RADIOLOGICAL INFO
Laser Safety
MISSOURI UNIVERSITY OF SCIENCE AND TECHNOLOGY
STANDARD PRACTICE
LASER SAFETY MANUAL
July 2008
5.0 Biological Effects of Laser Radiation
5.1 Radiation Hazards to the Eye and Skin
6.1 Chemical Associated Hazards
9.0 Warning Signs and Labeling Requirements
10.2 Other Protective Equipment
11.0 Roles and Responsibilities
13.0 Laser Accidents and Incidents
Appendices
A-1 Class 3R, 3B, and 4 Requirements Summary
The Missouri University of Science and Technology (Missouri S&T) policy is to protect personnel and property from harmful exposure to laser radiation. The Laser Safety Program described herein is primarily based on the American National Standards Institute “Guide for the Safe Use of Lasers” (ANSI Z136.1-2014). This guide is widely accepted and used within the fields of industry, education, research, and medicine. All lasers and laser systems must also be operated in accordance with federal guidelines (21 CFR J “Radiological Health” and 29 CFR 1910 “Environmental Health and Safety Standards”).
The Missouri S&T Environmental Health and Safety Department regulates lasers on the Missouri S&T campus. Laboratories with high-powered lasers (Class 3R (formerly Class 3a), 3B (formerly Class 3b), and 4) require special safety procedures.
accessible emission limit (AEL) – The maximum accessible emission level permitted within a particular laser hazard class.
aversion response – Closure of the eyelid, eye movement, pupillary constriction, or movement of the head to avoid an exposure to a noxious or bright light stimulant. In this standard, the aversion response to an exposure from a bright, visible, laser source is assumed to limit the exposure of a specific retinal area to 0.25 s or less.
continuous wave (CW) – In this standard, a laser operating with or modeled as having a continuous output for a period > 0.25 s is regarded as a CW laser.
controlled area – An area where the occupancy and activity of those within is subject to control and supervision for the purpose of protection from radiation hazards.
diffuse reflection – Change of the spatial distribution of a beam of radiation when it is reflected in many directions by a surface or by a medium.
laser – A device that produces radiant energy predominantly by stimulated emission. Laser radiation may be either highly coherent temporally, or spatially, or both. Laser is an acronym for Light Amplification by Stimulated Emission of Radiation.
laser classification – An indication of the beam hazard level of a laser or laser system during normal operation or the determination thereof. The hazard level of a laser or laser system is represented by a number or a numbered capital letter. The laser classifications are Class 1, Class 1M, Class 2, Class 2M, Class 3R, Class 3B, and Class 4. In general, the potential beam hazard level increases in the same order.
laser safety officer (LSO) – One who has authority and responsibility to monitor and enforce the control of laser hazards and effect the knowledgeable evaluation and control of laser hazards.
maximum permissible exposure (MPE) – The level of laser radiation to which an unprotected person may be exposued without adverse biological changes in the eye or skin.
nominal hazard zone (NHZ) – The space within which the level of the direct, reflected, or scattered radiation may exceed the applicable MPE. Exposure levels beyond the boundary of the NHZ are below the appropriate MPE.
pulsed laser – A laser that delivers its energy in the form of a single pulse or a train of pulses. In this standard, the duration of a pulse is less than 0.25s.
shall – The word “shall” is to be understood as mandatory.
should – The word “should” is understood as advisory.
specular reflection – A mirror-like reflection.
“Laser” is an acronym for Light Amplification by Stimulated Emission of Radiation. A laser produces an intense, coherent, directional beam of radiation in the ultraviolet, visible, or infrared regions of the electromagnetic spectrum. There is a high concentration of energy per unit area both at the laser end and at the far end of the beam.
Laser radiation transmits energy which, when a laser beam strikes matter, can be transmitted, absorbed, or reflected. A material that transmits a laser beam is transparent. If the beam is not transmitted, the material is opaque and the incident radiation is absorbed or reflected.
Absorbed laser energy appears in the target material as heat. (At certain, usually short, wavelengths photochemical reactions may also occur.) Absorption and transmission are functions of the chemical and physical characteristics of the target material and the wavelength of the incident radiation.
Reflection is primarily a function of the physical character of the target’s surface material. A smooth polished surface is generally a good reflector. A rough uneven surface usually is a poor reflector, causing the reflected energy to be scattered in all directions thereby reducing the energy or power density, producing a “diffuse” reflection. A reflector such as a flat mirror changes the direction of an incident beam with little or no absorption (specular reflection). A curved mirror or surface will change the divergence angle of the impinging laser beam as well as its direction.
5.0 Biological Effects of Laser Radiation
Biological effects from laser radiation depend on the radiant exposure, wavelength, source size, exposure time, environmental conditions, and individual susceptibility.
5.1 Radiation Hazards to the Eye and Skin
The eye is the most important organ to protect. At visible wavelengths, laser radiation impinging on the eye is focused on the retina and, if sufficient energy is absorbed, can cause cell destruction. The focusing effect of the cornea and lens can concentrate energy on the order of 100,000 times on the retina. This can cause burning of the retina. At longer and shorter wavelengths, such as the far infrared and the ultraviolet, radiation striking the eye is absorbed in the cornea and the lens rather than being focused on the retina. Although these structures are less easily damaged than the retina, excessive energy absorption can cause cell damage and impairment of vision.
The skin and eyes are equally vulnerable in the ultraviolet and infrared regions of the spectrum. Low-powered and medium-powered lasers often do not cause skin injuries. High-powered Class 4 (See Section 7.7) lasers can cause injury to the skin as well as the eyes. A skin burn will normally heal, whereas an eye injury can cause scarring or permanent loss of vision.
There are usually no eye hazards from viewing laser beams reflected from a dull or rough surface. The energy from the laser beams are often dispersed and scattered in different directions. Lasers reflected from a flat shiny surface can be nearly as intense as the original laser beam. Protective eyewear (See Section 10.1) is often worn to protect the eyes.
A non-beam hazard is defined as a hazard that is not a result from direct human exposure to a laser beam. Non-beam hazards include chemical, physical, and human factors.
6.1 Chemical Associated Hazards
Laser generated airborne contaminants (LGAC), compressed gases, dyes, and solvents are the most likely chemical hazards resulting from laser usage. Explosive and other highly toxic materials can also be used in laser research laboratories. LGAC’s may result when a high-powered laser beam (Class 3B and 4) interact with matter. In this case the laser beam can vaporize the object it is directed toward and release hazardous airborne contaminants. Other hazardous substances include liquid nitrogen and other cryogenic fluids that are used as coolant for certain laser systems. When these cryogenic fluids evaporate, they replace atmospheric oxygen. Recommended control measures for chemical hazards include the installation of exhaust ventilation, required use of respiratory protection, and utilizing sensors and alarms that can detect hazardous gas.
The most dangerous non-beam hazard is electrical shock, which in the extreme case can result in electrocution. Capacitors are used for pulsed lasers, and continuous-wave lasers use high voltage power supplies. The risk for electric shock increases during maintenance or installation of these systems. Therefore, it is imperative that any electrical maintenance of a laser system be performed by knowledgeable persons. Fire hazards exist in and around some laser operations, but are usually limited to continuous-wave lasers with an output power above 0.5 watts. High-voltage laser power supplies may produce lower-energy x-rays, but sufficient shielding is normally installed in commercial lasers to prevent x-ray leakage.
This section addresses ergonomics, waste disposal, limited work space, and the use of chillers. It is important that the LSO be aware and address issues associated with laser system designs, such as poor laser workstation layout and other ergonomic issues that could result in physical injury. The issue of laser waste disposal is also of concern, because contaminated laser-related material must be handled in conformance with appropriate federal, state, and local guidelines.
Lasers are classified in terms of their potential to cause biological damage. The pertinent parameters are laser output energy or power, radiation wavelength, exposure duration, and cross sectional area of the laser beam at the point of interest. Most commercial lasers have an attached label specifying the classification of that laser. The hazard classification of a laser can be determined using ANSI Z136.1-2007 Section 3 and Appendix C. There are 7 different classes for lasers. (The department of Environmental Health and Safety keeps a copy of this standard for reference)
A Class 1 laser is defined as a laser that during operation cannot emit accessible laser radiation levels in excess of the applicable Class 1 AEL. A Class 1 laser is considered to be incapable of producing damaging radiation levels, and is, therefore, exempt from most forms of surveillance. Example: laser printers
A Class 1M laser is defined as a laser that during operation cannot emit accessible radiation levels in excess of the applicable Class 1 AEL under the conditions of measurement for the unaided eye, but exceeds the Class 1 AEL for telescopic viewing but does not exceed the Class 3B AEL.
Class 2 lasers and laser systems are visible (0.4 to 0.7 mm) continuous wave (CW) and repetitive-pulse lasers and laser systems which can emit accessible radiant energy exceeding the appropriate Class 1 AEL, but not exceeding the Class 1 AEL for any applicable pulse (emission) duration < 0.25 seconds and not exceeding an average radiant power of 1mW.
A Class 2 laser is a low-powered laser in the visible range that may be viewed directly under carefully controlled exposure conditions. These lasers are considered safe because the natural reflex of the eye will prevent average exposure from causing damage. Example: laser pointers
A Class 2M laser is defined as any laser that during operation cannot emit accessible laser radiation levels in excess of the applicable Class 2 AEL under the conditions of measurement for the unaided eye, but exceeds the Class 2 AEL for telescopic viewing but does not exceed the Class 3B AEL. The maximum exposure duration is assumed to be no more than 0.25 seconds. A Class 2M laser poses the same ocular hazards to the unaided eye as Class 2 lasers, but are potentially hazardous when viewed with optical aids (i.e. telescope).
7.5 Class 3R (formerly Class 3a)
Class 3R lasers and laser systems include those which have an accessible output between 1 and 5 times the Class 1 AEL for wavelengths shorter than 0.4 um or longer than 0.7 mm, or less than 5 times the Class 2 AEL for wavelengths between 0.4 and 0.7 mm.
Class 3R lasers will normally not produce injury if viewed only momentarily by the unaided eye. The Class 3R lasers may be a hazard if viewed using optics, e.g., telescopes, microscopes, or binoculars. Example: HeNe lasers above 1 milliwatt, but not exceeding 5 milliwatts; some laser pointers
7.6 Class 3B (formerly Class 3b)
Class 3B lasers and laser systems include:
- Ultraviolet (0.18 to 0.4 mm) and infrared (1.4 mm to 1 mm) lasers and laser systems which can emit accessible radiant power in excess of the Class 3R AEL, but which (a) cannot emit an average radiant power in excess of 0.5 W for = 0.25 seconds or (b) cannot produce a radiant energy greater than 0.125 Joules within an exposure time < 0.25 seconds.
- Visible (0.4 to 0.7 mm) or near-infrared (0.7 to 1.4 um) lasers or laser systems which emit in excess of the AEL of Class 3R but which (a) cannot emit an average radiant power in excess of 0.5 W for = 0.25 seconds and (b) cannot produce a radiant energy greater than 0.03 Joules per pulse.
Class 3B lasers may cause severe eye injuries through direct or specular exposure. Examples: continuous lasers not exceeding 0.5 watts for any period greater than 0.25 seconds, pulsed visible lasers not emitting more than 0.03 joules per pulse, pulsed infrared or ultraviolet lasers not emitting more than 0.125 joules during any period less than 0.25 seconds.
Class 4 lasers and laser systems are those that emit radiation that exceed the Class 3B AEL.
Class 4 lasers are a hazard to the eye from the direct beam, specular reflections, and sometimes even from diffuse reflections. Class 4 lasers can also start fires and can damage skin. Example: lasers operating at power levels greater than 500 milliwatts for continuous wave lasers or greater than 0.03 Joules for a pulsed system.
A summary of the laser safety requirements for Class 3R, 3B, and 4 is in Appendix A.
No user safety rules are necessary for Class 1 lasers, but looking into the direct beam should be discouraged as a matter of good practice.
A Class 1M laser should be clearly labeled with the sunburst laser symbol (see section 9) and the wording “Laser Radiation – Do Not Stare into Beam”
For Class 1M lasers, education and training shall be provided to all operators, maintenance, and service personnel.
Never allow a person to continuously stare into the laser source or never direct the laser beam at a person’s eye.
A Class 2 and 2M laser shall be clearly labeled with the sunburst laser symbol (see section 9) and the wording “Laser Radiation – Do Not Stare into Beam or View Directly with Optical Instruments”
For Class 2 and 2M lasers, education and training shall be provided to all operators, maintenance, and service personnel.
A Laser Warning Sign should be posted on all doors able to access the lab in accordance with Section 9.1.
A Class 3R laser shall be clearly labeled with the sunburst laser symbol (see section 9) and the wording “Laser Radiation – Avoid Direct Eye Exposure.”
The beam path should be enclosed as much as possible to prevent an individual from placing their head or reflecting objects into the beam path.
For Class 3R lasers, education and training shall be provided to all operators, maintenance, and service personnel.
The laser system shall only be used under the supervision of a responsible person who is familiar with the potential hazards of the laser.
Protective housing which encloses the laser shall be provided with an interlock system which is activated when the protective housing is opened or removed during operation and maintenance. Fail-safe interlocks shall be provided for any portion of the protective housing which, by design, can be removed or displaced during operation and maintenance.
Portions of the protective housing that are only intended to be removed from any laser or laser system by the service personnel, which then permits direct access to laser radiation shall either:
- be interlocked (fail-safe interlock not required)
- require a tool for removal and shall have an appropriate warning label on the panel
If the interlock can be bypassed or defeated, a warning label with the appropriate indications shall be located on the protective housing near the interlock.
For Class 3B and 4 lasers, education and training shall be provided to all operators, maintenance, and service personnel.
A Class 3B laser or laser system should be provided with a master switch.
A Class 4 laser or laser system shall be provided with a master switch. This master switch shall effect beam termination and/or system shutoff and shall be operated by a key, or by a coded access.
The laser beam path shall be controlled. Section 4.3.6 of the ANSI Z136.1-2007 describes ways to control the beam path.
A Class 3B laser or laser system should be provided with a permanently attached beam stop or attenuator.
A Class 4 laser or laser system shall be provided with a permanently attached beam stop or attenuator.
Class 3B lasers shall be operated in a controlled area, unless the beam path is completely enclosed.
Class 4 lasers shall be operated in a controlled area, where all entryway safety controls shall be designed to allow both rapid egress by laser personal at all times and admittance to the laser controlled area under emergency conditions. If the laser is not fully enclosed, laser operation shall be in a light-tight room with interlocked entrances to assure that the laser will shut off when the door is opened.
A Class 3B laser shall be clearly labeled with the sunburst laser symbol (see section 9) and the wording “Laser Radiation – Avoid Direct Exposure to Beam.”
A Class 4 laser shall be clearly labeled with the sunburst laser symbol (see section 9) and the wording “Laser Radiation – Avoid Eye or Skin Exposure to Direct or Scattered Radiation.”
Whenever appropriate and possible, Class 4 lasers or laser systems should be controlled and monitored at a position as distant as possible from the emission portal of the laser or laser system.
SOPs should be written for Class 3B lasers.
SOPs shall be written for Class 4 lasers.
For Class 3B lasers, a warning light or buzzer should indicate laser operation. This is especially important when the beam is not visible, i.e. Class 3B ultraviolet or infrared lasers.
For Class 4 lasers, a warning light or buzzer shall indicate laser operation.
9.0 Warning Signs and Labeling Requirements
Laser controlled area warning signs shall be of the three panel format. Area warning signs are not required for Class 1 and 1 M lasers.
The laser hazard symbol (a sunburst pattern consisting of two sets of radial spokes of different lengths and one long spoke, radiating from a common center) is on both the Caution Warning Sign and the Danger Warning Sign.
Sign information and warnings shall conform to the following specifications:
1. Above the tail of the sunburst, special precautionary instructions or protective action may be applicable, for example:
- Laser Protective Eyewear Required
- Invisible Laser Radiation
- Knock Before Entering
- Do Not Enter When Light is On
- Restricted Area
2. Below the tail of the sunburst, the type of laser (i.e. Nd:YAG, Helium-Neon, etc.), or the emitted wavelength, pulse duration (if appropriate), and maximum output shall be written or printed.
3. In the bottom right-hand corner of the Caution and Danger Warning Signs, the class of the laser or laser system shall be written or printed.
9.1.1 Caution Signs
An area which contains a Class 2, Class 2M and Class 3R laser should have a CAUTION Sign (Figure 9.1-1); Although not recommended by this standard.
9.1.2 Warning Signs
All areas with Class 3B and most Class 4 laser controlled areas shall have a WARNING sign (Figure 9.1-2)
9.1.3 Danger Sign
Extremely high power or high pulse energy Class 4 areas shall have a DANGER sign (Figure 9.1-3)
Class 2 and 2M lasers or laser systems should have appropriate warning labels with the sunburst logotype symbol (located in both Figures 9.1-1 and 9.1-2) and an appropriate cautionary statement (see section 8.3).
Class 3R, 3B, and 4 lasers or laser systems shall have appropriate warning labels with the sunburst logotype symbol (located in both Figures 9.1-1 and 9.1-2) and an appropriate cautionary statement (see sections 8.4 & 8.5). The label shall be affixed to a conspicuous place on the laser housing or control panel.
Enclosure of the laser equipment or beam path is the preferred method of control, since the enclosure will isolate or minimize the hazard. However, if that is not possible other forms of protective equipment shall be used.
Eye protection devices which are specifically designed for protection against radiation from Class 3B lasers or laser systems should be administratively required and their use enforced when engineering or other procedural and administrative controls are inadequate to eliminate potential exposure in excess of the applicable maximum permissible exposure (MPE).
Eye protection devices which are specifically designed for protection against radiation from Class 4 lasers or laser systems shall be required and their use enforced when engineering or other procedural and administrative controls are inadequate to eliminate potential exposure in excess of the applicable MPE.
Laser protective eyewear is usually not required for Class 2, Class 2M and Class 3R lasers or laser systems except in conditions where intentional long-term (>0.25 seconds) direct viewing is required.
Laser protective eyewear may include goggles, face shields, spectacles, or prescription eyewear using special filter materials or reflective coatings (or a combination of both) to reduce the potential ocular exposure below the applicable MPE level.
Eyewear shall have the following requirements:
- Protective eyewear shall be used only at the wavelength and energy/power for which it is intended.
- Label the protective eyewear with the laser type and/or light wavelength that the eyewear is designed for.
- Keep protective eyewear in good condition. Replace damaged or defective eyewear.
ANSI Z136.1-2007 Section 4.6.2 can be used to select appropriate eyewear.
10.2 Other Protective Equipment
Protective eyewear should not be considered the primary means to protect against laser radiation. Protective equipment such as beam stops, shields, safety interlocks, and warning lights and horns shall be maintained in proper operating condition and shall be utilized whenever indicated to prevent harmful exposure to laser radiation.
11.0 Roles and Responsibilities
A laser safety officer (LSO) shall have the responsibility and authority to monitor and enforce the control of laser hazards and effect the knowledgeable evaluation and control of laser hazards. The Radiation Safety Officer will designate a LSO. The LSO responsibilities include the following:
- Maintain records of all Class 3B and 4 lasers and laser operators
- Perform a periodic inspection of laser equipment
- Provide appropriate warning signs for posting
- Provide guidance on proper protective eyewear
- Assist Laser User with the controlled laser area and laser protection enclosures
- Participate in accident investigations involving lasers
- Periodically audit the departmental Laser Safety Program
- Maintain the laser safety training program
A Laser User is the person responsible for the use and maintenance of a laser or laser system. Laser Users are responsible for the following:
- Comply with all requirements written in the Laser Safety Manual.
- Notify the LSO of any new Class 3R, Class 3B and Class 4 laser on the Missouri S&T campus for a preliminary safety review as well as an inventory update. They should also notify the LSO of any major changes to a current Class 3R, Class 3B or Class 4 laser already on the Missouri S&T campus.
- Notify the LSO of any suspected overexposures to laser radiation.
- Responsible for writing and maintaining Laser Standard Operating Procedures (LSOPs) and training persons who wish to operate the laser they are the designated user for.
Laser Operators include persons who use the laser equipment. Laser operators shall use the laser equipment in accordance with the Laser Safety Manual, as well as any manufacturer’s laser-specific safety guidelines.
A laser safety training program shall be required for Class 3B and 4 lasers and laser systems. A laser safety training program should be required for Class 1M, Class 2, Class 2M and Class 3R lasers and laser systems. Any user of a laser system shall be trained. Users include operators, technicians, engineers, maintenance and service personnel, and any other personnel who work with or could potentially be exposed to laser radiation in excess of Class 1. The LSO will provide assistance, if needed, for creating and implementing a laser safety training program. The laser safety training program shall include warnings against misuse of lasers as well as the information in ANSI Z136.1-2007 Section 5.
13.0 Laser Accidents and Incidents
Persons receiving or suspected of having received a harmful laser light exposure must report such a fact or suspicion immediately to the named responsible person and the LSO. The LSO can be reached during business hours (Monday thru Friday, 8:00 AM to 4:30 PM) at 341-4305. For all emergencies, contact the University Police at 911.
- American National Standard for Safety Use of Lasers; ANSI Z136.1-2007.
- Laser Radiation Safety Manual; University of Missouri-Columbia Environmental Health and Safety; 1986.
- UNC-CH Laser Safety Manual; University of North Carolina at Chapel Hill Environmental Health and Safety; http://ehs.unc.edu/radiation/laser/index.htm.
- 21 CFR Subchapter J “Radiological Health”.
- 29 CFR Part 1910, Occupational Safety and Health Administration.
Class 3R, 3B, and 4 Requirements Summary
Table A-1 Requirements Summary
|
Requirement |
Laser Class |
||
|
|
3R |
3B |
4 |
|
Warning Signs |
-- |
X |
X |
|
Warning Labels |
X |
X |
X |
|
Enclosed Beam Path |
-- |
-- |
-- |
|
Supervision and/or use by knowledgeable person |
X |
X |
X |
|
Interlocks on Removable Protective Housing |
|
X |
X |
|
Service Access Panel Locks |
|
X |
X |
|
Key Control (master switch) |
|
-- |
X |
|
Beam Path Control |
|
X |
X |
|
Beam Stop or Attenuator |
|
-- |
X |
|
Laser Controlled Area |
|
X |
X |
|
Controlled Operation (distant operation) |
|
|
-- |
|
Standard Operating Procedures |
|
-- |
X |
|
Warning Light or Buzzer |
|
-- |
X |
|
Protective Eyewear |
|
-- |
X |
|
Training |
-- |
X |
X |
|
-- Recommended X Required |
|||