Chapter 11: Laser Safety

Effective Date: July 1, 1997 (Issue No. 2)

Last Updated: December, 2014

A. Introduction

The HKUST laser safety program is designed to be in conformance with the American National Standards Institute (ANSI) Standard for Safe Use of Lasers (ANSI Z136.1-2000), ANSI Standard for the Safe Use of Lasers in Educational Institutions (ANSIZ136.5- 2000) and the Hong Kong Government Electrical and Mechanical Services Department Code of Practice for the Safe Use of Lasers. Appendix 11A is a glossary of laser-related terms.

Most lasers are capable of causing eye injury to anyone who looks directly into the beam, specular reflections. In addition, diffuse reflections of a high power laser beam can produce permanent eye damage. High power laser beams can burn exposed skin, ignite flammable materials, and activate toxic chemicals that release hazardous fumes, gases, debris, and radiation. The equipment and optical apparatus required to produce and control the laser energy may also introduce additional hazards associated with high voltage, high pressure, cryogenics, noise, radiation, and toxic materials. Therefore, each proposed experiment or operation involving a medium to high power laser must be evaluated to determine the hazards involved and the appropriate safety measures and controls that will be required. The two most hazardous situations exist during alignment and servicing of equipment.

 

B. Responsibilities

The safe operation of a laser is the responsibility of both the supervisor of the area or lead experimenter and the employee/student who performs the work.

Supervisors must ensure that all individuals, including outside service technicians, understand and follow all controls and procedures described in this chapter, in assembly instructions/manuals and in relevant safety procedures and also understand the hazards and comply with the safety requirements. The employee/student must keep the supervisor fully informed of any departure from established safety procedures or of any request to perform unsafe tasks. All laser eye or skin exposures (greater than the Maximum Permissible Exposure, or MPE) and injuries from laser-support equipment must be reported to the Health, Safety and Environment Office (HSEO). MPE limits are summarized in Appendix 11B.

The campus Laser Safety Officer (Occuaptional Hygienist in HSEO) will assist the area supervisor and experimenter in ensuring that safety requirements are followed and in evaluating and controlling hazards.

 

C. Personnel Qualification

All personnel who operate Class 3 or Class 4 lasers must have:

• successfully completed the laser safety training course provided by HSEO. Exemptions may be granted by a Department Head upon evaluation of the staff’s previous training and experience. A copy of the exemption shall be sent to HSEO for documentation. In cases of exemption, as well as all other cases, the laser supervisor is responsible for ensuring compliance with HKUST safety requirements.

• read this program.

• read the departmental safety procedure (DSP) and operational safety procedures (OSPs), if any.

In addition to these general requirements, operators of all lasers or laser systems (including Class 1 and Class 2a) must have

• Read any safety instructions provided by the manufacturer of the equipment.

• Received from the lead experimenter a thorough review of the laser equipment to be used. Further training may be required by the person in charge of laser.

Personnel supervising Class 3 or Class 4 laser operations must

• Register the lasers with the campus Laser Safety Officer (Registration of Laser System)
• Ensure that all authorized users of such equipment have been registered with the campus Laser Safety Officer (Registration of Laser Worker)

Laser system supervisors must ensure the manufacturer has provided adequate training and personal protection to its employers who perform the service and maintenance tasks. 

 

D. Medical Surveillance

All individuals who will work in areas where they may be exposed to laser radiation from a Class 3 or Class 4 laser are required to have an eye examination prior to the work assignment and after any confirmed or suspected accidental exposure where an eye injury may have occurred. An eye examination is also recommended when the employee/student terminates from HKUST. To schedule a laser eye examination, the supervisor or the employee/student shall contact HSEO.

Short term visitors for whom arrangements for an eye examination are not feasible may have this requirement waived by the Department Head upon evaluation of experience, level of involvement and work supervision at HKUST.

 

E. Laser Hazard Analysis

Before appropriate controls can be selected and implemented, laser hazards must be identified and evaluated. Three aspects of the application of a laser or laser system influence the total hazard evaluation and thereby influence the application of control measures:

• The capability of the laser or laser systems for injuring personnel.
• The environment in which the laser is used.
• The personnel who may use or be exposed to laser radiation.

To simplify this process, laser and laser systems are grouped according to their capacity to produce injury, and specific controls are then described for each group. For instance, a Class 3 or Class 4 laser requires stringent controls including restrict access into the laser area, but Class 1 and Class 2 lasers need only a few controls and has no restrictions on access. (Lasers manufactured after August 1, 1976, are classified and labeled by the manufacturer.)

 

F. Laser Classification

Controls required for the safe use of lasers are determined by the laser classifications outlined below. Check the manufacturer’s operating instruction or the laser hazard label for the correct classification. Consult HSEO concerning your laser’s classification if there is any question.

Class 1 Laser

Class 1 laser is considered to be incapable of producing damaging radiation levels and is therefore exempt from most control measures or other forms of surveillance.

Class 2 Laser (Low Power)

A Class 2 laser emits light in the visible portion of the spectrum (400-700 nanometers), and eye protection is normally afforded by the normal human aversion response to bright radiant sources. It may present some potential for hazard if viewed directly for extended periods of time.

Class 3 Laser (Medium Power)

A Class 3 laser may be hazardous under direct and specular reflection viewing conditions, but the diffuse reflection is usually not a hazard. Class 3 is divided into two subclasses, 3a and 3b, with slightly different control requirements. A Class 3 laser is normally not a fire hazard.

Class 4 Laser (High Power)

A Class 4 laser is a hazard to eye and skin from the direct beam, specular and diffuse reflections. A Class 4 laser can also be a fire hazard.

 

G. Laser Hazard Control Plan

A "laser hazard control plan" is required for experiments involving Class 3 or Class 4 laser systems. The purpose of the LHCP is to provide a preliminary assessment of the laser hazard associated with the experiment. For more sophisticated experimental setups, an operation safety procedures (OSP) may be required in addition to the LHCP to provide more details on relevant procedures and control measures adopted to control the hazards involved.  Users are required to update the LHCP to reflect personnel or procedural changes recorded in the plan yearly.

 

H. Operational Safety Procedures (OSP)

An operational safety procedure is generally required for operations involving high power lasers and experimental setups with the use of multiple lasers. The purpose of the OSP is to provide a written description of the hazards of the particular laser operation including both beam and non-beam hazards. Furthermore the OSP is to establish the appropriate engineering, administrative and personal protective equipment type controls which are required for conducting the laser operation safely. The laser operation specific OSP must be written by the laser supervisor and approved by the Department Head and HSEO.

An OSP is required for any laser operation when:

• Two or more Class 3 lasers will be used in the same area by different operators without intervening barriers.

• The safety interlock system has multiple, separately interlocked zones, or interlock system that does not conform to the conditions of Section I.

• The laser uses dyes requiring moderate or strict controls or toxic gases (see Appendix 11C).

• A laser installation does not include all the required controls specified in this manual (e.g. temporary operations).

• Modifications to commercial lasers or laser systems decrease the design safety.

• A Class 2, Class 3, or Class 4 laser or laser system is operated off-site or for outdoor applications.

• The beam of a Class 2, Class 3 or Class 4 laser must be viewed directly or where it is necessary to work with the eye or with optical viewing aids close to the laser beam.

• Unattended operations of Class 3 or Class 4 lasers do not conform to the conditions of Section I. Other non-optical hazards may be involved that require an OSP (e.g. electrical or pressure).

Request assistance from HSEO if no OSP is available. An approved copy of the OSP must be available in the immediate area of the laser.

 

I. Controls for Class 1 and Class 2 Lasers

Incidental viewing of Class 2 laser beams, although painful, will probably not produce permanent eye damage. In some cases, however, they are capable of causing injury if stared into for extended periods. The best rule to follow is never to look directly into a laser beam or at a specular reflection, regardless of its power.

Beam Control

To minimize direct eye exposure, observe these precautions:

• Terminate the beam at the end of its useful path.

• Locate the beam path at a point other than eye level.

• If it is necessary to beam across pedestrian or vehicular thoroughfares, select a height so as to avoid the eyes of passers-by.

• Minimize specular reflections and use nonreflective tools.

• Enclose beams as much as possible.

• Locate lasers so that no beam hazard exists at the point of entry for the room.

Warning Signs and Labels

Post appropriate warning signs as described by the ANSIZ136.1 at each entrance to the operating area.  Contact HSEO for details and appropriate sign to be posted at the entrance. 

Training and Qualification

See Section C for details.

Alignment

Users should establish a written beam alignment procedure for their experimental setups. The purpose of the alignment procedure is to ensure safety of all research personnel while performing beam alignment for a specific experimental setup.   

 

J. Controls for Class 3 and Class 4 Lasers

Class 3 and Class 4 include lasers with a broad range of radiant powers and energies, from those of minimal eye hazard (1-mW alignment or demonstration lasers) to those capable of causing severe skin burns and significant eye injury. Class 4 lasers are capable of creating a fire hazard.

 

Selecting Controls

An early consideration when designing a laser system is to include those controls that will permit the system to be designated as a Class 1 embedded laser (Section J). If this is not possible, then implement those controls described in this section that are prescribed for the laser classification to be used. Class 4 lasers require more rigid control measures, including an OSP, not only because there is a greater likelihood that the direct beam and specular reflections will have sufficient energy to cause injury, but also because of the greater risk of injury from hazardous diffuse reflections.

 

Training and Qualification

A laser operator shall meet both the training requirements stated in Section C and the operational qualifications required by HSEO. For each laser or laser system containing a Class 3 or Class 4 laser, the operators shall be specifically authorized to operate the equipment by the department and HSEO, and a list of authorized personnel shall be posted near the equipment.

 

Eye Examination

All persons who will work near Class 3 or Class 4 lasers are subject to the requirements stated in Section D.

 

Controlled Laser Areas

Class 3 and Class 4 lasers shall be operated only in areas specifically designed for laser operations. The facility shall be an enclosed room or laboratory area with walls that confine laser radiation to this area. Access to the area during laser operation requires the permission of the responsible operator.

 

Spectators

Spectators or visitors shall not enter controlled laser areas during laser operations unless prior permission has been obtained (from the laser operator) and protective measures taken. The supervisor of the operation must give special attention to the orientation of persons who are unfamiliar with the hazards in the laser area.

 

Admittance and Egress

Laser laboratories and controlled areas shall be designed so that personnel can enter and leave under emergency conditions. Doors to controlled laser areas shall not be locked when personnel are within the controlled area. (Deviation from this requirement will require a Hazard Analysis by HSEO.)

 

Warning Signs and Labels

Each entrance to a controlled laser area shall be posted with an appropriate laser warning sign. The warning sign should contain information on the type and power of the lasers used in the area. A laser classification label shall be conspicuously affixed to the laser housing. Laser users shall keep signs and labels current and legible.

 

Warning Devices

Personnel access into controlled laser areas containing any Class 3 laser that has greater than 5mW total power or any Class 4 laser shall be regulated by the use of a standard safety access light panel (available from FMO-LS). Red light indicates laser is in operation and unauthorized entry is prohibited.

 

Safety Interlocks

Access doors to a controlled laser area in which a Class 3 laser system with greater than 5mW total accessible power or a Class 4 laser system is being operated shall be equipped with safety interlocks to inhibit laser beam propagation when the interlock circuit is broken. Each Class 3 and Class 4 laser shall be provided with a key-controlled master switch that prevents laser light propagation onto the laser table or into an experiment when the key is removed. All protective enclosures that surround laser devices and high-voltage electrical sources shall also be equipped with safety interlocks. Laser users shall test the interlocks quarterly to ensure that they are operational. A written record shall be kept of each test made.

Authorized individuals in or outside a laser area controlled by an entry warning light are allowed to access if all of the following conditions are met:

• There is no laser radiation hazard at the point of entry.

• The required protective devices are worn by the personnel entering the area.

• A 15-sec clock designed into the interlock control circuit will automatically reactivate the interlock chain. The interlock bypass switch may be manually operated to extend the bypass period.

• The external interlock bypass switch shall be key- or cypher-lock operated.

• There are no hazards other than laser radiation that require an interlock system.

• Individuals entering the controlled area are aware of and follow all applicable administrative and procedural controls.

Deviation from these procedures may be acceptable if other precautions and controls are employed to provide a similar level of protection. These approaches shall be evaluated and approved by the Department Head and HSEO.

 

Beam Control

The entire beam path of Class 3 and Class 4 lasers, including the target area, should be surrounded by an enclosure equipped with interlocks that prevent operation of the laser system unless the enclosure is properly secured.

When total enclosure of the laser beam path is not practical, both the nonenclosed laser beam and any strong reflections (> MPE) shall be terminated at the end of their useful path using such devices as backstops, shields, or beam traps.

The laser system shall be securely mounted on a stable platform to maintain the beam in a fixed position during operation and limit beam traverse during adjustments. The laser should be oriented so that the beam is not directed toward entry doors. Primary beams and dangerous reflections shall be confined to the optical table or enclosed, and open beam paths should be clearly identified and shall not cross populated areas or traffic paths. When the beam path is not totally enclosed, the laser system shall be located so that the beam will be outside the normal eye-level range, which is between 4 to 6 ft (1.2 to 2m) from the floor in areas accessible to personnel. A beam path that exits from a controlled area shall be enclosed wherever the beam power exceeds the Class 1 AEL.

The addition of beam-stopping panels to the sides of optical tables is recommended.

Deviation from these procedures may be acceptable if other precautions and controls are employed to provide a similar level of protection. These approaches shall be evaluated and approved by the Department Head and HSEO.

 

Reflection Control

Materials (with a low reflective coefficient) that diffusely reflect laser radiation shall be used in place of specularly reflective surfaces wherever possible. To minimize personnel exposure, specularly reflecting surfaces that are needed for beam-path control should be enclosed or shielded. Non-reflective tools should always be used.

 

Invisible Beams

Ultraviolet (UV) and infrared (IR) lasers that emit invisible beams require several additional controls:

• Visual or audible beam-warning devices shall be installed in areas containing radiation in excess of the MPE. These warning devices shall be clearly identified and visible from all such areas.

• Shielding shall be installed that will attenuate UV radiation to levels below the Class 1 AEL at all points where personnel may be located.

• Hazardous concentrations of by-products formed by the reaction of intense UV radiation with materials in the area must be controlled.

• Infrared beam enclosures and backstops shall be fabricated of IR-absorbent material. For Class 4 lasers, the absorbent material shall also be fire-resistant.

 

Beam Mapping

Controlled laser areas shall be surveyed with appropriate measuring devices to locate and identify direct and reflected beams that exceed the MPE. Shielding will be required to limit unwanted radiation. Particular care shall be taken to locate, identify, and shield invisible beams that come from IR or UV lasers.

 

Direct Viewing

Personnel shall never look directly into any laser beam. The primary beam and specular reflections of Class 3 or Class 4 lasers are particularly hazardous. In those cases where it is necessary to directly view a beam from a Class 3 or Class 4 laser, special provisions, such as filters, are mandatory. An OSP shall be prepared for operations where the beam of a Class 3 or Class 4 laser must be viewed directly or where it is necessary to work with the eye or optical viewers close to the laser beam.

 

Alignment

Perform the alignment of laser optical systems (mirrors, lenses, beam deflectors, etc.) in such a manner that the primary beam or a specular or diffuse reflection of a beam does not expose the eye and skin to a level above the applicable MPE.

 

Optical Viewing Aids that Concentrate Light

Using optical systems such as cameras, telescopes, microscopes, and endoscopes to view laser beams may increase the eye hazard. Therefore, it is extremely important that interlocks or filters be placed on these instruments to prevent eye exposures above the Class 1 MPE.

Note: Normal or prescription eyewear is not considered to fall into this category.

 

Eye Protection

Safety equipment designed to protect the eye from laser radiation of a given wavelength and intensity shall be used if all other controls are unable to eliminate exposures above the MPE. Even when the radiant levels are considered to be safe, it is good practice to wear eye protection when lasers are in use. The supervisor or lead experimenter of the laser equipment will determine the appropriate laser eyewear. Assistance can be sought from HSEO.

 

Remote Operation

A laser beam line that may be illuminated in an area not under the direct observation and control of the laser operator, either by opening shutters or activating the laser, is a remotely operated beam line. Before illuminating such a remotely operated area, the area must be swept to ensure that the area is unoccupied, or an audible warning of impending safety status change or firing, followed by a countdown to the status change, must be made.

 

Unattended Laser Operation

A laser is unattended if none of its authorized operators are in the laser area. If it is not in use, deenergize its power supply and remove the keys from power switches or master interlocks, or lock the laser area to prevent access.

An unattended laser may be operated if its beam is contained in an interlocked enclosure (e.g. a laser room or a beam tube) and if

• An authorized operator is available, or

• A Hazards Analysis has been performed to identify the hazards and necessary controls by HSEO, and these controls are in place.

• Proper signs are posted; lights and the door interlock (if required) are functional. Signs must indicate who should be notified if an emergency occurs.

 

Temporary Installations

Occasionally, it may be necessary to remove protective enclosures or override equipment interlocks or other safety devices for service adjustments, maintenance, special training exercises, etc. In these instances, a temporary controlled laser area shall be set up. Specific methods of handling situations of this type must be described in an OSP. Because the area will not have all the standard safety features, the OSP shall describe provisions for protecting personnel who could be exposed. When the entire beam path is not fully enclosed, restrict access into the area to persons wearing proper protective equipment. Make sure that all optical paths from the restricted-access area are adequately covered to prevent escape of laser radiation greater than the Class 1 AEL.

 

Multiple Occupancy

A controlled laser area should have only one laser or laser system. However, when more than one laser or laser system operation is necessary, install appropriate shielding and define the conditions of coexistence and methods of maintaining a safe work environment. If two or more Class 3 and 4 lasers are operated in the same area by different operators without intervening barriers, then an OSP shall be written and approved. A summary of user control measures can be found in Table 1.

 

Table 1. Summary of laser control measures.

		Laser Classification
Controls		1	2	3a	3b	4
Administration
	Authorized operator	a	c	c	b	b
	Education and training	a	b	b	b	b
	Eye examination	a	a	b	b	b
	Spectator control	a	d	d	b	b
	Eye protection	a	a	d	b	b
	Alignment procedures	a	a	b	b	b
	Fiber optic procedures	a	a	b	b	b
	OSP	a	a	a	b	b
Engineering
	Service access panels	c	c	c	c	b
	Protective housing	b	b	b	b	b
	Interlocks on protective housing	c	c	c	b	b
	Key master switch	a	a	a	b	b
	Beam stop or attenuator	a	d	d	b	b
	Labels on laser	b	b	b	b	b
	Laser area interlocks	a	a	a	b	b
	Open beam path controls	a	d	d	b	b
	Area posting	b	b	b	b	b
	Laser outdoor controls	a	a	d	b	b
	Viewing portal controls	a	d	d	d	d
	Collecting optic controls	a	d	d	d	d
	Non-reflective tools	a	b	b	b	b
	No hazard at room entrance	a	d	b	b	b
	a = no requirement b = required control c = required if embedded (enclosed) Class 3 or 4 lasers d = required if MPE is exceeded

 

 

K. Converting to a Class 1 Embedded Laser

Any laser or laser system can be converted to a Class 1 enclosed laser by including all of the following controls in the laser system design. These controls will effectively enclose the laser, thus preventing personnel contact with the emitted radiation while permitting unrestricted access into the area.

 

Protective Housing

House the laser system within a protective enclosure to prevent escape of laser radiation above the Class 1 AEL. The protective housing must prevent personnel access to the laser system during normal operations. Personnel entering the enclosure to perform maintenance or adjustment tasks shall be made aware of the higher risks and shall comply with the control measures for the higher-risk laser class.

Protective housings that enclose embedded Class 3 and 4 lasers or laser systems shall be provided with an interlock system. Service adjustments or maintenance work performed on the laser system must not render the interlocks inoperative or cause exposure levels outside the enclosure to exceed the MPE unless the work is performed in a laser area with limited access and appropriate safeguards, supervision, and controls.

 

Fail-Safe Design

The protective enclosure and the laser system must be designed and fabricated so that if a failure occurs, the system will continue to meet the requirements for an enclosed laser operation.

Modifications to commercial laser systems must be evaluated. Contact HSEO for an evaluation. If the modifications decrease the safety controls, an OSP will be required.

 

Attenuated Viewing Windows (Portals)

Viewing windows shall contain a suitable filter material that will attenuate the transmitted laser radiation to levels below the MPE under all conditions of operation.

 

Warning Signs and Labels

Label the outside of the enclosure with CAUTION signs that give the laser system classification (Class 1). In addition, service access panels must have a label describing the laser embedded within the system. Make sure these labels may be easily seen and read.

 

L. Optical Fiber Communication Systems

Optical fiber transmission cables (OFCSs) -- lasers or laser systems that employ optical cables -- shall be considered enclosed systems with the optical cable forming part of the enclosure. If disconnection of a connector results in accessible radiation above the applicable Class 1 AEL, then appropriate engineering and administrative controls consistent with the hazards classification shall be applied.

When hazardous laser radiation levels (> MPE) may be present at the end of optical fibers, a label with the appropriate laser CAUTION or DANGER tag shall be attached, and the optical fiber shall be capped off when not in use.

 

M. Controlling Associated Hazards

Many hazards other than laser radiation can be found in the laser area and must also be adequately controlled. Electrical Equipment and Systems

Always be aware of the high risk of injury and fire in laser operations because of the presence of electrical power sources. The installation, operation, and maintenance of electrical equipment and systems shall conform to the standards stated in electrical safety program, Chapter 5. Metal laser tables shall always be bonded to the building ground. Note: This particular hazard has caused at least 15 fatalities and numerous serious injuries in the USA alone and should be carefully addressed.

 

Lighting

Adequate lighting is necessary in controlled areas. If lights are extinguished during laser operation, provide control switches in convenient locations or install a radio-controlled switch. Luminescent strips should be used to identify table and equipment corners, switch locations, aisles, etc. When natural light is not sufficient for safe egress from a laser area during an electrical power failure, install emergency lighting.

 

Pressure

Pressure vessels and systems used in conjunction with lasers shall meet the requirements of pressure safety program. Controls for toxic gas systems can also be found in pressure safety program described in Chapter 5.

 

Ionizing Radiation

A laser operation may involve ionizing radiation that originates from the presence of radioactive materials or the use of electrical power in excess of 10 kV. Contact HSEO to get an evaluation of these hazards before starting an operation.

 

Nonionizing Radiation

Microwave and radiofrequency (RF) fields may be generated by laser systems or support equipment. For specific guidance, contact HSEO.

 

Hazardous Materials Control

Bring into the laser area only those hazardous materials and minimum quantities that are needed for the operation. Make certain that these materials are properly used, stored, and controlled. Do not, without providing adequate controls, allow laser beams and strong reflections to impinge on combustible materials, explosives, highly flammable liquids or gases, or substances that decompose into highly toxic products under elevated temperatures. Conduct or sponsor tests that establish the effects of beam interactions with hazardous materials. Test results can then be used to determine safe parameters for laser operation. Contact HSEO for more specific controls.

 

Reference

1. David Sliney and Myron Wolbarsht, Safety with Lasers and Other Optical Sources-A Comprehensive Handbook (Plenum Press, New York, 1980).

2. George Clayton and Florence Clayton, eds., Patty’s Industrial Hygiene and Toxicology, 3rd. Rev. Ed., Vol. 1, Chap. 11, General Principles (John Wiley and Sons, New York, 1978) pp.376-402.

3. American National Standard for the Safe Use of Lasers, ANSI Z136.1-2000, American National Standards Institute, New York.

4. American National Standard for the Safe Use of Optical-Fiber Communication Systems Utilizing Laser-Diode and LED Sources, ANSI Z136.2, American National Standards Institute, New York.