Control Measures

Control measures shall be devised to reduce the possibility of exposure of the eye and skin to hazardous laser radiation and to other hazards associated with the operation of lasers and laser systems. This applies during normal operation and maintenance by users, as well as by Manufacturers during the manufacture, testing, alignment, servicing, etc. of lasers and laser systems.

There are four basic categories of controls useful in laser environments. These are engineering controls, personal protective equipment, administrative and procedural controls, and special controls. The controls to be reviewed here are based upon the recommendations of the ANSI Z-136.1 standard.

The controls specified by the ANSI Z-136.1 standard have been rather universally adopted by industry, medicine and government as the “user requirements” of lasers. In general, the controls are rather easily implemented by the LSO of the facility.

For all users of lasers and laser systems, it is recommended that the minimum radiation level be used for the required application. If levels higher than the MPE are required, it is recommended that such higher powered lasers be “embedded” in a Class I laser system configuration whenever feasible.

Designs for lasers, laser systems, and the associated work areas shall be predicated upon the classification of the laser or lasers used. Generally, all purchased systems will be classified by the manufacturer in accordance with the Federal Standard. However, it is the responsibility of the LSO to confirm the classification and recommend or approve all control measures prior to laser equipment or facility use.

Important in all controls is the distinction between the functions of Operation, Maintenance and Service. First, laser systems are classified on the basis of level of the laser radiation accessible during operation. Maintenance is defined as those tasks specified in the user instructions for assuring the performance of the product and may include such tasks as routine cleaning or replenishment of expendables. Service functions are usually performed with far less frequency than maintenance functions (vis: replacing the laser resonator mirrors, repair of faulty components) and often will require access to the laser beam by those performing the service functions. Service functions should be clearly delineated as such in the product’s manuals.

B. Laser Safety Officer:
The LSO has the authority to monitor and enforce the control of laser hazards and effect the knowledgeable evaluation and control of laser hazards. The LSO administers the overall laser safety program where the duties include, but are not limited to items such as confirming the classification of lasers, effecting (or doing) the NHZ evaluation, assuring that the proper control measures are in place and approving substitute controls, approving SOP’s, recommend and/or approve eyewear and other protective equipment, special appropriate signs and labels, approve overall facility controls, effect proper laser safety training as needed, effect medical surveillance and designate the laser/incidental personnel categories.

The LSO should receive detailed training including an understanding of lasers, laser bioeffects, exposure limits, classifications, NHZ computations, control measures (including area controls, eyewear, barriers…) and medical surveillance.

In many industrial situations, the LSO will be a parttime activity, depending on number of lasers and general laser activity. The individual is often in the corporate industrial hygiene department or may be a laser engineer with safety responsibility. Some corporations implement an internal laser policy and effect safety practices based upon the ANSI Z-136.1 standard as-well-as their own corporate safety requirements.

C. Beam Path Controls:
There are some uses of Class IIIB and IV Class IV lasers where the entire beam path may be totally enclosed, other uses where the beam path is confined by design to significantly limit access and yet other uses where the beam path is totally open. In each case, the controls required will vary as follows:

1. Enclosed (Total) Beam Path:
Perhaps the most common form of a Class I laser system is a high power laser that has been totally enclosed (embedded) inside a protective enclosure equipped with appropriate interlocks and/or labels on all removable panels or access doors. Beam access is prevented, therefore, during operation and maintenance.

Such a completely enclosed system, if properly labeled and properly safeguarded with a protective housing interlocks (and all other applicable engineering controls), will fulfill all requirements for a Class I laser and may be operated in the enclosed manner WITH NO ADDITIONAL CONTROLS for the operator.

It should be noted that during periods of service or maintenance, controls appropriate to the class of the embedded laser may be required (perhaps on a temporary basis) when the beam enclosures are removed and beam access is possible. Beam access during maintenance or service procedures will not alter the Class I status of the laser during operation.

2. Limited Open Beam Path:
It is becoming quite commonplace, particularly with some industrial materials processing lasers, to have an enclosure that surrounds the area around the laser focusing optics and encloses the immediate area of the workstation almost completely. Often, a computer controlled positioning table is located within this enclosure; there is often a gap of less than one-quarter of an inch between the bottom of the enclosure and the top of the material to be laser processed. Such a design provides the needed mobility relative to the stationary laser.

Such a system would not meet, perhaps, the stringent “human access” requirements of the FLPPS for a Class I laser, but the real laser hazards are well confined. Such a design provides what can be called a limited open beam path. In this situation, the ANSI Z-136.1 standard recommends that the LSO shall effect a laser hazard analysis and establish the extent of the NHZ. In many system designs, (such as described above), the NHZ will be extremely limited and procedural controls (rather than elaborate engineering controls) will be sufficient.

Such an installation will require a detailed standard operating procedure (SOP). Training is also needed for the system operator commensurate with the class of the embedded laser.

Protective equipment (eye protection, temporary barriers, clothing and/or gloves, respirators ..etc) would be recommended, for example, only if the hazard analysis indicated a need or if the SOP required periods of beam access such as during setup or infrequent maintenance activities. Temporary protective measures for service is handled in a manner similar to service of any embedded Class IV laser.

3. Totally Unenclosed Beam Path:
There are several specific applications areas where high power (Class IIIB and Class IV) lasers are used in an unenclosed beam condition. This would include for example, open industrial processing systems (often incorporating robotic delivery), laser research laboratory installations, surgical installations…etc.

Such laser uses will require that a complete hazard analysis and NHZ assessment be effected by the LSO. Then, the controls implemented will reflect the magnitude and extent of hazards associated with the accessible beam.

For example, some 100 watt Nd:YAG laser processing systems may require beam access controls during use. As summarized in Table VII-2, the intrabeam (direct) hazard extends from 792 to 1410 meters, depending upon whether a 10 second or 8 hour MPE criteria is used in the NHZ calculation. Similarly, with a lens on the laser, the hazard exists over a range from 6.3 to 11.3 meters. The diffuse reflection zone is, however, markedly smaller; it ranges from 0.8 to 1.4 meters. None-the-less, this analysis suggests that operating personnel and support staff close to the laser would still need laser eye protection, even for diffuse reflections.

If, however, the LSO provides a detailed procedural control to limit the “beam on” condition only to situations where the lens was in place and the beam was only focussed onto the workpiece, then the extent of potential hazard would be limited to diffuse reflections and, in a “worst case” scenario, to the specular reflections of the focussed beam. This implies a maximum hazard region that extends no greater than about 30 feet. This certainly would project outside a typical laser processing area; hence the LSO would be proper in requiring either a barrier be placed just inside the entrance way so as to prevent an unlikely stray beam from going out a doorway, or requiring a means of entryway interlocking.

Similar analysis are also given in Table VII-2 for a 500 Watt CO(2) and a 5 Watt argon laser. Note that the NHZ’s do not vary for the CO(2) laser (because the MPE values are nearly identical for 10 second and 8 hour criteria). Also note that the diffuse reflection NHZ’s are very small except for the 8 hour criteria for the argon laser. In most cases, 0.25 seconds be used with visible lasers unless intentional staring is possible.

D. Laser Controlled Area:
When the entire beam path from a Class IIIB or Class IV laser is not sufficiently enclosed and/or baffled such that access to radiation above the MPE is possible, a “laser controlled area” is required. During periods of service, a controlled area may be established on a temporary basis. The controlled area will encompass the NHZ. Those controls required for both Class IIIB and Class IV installations are as follows:

1. Posting with Appropriate Laser Warning Signs:
CLASS IIIA (BEAM IRRADIANCE 2.5 mW/cm(2)), CLASS IIIB AND CLASS IV LASERS: Require the DANGER sign format: white background, red laser symbol with black outline and black lettering, Figure VII-1. Note that under ANSI Z-136.1 criteria, area posting is required only for Class IIIB and Class IV lasers.

CLASS II OR CLASS IIIA AREAS (IF THE LSO CHOOSES TO POST): All signs (and labels) associated with these lasers (when beam irradiance for Class IIIA does not exceed 2.5 mW/cm(2)) uses the CAUTION format: yellow background, black symbol and letters.

During times of service and other times when a temporary laser controlled area is established, a NOTICE sign format is required: white background, red laser symbol with blue field and black lettering, Figure VII-3. This sign is only posted during time when service is in progress.

2. Operated by Qualified and Authorized Personnel:
This includes appropriate training of the individuals in aspects of laser safety (see Laser Training).

3. Transmission from Indoor Controlled Area:
The beams shall not, under any circumstances, be transmitted from an indoor laser controlled area unless for specific purposes (such as testing). In such cases, the operator and the LSO must assure that the beam path is limited to controlled air space.

E. Class IV Laser Controls – General Requirements:
Those items recommended for Class IIIB but required for Class IV lasers are as follows:

  1. Supervised directly by of an individual knowledgeable in laser safety.
  2. Require approved entry of any non-involved personnel.
  3. Terminate all potentially hazardous beams in a beam stop of an appropriate material.
  4. Use diffusely reflecting materials near the beam, where appropriate.
  5. Personnel within the laser controlled area are provided with appropriate laser protective eyewear.
  6. Secure and locate the laser such that the beam path is above or below eye level in any standing or seated position.
  7. Have all windows, doorways, open portals…etc. from an indoor facility covered or restricted so-as-to reduce transmitted beams below appropriate ocular MPE level.
  8. Require storage or disabling of lasers when not in use.

F. Entryway Control Measures (CLASS IV):
In addition, there are specific controls required at the entryway to a Class IV laser controlled area. These can be summarized as follows:

1. All personnel entering a Class IV area shall be adequately trained and provided proper laser protective eyewear.
2. All personnel shall follow all applicable administrative and procedural controls.
3. All Class IV area/entryway controls shall allow both rapid entrance and exit under all conditions.
4. The controlled area shall have a clearly marked “Panic Button” (disconnect switch) that allows rapid deactivation of the laser.

In addition, Class IV areas also require some form of area-entryway controls. In the past, doorway interlocking was customary for Class IV installations. Now, the ANSI Z-136.1 (1986) standard provides three options that allow the LSO to provide an entryway control suited for the installation. The options include:

Non-Defeatable Entryway Controls: A non-defeatable control, such as a magnetic switch built into the entryway door which actuates a “beam off” condition when the door is opened is one option. In this case, training is required only for persons regularly working in the laser area.

Defeatable Entryway Controls: Defeatable controls may be used at an entryway, for example, during long term testing in a laser area. In this case the controls may be temporarily by- passed if it is clearly evident that there is no hazard at the point of entry. Training is required for all personnel who frequently require area entry.

Procedural Entryway Controls: A blocking barrier, or screen, or curtain which can block or filter the laser beam at the entryway may be used inside the controlled area to prevent the laser light from exiting the area at levels above the applicable MPE level. In this case, a warning light or sound is required outside the entryway that operates when the laser is energized and operating. All personnel who work in the facility shall be appropriately trained (see Laser Training).

G. Administrative and Procedural Controls:
Administrative and Procedural Control Measures are summarized in Table VII-3 and detailed below:

1. Standard Operating Procedures:
One of the more important of the so-called administrative and procedural controls is the written Standard Operating Procedure (SOP). The ANSI Z-136.1 standard requires an SOP for a Class IV laser and recommends SOP’s for Class IIIB lasers.

The key to an effective SOP is the involvement of those individuals that operate, maintain and service the equipment in the preparation along with guidance from the LSO. Most laser equipment is provided with instructions for safe operation by the manufacturer, however sometimes these are not well suited to a specific application due to special use conditions.

2. Alignment Procedures:
One of the highest rate of laser eye accidents occurs during alignment tasks. Such procedures must be done with extreme caution. A written SOP is recommended for all recurring alignment tasks.

3. Limitations on Spectators:
Persons unnecessary to the laser operation should be kept away. For those who do enter the laser area, appropriate eye protection and instruction is recommended.

4. Protective Equipment:
Protective equipment for laser safety generally means eye protection in the form of goggles or spectacles, clothing and barriers and other devices designed for laser protection.

Laser Protective Eyeware:
This includes special prescription eyewear using high optical density filter materials or reflective coatings (or a combination of both) to reduce the potential ocular exposure below MPE limits. Some applications, such as use of high power excimer lasers operating in the ultraviolet, may also dictate the use of a skin cover if chronic (repeated) exposures are anticipated at exposure levels at or near the MPE limits for skin. In general, it is recommended that other controls be employed rather than reliance specifically on the use of protective eyewear. This argument is predicated on the fact that so many accidents have occurred when eyewear was available but not worn. There are many reasons cited for this, but the most common is that laser protective eyewear is often dark, uncomfortable to wear and limits vision.

See Personal Protective Equipment.

Laser Barriers and Protective Curtains:
Area control can be effected in some cases using special barriers which have been specifically designed to withstand either direct and/or diffusely scattered beams. In this case, the barrier will exhibit a Barrier Threshold Limit (BTL) for beam penetration through the barrier during some specified exposure time (typically 60 seconds). The barrier is located at a distance from the laser source so that the BTL is not exceeded in the “worst case” exposure scenario.

Currently available laser barriers exhibit BTL’s ranging from 10 W/cm(2) to 350 W/cm(2) for different laser wavelengths and power levels. An analysis is usually required (done in a manner similar to the NHZ evaluations described previously) that establishes the recommended barrier type and installation distances for a given laser.

Important in the design is the factor of flammability of the barrier. It is essential that the barrier not support combustion and be consumed by flames following an exposure.

Engineering Controls:
The most universal controls are so-called engineering controls (see Table VII- 4). Usually, these are items built into the laser equipment that provide for safety. In most instances, these will be included on the equipment provided by the laser manufacturer as so-called “performance requirements” mandated by the FLPPS.

Specifics on some of the more important engineering controls recommended in the ANSI Z-136.1 standard are detailed as follows:

1. Protective Housing:
A Laser shall have an enclosure around the laser which limits access laser radiation at or below the applicable MPE level. A protective housing is required for all classes of lasers, except of course, at the beam aperture.

In some cases, the walls of a properly enclosed room area can be considered as the protective housing for an open beam laser. Such a “walk in” enclosure can also be a CDRH Class I provided that controls preclude operation with personnel within the room (vis: pressure sensitive floor mat switches, IR sensors, door interlocks..etc.).

2. Master Switch Control:
All Class IV lasers and laser systems require a master switch control. The switch can be operated by a key or computer code. When disabled (key or code removed), the laser is not capable of operation. Only authorized system operators are to be permitted access to the key or code. Inclusion of the master switch control on Class IIIB lasers and laser systems is also recommended but not required.

3. Optical Viewing System Safety:
Interlocks, filters or attenuators are to be incorporated in conjunction with beam shutters when optical viewing systems such as telescopes, microscopes, viewing ports or screens are used to view the beam or beam reflection area. For example, an electrical interlock could prevent laser system operation when a beam shutter is removed from the optical system viewing path. Such optical filter interlocks are required for all but Class I lasers.

4. Beam Stop or Attenuator:
Class IV lasers require a permanently attached beam stop or attenuator which can reduce the output emission to a level at or below the appropriate MPE level when the laser system is on “standby.” Such an beam stop or attenuator is also recommended for Class IIIA and Class IIIB lasers.

5. Laser Activation Warning System:
An audible tone or bell and/or visual warning (such as a flashing light) is recommended as an area control for Class IIIB laser operation. Such a warning system is mandatory for Class IV lasers. Such warning devices are to be activated upon system start up and are to be uniquely identified with the laser operation. Verbal “countdown” commands are an acceptable audible warning and should be a part of the standard operating procedures (SOP).

6. Service Access Panels:
The ANSI Z-136.1 standard requires that any portion of the protective housing that is intended to be removed only by service personnel and permit direct access to an embedded Class IIIB or Class IV laser will have either an interlock or require that a tool is used in the removal process. If an interlock is used and is defeatable, a warning label indicating this fact is required on the housing near the interlock. The design shall not allow replacement of a removed panel with the interlock in the defeated condition.

7. Protective Housing Interlock Requirements:
Interlocks which cause beam termination or reduction of the beam to MPE levels must be provided on all panels intended to be opened during operation and maintenance of all Class IIIA, Class IIIB and Class IV lasers. The interlocks are typically electrically connected to a beam shutter and, upon removal or displacement of the panel, closes the shutter and eliminates the possibility of hazardous exposures.

For embedded Class IIIB and Class IV lasers only, the interlocks are to be “failsafe”. This usually means dual redundant electrical series connected interlocks are associated with each removable panel.

Adjustments or procedures during service on the laser shall not cause the safety interlocks to become inoperative or the laser radiation outside a Class I laser protective housing to exceed the MPE limits, unless a temporary laser controlled area is established.

8. Remote Interlock Connector:
All Class IV lasers or laser systems are to be provided with a remote interlock connector to allow electrical connections to an emergency master disconnect (“Button panic button”) interlock or to room, door or fixture interlocks. When open circuited, the interlock shall cause the accessible laser radiation to be maintained below the appropriate MPE level. The remote interlock connector is also recommended for Class IIIB lasers.

I. Safety Procedures – General Basic Precautions:
The LSO shall be notified of the purchase of any laser, regardless of the class. Such notification should include the classification, media, output power or pulse energy, wavelength, repetition rate (if applicable), special attachments (frequency doublers…), beam size at the laser aperture, beam divergence and users.

No attempt shall be made to place any shiny or glossy object into the laser beam other than that for which the equipment is specifically designed.

Eye protection devices which are designed for protection against radiation from a specific laser system shall be used when engineering controls are inadequate to eliminate the possibility of potentially hazardous eye exposure (i.e., whenever levels of accessible emission exceed the appropriate MPE levels.) This generally applies only to Class IIIB and Class IV lasers. All laser protective eyewear shall be clearly labeled with optical density values and wavelengths for which protection is afforded.

Skin protection can best be achieved through engineering controls. If the potential exists for damaging skin exposure, particularly for ultraviolet lasers (200-400 nm), then skin covers and or “sun screen” creams are recommended.

HANDS – Most gloves will provide some protection against laser radiation. Tightly woven fabrics and opaque gloves provide the best protection.

ARMS – A laboratory jacket or coat can provide protection for the arms. For Class IV lasers, consideration should be given to flame resistant materials.

Accident data on laser usage has shown that Class I, Class II Class IIA and Class IIIA lasers are normally not considered hazardous from a radiation standpoint unless illogically used.

DIRECT EXPOSURE on the eye by a beam of laser light should always be avoided with any laser, no matter how low the power.

2. CLASS IIIB Lasers:
Laser beams shall be contained whenever possible. When uncontained beams are used, the following precautions shall be taken:

A Class IIIB warning sign shall be placed at all entrances to the area when the laser beam is operating and access must require authorization of persons responsible for the area.

The laser beam shall be terminated at the limit of its useful distance. A dull black (highly absorbing/low reflectance) surface is recommended for visible frequency lasers and beam traps or terminators with total absorbers appropriate to the wavelength for UV and IR lasers.
br> Specularly reflecting surfaces in or near the beam path shall be minimized.

The area shall be well lighted to constrict pupils. . A standard operating procedure is suggested for all Class IIIB lasers including emergency procedures.

The laser shall be positioned and the beam contained such that the beam does not exit the immediate area of use.

3. CLASS IV Lasers:
The same requirements as for Class IIIB lasers shall be followed. In addition, the following safeguards are required:

A total hazards review shall be conducted before a high power laser is used. This shall include evaluation of Nominal Hazard Zones (NHZ), measurements (if deemed necessary and other such analytical techniques.

Devices shall be located in an area designated specifically for laser operations (laser controlled area). Access during operation must require authorization of the person responsible for the area. In conditions where the beam path is not completely enclosed, access shall be limited.

An entryway control shall be used. This may include:

A non defeatable entryway interlock at the doorway
A defeatable entryway interlock at the doorway
Procedural entryway controls including a warning light immediately outside the room. One form of such a warning light could indicate conditions of enabled laser (high voltage on), laser on (beam on) and area clear (no high voltage or beam on)

Such measures shall permit rapid egress by the laser personnel at all times and admittance to the area under emergency conditions.

A control-disconnect switch or equivalent device shall be available near the exit for deactivating the laser.

A notice outside the area shall indicate the meaning of the blinking light.

Care must be taken to insure that the hands, arms, or other parts of the body do not intersect the beam.

The system must have provision(s) for quickly disengaging the laser power source from the electrical main during emergency.

The beam shall be terminated by a highly absorbent beam trap of fire resistant material.

For infrared lasers, since the radiation is invisible, areas which are exposed to reflections of the beam shall be protected by fully enclosing the beam and target area.

Ultraviolet laser beam radiation shall require a beam shield which attenuates the radiation to acceptable levels.

A countdown procedure shall be used to signify the firing of single pulse laser types (eg.: Q-switch) to ensure all present are aware of the time of the operation.

The use of laser protective eyewear is mandatory with Class IV lasers. Protective eyewear shall be fabricated of plastic or glass absorption filters appropriate for the laser. All laser protective eyewear shall be clearly labeled with optical density values and wavelengths for which protection is afforded.

J. Engineering Control Measures:
Engineering control measures (items incorporated into the laser or laser system by the Manufacturer or designed into the installation by the user) shall be given primary consideration in instituting a control measure program for limiting access to laser radiation.

If engineering controls are impractical or inadequate, administrative and procedural controls and personnel protective equipment approved by the LSO shall be used. If, during periods of service to a laser or laser system, the level of accessible emission exceeds the applicable MPE, temporary control measures may be instituted, as deemed appropriate by the LSO.

1. Laser Use Without Protective Housing (All Classes):
In some circumstances, such as during the manufacture of lasers, and during research and development, operation of an unenclosed laser or laser system may become necessary. In such cases, the LSO shall determine the hazard and ensure that controls are instituted appropriate to the class of maximum accessible emission to ensure safe operation.

Such controls may include but are not limited to:

Access restriction
Eye protection
Area controls
Barriers, shrouds, beam stops, etc.
Administrative and procedural controls
Education and training.

2. Laser Controlled Areas:
The following control measures apply to Laser Controlled Areas containing Class IIIB and Class IV lasers and laser systems. (Laser laboratories containing Class IIIB and Class IV lasers or laser systems are considered laser controlled areas.)

Laser devices shall be isolated in an area designed solely for laser operations. Access to such an area shall require appropriate authorization.

Special emphasis shall be placed on control of the path of the laser beam.

All persons using such lasers or laser systems shall be duly informed about the potential hazards of laser operations.

Only authorized personnel shall operate laser systems. Visitors shall not be permitted into the laser-controlled area unless appropriate supervisory approval has been obtained and protective measures taken.

Alignment of laser optical systems (mirrors, lenses, beam deflectors, etc.) shall be performed in such a manner that the primary beam or specular reflections cannot expose the eye to a level above the appropriate intrabeam MPE.

Whenever possible, the entire beam path, including the interaction area, that is, the area in which irradiation of materials by the primary or secondary beam occurs, should be enclosed. Enclosures should be equipped with interlocks so that the laser system will not operate unless such enclosures are properly installed.

For pulsed systems, interlocks shall be designed so as to prevent firing of the laser by dumping the stored energy into a dummy load. For cw lasers, the interlocks shall turn off the power supply or interrupt the beam by means of shutters. Interlocks shall not allow automatic reenergizing of the power supply but shall be designed so that after tripping the interlock, the power supply or shutter must be reset manually.

Eye protection devices which are designed for protection against radiation from a specific laser system shall be used when engineering and procedural controls are inadequate to eliminate potentially hazardous exposures.

Whenever possible, the laser system should be fired and monitored only from remote positions.

An alarm system (e.g., an audible sound or a warning light which is visible through protective eyewear) or a verbal “countdown” command should be used prior to activation.

The audible system may consist of a bell or chime which commences when a pulsed laser power supply is charged for operation, for example, during the charging of capacitor banks. Systems should be used in which a warning will sound intermittently during the charging procedure (pulsed systems) and continuously when fully charged.

In order to safely operate a Class IV laser or laser system, a laser warning system shall be installed.

A laser activation warning light assembly shall be installed outside the entrance to each laser room facility containing a Class IV laser or laser system.

In lieu of a blinking entryway warning, the entryway light assembly may alternatively be interfaced to the laser in such a manner that a light will indicate when the laser is not operational (high voltage off) and by an additional light when the laser is powered up (high voltage applied) but not operating and by an additional (flashing) light when the laser is operating.

A laser warning sign shall be posted both inside and outside the laser controlled area.

Under conditions where the entire beam path is not enclosed, safety latches or interlocks shall be used to prevent unexpected entry into laser controlled areas. Such measures shall be designed to allow both rapid egress by the laser personnel at all times, and admittance to the laser controlled area in an emergency condition. For such emergency conditions, a “panic button” (control-disconnect switch or equivalent device) shall be available for deactivating the laser.

Under conditions where the entire beam path is not completely enclosed, access to the laser controlled area shall be limited only to persons wearing proper laser protective eyewear when the laser is capable of emission. In this case all other optical paths (for example, windows) from the facility shall be covered or restricted in such a way as to reduce the transmitted intensity of the laser radiation to levels at or below the MPE for direct irradiation of the eye. Specularly reflecting surfaces which are not required when using the laser shall be removed from the beam path.

3. Temporary Laser Controlled Area:
Should overriding interlocks become necessary for special training, or during service, or maintenance, and access to Class IIIB or Class IV lasers is possible, a temporary laser controlled area shall be devised, following specific procedures approved by the LSO. These procedures shall outline all safety requirements necessary during such operation.

Such temporary laser controlled areas, which by nature will not have the built in protective features, as defined above for a laser controlled area, shall nevertheless provide all of the safety requirements for all personnel, both within and without the temporary laser controlled area during periods of operation with the interlocks defeated.

K. Optical Fiber (Lightwave) Comminication Systems (OFCS):
Under normal operation such systems are completely enclosed (Class I) with the optical fiber and optical connectors forming the enclosure. Under installation or service conditions, or when an accidental break in the cable occurs, the system can no longer be considered enclosed. If engineering controls limit the accessible emission to levels below the applicable MPE (irradiance), no controls are necessary. If the accessible emission is above the MPE, the following requirements shall apply:

Only authorized trained personnel shall be permitted to perform service on lightwave transmission systems if access to laser emission is required.

Only authorized trained personnel shall be permitted to use the laser test equipment (Optical Loss Test Set, Optical Time Domain Reflectometer, etc.) during installation and/or service.

All unauthorized personnel shall be excluded from the immediate area of access to laser radiation during service and installation when there is a possibility that the system may become energized. The immediate area shall be considered a temporary laser controlled area.

Staring into the end of any broken, severed or unterminated optical fiber or cable shall be avoided.

The end of any broken, severed or unterminated optical fiber shall not be viewed with unfiltered optical instruments (microscopes, telescopes, etc.) An exception to this is the use of indirect image converters such as an infrared image converter or closed circuit television system for verification that a fiber is not energized.

During a splicing operation (either installation or service) if it is required that the ends of the fiber be examined with an eye-loupe for a satisfactory cut, only an eye-loupe containing an appropriate filter shall be used. If a fusion splicer is used, rigid adherence to the appropriate operating safety procedures shall be done.

Guidelines for Laser Safety and Hazard Assessment
Source: Occupational Safety & Health Administration, Guidelines for Laser Safety and Hazard Assessment PUB 8-1.7 (tablular data and equation illustrations have been omitted).