1
Laser Safety
Where Are We?
Introduction
No laser user wants to receive a laser eye injury or skin burn (well some physicians think of a minor laser finger burn as a rite of passage). This statement is like saying none of us want a speeding ticket, yet we all keep on exceeding the speed limit. So how is our laser safety gene doing? If we are honest with each other, the answer is we could be doing better, but that takes effort and not all laser users see the need for such effort.
A Safety Culture
A survey in 2005 stated that 70% of U.S. drivers wear their seat belts. While this statement seems far removed from laser safety, it really is not. For the survey results demonstrate a cultural shift that took years to take root. Now people expect drivers and front seat passengers to be wearing a seat belt. Law enforcement has started giving tickets rather than warnings for those who are not wearing their seat belts. Child safety seats are similar in usage today. One day bus riders will buckle up.
Getting back to laser safety, what the survey above represents is a cultural change. One that laser safety is in the midst of, group responsibility over individual safety. Another analogy is smoking; the concern over secondhand smoke exceeds the argument that it is my lungs and if I want to smoke I will. We will not even go into health-care costs related to smoking. For years one could enter a laser lab and if they were smoking, everyone would protest due to the concern of particulates on optics, with no concern to the individual’s safety. Yet one could enter the same laser use area and not put eyewear on and few would say a word of warning or protest. The environment is one in which each person makes their own risk decision. If eyewear is required in a laser setting, all in the room or in hazard zone need to be wearing eyewear, and it is the responsibility of all in the area to make sure anyone entering puts on eyewear, not to leave it to a matter of personnel choice.
ANSI Z136.8 Safe Use Of Lasers In Research, Development, And Testing
The publication of the Z136.8 standard is a positive step in a laser safety culture. Why? It is the first laser American National Standards Institute (ANSI) standard that addresses many of the real-world situations found in the research setting, regardless if it is academic or commercial product development setting. It needs to be adopted by any institution that is engaged in research.
Laser Incident
What follows is the official report on a laser incident that occurred at a U.S. government research lab. At the end, you will find my interpretation of the incident, why it occurred, and how it could have been avoided. This case study demonstrates a number of important points that will be built on in later chapters of this book. Even a novice to lasers and laser safety, on review of this incident, will see areas for improvement and, more importantly, where a lack of safety awareness or concern contributed to the incident (Figure 1.1).
Figure 1.1
Laser lab setup.
Accident Description From Initial Accident Report (Source: Department Of Energy, 2005)
At approximately 12:00 pm, Wednesday, January 19, 2005, a researcher sustained a laser injury to his right eye while working in Solar Energy Research Facility (SERF) Lab E-218.
The light involved in this incident is generated by a neodymium:yttrium aluminum garnet (YAG) laser–driven optical parametric oscillator (OPO). The light exiting the equipment housing has a wavelength of 750 nm and a power of 200 mW/20 mJ. The light beam exiting the laser/OPO unit is noncoherent (i.e., divergent), so it is not a true laser beam. However, it does produce very high pulsed energies that present the same hazards as a laser beam and is managed as a laser accordingly. The beam is attenuated to a power in the range of 200 nW/20 nJ through the use of neutral density filters with optical density (OD) ranging from 3.0 to 7.0 before contacting the samples being tested to not overpower the samples. A more powerful than necessary laser/OPO unit is used for this work since it is tunable to the wavelength needed for the sample tests. The power level of the attenuated light beam is unlikely to cause an eye injury; however, laser safety glasses are required whenever the unit is operating.
Other standard laser safety controls are also in effect for this activity, such as an automatic beam shutter that is interlocked with the lab entry doors, beam blocks, and nonreflective surfaces.
The light beam is used to excite carrier pulses in semiconductor systems, solid-state devices, and photovoltaic cells. Instrumentation records the minority carrier lifetime characteristics of the samples being tested, the primary objective of this activity. The samples are mounted in a target box, which is a box providing light and radio frequency shielding of the sample (i.e., the box is not necessarily a safety control, although it does enhance the safety of the activity). The laser/OPO unit and target box are mounted on a standard laser table and are situated about 6 ft. apart. The light beam is open to the lab in between the laser/OPO housing and the target box with the beam shutter and attenuating ODs situated in between the two.
At the time of the incident, a researcher (R1) and his team leader (TL) were testing new sample instrumentation. When there was an apparent problem with the new instrumentation, the TL went to another part of the lab to obtain a different test sample.
Initial investigation findings indicate that while this was occurring, R1 removed the neutral density filters in an attempt to obtain a response from the test sample. Removal of the neutral density filters resulted in full beam power onto the test sample.
(At some point during this process, R1 removed his laser safety glasses.) R1 then manipulated the test sample with a pair of stainless steel tweezers in a further attempt to obtain a response from the test sample. At this point, R1 reports he experienced seeing a flash of light off of the surface of the test sample. He states that he did not feel any pain or sensation when this happened. He then noticed dark floaters in his field of vision (right eye) on looking up at a scope located on an overhead shelf.
The worker informed his team leader of this condition. Both reported to Medical Services where R1 described his symptoms as seeing floaters and a yellowish-orange spot in his upper field of vision. The worker was transported by his team leader to Denver Eye Surgeons for medical assessment and treatment. The initial report from Denver Eye Surgeons is that the worker sustained a 2-mm retinal burn and is being referred to a retinal specialist for examination and treatment as necessary. Denver Eye Surgeons administered a steroid injection to reduce inflammation and swelling.
A follow-up examination was conducted on Monday, January 24, 2005. The size of the damaged eye area has reduced from the initial 2-mm burn to a 500-mm wound in the top layer of the retina and a 200-mm wound in the second retinal layer. The swelling and inflammation immediately following the incident may have slightly distorted the initial damage estimate.
The preceding is the official accident report submitted a few days after the event. Now let us take a closer look with a little more informative description and uncover a few additional details.
At approximately 12:00 pm, Wednesday, January 19, 2005, a worker sustained a laser injury to his right eye while working in SERF Lab E-218. Contractor is a grad student, who has been at the laboratory for 3 years. He was working in a two-person lab, principal investigator (PI) and himself. Experiment involved decay elements and exposure to radio frequency. Laser protective eyewear is used in this lab. The use of an oscilloscope is critical to this project. The oscilloscope can be read with laser protective eyewear if one is close to the scope. Unfortunately, if one is near the experimental setup, the oscilloscope is difficult to read. The setup was well established and consisted of a combination of open and closed beam portions. The PI had left the room to obtain another sample. The student was pulling out beam attenuators and reached in to remove the target. He received a reflection off the target onto his right eye; he was not wearing his laser protective eyewear for he was viewing the oscilloscope. The equipment in use at the time of the incident incorporates a Class 4 YAG laser. The wavelength being used was 750 nm and a power of 200 mW/200 nJ attenuated to 200 nW/20 nJ used to illuminate a sample. Standard operating procedures consisted of a number of boilerplates, and do’s and don’ts around lasers. Laser safety training at facility is computer based. At this time, no record of the student’s training can be found. Also it is uncertain if the laser safety officer (LSO) performed any assessment of the setup. The LSO is primarily an industrial hygiene. The senior researcher and facility Environmental Health and Safety (EH&S) point of contact are required to review the paperwork once a year. In this case, that is the LSO.
The light beam is used to excite carrier pulses in semiconductor systems, solid-state devices, and photovoltaic cells. Instrumentation records the minority carrier lifetime characteristics of the samples being tested, the primary objective of this activity. The samples are mounted in a target box, which is a box providing light and radio frequency shielding of the sample (i.e., the box is not necessarily a safety control, although it does enhance the safety of the activity). The laser/OPO unit and target box are mounted on a standard laser table and are situated about 6 ft. apart. The light beam is open to the lab in between the laser/OPO housing and the target box with the beam shutter and attenuating ODs situated in between the two.
At the time of the incident, a researcher (R1) and his team leader (TL) were testing new sample instrumentation. When there was an apparent problem with the new instrumentation, the TL went to another part of the lab to obtain a different test sample.
The investigation team determined that a reflected light from a laser beam to the right eye was the direct cause of the injury. The root and contributing causal factors and area for improvement are briefly summarized here.
Root Causes
The grad student removed his laser eye protection (LEP) part way through the activity, in direct violation of an established work procedure.
The work planning for this activity by the RI and grad student was less than adequate.
Management and supervision of laser activities was less than adequate, both for this specific activity and for laboratory-wide activities.
The hazard controls established in the safe operating procedure (SOP) for E-218 were less than adequate, and the processes for reviewing and updating all laser activity SOPs were less than adequate.
The roles and responsibilities of the LSO may not meet current consensus standards and the LSO resources available to support laboratory activities may not be adequate.
Laser safety training is less than adequate based on the demonstrated performance of staff, and improvements to the training record keeping processes are needed.
Reliance on laser protective eyewear is being utilized where additional engineering controls may be reasonable and appropriate.
Figure 1.2 is an image of the laser lab. Figure 1.3 shows the two pairs of laser protective eyewear worn in the lab. You should be able to pick out a number of good practices that are missing. Before any discussion of those and ways to improve the setup, look at the number one problem.
Figure 1.2
View of oscilloscope in lab.
Figure 1.3
Eyewear used in lab.
Problem Number 1
This experimental setup was close to a year old, but still looked very much like it did on week 4. I am sure even the users who were the developers of the system felt it could be laid out better. To make the necessary changes would mean taking some time away from the actual work. Here is where the critical fault lies. No one thought his or her or anyone else’s safety was worth the day it might have taken to reconfigure the experimental setup.
Additional Issues
No safe means was set to allow the laser to stay on while samples were changed. A possible solution would be a shutter, or even a beam dump could have blocked the beam and allowed safe sample exchanges.
I have used this accident as a teaching exercise (I only wish it was hypothetical, rather than a true case). Following is a list of comments from my students:
Student should not have been left alone
Beam was open on the table
Clutter on the table
Poor cable management
Oscilloscope should be relocated
Oscilloscope fine where it is
Use of shiny tweezers
Laser emission light out
Standard operating procedures too generic
Poor eyewear choice
Lack of warning sign
Poor understanding of hazard
I am sure you might have some additional information that will explain some of the preceding comments.
My Spin On Why This Happened And How Simple Steps Could Have Avoided The Accident
During setup of a project or initial proof of principle, safety is not always a high priority. Organizations where safety is an integral step of any project are far ahead of the safety curve. In the accident described earlier, the simple fact is at no time did anyone consider it worth the time of effort to reevaluate the experimental setup or ask can we do this in a safer or more efficient manner.
Why did the beam path have to be completely open? Why not the system be shut off during sample change or a beam block to alternate path been setup during the change process? An interlock or mechanism could have been put into place to prevent one from removing the neutral density filter. For that matter not only could the oscilloscope have been relocated, but better eyewear could have been acquired, allowing visibility.
The answer to all these questions is not things were working so why mess around with it. So let us ask again were things really working or had random chance just not caught up with them.
Making Laser Safety Easier
Now the question is how one makes laser safety easier, an article the author wrote for SPIE Professional magazine helps point us in the right direction. Building on that article, following are five steps to help reduce the odds of a laser injury or incident.
On-the-Job-Training
Today every institution where Class 3B and Class 4 laser use is present has some requirement for fundamental laser safety training. The driver for this training may be from fear of regulatory bodies, compliance with ANSI Z136 series requirements, or just doing the right thing. How much can we expect from this laser safety introduction? It should make the user more aware of potential laser hazards, maybe more inclined to follow laser safety rules. The truly critical laser safety training is onthe-job-training (OJT). Effective OJT and mentoring is the most proven means to prevent or avoid a setup leading to an accident. The trainer needs to have the patience to explain the setup, what the goal is, and what problems they have encountered. The trainer should also explain the sources of known reflections, non-beam hazards, and how to use safety tools such as viewers and eyewear. The trainee needs to be observed doing tasks, even if they were hired as the expert on the equipment, at the very least to evaluate their safety culture. The trainee also needs to feel they can ask questions and receive supportive responses. The mentor’s or trainer’s body language can unknowingly discourage any further questions. Both parties need to be in agreement prior to letting the new users’ work unsupervised. See Chapter 4 for sample forms to document OJT. OJT depending on the task or system is usually more than a 1-day operation. Much also depends on the experience of the one being trained. However, neither should be in a rush to get the job done. For our goal is confidence in getting the task performed by all parties and a safe operation; see Chapter 10 for greater insight and explanation.
Housekeeping
Numerous laser incidents can be traced to poor housekeeping. Laser housekeeping is not the childhood activity of hiding everything under your bed or now optical table, but rather setting time aside to keep work spaces (optical table and work area) clean. By clean I mean free of unused tools, equipment, reflection sources, cleaning solvents, storage boxes, and so on. Granted space is an ever-present problem as well as the time to clean, storage lockers, and shelves over the optical table can help. Setting a dedicated day and time to clean in your schedule is the best proven solution (once a month, once a week is better). Waiting for that open afternoon in your schedule will never happen. The best solution is to try incorporating housekeeping into your daily routine. Address problems as they arise. This will make housekeeping a less daunting task. The more clutter you have from things you might need one day to just excess optics on the table sends a subliminal message to observers and funding sources. The message is if the work is performed in such a disorganized mass how good can their science be? How reliable are their results?
Maybe what the industry needs is an equivalent to a Merry Maids cleaning service, Optics Dusters are Us. Now there is a business opportunity for you.
Look for Stray Reflections
In reviewing laser accident reports in the research and academic environment, the most common scenario is the lack of eyewear usage during laser alignment. A number of these cases involve a failure to look for stray reflections. A 1 mW/cm2 (continuous wave) in the wavelength range of 400–1400 nm equals 100 W/cm2 at one’s retina. This is about the maximum one’s eye can tolerate. It is easy to see (excuse the pun) that the typical 4% reflection off an uncoated optics could easily be above the safe threshold. As a reminder, the macula/fovea portion on one’s retina where 400–1400 nm light is focused to is the critical vision portion of your eye. Hence, as alignment is performed, one needs to go optic to optic and be checking for stray reflections at each. Beam splitters have been involved in several accidents when the user forgot to block the unneeded split. This is why the use of remote viewing and motorized mounts should always be encouraged and considered, especially as a system matures from proof of principle to routine operation.
Contain Reflections
Following from preceding step, if stray reflections are identified or expected, containment or blocking those reflections is critical to preventing laser accidents. Sometimes it is as simple as placing a card behind or above an optic in a mount. The author has encountered incidents where users have a known unblocked reflection that seems unlikely anyone will be in front of, because the angle is too steep or the power is too low to cause injury. In each case, some circumstances arose that placed someone in danger or the output was higher than believed. In conclusion, beam blocks, perimeter guards, table enclosures, and beam dumps all add to your safety and those around you. USE THEM!
Eyewear
Finally, I would be banished from the U.S. laser safety community if I did not mention laser protective eyewear. It is fitting that eyewear be mentioned last. They are not your first line of defense but rather the last. It is the four steps mentioned earlier that provide the real safety. Laser eyewear is like a seat belt, if all road rules and conditions are followed it will never be needed but if any fail it might save your life. Your laser eyewear is your seat belt. We have two types of eyewear:
Full protection: This has a sufficiently high OD to block any direct or stray beams and should always be used with invisible wavelengths.
Alignment eyewear: This should be used with visible beams when they need to be seen.
Today with new filter and styles of laser eyewear, one can be found for just about all applications.
Summary
This chapter discusses a real-life incident and five areas where laser safety can be addressed. This should give one sufficient food for thought to allow them to revisit their own laser use area and find ways to make it safer. If not, read this chapter again.