LSM Table Of Contents

UCSF LASER SAFETY MANUAL

CHAPTER 1 LASER RADIATION

A. Properties of Laser Radiation
B. Generation of Laser Radiation

Laser Radiation

A. Properties of Laser Radiation

Laser radiation has several properties to consider for its safe use:

• wavelength
• coherence
• output power
• radiant exposure

1. Wavelength

Light is a form of electromagnetic radiation. A characteristic of light is its wavelength. The different wavelengths are detected by our eyes in the visible wavelength spectrum as different colors. Lasers generate light over a spectrum that extends beyond the visible to include the ultraviolet and at the other extreme the infrared wavelengths. The wavelength of light emitted is determined by the material that serves as the laser medium. Laser light is said to be monochromatic. The actual case is that a narrow spectrum of wavelengths may be generated, but are vary close together so as to appear monochromatic, for some uses. Some laser materials may emit at different wavelengths depending upon the optical components in the laser cavity or beam path. There are also multiline lasers that emit different wavelengths simultaneously and the wavelength used can be controlled through means such as filters to remove unwanted wavelength(s).

2. Coherent

Light waves that travel in phase with one another create an additive feature and so a very bright beam can be projected compared to a similarly powered non-coherent light source. The monochromatic nature of laser light allows for the existence of a coherent source to propagate some distance. Light of different wavelengths cannot remain coherent for great distances as the wavelengths would become out of phase with one another.

3. Irradiance

Irradiance is the power density of a laser beam. The units for this measure is Watts per cm². The power of a beam is divided by the cross sectional area of the beam. Laser beam cross sectional modes are described as TEM modes and theses describe the actual spatial distribution of the laser beam energy across a beam profile. Because the irradiance is dependent upon the cross sectional area of the beam at a point of interest, the aperture diameter is an important consideration as is the delivery optics of the beam. Optical lenses can focus a beam to a smaller area and so raise the power density, while a divergence of the beam can cause an increase in the area and so lower the power density of the beam. A laser that can have a certain interaction with a material at one distance from a focal point can have a different interaction at a different distance from a focal point. Generally the greater the irradiance, the greater the hazard of the laser. A laser operating in a continuous wave mode is described by its irradiance.

4. Radiant exposure

Many lasers do not operate in a continuous wave mode, but instead operate in a pulsed mode. In many applications, the laser is actually emitting light over a much shorter duration of time during each second than not. Peak power per pulse can be optimized by adjusting the pulse length so as to deliver the energy in a shorter amount of time to attain the energy density desired. The unit of energy density are Joules per cm². Radiant exposure is determined by the power density, pulse duration and frequency.

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B. Generation of Laser Radiation

1. Stimulated Emission

Laser is an acronym for light amplification by stimulated emission of radiation. The operation of a laser requires that a population inversion be established in a material where the majority of the atoms are in an excited state. This situation is the opposite of the situation at thermal equilibrium where most of the atoms in a material are at ground state and only a relative few are in an excited state. Creating the population inversion is achieved by using an excitation source such as a flash lamp or electricity. Some of the atoms in the excited state undergo spontaneous emission in which an electron returns to a lower or ground state and emits a photon of light. These photons interact with the excited atoms and cause a stimulated emission to occur in which the electrons drop to the lower state and emit a photon with the same wavelength as the incident photon. These photons created in the stimulated emission have not only the same wavelength, but are in phase with the incident photon and so the property of coherence is achieved. The laser cavity acts as a feedback mechanism until the photons escape through one end of the laser cavity as a laser beam. Further beam optics may shape the beam for the application of interest.

2. Lasing Media

Lasing media can be in different physical forms: solid, liquid or gas. The lasing medium with its characteristic excited states and energy levels determines the wavelength(s) of the laser beam. A solid glass rod doped with a lasing material, a semiconductor, a liquid dye medium or an enclosed volume of gas in a tube may serve as media. A common solid glass laser might be a Nd:YAG crystal which emits a laser light in the infrared region of the spectrum. A common gas laser might be the argon ion laser which emits a green laser beam. Another gas laser is the carbon dioxide laser which emits an infrared beam while a helium neon laser is frequently used to emit a red beam. Liquid dye lasers can be tuned to emit a laser wavelength determined by the dye utilized.

3. Types of excitation sources.

Flashlamps, plasma discharge tubes, high voltage current and radiofrequency devices are all sources used to excite the lacing media. Some lasers are used to "pump" other lasers in various applications. It is important to remember that the excitation device itself can present a serious non -beam hazard

OEH&S Laser Safety Manual Chapter 2

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CHAPTER 2 ANCILLARY HAZARDS & CONTROL MEASURES

A. Toxic dyes
B. Airborne Contaminants
C. Cryogen
D. Compressed gases
E. High Voltage
F. Collateral radiation
G. Fire and explosion
H. Noise

Ancillary Hazards and Control Measures

Ancillary Hazards are hazards that are associated with the laser system that are "non-beam" in nature. The hazards associated with laser systems must also be accounted for in the standard operating procedures and in maintenance and repair operations.

A. Toxic Dye Hazards

Some lasers use a dye as the lacing medium that receives energy from an excitation source that may include another laser. The use of dyes allows for a laser that can be used at different wavelengths depending upon the application. The dyes may have carcinogenic or mutagenic properties (consult the Material Data Safety Sheet for the dyes in use) and must be handled safely when mixing the dye. The solvents used may themselves be flammable, toxic or present other health hazards. Again, consult the MSDS for the hazards and proper handling of the solvents.

The dye usually is packaged as a powder and so care that should be exercised in handling and mixing the dyes. A chemical fume hood should be used to mix the dyes in order to reduce exposure from volatile solvents. Personnel protective equipment should include a labcoat, gloves, and safety goggles. Any spills should be cleaned up using proper protective equipment and the waste disposed of as hazardous chemical waste.

B. Airborne Contaminants

Interaction of laser radiation with target material may produce toxic dusts, vapors and gasses and in the case of clinical usage, biologically active materials may become airborne. Toxic products must be properly controlled by use of ventilation and filtration. Protective filtered masks and face shields may also be needed in clinical settings to comply with the blood borne pathogen standard.

C. Cryogen Hazards

Cryogenic liquids may be utilized in some laser systems for cooling the laser head or other components. These liquids present hazards for the skin and eye should they be released during handling or use. Protective equipment includes the use of insulated gloves, goggles and face shield. Should the liquid be allowed to warm to room temperature, it will expand to many times its volume and displace the oxygen in the room or storage cabinet. The specific hazards associated with the gas may be found in the MSDS for the gas.

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D. Compressed Gas Hazards

Compressed gases may be used as a component gas of a lacing medium (e.g., fluorine for an excimer laser). A compressed gas cylinder can present a hazard on its own if a valve fails and the compressed gas escapes in such a way as to propel the tank as a missile. Compressed gas cylinders must be restrained to prevent damage to the nozzle or regulator and to control their motions during an earthquake. If the tank is to be stored upright, it must be secured to a wall or upright column by two straps or chains that are positioned at two levels; one third and two thirds of the height of the tank.

The gas itself may pose a hazard which may be toxic, corrosive, or flammable in nature. It may be necessary to store the cylinder in a gas cabinet that has its own ventilation that can evacuate the gas in and emergency. The laser facility may need to have an emergency ventilation capacity to remove a gas and a monitoring system that is sufficiently sensitive to detect the presence of the hazardous gas. Consult the MSDS for safety measures concerning gases.

E. High Voltage Power Hazards

The high voltage power supply for laser systems has been responsible for serious injuries and electrocutions. It is important to know the hazards associated with the power supply of the laser system. Capacitor systems can retain dangerous amounts of power after the main power is disconnected. These should be discharged before attempting any repair work on the laser. Only qualified persons should work on high voltage power supplies.

F. Collateral Radiation Hazards

Laser excitation systems and power supplies may produce hazardous collateral radiation. These hazards are often controlled by the use of protective safety housings or enclosures. When these safety housings are removed, then the hazard may not be adequately controlled. The excitation source may generate intense ultraviolet radiation that can injure both eye and skin. Blue light is a hazard that involves the light reaching the retina and causing photochemical injuries that exceed the injury caused by thermal interactions alone. Laser power supplies that create energies greater than 15 kiloelectron volts may be a source of x-rays. Electric discharge lasers of sufficient energy may also generate x-rays. The protective housing of these lasers are required to shield against x-rays and so must be used as designed.

G. Fire and Explosion Hazards

Class 4 lasers present a fire hazard. Lasers being operated in continuous wave (CW) mode with a beam power that exceeds 0.5 watt can cause combustion in flammable materials left in the bream path. Beam stops, barriers, and curtains used with Class 4 lasers must be made of non-combustible materials for fire prevention. All Class 4 laser facilities must have a type ABC fire extinguisher readily available as a fire precaution. Laser users should also receive fire safety training.

Explosion hazards in the laser facility include the storage and use of flammable solvents and gasses (both cryogenic and compressed), and the potential implosion from dewars and excitation flashlamps. Proper storage and control of these should reduce the potential hazard.

H. Noise Hazard

Some laser systems generate significant levels of noise in the laser facility. If the noise level seems unpleasant or painful, contact the laser safety officer in order to have a noise survey performed.

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OEH&S Laser Safety Manual Chapter 3

Laser Safety Program

A. Program Responsibilities

Laser Safety Committee. The UCSF Laser Safety Committee (LSC) sets university laser safety policy and is responsible for program implementation and oversight.

Laser Safety Officer. The Laser Safety Officer (LSO) is a function of the Radiation Safety Officer and is responsible for program development, day to day program implementation, and compliance. The LSO acts as a technical advisor to the Laser Safety Committee regarding laser safety and regulatory affairs. Safety concerns associated with the use of lasers is communicated to the LSC. All laser use registrations shall be reviewed by the LSO. Classification of the hazard of individual lasers shall be made by the LSO. Investigation of any laser incidents and maintenance of records associated with the laser safety program are the responsibility of the LSO.

Environmental Health & Safety. The Office of Environmental Health & Safety is under the direction of the Radiation Safety Officer and is responsible for providing personnel and resources for developing and implementing the laser safety program. Administrative functions of the program are performed by staff. All Class 3a, 3b, and 4 lasers used on campus must have an approved laser use registration. This laser use registration serves to assure the Laser Safety Committee that the laser use has been examined and found to be safe. Registration of laser use serves also as a means to track lasers and the users on campus.

Department Chairs. The chairperson of each department that uses lasers is responsible for assuring that principal investigators operate lasers safely and implement the laser safety program.

Principal Investigators. Principal investigators (P.I.) are directly responsible for implementing the laser safety program especially hazard controls, oversight of ancillary hazards, and informing the LSO of changes which affect the use of lasers and users. It is the responsibility of the P.I. to assure that all laser users operating lasers under the laser use registration have met the safety training and eye exam requirements set forth by the Laser Safety Committee.

Laser Users. Users are responsible for their own safety in the laser facility. All users must meet the laser safety requirement prior to using a laser and joining a laser user authorization. All laser users are responsible for following specific hazard controls and notification requirements.

B. Scope of the Program

The UCSF Laser Safety Program primarily addresses the safety concerns of Class 3a, 3b, and 4 lasers. These classes of lasers are operated under Laser Use Registrations which describe the laser's use, class and any associated laser safety measures. The file of Laser Use Registrations is maintained by Environmental Health & Safety.

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C. Acquisition, Modification, Sale or Transfer of Lasers

The principal investigator is responsible to inform the LSO of any acquisition, modification, sale or transfer of lasers.

D. Laser Use Registration

A laser use registration is initiated by a principal investigator by completing a registration form. The form (please find the registration form and instructions in the Laser Safety Policy Appendix) is sent to the LSO and a site visit is made by the LSO with the principal investigator to review the intended use of the laser, the laser facility, the specific hazards of the laser system, need for hazard controls (engineering and administrative), and hazard classification of the laser system. The registration must be modified if the use of the laser or the hazard controls in place are changed significantly. When the Laser Safety Officer is satisfied that the facility is safe, the registration can be approved. Termination of the laser use registration is done at the initiative of the principal investigator or under special circumstances by the Laser Safety Committee. The use of a laser may be suspended by order of the Laser Safety Officer in the circumstance of a risk to the health or safety of persons in immediate danger.

E. Laser Safety Training

Laser users must have adequate laser safety training. General laser safety information can be gained from reading the Laser Safety Training section of the Laser Safety Manual. University policy on laser safety is covered in the policy section of the manual. Each laser user is required to read the Laser Safety Manual (both training and policy sections) and to sign the Laser Safety Training Supplement to document this training. This form is to be sent to the LSO so that the user database can be kept current.

Specific safety training is the responsibility of the principal investigator to supply and document. Such safety training shall include hands on use of the laser, personnel protective equipment (e.g., eyeware) the Standard Operating Procedures and the Operators Manual for the laser, and safety features of the laser system. Environmental Health & Safety can provide some general laser safety training as requested in specific instances. Documentation of specific training shall be documented on the Laser Safety Training Supplement.

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F. Laser Safety Inspections

All laser facilities are inspected by the Laser Safety Officer or designated staff of Environmental Health & Safety to assure that the laser is being operated in a safe manner. Inspection reports are maintained by Environmental Health & Safety and a copy submitted to the Principal Investigator. It is the responsibility of the P.I. to correct any unsafe conditions.

G. Eye Examinations

For laser workers operating a Class 3b or 4 laser system, during the pre-employment health examination, the person’s ocular history is reviewed and a visual acuity test is performed.  No special eye examination is required.  For a suspected exposure, an ocular and vision examination shall be administered.  This special exam follows the recommendation under ANSI Z136.  Examples of tests are visual acuity, macular function, color vision, fundoscopic examination and a skin examination. 

The following from ANSI Z136.3 (2005) describes the pre-employment examination.

American National Standard for Safe Use of Lasers in Health Care Facilities
ANSI® Z136.3 – 2005   (Revision of ANSI Z136.3-1996)

Medical Surveillance Documentation and Examinations.  (Section 6.3)
General Procedures for Laser Personnel.  (Section 6.3.1)

“An ocular history is reviewed, and if no problems are identified, and if the visual acuity is found to be 20/20 in each eye for far and near vision, and if the central (macular) visual field is normal as tested by an Amsler Grid or similar pattern, no further examination is required.”

H- missing paragraph

I. Beam Management

Laser beams shall be restricted to the immediate location of use. Beams should be enclosed whenever practical. Beam blocks must be used to terminate beams. The use of shutters, collimators, curtains, and other beam control devices are suggested. The path of an invisible laser beam shall be documented on location.

J. Signs and Labeling

All access points to a laser facility (Class 3b and 4) must be posted with an ANSI standard laser hazard sign. Laser enclosures must be labeled to alert users to the laser hazards per the ANSI standard (Z136.1). There must be a clear indication visual / audible that the laser is in operation upon entry to a controlled area prior to entering a hazard zone. Refer to Appendix on Laser Signs and Posting for required information on the signs and labels.

K. Access Control

Whenever the laser is in operation, access to laser facilities is restricted to laser users or persons being escorted by laser users. Access control must be maintained by positive means such as secured doors. Engineering controls (physical interlocks which cut the power to the laser or reduce its emission level to below Maximum Permissible Exposure levels ), emergency stop or panic buttons and keyed control of the laser itself may be required to provide a safe laser environment. It is recognized that in a clinical setting, such tight control of egress and ingress of personnel may not be practical due to the demands of the work and so a greater reliance on administrative controls may be necessary than in a research setting. A nominal hazard zone determination shall be made for lasers with open beams and clearly indicated. The hazard zone shall be contained wholly in a controlled area and directed away from entry ways. Only authorized and trained personnel wearing appropriate personnel protective equipment may be admitted during laser operation.

Appropriate laser safety eyeware shall be available for all personnel in the controlled area. The eyeware shall be stored in a way that it is available to authorized users at the point of entry into the controlled area when the laser is operating.

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L. Laser Incidents

Any incident which presents potential for laser exposure/injury shall be reported to the area responsible person(s). The circumstances of the incident shall be documented and forwarded to the Laser Safety Officer for investigation of the incident and a determination of procedures to prevent future recurrence of the incident. The principal investigator and laser users shall assist the laser safety officer in the investigation of the incident. A report of the investigation will be provided to the principal investigator and the Laser Safety Committee and a copy kept in file of Environmental Health & Safety for review. Please refer to the appendix for a Laser Incident Report Form to be returned to the Laser Safety Officer. The principal investigator is responsible for filing any necessary reports to the Office of Risk Management.

The initial report to the Laser Safety Officer shall include:

1. Time and Place of the incident.
2. Names of persons present / involved with the incident.
3. A description of what happened (chronological order). Please include a reference to the laser involved, its properties (wavelength, pulse duration, power and the distance of personnel from the beam at time of incident.)
4. Describe any injuries and what the injured party was doing at the time of the injury.
5. State if any medical assistance was provided or medical evaluation performed.

OEH&S Laser Safety Manual Chapter 4

CHAPTER 4 LASER HAZARD CLASSIFICATION

A. Determination of the Laser Hazard Classification
B. Hazard Classifications

Laser Hazard Classification

A. Determination of the Laser Hazard Classification

A laser hazard classification scheme is a tool that is used in determining the appropriate controls required to safely operate a laser based upon the risk or hazard it poses to users. The ANSI standard Z136.1 provides guidance for the classification for lasers, and manufactured lasers are required to be labelled with the hazard class. The laser safety officer will classify the hazard class of any lasers that are produced or modified at UCSF. The principal investigator is responsible to assist the LSO by supplying radiometric parameters of the system under evaluation. At the discretion of the LSO, a laser may be given a different (more consecrative) hazard rating than the one a manufacturer has given the device.

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B. Hazard Classifications

Class 1 (Eye Safe or Enclosed Lasers)

Class 1 lasers are lasers of such low power that injury cannot be caused from viewing the accessible laser radiation for the maximum possible duration. Many lasers are made class 1 by being enclosed into an interlocked system such that the laser radiation is inaccessible by the user. An example is a laser printer or a laser compact disk player. A qualified repair person may be able to access the laser for repair and would then be subject to the controls appropriate for the laser based on its radiometric properties and wavelength(s). No Laser Use Registration is required.

Class 2 (Aversion Response Safe)

Class 2a lasers are defined as visible lasers which are not intended to viewed and do not exceed the class 1 accessible emission limit (AEL) for an exposure duration less than or equal to 1000 seconds. An example of such a laser is the laser used at the grocery store.

A Class 2 laser is defined as a visible laser that will not cause injury to the eye when viewed for 0.25 seconds or less. The human aversion response of blinking or turning away from the beam is triggered by the bright glare of the visible beam entering the eye, and is estimated to be 0.25 seconds. If collecting optics are used in viewing the beam, or if one overrides the natural aversion response or is incapable of averting the eyes from the beam, then eye injury may result. Class 2 lasers may not exceed a radiant power of 1 mWatt. Class 2a and 2 lasers do not require a Laser Use Registration.

Class 3a and 3b (Intrabeam / Specular Reflection Hazard)

Class 3 lasers are defined as lasers which may cause injury through intrabeam viewing or through viewing a specular reflection for less than 0.25 seconds. Viewing a diffuse reflection from a class 3 laser generally will not cause injury to the eye. Class 3a lasers are defined as; an invisible laser with a radiant power which does not exceed 5 times the Class 1 AEL or a visible laser with a radiant power that does not exceed 5 mW. Class 3b lasers exceed the radiant power of Class 3a lasers but cannot exceed the upper power limit of 500 mW. Class 3a and 3b lasers do require a Laser Use Registration.

Class 4 (Diffuse Reflection and Fire Hazard)

Class 4 lasers possess the same hazards as Class 3 lasers but, because of their increased beam power (greater than 500mW), they may cause eye injury through viewing a diffuse reflection of the beam. Skin injury may also be possible from exposure to the laser radiation as well as a fire hazard. A Laser Use Registration is required for all Class 4 lasers.

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OEH&S Laser Safety Manual Chapter 5

CHAPTER 5 PURPOSE OF THE LASER SAFETY PROGRAM

A. Purpose of the Laser Safety Program
B. Program Authority
C. Standards for Safety
D. Laser Safety Program Components

A. Purpose of the Laser Safety Program

Laser technology is used in a variety of applications at the University of California San Francisco. Laser radiation presents a potential risk to researchers, workers, medical staff and patients. The Laser Safety Program is established in order to provide a safe environment at the university for the use of lasers. The university policy for the safe use of lasers is presented in this section of the manual and basic laser safety training materials follow in the second part of this manual for the use of researchers and workers using lasers.

B. Program Authority

The Laser Safety Program is established by a charge given Environmental Health & Safety from the Dean of Academic Affairs to have a program for laser safety. A recommendation is made that a campus wide Laser Safety Committee made up of faculty serve to form policy and ensure its implementation. The Radiation Safety Officer and Environmental Health and Safety support the work of the Laser Safety Committee and implement the laser safety program.

C. Standards for Safety

The California Code of Regulations (CCR) Title 8, Subchapter 7 General Industry Safety Orders, Section 3203 (Injury and Illness Prevention Program) regulates laser hazards. Standards for safe use of lasers adopted for use by the laser safety program include ANSI Z136.1 Safe Use of Lasers and Z136.3 ANSI for the safe use of lasers in health care facilities.

D. Laser Safety Program Components

The Laser Safety Program at UCSF primarily covers Class 3a, 3b and 4 laser systems on the campus. This program has several functions:

1. Administration

2. Registration of Laser Use

3. Laser Safety Training

4. Laser Facility Inspection

5. Laser Incident Management

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CHAPTER 6 METHODS TO CONTROL LASER BEAM HAZARDS

A. Administrative Controls
B. Engineering Controls
C. Personnel Protective Equipment

Methods to control laser beam hazards

The primary hazard associated with the laser is eye injury caused by intrabeam viewing or the viewing of spectral or diffuse reflections. Hazard control methods are used to prevent the laser beam from entering the eye. A variety of control methods are used to prevent injury.

A. Administrative Controls

1. Standard Operating Procedures

The Laser Safety Program requires the development and documentation of SOP's for alignments, maintenance and normal operations. These SOP's are the logical place to document in-house administrative controls. The SOP's can then be used to train individual users in the lab setting. Administrative controls will not positively impact the laser safety environment unless they are kept up to date and are reinforced by the PI through example and action.

2. Signs and Warning Labels

All access doors to rooms which contain Class 3a, 3b, or 4 lasers are to be posted with a sign marked with the word, "DANGER," the international laser symbol, a description of the laser class, the wavelength, and the laser power. A room containing more than one laser may include information for each laser on the same sign. It is strongly recommended that an interlocked lighted sign be located outside of the laser facility to further warn staff of the presence of laser radiation. All Class 3a, 3b, and 4 lasers are to be marked with the appropriate labels indicating the laser class, laser hazard, and identifying the laser aperture. These are specified in 21 CFR 1040.10 (g).

3. Repair of Laser Systems.

The repair of lasers are to be done by qualified persons who are familiar with the laser and the hazards confronted by the exposed laser cavity, bypassed interlocks and the ancillary hazards of the laser system. Standard Operating Procedures are to be followed and proper protective equipment shall be used.

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B. Engineering Controls

1. Access Control.

All Class 3b and 4 laser facilities are to have appropriate access controls to prevent unauthorized personnel from entering the facility while the laser is in operation. Key or combination locks are useful for this purpose. Doorways to laser facilities are to be kept closed all times, and locked when the laser user is not in direct attendance. An interlock should be used to reduce the power of the laser emission to the MPE or less when entry to the controlled area is opened. This may not be desirable in a medical setting where patient treatment may be compromised. Emergency shut off (panic) switches shall be located at the laser and at the door(s) to the facility.

Access to Class 3b and Class 4 lasers will be limited to personnel trained it the use of the laser system. Each Class 3b and Class 4 laser and its Nominal Hazard Zone (NHZ) will be completely contained within a controlled area. The NHZ will be clearly marked and will be directed away from the area entry.

All non-essential specular reflecting surfaces shall be removed from the NHZ.

Appropriate laser eyeware shall be available for all personnel in the controlled area. The eyewear shall be available so that personnel may enter the laser facility with the appropriate eyewear at hand.

2. Protective Housings, Interlocks and Shutters.

All Class 3a, 3b an 4 lasers are to have a non-flammable protective housing sufficient to contain the beam an excitation device. It is strongly recommended that the housing be interlocked such that the laser cannot normally be operated with the cover removed. If a housing interlock is required, it must not be disabled except with the approval of the LSC.

Most Class 3b an 4 lasers are equipped with a shutter mechanism which prevents the beam from leaving the housing when activated. If a shutter is required, it must be operational and is not to be disabled except with the approval of the LSC.

3. Key Operation, Power On Indication and Power Meters.

Many laser systems are equipped with key switches that prevent operation when the key is removed. If a key switch is required, it must not be disabled except with the approval of the LSC. In order to prevent unauthorized personnel from operating the laser, the key should be removed from the laser control and stored in a secure location whenever the laser is not being used.

All class 3b and 4 lasers need to have a lighted power on indicator clearly visible to persons in the laser facility. the power on indicator should be interlocked to prevent the laser from being operated if the indicator is not functioning.

It is highly recommended that the laser system have a power level meter to inform the user of the operating power of the laser. Medical lasers are required to have an integral power meter to indicate the power of the beam that is accurate to within 10 percent.

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4. Optical Tables, Beam Alignment, and Remote Viewing Systems.

Most research laser use entails the use of poetical tables to manipulate beams. Therefore, the safety issues associated with the specific optical table components and the general table environment must be considered, The primary intent is to prevent the bream from leaving the table top. Optical components must be aligned and secured properly to assure beam control. Secondary reflections must be considered and contained if possible.

Beam height should be planned to avoid eye level (both standing and sitting) in the facility. In situations where the beam needs to be directed to another area, it is important to consider enclosing the beam, or using fiber optics.

Beam alignment is the most hazardous aspect of laser use and results in the majority of eye injuries. For this reason , beam alignment procedures must be carefully thought out, formalized, documented, and users properly trained on the procedures. Beam alignment should be performed at the lowest possible beam power, preferably below the MPE.

If the beam power cannot be reduced, it is recommended that a lower powered laser be used to align the optics. If alignments are being done with power levels above the MPE, the user must use appropriate laser eyeware during the procedure. This eyeware normally will be of minimal optical density (OD) because the protection required is from a reflected beam, an not from intrabeam viewing. Alignments must be done so that the user is never looking directly into the beam.

When possible, it is advisable to have two users work together when performing alignments, so as to remind each other of safety considerations. One of the safest methods to use for viewing the beam is the use of a remote camera system. Remote viewing,although expensive, virtually eliminates the eye hazard associated with alignment procedures.

5. Enclosures, Beam Barriers, Beam Stops and Collimation.

Whenever possible, enclose as much of the beam as possible. Enclosures may be simple in design and use of materials and yet contain the beam in a safe manner. It is necessary to label the enclosure in order to inform persons that the laser beam is inside. Be careful not to use flammable enclosure materials with Class 4 systems.

Another effective an versatile tool for reducing the hazard from stray laser radiation is the use of beam barriers or beam curtains to surround all or part of the laser system. Labyrinth designs can be used to limit the hazard while maintaining ready access to laser systems. Avoid the use of flammable beam stops with Class 4 lasers.

Beam collimators can be used to restrict the path of the beam in the event of misalignment.

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6. Beam Focus

The hazard presented by a laser beam of a given diameter may be altered by changing the diameter of the beam and so lowering the irradiance and so reducing intrabeam viewing hazards, while creating the possibility of increased scattering. Conversely, focusing the beam into a smaller diameter will increase the irradiance of the beam at the point of focus. Past the point of focus, the beam will diffuse and so the irradiance will decrease and with it the hazard of the beam.

7. Beam Filtration, Frequency Doubling Crystals and Pumping Lasers

Filters may be used to alter the characteristics of a laser beam such as removing unwanted wavelengths. Prolonged exposure may cause some filters to be altered and so lose the ability to alter the beam as designed.

Frequency Doubling Filters such as potassium tri-phosphate may be used to increase the frequency of the laser light and reduce the wavelength. This presents the laser user with multiple wavelengths of laser light and the hazards associated with each wavelength must be addressed.

A laser may be used as a pumping source for another lacing material and so generate a laser beam of another wavelength(s). This again creates the situation of multiple wavelengths of laser light to consider in setting up a laser system and facility for safe use.

8. Preventing Reflections

Objects placed in the laser beam path may reflect the laser light in a specular reflection or diffuse reflection. Controlling the hazards of reflection includes eliminating unnecessary items from an optical bench, using non-reflective surfaced objects in the beam path, and containing hazardous reflections. Invisible wavelength reflection should also be considered in controlling reflections. In a clinical setting, the use of anodized implements to reduce reflections while treating a patient with laser light is a useful strategy.

9. Invisible Beam Hazards

Ultraviolet or infrared wavelengths are invisible. The path of the laser beam shall be clearly identified. On an optical table, the path of the beam can be identified with strips of tape. The use of fluorescent cards or infrared intensifiers should be available for use in alignment procedures.

10. Repair and Maintenance Hazards

Only qualified persons should perform laser system maintenance or repair. Access to laser radiation may be a source of increased hazard when safety housings are removed. Appropriate laser safety eyeware and skin protection shall be used in repair and maintenance procedures whether these are performed by vendors or UCSF employees, or researchers. Established safety policies at UCSF shall be followed by all and a vendor's safety procedures shall be followed while working on equipment at UCSF. In the event of a conflict in policies, the Laser Safety Officer should be consulted prior to the work being performed.

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C. Personnel Protective Equipment

1. Eyeware

Eyeware is only one part of a laser safety program. Engineering controls are used to the extent possible to protect people. The use of appropriate protective eyeware is essential during beam alignment procedures. Most laser accidents occur during beam alignment operations and could be avoided if proper eyeware had been worn. Protective eyeware should permit viewing of the laser beam. Accidents happen when the eyeware is removed in order to see the beam.

Protective eyeware shall be labelled with the wavelength of light that it is protecting the user and the optical density of the eyeware at that wavelength. Selection of laser safety eyeware must be based upon the wavelengths to be encountered, the required optical density to reduce transmitted laser light to nonhazardous levels and the comfort of the wearer. Please refer to the Appendix F. for guidance in the selection of laser safety eyeware.

2. Skin Protection

Ultraviolet laser beams or excitation sources can present severe hazards to exposed skin. Scattered or diffuse reflection of UV laser light that cannot be enclosed may require the use of protective coverings for the skin. Gloves, face shield and labcoat are examples of the coverings that may be required for use with UV lasers when the scattered or reflected light cannot be contained.