The 9 Essentials of Laser Safety
The laser has swept across modern society. New applications and techniques arise every month in journals and trade publications. Power outputs are now at a range never envisioned before, ranging up to 300 kW for industrial and weapon applications. Open beam applications such as LIDAR, facial recognition, and retinal scanning are now common, and diode-fiber applications are ever increasing. Thus, laser safety is extremely important to both the developer and user community. We have to address both real and perceived laser hazards.
Visible lasers, especially in the green spectrum, can cause uneasiness and apprehension, even when they emit below the threshold where they might cause injury from glare or flash blindness. It is important that people are educated about the proper use of lasers and associated risks.
|Class||Output||Application||LSO / Laser Safety Program|
|Class 1||<0.39 mW visible||Nanolasers||No|
|Class 1 Product||Higher class laser, but embedded so no hazard exists during normal operation||Laser printer, microwelder||During service, possible need exists|
|Class 1M||Invisible wavelengths; safe for viewing, unless viewed by optical instruments||Free-space communication||Depends on application and location accessibility|
|Class 2||<1 mW visible||Laser pointer, bar code scanner||No|
|Class 2M||Visible wavelengths; safe for viewing, unless viewed by optical instruments||Free-space communication, some interferometers||Depends on application and location accessibility|
|Class 3R||1-5 mW, continuous-wave visible; safe for momentary viewing||Most green pointers||No|
|Class 3B||5-500 mW continuous-wave; cannot produce 125 mJ/pulse in less than 0.25 second||Spectrometry, alignment||Yes|
|Class 4||>500 mW continuous-wave; cannot produce greater than 125 mJ in less than 0.25 second||Industrial lasers, laser weapons||Yes|
Laser safety comprises a mixture of compliance and risk awareness. If a lab or company is using Class 3B or Class 4 lasers (those with the potential to cause harm to someone or damage equipment), the compliance requirements are rather straightforward. Most facilities focus on these compliance items and leave risk abetment to users. To mitigate potential risk, users should:
- Use beam blocks
- Keep beams on the optical table
- Use enclosures
- View remotely
- Wear proper eyewear and respect barriers
- Perform on the job training
- Follow alignment procedures.
So, what are the critical laser safety elements for both safety and compliance?
1. A laser safety officer (LSO) is a must.
Although the vast majority of LSOs work in that role only part time, someone has to bear responsibility for laser safety. The LSO is the person any regulatory inspector is going to ask to see and is expected to perform all LSO duties. The best LSO is someone who helps come up with solutions and suggestions to assist the user in their efforts. This can include better eyewear, improved detection devices, enclosure options, etc. Critical responsibilities of the LSO are:
- Make sure laser safety training is relevant to actual laser work and risk
- Assist in laser eyewear selection when eyewear is needed
- Review hazards and see that effective control measures are in place and functional
- Review any required documentation.
For a part-time LSO to be effective, management must be supportive and allow them the time to do their job.
2. Cover all the bases of laser safety training.
There are two types of laser safety training. From a regulatory and standards point of view, all Class 3B or Class 4 users, or those with potential exposure, need a basic awareness training. I call this institutional training. However, duration and quality of such training varies considerably. An effective training presentation needs to be customized to address laser use at the facility; a canned presentation will not suffice.
The second and more critical laser safety training is a documented on-the-job training (OJT) or mentoring. Everyone should get an orientation to the laser systems they will be working with, as well as site-specific safety (where reflections come from, what not to touch, etc.). Documenting the training with a signature of both trainer and trainee will not only protect the institution, but make everyone take the training seriously. OJT training should not have a preset timeframe and can also be augmented by ongoing mentoring.
3. Evaluate, analyze, and mitigate the hazards.
From a safety department perspective, all accidents are preventable. However, users cannot eliminate all risk. The LSO is tasked with finding a balance between these two philosophies. In industry, laser safety is almost always engineered into the product, whereas in medicine, laser safety is dependent on a checklist system. Fabrication approaches laser safety somewhere in between these two poles. In research, such as a lab, all bets are off, because beam manipulation is the routine activity rather than a rarity, which is why beam enclosure, beam detection, beam blocks, perimeter guards, good work practices, and eyewear are so critical to reducing risk.
In addition, users must be expected to follow correct work safety protocol. Each time someone peaks under their eyewear and nothing happens it just reinforces that bad practice. Anyone who sees this sort of behavior is obligated to say something. On the other hand, the LSO needs to remember that very restrictive controls will drive users to find workarounds. It is important to find the balance between safety and risk. "Safety through cooperation" needs to be the mantra.
4. Wear appropriate laser protective eyewear.
While laser eyewear should be the last line of defense, it is the first protection people think of. However, as power outputs have gone up and systems have the potential to produce a wide range of wavelengths, useful eyewear becomes more of a challenge. For some systems, the reduced visibility from protective eyewear makes the system nearly unusable. Frame comfort can also be an issue, including weight, limitations on peripheral vision, and ability to wear in a cleanroom setting. If one needs eyewear with an optical density (OD) of 7 or greater, eyewear should be replaced with remote viewing or motorized mounts. In the future, the best solution will be eyewear with an opaque face plate and a smart-phone-style camera displaying the field of view either directly on the retina or on a heads-up display. But until technology catches up, eyewear selection will need to take into consideration items like OD, visual light transmission, fit, acuity, and lighting conditions during use.
5. Control access.
The laser standards (US or IEC) all call for some type of access control to keep the unapproved out of harm's way. Access control to a Class 4 use area is one of the most greatly misunderstood laser safety standards, and there are several ways to accomplish it.
The first option is a nondefeatable system, meaning that whenever the entryway door is opened, the laser falls to a safe condition, via a shutter blocking the beam or powering off. However, no one likes this option—it's too hard on equipment and users' hearts.
The next option is a defeatable interlock. Here, approved users commonly have a swipe card, key pad, secret word, or some means for them to enter without interrupting the laser system. This is the most common approach. In reality, entryway interlocks are more for management's peace of mind than protection of users, because unless the system produces ionizing radiation, interlocks do not protect the authorized users from harm.
The last and broadest option for access control is an administrative approach. This can be as simple as a sign (common for operating rooms) to an electronic lock that just keeps people out but is not connected to the laser system. These systems can also be tied to training databases, whereby permission will only be granted to those who have up-to-date training. However, this option is costly and not common.
6. Post warning signs.
While warning signs are informative, we all know they become invisible over time. The purpose of the warning sign is to mark the boundary of safe from non-safe zone, termed Nominal Hazard Zone or Nominal Ocular Hazard Distance. These signs should inform people what hazards they may face going forward, including OD and wavelength, and what protection may be needed.
What about illuminated signs? The major issue with these is that the majority are connected to the laser power supply, meaning as soon as the laser is turned on the light comes on. But just because the system is on, doesn't mean the beam is accessible and therefore harmful. The beam could be blocked, such as during a warmup period. Hence, in many cases the illuminated sign is on all the time, and they become as invisible as warning signs on the door. Despite their limitations, their operation should be part of laser safety training.
Two alternatives to connecting to the power supply are to tie to a shutter or have a multi-status sign. The incorporation of flat screens into interlock systems allows visualization of not only laser status, but also active locations in the room. Another option is scroll illuminated lights, where the message moves across the face of the sign or the sign blinks. Their activity produces a greater chance of catching one's attention and being read.
7. Complete all the paperwork.
Every laser safety program requires a certain level of paperwork. A laser safety chapter in the Environment, Health, and Safety Manual describes the elements of the laser safety program and required forms. They include:
- The standard operating procedure (SOP): The SOP has been part of laser standards for many years. Today the SOP can take several forms, from a traditional SOP outlining hazards (including nonbeam) and mitigation steps, to a risk analysis document.
- Training documentation: Training requires training records—the phrase "not documented, not done" is still as true today as when first said.
- Audits: Laser standards also call for periodic audits to determine if control measures are in use and still functional.
- Other: records of interlock tests, retraining records, user signatures on SOPs, etc. The list goes on as you finetune the elements of your program.
8. Drop the medical surveillance.
Long engrained in laser safety programs is the baseline eye exam, which actually has not been part of laser safety standards since 2007. That's right, it is no longer required. An eye exam is only required when an injury is suspected. Some firms have dropped the baseline while others have kept it, falsely thinking it gives some liability protection, or afraid removal will show a lesser commitment to safety. However, the value of the baseline exam has not been proven, and therefore standard bodies have dropped it.
9. Prepare for accidents, but hope they never happen.
An item many are not prepared for is what to do if an incident occurs. Do people know who to report an incident to? How to react? Is there a medical response planned? Who will perform a follow-up investigation? These are all important questions, and like insurance, we hope we never have to use them, but we want to have a policy in our pocket if needed.
Is laser safety achievable in today's competitive and changing environment? The answer is YES, but it does take effort, resources, time, and a desire to achieve it. Laser safety cannot just be dictated with the expectation that the job is done; users must see its advantage to them, which is the sales job of the LSO. Ultimately, all safety comes down to the user/operator actions.
Laser safety should not be looked upon as a hinderance to getting work done, but as an element that contributes to safe continuous operation.
Kenneth Barat is a former LSO for Lawrence Berkeley National Laboratory and National Ignition Facility. He has authored several texts on laser safety, including Laser Safety in the Lab and How to Set Up a Laser Lab (SPIE Press). He is currently the owner of a laser safety consultancy called Laser Safety Solutions.
He also offers in-company and online courses on Basic Laser Safety through SPIE.
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