated optics/mirrors are surrounded by an enclosure that blocks what would otherwise be considered a freespace beam.  This is common among laser cutters and welders.  PPE is still recommended.
      • Totally Unenclosed Beam Path – these systems have no enclosure and require detailed NHZ analysis and safety controls. 
    • Often the room containing a laser system is considered a Laser-Controlled Area.  This room should be labeled with warning signs and interlocking doors. These areas should also only be occupied by qualified operators and authorized personnel.
    • Class IIIB & IV lasers have other safety recommendations.  The room containing the laser should be supervised by a person trained in laser safety.  Also, the laser system should have a beam blocker that is able to absorb the energy that the laser transmits, if it has an open beam path.  The appropriate laser safety goggles and other personal protective equipment should be available outside of the entryway to the room.  
    • Class IV lasers in particular should have safety controls at the entryway.  One such control is an interlocking door or a “panic button” (quick disconnect switch, or emergency power off button).  There are a few options for the proper way to equip the entryway the laser room:
      • Non-defeatable Entryway Control – magnetic switch that cuts power to the laser when the door is open.
      • Defeatable Entryway Control – sometimes necessary for emergency situations or training purposes.
      • Procedural Entryway Controls – this can be as simple as a curtain that blocks the beam or a barrier that blocks entry, or just proper training for laser operators.
      • Entryway Warning Systems – laser warning sign with a light that indicated that the beam is on.  
    • Sometimes it is necessary to have safety control measures in a temporary setup in order for the LSO to train laser operators.  The procedures are as follows:
      • SOP – standard operating procedures are to be developed by the LSO for all in house laser systems.  For the most part, this can be based on the SOPs established by the laser manufacturer.  However, new procedures must be established for custom setups.
      • Alignment Procedures – any operational or maintenance related tasks that include alignment can be potentially dangerous.  It is important for these procedures to be adhered to by the operator. 
      • Limitations of Spectators – there should not be unnecessary spectators around the laser while it is being operated. 
      • PPE – personal protective equipment  should be available and provided by the employer, but should be maintained by the LSO and laser operators.
        • Laser safety goggles specific to the laser wavelength and power range must be near the laser or outside of the laser room.  Gloves and lab jackets must also be worn for lasers that have the potential of damaging or burning skin.
        • Barriers or curtains with the appropriate threshold limit should enclose any area containing a Class IV laser.  
    • There are a variety of engineering controls that can enhance the safety of the laser system:
      • Protective Housing – this limits the access to the beam where it exceeds the MPE limit.  This can be a metal enclosure around the laser system or can be considered the walls around the laser room. 
      • Master Switch Control – this disables the power to the laser so that it cannot accidentally be turned on by untrained personnel. 
      • Optical Viewing System – if the system contains apertures, shutters, or viewing screens, they should be used with considerations about how they will interact with the interlocks. 
      • Beam Stops – required for Class IV systems to be used when the laser is on standby mode. 
      • Warning System – a warning sound or flashing light should be turned on when a lasers Class IIIB and above are activated.  
      • Service Panels – should have interlocks so that the protective housing cannot be opened while the laser is operating. 
      • Remote Interlock – allows Class IV laser to be disconnected from the outside of the laser room. 
    • Custom setups and R&D applications in which the laser is being operated without a protective housing must be monitored by the LSO so that they may determine the hazard and ensure that proper SOPs are in place. 
    • Optical Fiber Communication Systems are considered Class 1 if the beam is complete contained by the light guide.  These systems become hazardous if the fiber breaks.  For that reason, only trained personnel should work with or service these systems. 

If you need a LSO or are a LSO, please take a look at our courses today. It’s free to enroll your company and you can add students as often as you need. Or order our LSO Kit bundle to train your employees in the basics of laser safety.

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