Laser Accidents – They Do Happen!
This past summer in United Kingdom, at least three serious laser accidents in universities were reported. Unfortunately, the laser workers involved in these accidents have all damaged their eyesight. It is not known yet whether persecutions are pending, but these incidents will not put these universities in a very good light with the regulatory authorities and the public. The following is a report* on one of these accidents in which the laser worker lost the central vision in one eye.
A Laser Accident - The Perils of Not Following Safety Procedures
Late one August afternoon in a British university, a postgraduate student was aligning two lasers at different wavelengths that had been set up in a relatively new configuration. The beam from a dye laser (720 nm, 10 mJ, 10 ns pulse at 10 Hz) was passed through a dichroic mirror coated for high reflection at 266 nm in order to combine it with the beam from a fourth harmonic Nd:YAG laser (266 nm, 50 mJ, 10 ns pulse at 10 Hz). This configuration resulted in a partial reflection from the rear of this mirror (approximately 5% of the dye laser beam) in an upward direction. Temporarily forgetting the presence of the stray beam, the person on leaning over the top of the apparatus received a single pulse of light from the dye laser reflection. This immediately left a blind spot in the central vision in one eye. The person was not wearing protective eyewear as it was claimed they could not see the beams that were being aligned. The experiment was shut down and the person was accompanied to the local hospital Eye Unit. On examination the person was informed that there was a small burn on the fovea and that he would be referred to somewhere else with the expertise to handle laser-induced eye injury as a matter of urgency.
As to the absence of beam enclosures – drainpipes has been used previously however because of the orientation of the experiment being changed these had not been re-incorporated at this stage. The source of the reflection has allegedly been identified prior to the injury and this has been listed as an action to do by the injured person.
There was some concern with regard to the examination and advice received from the local hospital Eye Unit. It was concluded that the most appropriate action was to get the injured person to a hospital (with the expertise to handle laser-induced eye injury) in another city as soon as possible to obtain a second examination. It was confirmed that the fovea had been damaged leading to a blind spot and peripheral blurring in the left eye. Due to the nature of injury, further eye examinations have been carried out since the accident and it is likely that more visits may be necessary over the next few years.
Laser users and supervisors need to be reminded of their responsibilities for operating safe systems of work when working with high power lasers. Good training and the use of protective eyewear are essential.
Risks assessments need to be scrutinized, monitored and audited so that they are suitable and sufficient. Especially three elements related to the optical hazard need to be covered (i.e. initial set up/alignment, normal operation/tweaking and the introduction of new components) and protocols detailing precautions needs to be in place. Appropriate justification of procedures outside of conventional guidance need to be documented. Associated hazards need to be dealt with also.
The importance of following procedures, such as eliminating stray beams/reflections and enclosing exposed beams as far as reasonably practicable needs to be strongly re-emphasized. Human factors need to be taken into account especially where there may be hazardous open beam work; in this case an eagerness to get results may have been a contributory factor.
Procedures in the event of an injury or suspected injury need to be in place and effective. It is worth considering whether or not it is best to send persons with eye injuries directly to the hospital with the expertise rather than to the local Eye Unit that may have not experience of laser eye injuries. In most laser eye injuries there is not a lot that can be done to rectify damage; it is essential that competent examinations are carried out as soon as possible and within 24 hours of the injury. Emergency procedures in place need to be checked as to whether they are appropriate (all Class 3b/Class 4 laser users and their supervisors need to be aware of what to do).
Safety Reminders for HKUST Laser Users
- Register lasers systems (Class 3a or above, except for laser pointers) with SEPO
- Compile an Operational Safety Procedure (OSP) for the operation
- Ensure operators attend general laser safety training offered by SEPO
- Have supervisors conduct hands-on, operational-specific safety training
- Use beam-path enclosures and beamstops wherever applicable
- Set up laser table at waist level
- During alignment, use the following:
- Use a visible low-power laser as tracer
- Start with lowest power possible
- Use viewing device (e.g. fluorescent card) for invisible beam if practicable
- Wear appropriate eye protection whenever possible
- Understand that there may be additional potential hazards (electrical, chemical, mechanical, and fire) in a laser laboratory
Finally, it is safe to say that, in most laser accidents, safety procedures are already in place. It is unfortunate that these accidents did happen. These accidents are all avoidable if safety procedures are followed. This fact cannot be over-emphasized.
*The information on the laser accident was adapted with permission from the December 1999 issue of the AURPO Newsletter published by Association of University Radiation Protection Officers.