Laser eye injuries are an integral part of the history of lasers, but with a cultural change among experimentalists, that need not be the case.
- Laser Safety: Little Mistakes with Big Consequences
Ken Barat, Lawrence Berkeley National LaboratoryOne cannot help but wonder why laser eye accidents have not diminished as laser technology has matured. Why have these injuries not been eradicated, like smallpox? Surely the biological and psychological causes are known, yet every year there are dozens of new injuries.
This retinal burn, caused by a Nd:YAG rangefinder, resulted in nearly complete vision loss.
The answer, of course, is the carelessness that accompanies familiarity with medium- and high-power lasers. This is particularly true in academic and high tech R&D environments, where experiments are quickly assembled and success depends more on ingenuity and inventiveness than on adherence to safety rules. Every laser user this author has encountered over the years, has jettisoned his or her protective eyewear, or bypassed some other common safety precaution in an effort to get work done in what appeared as a faster or more efficient manner.
Yet an examination of the record of laser accidents reveals that, in virtually every case, the injury results from a carelessly taken shortcut, a shortcut taken by someone who should know better but in the interest of expediency, takes an unnecessary and ultimately very costly risk. The most common shortcut involves the misuse or nonuse of eyewear. Laser protective eyewear is accused of being uncomfortable to wear; interfering with peripheral vision; reducing visibility and of blocking the exact wavelength that the user needs to see, that is, the wavelength of the laser. All these accusations contain a grain of truth, but no more. Laser-safe eyewear is available in dozens of designs to minimize the discomfort and with new filters to yield greater clarity. And while eyewear necessarily attenuates the wavelength of the experimentalist’s laser, the knowledgeable laser-safety officer can recommend controls, i.e., remote viewing, or eyewear designed for laser alignment, which provides protection while still allowing visualization of the beam.
Nonetheless, the failure to use protective eyewear is the common denominator of almost all laser eye accidents. Consider the following five cases, four at institutions within the Department of Energy complex, where lack of eyewear, often coupled with other mistakes, has resulted in dramatic effect, not only to the individual, but also to the project and in some cases to the entire institution where the accident happened.
Note: Since the original publication of this article (2005) DoE facilities have been laser injury free (several documented near misses have occurred); the same cannot be said of academic research institutions.
A student suffered permanent vision loss by looking directly into the target chamber of a laser experiment without safety eyewear (recreated here). The injury resulted in a multiweek shutdown of all scientific work at the lab. Be conscientious that violating laser safety protocols poses not only a risk to the individual, but also a severe imposition to one’s colleagues.
Los Alamos National Laboratory July 2004
On July 14, 2004, an undergraduate student was injured at Los Alamos National Laboratory (LANL) while working with two flash-pumped, Q-switched Nd: YAG lasers. She and the LANL scientist mentoring her were using one of the lasers to generate and suspend particles inside a target chamber, and the other laser to monitor the suspended particles. The two beams were perpendicular to each other, the particle-generating beam propagating vertically and the particle-monitoring beam propagating horizontally. The scientist wished to view the suspended particles in the chamber, so he disabled the Q-switch of the particle-monitoring laser but left its lamps flashing to illuminate the interior of the target chamber. He peered into the chamber off axis, saw that the first laser was creating the particles, and invited the student to look. When she viewed at a direct line of sight, she immediately saw a flash and a reddish-brown spot in her eye. The injury was subsequently diagnosed as laser-induced: the laser had vaporized a 400 x 250 micron hole through her fovea and into the chorid layer.
Neither the scientist nor the student was wearing protective eyewear at the time of the accident. Apparently they assumed that the particle-monitoring laser was disabled and failed to confirm this condition. Although the exact condition of the particle-monitoring laser at the time of the accident is unclear, it obviously was not disabled. Nor was its perceived safe mode confirmed prior to viewing.
The student’s retinal cells will not regenerate and she has suffered a permanent loss of approximately one third of her fovea, the critical vision area, of her left eye. Beyond the physical injury to the student, this accident helped precipitate a multimonth shutdown of all scientific work at LANL.
It would appear that the major mistake that led to this accident was the experimenters failure to check if the disabling of the Q-switch was effective and had blocked any laser radiation from being produced. The accident could easily have been avoided if the experimenters had set up a CCD camera to observe the chamber, instead of putting their eyes at risk.
In one incident, a misaligned laser crystal resulted in an eye injury, lost work and a labwide shutdown. The accident could have been prevented with the use of safety eyewear or remote monitoring of the experiment. Be aware of the potential hazards in an experimental setup.
Brookhaven National Laboratory
In September 2003, two Brookhaven scientists were aligning an Alexandrite laser to excite fluorescence from a crystal in a target chamber when one of them sustained a permanent eye injury. One scientist observed the fluorescence as the other adjusted the laser. The individual observing the fluorescence did not wear eyewear. A slight misalignment of the laser caused its beam to miss the crystal entirely and emerge through the observation port. Unfortunately, the scientist viewing in was using a mirror to observe the fluorescence, and unwittingly swept the beam across both his eyes. He suffered hemorrhaging and permanent vision impairment in both eyes.
The injured scientist was unable to work for a month, and although there has apparently been some recovery of vision, he is still able to read only with difficulty. In addition to the personal injury sustained, the accident resulted in a multiweek halt of all laser-related work in the scientists’ division while an investigation was conducted.
The most obvious error in this incident was the lack of protective eyewear. Although eyewear that blocks in infrared Alexandrite radiation while passing most of the visible spectrum is available, an even safer alternative would have been to use a CCD camera to monitor the fluorescence.
The failure to wear protective eyewear is the common denominator in most laser eye accidents. Do not assume that an experimental setup is safe. Be sure to block all potential stray reflections from an optical bench, especially those leaving the horizontal plane of the setup.
Argonne National Laboratory, Advanced Photon Source
Observing fluorescence is just one of many reasons that experimentalists find to remove their protective eyewear. In September 2004, an experienced laser experimenter at Argonne National Laboratory, suffering from a slight eye infection, raised his protective eyewear momentarily to rub his eye. At that moment, he experienced what looked to him like a bright flash, and afterward the vision in his left eye was cloudy. A subsequent examination revealed he had experienced a laser burn of the retina. A polarizer on his optical bench (which should have had it’s upward reflection blocked) had reflected the beam of a Ti:sapphire laser into his eye.
Although his vision has returned nearly to normal, all laser operations at Argonne’s Advanced Photon Source were suspended for several weeks and an extensive investigation was conducted of the entire laser safety program.
In addition to the usual eyewear error, a second error was involved in this accident. A careful experimentalist blocks all stray reflections from his optical bench, especially those that leave the horizontal plane of the experiment. In this case at Argonne, it was an unblocked beam, angling up from the optical table, which caused the injury.
University of California, Berkeley Campus
An unfortunate habit adopted by some experimentalists is to strictly adhere to laser-safety rules when setting up an experiment, but to relax their vigilance once the experiment is running and “safe.” That was the case when a Berkeley graduate student sustained an eye injury from a Nd:YAG laser in March 2004. He had carefully worn eyewear in the afternoon when he set up the experiment, but when he returned to take some data after dinner he didn’t bother with eyewear because, he felt, there were no exposed beams that posed any danger; since the system is aligned. Leaning over the optical table and making a slight adjustment to a power meter, however, he saw a flash and heard a loud popping sound. He sustained a serious injury to his left eye. Checking for stray reflections while aligning or prior to removing his eyewear could have avoided his injury.
The student still experienced some vision impairment months after the accident. Moreover, this accident led to a prolonged investigation and a significant decline in funding for the research group.
A cultural change among experimentalists is required to make laser eye accidents, such as this retinal burn from an Nd:YAG, a thing of the past.
Argonne National Lab
Although careless workers can sometimes emerge from laser accidents with little or no long-term vision impairment, they are not always so lucky. While manipulating the 800-nm beam from a Ti:sapphire laser with a mirror in October 2001, an Argonne scientist with over 15 years laser experience suffered a serious eye injury when the beam hit his unprotected eye. His vision went from 20/50 before the accident to near-blindness after, and even years later he cannot read large print.
How can we prevent laser accidents? Nothing short of a fundamental cultural change among laser experimentalists will be required. Such a cultural change would not be unprecedented. Forty years ago, seat belts were almost universally dismissed as an unwanted intrusion into the traveling experience, even though many cars came equipped with them. The use of laser eyewear has not fared as well during the same forty years, but a similar modification in behavior and sentiment is essential. Some of the day-to-day activities that can lead to such a change, and that can result in much greater safety in laser laboratories, include:
• Co-workers should challenge those who do not use laser protective eyewear.
• Treating evaluation for possible hazards as second nature, not as an afterthought.
• Safety professionals using reports of past accidents (lessons learned) to show how adhering to good practice could have prevented the injury.
• Reinforcing the consequences of an incident to the user and entire group so that users understand the impact they may impose on others as the result of a violation of laser safety protocols.
Meet the author
About the Author: Ken Barat is the Laser Safety Officer at the Lawrence Berkeley National Laboratory in Berkeley, California. firstname.lastname@example.org