9.1 -- Laser Safety

PURPOSE AND SCOPE

The purpose of the Laser Safety Program is to establish the Temple University policy for the standardized safe use of all clinical/research lasers at Temple University.  This program is based primarily on guidance provided by the American National Standard Institute (ANSI) Z136 document series, specifically, document Z136.1, the American National Standard for Safe Use of Lasers (ANSI, 1993).

The Temple University Laser Safety Program establishes documentation, responsibility, and protocol for the safe use and hazard control of all Temple University Class 3b and 4 lasers.  This program is designed to provide reasonable and adequate guidance to facilitate the safe uses of lasers and result in reduced risk of laser injury.

This chapter covers the different classes of lasers and the required controls for each.  Compliance with the Temple University Laser Safety Program includes (but is not limited to) laser classification and hazard evaluation, designation of specific responsibilities, laser registration, Standard Operating Procedures (SOP), and safety training of laser users.  All expectations and requirements are explained in this chapter.

RESPONSIBILITIES

Environmental Health and Radiation Safety Department (EHRS)

EHRS is responsible for implementation of the laser safety program and to ensure that laser operations are being performed in accordance with approved policies and regulatory requirements.  The Director of Environmental Health and Radiation Safety or designee is authorized to stop an operation if, in his/her judgment:  1) the laser is not being operated as specified in the SOP; 2) if the laser is being operated in any manner that is considered to be unsafe; 3) the laser is being operated in a manner that is in violation of Temple University Policies.  The EHRS Director may require specific actions to assure compliance with Temple University polices and federal regulations. EHRS is responsible for:

• To review and approve/disapprove the laser installation facilities and laser equipment of Class 3b and Class 4 lasers prior to use.
• Providing assistance in evaluating and controlling hazards
• Providing assistance in calculation and selection of proper laser safety eyewear
• Maintaining records of lasers and laser operators
• Conducting laser safety training
• Participating in accident investigations involving lasers
• Periodically auditing the departmental laser safety programs
• Participating in the Safety Committee

Clinicians/Principal Investigators (PI)

• Provide a completed Laser Registration Form to EHRS for each Class 3b and 4 laser (homemade or commercial).
• Provide a written standard operating procedure (SOP), in accordance with ANSI Z136.1-1993, for each laser operation involving either a Class 3b or Class 4 laser.  All SOPs should include at least a copy of the laser registration form, details concerning the hazards, controls, operating procedures (including start up/shut down, operation, alignment, safety precautions, and maintenance), and procedures to be followed in case of an accident.  Provide copies of the SOP to all laser operators and Environmental Health and Radiation Safety.
• Compile and submit to EHRS a complete list of personnel and students with potential exposure to energized lasers.  Ensure that those listed have received laser safety training from EHRS and have received training in the appropriate SOP’s for each laser in use.
• Maintain knowledge of the education and training requirements for laser safety; the hazards associated with lasers, their physical setups, uses; and the associated control measures for all lasers under their control.
• Establish and conduct a safety review procedure to perform hazard analyses, including the establishment of the Nominal Hazard Zone (NHZ) for all lasers and ensure that any necessary corrective actions are completed for all applicable laser systems
• Classify or verify classification of the laser(s) or laser system(s) for which he/she is responsible.
• Clinicians/PIs must ensure that lasers under their control are not operated or modified without his/her approval and will notify EHRS when modifications are made.
• Ensure that all laser operators using Class 3b and Class 4 lasers are registered for the medical surveillance program.
• Report known or suspected accidents to EHRS.
• Ensure the availability and use of appropriate protective equipment, such as eyewear, clothing, barriers, screens, and interlocks that may be required to assure personal safety.
• Ensure wording on area signs and equipment labels meet ANSI recommendations and that all required areas are properly posted.
• Suspend, restrict, or terminate laser operation by a laser operator that is not operating the laser as specified in the SOP or in any manner that is considered by the Clinician/PI to be unsafe.
• Inform spectators about and protect spectators against all potential laser hazards.

Laser Operator

• Attend laser safety training
• Be familiar with specific safety hazards of lasers being operated or working near.
• Follow standard operating procedures and comply with the requirements established by the Safety Committee, EHRS, and the Clinician/PI.
• Use Class 3b or Class 4 lasers only if specifically authorized by the Clinician/PI.
• Do not modify a laser device without receiving prior approval from the Clinician/PI.
• Report known or suspected accidents to the Clinician/PI and EHRS.
• Register for the medical surveillance program.
• Promptly inform the Clinician/PI and Environmental Health and Radiation Safety if unsafe conditions are noted in the use or operation of the laser.

LASER CLASSIFICATION

Lasers and laser systems are classified based on their capacity to cause injury.  For example, a Class 4 laser is more hazardous than a Class 3a laser and therefore requires precautions that are more stringent.  Commercial lasers are classified and certified by the manufacturer.  When a commercial laser is modified or when a new laser is constructed at Temple University, it is the responsibility of the Clinician/PI to classify and label the laser per the ANSI Standard (Z136.1-1993).

Class 1 Laser: A Class 1 laser is not capable of emitting hazardous laser radiation levels under any operating or viewing conditions and is therefore exempt from most control measures or other forms of surveillance.  Most lasers by themselves do not fall into the Class 1 category but when the laser is incorporated into consumer or office machine equipment the resulting system may be Class1, as is the case for laser printers (the laser itself is usually a Class 2 laser). 

Note:  If a higher powered laser is embedded in a Class 1 operating system and the Class 1 system housing is removed so that access to the embedded laser is possible, then you are no longer operating in a Class 1 environment.

Class 2 Laser (Low Power):

A Class 2 laser emits visible radiation (400-700 nm).  Eye protection is afforded by the normal human aversion response to bright light.  This type of laser may present some potential for hazard if intentionally viewed directly for periods exceeding 0.25 seconds (the human aversion response time).  Class 2a lasers are not intended for direct viewing but are not hazardous if viewed for up to 1000 seconds.

Class 3a Laser (Medium Power):

Class 3a lasers normally do not present a hazard if viewed momentarily with an unaided eye (because of the aversion response to bright light), but may present a hazard if viewed using collecting optics.  They are not capable of causing serious skin injury or hazardous diffuse reflections under normal use.

Class 3b Laser (Medium Power):

Class 3b laser systems are those which are capable of causing eye damage from short duration (< 0.25s) intrabeam viewing and/or viewing of the specular reflections.  They are not capable of causing serious skin injury or hazardous diffuse reflections under normal use.  Control measures emphasize preventing exposure to eye to the primary or specularly reflected beam. 

Class 4 Laser (High Power):

Class 4 lasers and lasers systems may cause severe eye injury with short duration exposure to the direct or reflected beam.  They may also cause severe skin damage and present a fire hazard. 

LASER HAZARDS

Exposure to the Laser Beam

Exposure to the laser beam can be achieved in one of three ways; intrabeam, specular reflection, and diffuse reflection.

• Intrabeam Exposure — occurs when the eye or skin is directly exposed to the primary laser beam.
• Specular Reflection — occurs when mirror-like surfaces reflect the primary laser beam.
• Diffuse Reflection — caused by rough surfaces that are capable of reflecting the laser beam in many directions.

Non-Beam Hazards

• ¹Electrical Hazards — Lasers and 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.  Proximate water sources can lead to potential electrical shocks.

• ¹Laser-Generated Air Contaminants (LGAC) — Air contaminants may be generated when certain Class 3b and 4 laser beams interact with matter.  LGAC include metallic fumes and dusts, metallic oxide fumes, chemical and gaseous vapors, and biological fragments from human and animal tissue.  Some of the compounds from various materials 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
• Mutagenic agents from laser surgery
• Heavy metals from etching
• Benzene from cutting polyvinyl chloride
• Cyanide, formaldehyde, and synthetic and natural fibers associated with other processes.

• ¹Collateral and Plasma Radiation — Collateral radiation may be produced by system components such as power supplies, discharge lamps and plasma tubes.  Such radiation may take the form of x-radiation, ultraviolet, visible, infrared, microwave and radiofrequency radiation.

• ¹Fire Hazards — Class 4 laser systems represent a fire hazard.  Enclosure of a Class 4 laser beam can result in potential fire hazards if enclosure materials are likely to be exposed to irradiances exceeding

10 W/cm2.

• Users of commercially available laser barriers should obtain appropriate fire prevention information from the manufacturer (of the laser barrier), as these materials normally cannot withstand high irradiance levels for more than a few seconds without some damage.
• Operators of Class 4 lasers should be aware of the ability of unprotected wire insulation and plastic tubing to catch on fire from intense reflected or scattered beams, particularly from lasers operating at invisible wavelengths.

• ¹Compressed Gases — Presently many hazardous gases are used in laser applications including chlorine, fluorine, hydrogen chloride, and hydrogen fluoride.  Compressed gas cylinders should be secured from tipping.  Typical safety problems that arise when working with compressed gases are:
• Working with freestanding cylinders that are not isolated from personnel.
• Inability to protect open cylinder (regulator disconnected) from atmosphere and contaminants
• No remote 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.

• ¹Laser 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.  A Safety Data Sheet (SDS) for dye compounds shall be available to and reviewed by all appropriate workers.
• 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.

LASER SAFETY CALCULATIONS

¹Maximum Permissible Exposure (MPE) – The level of laser radiation to which a person may be exposed without hazardous effects or adverse biological changes in the eye or skin.  The following parameters must be known to determine the MPE: the temporal output category (continuous wave, single-pulsed, or repetitively pulsed), the wavelength of the laser, the anticipated duration of the exposure, and the irradiance (for CW lasers) or radiant exposure (for pulsed lasers).  The MPE for occular and skin exposures can be found in ANSI Z136.1-1993 tables 5 and 7 for particular wavelengths and exposure durations.  ANSI Z136.1-1993 Table 6 is a list of various correction factors that may need to be considered when using tables 5 or 7.

¹Optical Density (OD) – Optical density is the parameter used to specify the attenuation afforded by a given thickness of any transmitting medium.  OD or absorbance is used in the determination of the appropriate eye protection.  If the OD exceeds a value of 6, engineering controls should be used to limit access to the laser beam instead of relying on protective eyewear.  OD is a logarithmic function defined by:

OD = log₁₀ [H / MPE] or

OD = log₁₀ [E / MPE]

Where H and E are defined as radiant exposure (H) or irradiance (E) at range r, measured in J*cm^-2 for pulsed lasers and W*cm^-2 for CW lasers.

¹Nominal Hazard Zone (NHZ) – The space within which the level of direct, reflected, or scattered radiation during operation exceeds the applicable MPE.  Exposure levels beyond the boundary of the NHZ are below the applicable MPE level; therefore, no control measures are needed outside the NHZ.  The NHZ for occular exposures (R_NOHD), the primary concern for laser exposures, is calculated using the following formula:

R_NOHD = (1/f) [(4F/p MPE)^1/2-a]

Where f  is the emergent beam divergence measured in radians; F is the total radiant power of a continuous wave (CW) laser, or average radiant power of a repetitively pulsed laser, measured in watts; and a is the diameter of the emergent laser beam in centimeters.

CONTROL MEASURES

Control measures are outlined in Table 3: Control Measures for the Four Laser Classes.  Control measures include engineering controls such as: protective housing, interlocks, signage and labeling, and administrative and procedural controls such as standard operating procedures, education and training, and protective equipment.  Please contact Environmental Health and Radiation Safety for guidance or questions about the items listed in Table 3.

Protective Eyewear: Protective eyewear is required for Class 3b and Class 4 lasers.  Protective eyewear must be selected based on ANSI standards for the classification of the laser in use.   Protective eyewear should be selected by:

• Determine the wavelength of the laser being used.
• Determine the maximum anticipated viewing duration
• ²For unintentional, accidental exposures to visible lasers (400-700 nm), use 0.25 seconds.
• ²For unintentional, accidental exposure to infrared lasers (700nm -1mm), use 10 seconds
• ²For unintentional, accidental exposure to UV lasers (100 – 400nm), use the laser on time, up to 8 hours.
• Determine the output irradiance or radiant exposure of the laser
• Calculate the optical density required, Environmental Health and Safety can provide assistance in performing the OD calculation.
• Select the proper OD eye protection needed for the specific laser and wavelength in use.
• Check the eyewear for cracks and pin holes, the integrity of the frame and filter, etc. regularly.

NOTE:  Laser eyewear is not intended for direct viewing (intrabeam or specular reflection viewing) of the laser beam

MEDICAL SURVEILLANCE

The Clinician/PI must ensure that laser operators, who work with Class 3b or Class 4 lasers, will have a baseline eye examination as defined by ANSI Z136.1-1993 in Appendix E by a consulting ophthalmologist.  The Clinician/PI is responsible for the cost associated with the eye examinations.  An exam should be scheduled through the Ophthalmology Department.  Eye exams shall be completed before beginning the assigned work and following any accidental exposure where an eye injury is suspected. 

EHRS recommends that each laser worker operating Class 3b and/or Class 4 lasers receive an exit eye exam with the consulting ophthalmologist at the time of termination.

ADULT VISITORS AND CHILDREN

Children are prohibited from visiting a laser laboratory without prior approval from EHRS.

Adults are discouraged from visiting laser laboratories while a Class 3b or Class 4 laser is running.  If however, an adult does visit while a laser is running, the Clinician/PI is responsible for the safety of the visitor.  This can be achieved, in part, by providing an escort, basic laser safety training, and appropriate laser safety eyewear.

SUPPORTING REFERENCES AND STANDARDS

• American National Standards Institute (ANSI). American National Standard for the Safe Use

of Lasers, ANSI Z136.1-1993.  New York: ANSI, 1993.

• Code of Federal regulations, Title 21, part 1040.  Performance Standards for Light-Emitting

Products.  Washington, DC:  Office of the Federal register.

• Laser Institute of America. Laser Safety: Hazards, Inspections and Controls. Orlando: Laser

Institute of America, 1996.

• Sliney, David & Myron Wolbarsht.  Safety With Lasers and Other Optical Sources. 

New York:  Plenum Press, 1980.

BIOLOGICAL EFFECTS

Table 1: Summary of Laser Biological Effects

Table 2: Summary of Bioeffects of Commonly Used Lasers

X = Hazard is present

Table 3: Control Measures for the Four Laser Classes

LEGEND             X =    Shall

·  =    Should,

¾  =  No requirement

   Ñ=  Shall if enclosed Class 3b or Class 4

MPE = shall if MPE is exceeded

NHZ = NHZ analysis required

Table 3 (con’t): Control Measures for the Four Laser Classes

LEGEND             X =    Shall

·  =    Should,

¾  =  No requirement

   Ñ=  Shall if enclosed Class 3b or Class 4

MPE = shall if MPE is exceeded

NHZ = NHZ analysis required  

Å = Applicable only to UV and IR Lasers