Non-Beam Hazards

In addition to the hazards directly associated with exposure to the beam, ancillary hazards can be produced by compressed gas cylinders, cryogenic and toxic materials, ionizing radiation and electrical shock.

Electrical Hazards

The use of lasers or laser systems can present an electric shock hazard. This may occur from contact with exposed utility power utilization, device control, and power supply conductors operating at potentials of 50 volts or more. These exposures can occur during laser set-up or installation, maintenance and service, where equipment protective covers are often removed to allow access to active components as required for those activities. The effect can range from a minor tingle to serious personal injury or death. Protection against accidental contact with energized conductors by means of a barrier system is the primary methodology to prevent electrical shock.

Additional electrical safety requirements are imposed upon laser devices, systems and those who work with them by the federal Occupational Safety and Health Administration OSHA, the National Electric Code and related state and local regulations. Individuals who repair or maintain lasers may require specialized electric safety-related work practices training.

Another particular hazard is that high voltage electrical supplies and capacitors for lasers are often located close to cooling water pumps, lines, filters, etc. In the event of a spill or hose rupture, an extremely dangerous situation may result. During times of high humidity, over-cooling can lead to condensation which can have similar effects. The following are recommendations for preventing electrical shocks for lasers for all classifications:

    1. All equipment should be installed in accordance with OSHA and the National Electrical Code.
    2. All electrical equipment should be treated as if it were “live”.
    3. Working with or near live circuits should be avoided. Whenever possible, unplug the equipment before working on it.
    4. A “buddy system” should be used when work on live electrical equipment is necessary, particularly after normal work hours or in isolated areas. Ideally, the person should be knowledgeable of first aid and CPR.
    5. Rings and metallic watchbands should not be worn, nor should metallic pens, pencils, or rulers be used while one is working with electrical equipment.
    6. Live circuits should be worked on using one hand, when it is possible to do so.
    7. When one is working with electrical equipment, only tools with insulated handles should be used.
    8. Electrical equipment that upon touch gives the slightest perception of current should be removed from service, tagged and repaired prior to further use.
    9. When working with high voltages, consider the floor conductive and grounded unless standing on a suitably insulated dry matting normally used for electrical work.
    10. Live electrical equipment should not be worked on when one is standing on a wet floor, or when the hands, feet or body is wet or perspiring.
    11. Do not undertake hazardous activities when truly fatigued, emotionally stressed, or under the influence of medication that dulls or slows the mental and reflex processes.
    12. Follow lockout/tagout procedures when working with hard-wired equipment.

Laser Generated Air Contaminants-The "Plume"

This is a term used to refer to the “cloud” of contaminants created when there is an interaction between the beam and the target matter. These air contaminants are mostly associated with Class 3b and 4 lasers, and range from metallic fumes and dust, chemical fumes, and aerosols containing biological contaminants.

Some examples include:

  • polycyclic aromatic hydrocarbons from mode burns on poly (methyl methacrylate) type polymers;
  • hydrogen cyanide and benzene from cutting of aromatic polyamide fibers;
  • fused silica from cutting quartz;
  • heavy metals from etching;
  • benzene from cutting polyvinyl chloride; and
  • cyanide, formaldehyde and synthetic and natural fibers associated with other processes.

 

Exposure to these contaminants must be controlled to reduce exposure below acceptable OSHA permissible exposure limits. The material safety data sheet (MSDS) may be consulted to determine exposure information and permissible exposure limits. In general, there are three major control measures available: exhaust ventilation, respiratory protection, and isolation of the process.

Whenever possible, recirculation of plume should be avoided. Exhaust ventilation, including use of fume hoods should be used to control airborne contaminants.

Respiratory protection may be used to control brief exposures, or as an interim control measure until other administrative or engineering controls are implemented. The laser process may be isolated by physical barriers, master-slave manipulators, or remote control apparatus. This is particularly useful for laser welding or cutting of targets such as plastics, biological material, coated metals, and composite substrates.

Collateral and Plasma Radiation

Collateral radiation, i.e., radiation other than that associated with the primary laser beam, may be produced by system components such as power supplies, discharge lamps and plasma tubes. Such radiation may take the form of x-rays, UV, visible, infrared, microwave and radio-frequency radiation. “Home-built” lasers are again of particular concern and should be independently examined. In addition, when high power pulsed laser beams (peak irradiance of the order of 1012 watts/cm2) are focused on a target, a plasma is generated which may also emit collateral radiation. X-rays may be generated by electronic components of the laser system (e.g., high voltage vacuum tubes, usually greater than 15kV) and from laser-metal induced plasmas.

Fire Hazards

The use of flame retardant materials is encouraged.

 

Opaque laser barriers (e.g., curtains) can be used to block the laser beam from exiting the work area during certain operations. While these barriers can be designed to offer a range of protection, they normally cannot withstand high irradiance levels for more than a few seconds without some damage, including the production of smoke, open fire, or penetration. Users of commercially available laser barriers should obtain appropriate fire prevention information from the manufacturer.

Operator of Class 4 lasers should be aware of the ability of unprotected wire insulation and plastic tubing to ignite from intense reflected or scattered beams, particularly from lasers operating at invisible wavelengths.

Compressed Gases

Many hazardous gases are used in laser applications, including chlorine, fluorine, hydrogen chloride, and hydrogen fluoride. The use of mixtures with inert gases, rather than the pure gases is generally preferred. Hazardous gases should be stored in appropriately exhausted enclosures, with the gases permanently piped to the laser using the recommended metal tubing and fittings. An inert gas purge system and distinctive coloring of the pipes and fittings is also prudent.

Compressed gas cylinders should be secured from tipping. Other typical safety problems that arise when using compressed gases are:

  • working with free-standing cylinders not isolated from personnel
  • regulator disconnects, releasing contents to atmosphere
  • no remove shutoff valve or provisions for purging gas before disconnect or reconnect
  • labeled hazardous gas cylinders not maintained in appropriate exhausted enclosures
  • gases of different categories (toxics, corrosives, flammable, oxidizers, inerts, high pressure and cryogenics) not stored separately

 

Laser Dyes

Laser dyes are complex fluorescent organic compounds which, when in solution with certain solvents, form a lasing medium for dye lasers. Certain dyes are highly toxic or carcinogenic. Since these dyes frequently need to be changed, special care must be taken when handling, preparing solutions, and operating dye lasers. The MSDS for dye compounds should be available to and reviewed by all appropriate workers.

The use of dimethylsulfoxide (DMSO) as a solvent for cyanide dyes in dye lasers should be discontinued, if possible. The DMSO aids in the transport of dyes into the skin. If another solvent cannot be found, low permeability gloves should be worn by personnel any time a situation arises where contact with the solvent may occur.

Preparation of dye solutions should be conducted in a fume hood. Personal protective equipment, such as lab coats, appropriate gloves, and eye protection are necessary when preparing solutions.

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