Computer Laboratory

Laser safety

Laser-safety inspection report: TAMPER Lab (room SE09)

Inspection checklist

  • Is the user familiar with the existing local rules and safe working procedures?
  • Is all the necessary documentation at hand (device manuals, safety book, RA, past inspection reports)?
  • Is the user comfortable with the risk assessment, local rules and safe working procedures?
  • Has the user been trained sufficiently?
  • Is the protective equipment (goggles, shields, blinds, etc.) available, adequate and in good condition?
  • Have there been any malfunctions or repairs of the equipment?
  • Have there been any changes in the way the equipment is used or in its environment that might affect safety?
  • Are the controls for beam safety still effective and adequate?
  • Are the controls for electrical safety still effective and adequate?

August 2004

  • The NewWave Quiklaze laser cutter and the associated Mitutoyo FS-60Y microscope have been installed on a low-vibration table with a large metal surface. At the time of the inspection, this surface still had no earth connection.

    An insulation fault in some cable or equipment near the table could connect the table surface with the 230 V supply. If someone then touches it, a dangerous current could flow through the body to earth via the metal panels directly below the carpet.

    ACTION ITEMS:

    • Install a protective-earth connection for the metal-table surface, in order to reduce the electrocution risk for a user working at the table.
      (September 2004: DONE)
    • Ask for PAT to be performed, to verify protective-earth impedance.
  • The laser is powered by a water-cooled unit that is located between numerous other devices below a large metal table. This may make it difficult to quickly detect a water leak that could lead to an insulation failure. The 110-V transformer used is – according to the user – not an insulation transformer. The bus bar supplying the room is not protected by a residual current device.

    ACTION ITEMS:

    • The laser and any other equipment near the metal table should only be supplied via a 30 mA/30 ms residual current device, as a simple additional precaution to reduce the electrocution risk further.
      (September 2004: DONE)
  • The metal table surface is unpolished. Simple tests with Class 2 laser-pointer reflections showed that, even though is is not a really diffusely-reflecting Lambert surface, a red laser beam diverges rapidly after reflection from the table surface. Therefore, the table is not considered to add a significant specular-reflection risk.
  • The laser user has expressed an interest in being able to realign the mirrors inside the laser head, in order to achieve a more uniform power distribution across the exposed target area, for better micromachining results. The existing risk analysis was based on the assumption that the laser will be operated only closed and mounted on a microscope. It will have to be revised for this activity. The user has already suitable protection goggles for this type of laser (LASERGUARD ARGON/Nd:YAG, OD > 7 for all three emitted wavelengths) to protect his eyes, but the laser control area is at present not adequately protected for an open parallel Class 3B beam. There is a window to a court yard with public access, which cannot yet be easily covered. Currently, only semi-transparent blinds are fitted that leave small gaps open near the window frame. In addition, the electrical risks of working on the opened laser head will have to be assessed.

    ACTION ITEMS:

    • Investigate whether fully opaque blinds can be installed, in order to eliminate any exposure risks to people in the court yard during any alignment work with the opened laser. (Being able to fully darken this room may be of advantage for future experiments anyway.)
      (September 2004: Ready-made blinds have been quoted, but would cost over 1500 GBP.) (January 2005: Materials have been purchased to make a fully opaque window cover for entirely darkening the room.) (October 2007: DONE – the move to room SE09, which had already proper laser blinds installed, has solved this problem.)
    • The user should visit the Occupational Health Service for an eye test.
      (September 2004: DONE)
    • The voltages found in the laser head during a pulse and between pulses should be understood before the laser head is opened.
    • The risk assessment and safe working procedure for this laser will have to be updated is the user wants to proceed with trying to realign the laser.

October 2007

The entire laboratory has moved from room GE10 (ground floor) to room SE09 (second floor). This move has improved the laser-safety situation in several ways:

  • There is no longer an accessible court yard outside the window. The nearest views through the windows are from a more than 50 m away building (CAPE) that has no offices facing this way (only a changing room for a clean room).
  • The new room is equiped with fully opaque blinds that can be used to eliminate any laser risk to anyone outside the room.
  • The new room no longer has a glass window in the door.

The laser user has also implemented two additional precautions since the last inspection that should substantially reduce even further the risk of accidental exposure to the beam:

  • The laser user has placed a movable opaque partition wall in front of the low-vibration table, such that there is no direct line of sight between the laser microscopes and the door. This partition can also easily be moved between the laser microscopes and anyone else who might be working in the same room (usually nobody).
  • Since the last inspection, the laser user has installed a safety curtain made from opaque plastic foil (cut from the anti-static bags in which semiconductors are delivered) on the head of the laser microscopes, such that the laser beam is now fully enclosed during the operation of the laser, without interfereing with easy access to the sample.

In addition to the original laser cutter application, there is now a second experimental setup installed in which laser diodes are used to probe semiconductor surfaces installed. The arrangement and type of microscope is very similar to that used for the laser cutter and we have performed a risk assessment for this new application. The resulting safe working procedure and inspecions checklist ended up being practically identical to that for the laser cutter.

The user sees currently no need for realigning the laser cutter, therefore we have postponed writing up a safe working procedure until the need actually arises.

October 2008 – October 2012

No significant changes to the setup.