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School of Physics Safety Manual

11. NON-IONISING RADIATION - LASER SAFETY

Laser Safety Organisation

The School Laser Safety Officer (SLSO) oversees all matters concerned with laser safety within the School and liaises with both the University Radiation Protection Officer and with specific Laser Safety Supervisors (LSS) within the School who are responsible for safe Schemes of Work and supervision in their specific areas. Terms of reference for and responsibilities of the School Laser Safety Officer, and Laser Safety Supervisors are contained within University of Exeter Local Rules for the use of Lasers and the Association of University Radiation Protection Officers Guidance on the Safe Use of Lasers in Education and Research.

Risk Assessments must be performed, and Local Rules and Schemes of Work must be written for each sphere of work involving lasers of classes 3B and 4. These rules should be brought to the attention of all employees and students who may be affected by them and should be displayed at each work area. These rules may in the first instance be drawn up by the user of the laser, but they must be approved and ratified by the SLSO and/or the LSS. It is the duty of the Head of School through his SLSO and LSS to ensure that the Local Rules are adhered to, and that all persons working with lasers in his School are properly trained in their use. It is the duty of each person whose work involves a laser to ensure that the Local Rules and safety procedures are adhered to.

Classification of Lasers

All working laser systems purchased from a manufacturer must carry a label stating the class of that system. This should not be removed or altered in any way unless the system is itself modified in such a way as to alter its class. Should this be done, the Laser Safety Service must be consulted over the reclassification of the system. In line with variously agreed national and international standards all lasers are assigned an appropriate classification. The criteria for the assigning of a class to a laser system are complex. A broad indication of the meaning of the class and the implications for the system it describes are contained within the Local Rules for the use of Lasers and the Association of University Radiation Protection Officers Guidance on the Safe Use of Lasers in Education and Research, and are summarised briefly below:

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  • Class 1. Lasers that are safe under reasonably foreseeable conditions of operation.
  • Class 1M. Lasers which are safe under reasonably foreseeable conditions of operation, but may be hazardous if the user employs optics within the beam
  • Class 2. Lasers that emit visible radiation in the wavelength range from 400 nm to 700 nm where adequate eye protection under reasonably foreseeable conditions is normally afforded by aversion responses, including blinking.
  • Class 2M. Lasers as per Class 2 but viewing of the output may be more hazardous if the user employs optics within the beam.
  • Class 3R. Lasers where direct intrabeam viewing is potentially hazardous but the risk is lower than for Class 3B lasers.
  • Class 3B. Lasers which are normally hazardous when direct intrabeam exposure occurs
  • Class 4. Lasers that are also capable of producing hazardous diffuse reflections. They may cause skin injuries and could also constitute a fire hazard. Their use requires extreme caution.

For rule-of-thumb purposes, for continuous-wave lasers, Class 2 lasers are powered below 1 mW, Class 3R lasers between 1 and 5 mW, Class 3B lasers between 5 and 500 mW, Class 4 lasers anything above this power.

Purchase and Installation of Lasers

A central register of lasers is maintained by the University Radiation Protection Service. In order that this may be kept up-to-date, the University Radiation Protection Officer (URPO) must be advised IN WRITING of the arrival of any new laser, and its situation, by the School Laser Safety Officer. The URPO will wish to inspect the installation of any newly-acquired or re-sited laser of class 3B or 4. Any laser manufactured on the University premises must be reported to the URPO before it is made operational, and again when it becomes operational, so that it may be entered on the inventory, and its output and labelling checked.

Before any new laser experiment is performed, or new laser of class 3B or 4 taken into use, a full Hazard and Risk Assessment must be made, and the successful completion of this must also be confirmed to the URPO.

All lasers must bear warning labels, and it is the responsibility of the purchaser or maker to ensure that these are affixed. The University Radiation Protection Service can advise and provide labels where necessary. The required labels are:

  • A "Triangle and Starburst" label.
  • A label stating the class of laser.
  • A label listing any hazards associated with the radiation.
  • A label detailing the output of the laser (wavelength, visible/invisible, etc)
  • A label indicating (preferably with an arrow design) the laser aperture.

The door of any laboratory where a laser of class greater than 1 is installed for use must bear a

"Triangle and Starburst" warning label. If a laser of class 3B or 4 is installed for use, this warning label must in addition bear the legend, "DANGER, laser beam", and the door must bear a notice stating the class of laser present.

No warning label is required on the door of any room where a laser of class 1 or 2 is in use temporarily for setting-up, alignment or demonstration purposes. However, all normal precautions must be taken to avoid accidental exposure of any eye to the beam.

General Rules for the Operation of Lasers

  • Before using any laser, ascertain its class and acquaint yourself with the special rules and restrictions which apply to that class of laser. Ensure that you have studied any Risk Assessment and experimental protocols relating to the laser (these should exist for any laser of class 3B or 4).
  • Under no circumstances may the output of a laser be viewed along its beam-path either directly, by specular reflection or with the aid of an optical instrument. In other words, NEVER LET A LASER BEAM ENTER YOUR EYE.
  • Always ensure that the laser beam cannot extend beyond its useful limit. A suitable beam-stop must be used to prevent the beam from leaving the experimental area.
  • Do not use a laser of a higher class than is necessary for the purposes of the experiment.
  • Do not tamper with an experimental setup in such a way as to negate the safety precautions and beam-limiting devices that have been incorporated.
  • Where an instrument incorporates a laser whose beam-path is protected by shielding and interlocks, DO NOT UNDER ANY CIRCUMSTANCES interfere with or attempt to override those precautions.
  • At the conclusion of an experiment, ensure that the laser is switched off or returned to a safe condition. NEVER LEAVE AN ACTIVE LASER UNATTENDED.
  • Never forget that a laser is a potentially dangerous power-source, and not a toy. Anyone found misusing a laser in any way will be subject to disciplinary action, and may be prevented from further use of lasers.
  • Always remember that you are responsible for the safety of others as well as yourself.
  • Always design and operate experiments in such a way as to eliminate all foreseeable dangers.
  • Guard against other, non-optical hazards associated with lasers, such as high voltage electricity, charged capacitor-banks, toxic chemicals for dye-lasers etc.

Lasers of classes 3B and 4

No undergraduate may have access to, or use, these classes of laser. A hazard and risk assessment MUST exist for every laser of these classes. The design of the laboratory in which the laser is used should incorporate:

  • complete absence of all specularly-reflecting surfaces (e.g. mirrors, glass-doored cupboards, bottles, polished apparatus, beam-path element holders, etc.) that are not an integral part of the beampath or experimental equipment.
  • a high light-level, enhanced by light-coloured walls. This has the dual effect of making the laboratory safer to move around in and of ensuring that the pupils of the eyes of all workers are as far closed as possible to restrict the aperture of the eyes.
  • a light system outside the laboratory door to warn unauthorised persons against entering the experiment zone. These should be interlocked with the laser switching circuitry, and fail-safe in design. A system of interlocked and fail-safe switches on the access doors either to switch off the laser or release shutters to occlude the accessible beam in the event of unauthorised access is desirable, but may not be appropriate in all cases.

All users of these classes of laser must be registered with the University Radiation Service as laser users, and must undergo training in the use of the laser to which they are registered, including the correct operation of safety procedures and interlocks. No ophthalmic testing is required. All new workers must sign a declaration that they have received training and have read and agree to abide by the relevant instructions and rules.

As far as is consistent with ease of use and safe handling, the beam-path of these classes of laser should be enclosed when the laser is in operation. Where this is not possible, guard-rails or screens should be provided to prevent accidental access to the beam. These lasers may never be operated hand-held; they may only be operated when secured in the required position.

The use of laser goggles is dependent upon the particular circumstance. While they can act as a

safeguard, especially for onlookers, they can create a false sense of security, and by rendering a

visible beam invisible can in fact create a hazard. However, when setting-up or aligning an open beam and in all cases when working with beams of wavelengths outside the visible spectrum, the use of the appropriate laser goggles is recommended.

Lasers of these classes must incorporate a key-switch to which only authorised users are issued the key. Keys must not be left permanently in the switch when the laser is not operating.

Laser Pointers

Laser pointers in Classes 1 and 2 will not be subject to registration when used for teaching purposes. Laser pointers in Class 3R must be registered with the University Radiation Protection Service. Registration will be limited to members of staff and Ph.D. and equivalent students whose application is supported by the School. Pointers in these classes have the potential to cause serious irreversible damage to the eye and there are strict rules governing their use (refer to the guidance documentation as before for non-ionising radiation, available from the documentation page of the Health, Safety and Environment Office website.

Laser pointers in Class 3B and abovewill not be registered or permitted for use by the University.

Although most laser pointers are marked with a class number, there have been instances of pointers exceeding the stated class. Also, American classification differs somewhat from the European system. The University Safety Office has equipment to measure the power output of lasers, and will be pleased to help where doubt exists.

Radio-Frequency Heaters

Apart from the risk of electric shock and burns arising from direct contact with the equipment, radio-frequency heating coils are hazardous in that they can induce dangerous voltages and heating currents in neighbouring conductors. Suitable screens should be provided to avoid dangerous voltages being induced in neighbouring metallic equipment which should also be effectively earthed. All metal ornaments such as rings, watches etc should be removed from the hands and wrists when working with radio-frequency heaters.

Ultra-Violet Radiation

Ultra-violet radiation shorter than approximately 340nm is extremely damaging to the eyes. Conjunctivitis generally results 4-8 days after exposure. Ultra-violet sources should always be properly shielded and eye protection worn by those working in the immediate vicinity of exposed sources. The principal sources of UV radiation are ultra-violet lamps, such as those used for sterilisation and electric arc welding.

                                                                                                                                                                                                                                                                       

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