12 - LASER SAFETY

 

12.1

INTRODUCTION

The laser represents a class of light emitting devices with unique characteristics. Certain of these characteristics can result in significant hazards. The light from a laser is collimated, coherent, can be of high intensity, and can cause burns to the eyes or skin or ignite flammable material. Laser power supplies frequently have high voltages at potentially lethal current levels. Some lasers employ potentially hazardous cryogenic fluid for cooling purposes. Manufacturing standards have been established which provide some safety features for lasers which include warning labels, beam shutters, power supply interlocks, and enclosures. In the research laboratory, it is sometimes necessary to defeat some of these safety features to perform maintenance or repairs or make modifications to the laser. In addition it is often necessary to work with unenclosed beams of moderate or high power to obtain or adjust an experimental setup. This situation can present potentially hazardous conditions which must be minimized by proper experimental design, engineering controls, personal protective equipment (such as eyewear) and proper training.

These guidelines are provided to protect University employees and students operating lasers and other personnel likely to be exposed to their hazards. A consensus standard for laser safety has been developed by the American National Standards Institute --- ANSI Z136.1 --- and that consensus standard is the basis for these guidelines.

12.2

RESPONSIBILITIES

12.2.1

Laser Supervisor/Principal Investigator

To ensure that all safety aspects are considered, the principal investigator must inform Environmental Health & Safety (EHS) of any intent to purchase, fabricate, or otherwise acquire a laser. EHS will review with the user the hazards of the proposed operation and make recommendations regarding the specific safety requirements that pertain to the proposed use, including procedures, laser control areas, training, and protective equipment.

The responsibility for laser safety is primarily that of the investigating scientist under whose direction the laser is being used. The guidelines that follow are intended as an aid in determining the minimum requirements for the safe laboratory use of lasers at the University. The flexibility required in a laboratory limits the ability to establish fixed rules governing laser use and, thus, the guidelines indicate an approach recommended to minimize hazards.

The basic approach is summarized as follows:

  • Thoroughly evaluate the hazards associated with the specific laser and its use;
  • Adequately train personnel in the safe use of lasers;
  • Define and provide appropriate protective equipment;
  • Reduce laser beam intensities to the minimum required to perform a desired procedure;
  • Implement the guidelines given in section 12.4 for the class of laser involved.
The principal investigating scientist must also investigate all eye exposures and suspected eye exposures and report them to EHS.

12.2.2

 


EHS performs the following functions:

  • Maintains the University's laser safety program.
  • Reviews and provides technical advice and safety approval for all laser operations.
  • Determines potential laser eye hazards and advises laser users and supervisors on appropriate eye protection.
  • Maintains an inventory of all lasers in University Facilities.
  • Assists in laser safety training.
  • Investigates all instances of suspected laser eye exposure.
  • Assists in classifying custom-built and modified lasers, and in complying with safety standards.

12.2.3

 


Laser users must:

  • Complete required safety training.
  • Know and follow the safe procedures developed for the use of the laser they work with.
  • Use required safety devices and personal protective equipment.
  • Report any suspected eye exposures to the laser supervisor.

12.3

LASER CLASSIFICATIONS

Lasers are classified according to the level of hazard associated with their light emission. Appropriate safe operation guidelines correlate with the following five classes of lasers.

  • Class 1: Cannot emit accessible laser radiation at known hazard levels (typically continuous wave [CW] <0.4 micro W at visible wavelengths).
  • Class 2: Low power visible spectrum lasers which emit above Class 1 power levels but do not exceed 1 mW.
  • Class 2A: Special-purpose lasers, not intended for viewing. Their power output is less than 1 mW. Many barcode readers fall into this category.
  • Class 3A: Intermediate power lasers (CW power of 1 to 5 mW).
  • Class 3B: Moderate power lasers (CW power of 5 to 500 mW or pulsed power to 10 J/cm2).
  • Class 4: High power lasers (CW power > 500 mW).

12.4

LASER SAFETY GUIDELINES

In an industrial environment, laser safety is provided primarily by engineering safety features which limit the possibility of exposure to laser hazards. This is possible because of well-defined and controlled applications of the laser. In contrast, in the research laboratory a large degree of flexibility is often required to obtain a desired result. This exposes personnel to potential and perhaps unnecessary hazards unless the experiment is well-planned. In the laboratory one is often forced to rely more heavily on administrative safety procedures than on engineered protections.

The primary hazard of lasers is eye damage due to intrabeam viewing. The well-collimated, coherent laser beam can be focused to a very small spot on the retina and cause destruction of the retina. For lasers with power less than 1 mW (Class 2) the natural brightness aversion reflex will normally protect the eye from serious injury. For higher power lasers, however, the injury can be instantaneous and permanent. For lasers with power near 0.5 W (and higher) merely the diffuse scattering of the beam can cause serious damage to the eye. It is essential, therefore, to evaluate all possible hazards associated with moderate and high power lasers to limit beam exposure.

Because of the flexibility often needed in a laboratory, two of the most important factors in a safe laser laboratory entail adequate safety training of personnel and a careful evaluation of potential hazards.

12.4.1

Class 1 Lasers This class of lasers is exempt from any precautions. As a matter of good practice, however, unnecessary exposure to Class 1 laser light should be avoided.

12.4.2

Class 2 Lasers

Precautions are required to prevent continuous staring into the direct beam or a beam reflected from a mirror-like surface. In most cases with Class 2 lasers, the natural brightness aversion reflex (blinking) generally provides protection from visible laser light. It is possible, however, to overcome the blink reflex and to stare into a Class 2 laser long enough to damage the eye.

12.4.3

Class 2A Lasers

This class of lasers causes injury only when viewed for more than 1,000 seconds.

12.4.4

Class 3A Lasers

In addition to the requirements of Class 2 lasers, precautions are required to prevent intrabeam viewing or specular beam reflections which may enter the eye. Class 3A lasers pose severe hazards when viewed through optical instruments (e.g., microscopes and binoculars).

12.4.5

Class 3B Lasers

Class 3B lasers will cause injury upon direct viewing of the beam or specular reflections. In addition to the requirements of Class 3A lasers, use the following engineering controls:

  • A protective housing,
  • Protective housing interlock systems that prevent emission of laser radiation when the housing is opened,
  • Viewing portals in the protective housing with filters and attenuators to preclude the emission of laser light at harmful levels,
  • For all optical instruments intended for viewing a laser or laser system, suitable means (e.g., filters, attenuators, or interlocks) to preclude the transmission of laser light in harmful levels under all conditions of operation and maintenance.
  • Operate lasers only in controlled areas in order to confine the laser hazards to well- defined spaces that are entirely under the control of the laser user. The area must be posted with appropriate warning signs that indicate the nature of the hazard and appropriate control measures.

When the use of uncontained beams is unavoidable, observe the following precautions:

  • Wear protective eyewear.
  • Place an appropriate laser hazard warning at all entrances to the area when the laser beam is operating, and limit access to the area to authorized personnel.
  • Terminate the laser beam at the limit of its useful distance. A dull black (highly absorbing/low reflectance) surface is recommended for visible frequency lasers. Beam traps or terminators with total absorbers appropriate to the wavelength of UV and IR lasers are recommended for those wavelength ranges.
  • Minimize specular reflecting surfaces in or near the beam path.
  • Light the space containing the laser well to constrict pupils.
  • Position the laser and contain the beam, such that the beam does not exit the area of use.
  • When it is necessary to align the beam, reduce its intensity as much as practical to reduce hazard potential.

12.4.6

Class 4 Lasers

Follow the requirements for Class 3B plus institute the following additional safeguards:

  • Equip all Class 4 lasers with a removable master key switch. The laser must not be operable when the key is removed.
  • Install electrical connections that allow the laser to be controlled by an area interlock system and remote shut-off devices.
  • Provide an integral or permanently attached beam stop or attenuator capable of preventing the emission of laser light at hazardous levels.
  • Conduct a hazard review before using a Class 4 laser. Write operating procedures based upon this review.
  • Limit access during operation of the laser to authorized personnel.
  • Employ a warning device at the area entrance to indicate the presence of the laser beam.
  • Enclose the beam path except when beam access is required.
  • Use appropriate protective eyewear unless the beam intensity has been reduced to a non-hazardous level.
  • Take procedural steps necessary to ensure that hands, arms, or other parts of the body do not intersect the beam.
  • Provide for a means to quickly disengage the laser power source from the electrical main during an emergency.
  • Use a highly absorbent beam trap of fire retardant materials to terminate the beam.
  • For infrared lasers (since the beam is invisible), protect areas which are exposed to reflections of the beam by fully enclosing the beam and target area.
  • For ultraviolet laser beam radiation, provide a beam shield which attenuates the radiation to acceptable levels.
  • Use a countdown procedure to signify the firing of single pulse lasers to ensure all present are aware of the firing of the laser.
  • Wear appropriate laser protective eyewear. Clearly label the eyewear with optical density values and wavelengths for which protection is afforded. Wear the eyewear whenever operational conditions may result in potential eye hazard.

12.5

NON-LASER BEAM HAZARDS

As mentioned above, lasers may have associated hazards not related to the laser beam itself. Listed below are some of these hazards and the recommended protective measures.

12.5.1

Electrical Hazards

Laser power supplies often involve potentially lethal voltage and current combinations. Even when the power supply is disconnected, capacitor banks may have dangerous stored electrical energy. Therefore, only qualified personnel shall perform service or maintenance on lasers and their power supplies. At times, access to the laser cavity is required for maintenance of optical components or other purposes while the system is operating. Personnel must be acutely aware of the voltages present within the laser cavity and which components may be energized in order that precautions be taken to avoid contact.

12.5.2

Vaporized Target Materials

When the laser beam is capable of vaporizing target material, it may emit toxic contaminants into the laboratory atmosphere. If this is possible, provide suitable local exhaust of laser target areas.

12.5.3

Laser Gases

Some lasers employ flowing gas systems. These gases may be toxic (e.g., CO, HF, etc.) Properly exhaust such gases and otherwise treat them as appropriate to their toxicity or hazard.

12.5.4

Cryogenic Coolants

Some lasers employ cryogenic coolants, and these materials must be properly handled. Address the hazards to skin or eyes associated with direct contact with ultra cold fluid. Also, provide proper exhaust of evaporating cryogenic liquid if sufficient cryogen is present to create a toxic or oxygen deficiency hazard.

12.5.5

Pump Lamps

Some pump lamps, such as high pressure arc lamps, may be hazardous due to the possibility of lamp explosion. Use appropriate lamp housings when lamps are operating. When handling the lamps, wear appropriate protective clothing and face/eye protection. In addition, some lamps emit substantial amounts of UV or other harmful wavelengths of radiation. Employ proper shields, filters, or personal protective equipment to limit exposure.

12.5.6

Chemical Hazards

Some lasers, such as dye lasers, employ chemicals that may be toxic. Follow the precautions given in the chemical safety section of this manual when using such lasers.

12.5.7

Ionizing Radiation

Potentially hazardous x-radiation may be generated from high voltage (>15 kV) power supply tubes. Appropriate shielding is required -- contact the Radiation Safety Officer, x5206.

12.6

REFERENCES

American National Standard for the Safe Use of Lasers, ANSI Z-136.1 (2014) American National Standards Institute.

Health & Safety Manual, PUB-3000, Lawrence Berkeley laboratory (1995)

Laser Safety Guide (Twelfth Edition, 2015) Laser Institute of America, Orlando Florida.