KEN BARAT, LASER SAFETY SOLUTIONS
From the very first use of lasers, a key safety practice has involved providing some type of indication to alert people that they are about to enter a room where a laser is on or powered up. Further emission indicators on the laser, its power
supply, or both, are also routine. The ANSI standard Z136.1 for Safe Use of Lasers states:
A Class 3B Laser Control Area (LCA) should and a Class 4 LCA shall
have an area warning device that is visible prior to entering the area.
The purpose of the area warning device is to ensure that persons who are about to enter the LCA are aware that a laser is emitting or is about
to begin emitting accessible laser radiation within the area.
The standard defines a visible warning device as any device, mechanical or electrical, that indicates when the laser is operating. Examples include an illuminated single lamp or a laser warning sign that is lighted or that flashes when the laser is operating. This light, or lighted sign, can be electrically interfaced and controlled by the laser power supply so that the light is on, or flashing, only when the laser is operating. The use of a manually controlled light is acceptable, but this option is open to human error.
The standard also allows the laser emission indicator to serve as the visible warning device, though it is never a good idea to rely on this as the sole indicator. If used, the emission indicator should be clearly noticeable under all anticipated lighting conditions. It should be conspicuously different from general lighting. And it should have a specific meaning within the operational area where it is used. In real life, however, few indicators can check off all these boxes.
Visible warning indicators
Under Z136.1, the laser safety officer may determine that the visible laser radiation emission indicator is not easily visible everywhere within the laser control area. In such cases, the officer should consider adding another indicator, such as a laser warning light or a lighted sign, that is viewable throughout the area and that indicates when the laser is operating. This light or lighted sign could be electrically interfaced with and controlled by the laser power supply so that the light is on or flashing only when the laser is operating. The indicator should also be visible through laser protective eyewear.
If the laser use area is large, or if an area has multiple laser use areas within it, internal warning lights are more than just warranted, they are essential. Experience demonstrates, however, that in the typical laser lab the assumption of user awareness is favored over the use of internal warning lights.
The colors selected for indicators and signage within a laser use area are important because they must take the possibility of operator color blindness into account, as well as the effects of safety eyewear. In some cases, signs using white lettering contrasted against a black background address these issues. Otherwise, per ANSI standards, green indicators typically give the “all clear,” yellow designates an energized laser, and red denotes that the laser is actively emitting light. The International Electrotechnical Commission (IEC)
further supports the use of illuminated warning signs on the outside of laser-controlled areas to indicate that the laser is in use and that door interlocks (if fitted)
are operational. These signs should clearly indicate whether the laser control area is safe to enter or not.
I look forward to the implementation of hologram figures positioned outside laser labs and AI-equipped robots that talk to you if you wish to enter.
Signage can be a useful administrative control, especially when a nonlocking system is being used. Signs help to avoid unnecessary interruptions of laser emission. To employ this approach effectively, a sign must be appropriately connected
so that it indicates that the laser is “on” only when the laser is being operated. My experience is that manually activated lights can work well when they become part of a group’s normal operation or culture.
In the early days of laser use, the exterior illuminated indicator was a red light bulb. The drawback to these lights was that they came on whenever the laser received power, which could be all the time and regardless of whether the beam could be accessed. In other words, these lights did not necessarily indicate whether an active hazard was in effect, and they could become meaningless over time.
This arrangement also pushed lights
to have a fail-safe circuit: If the bulb
went out, the laser would not operate.
I know of one case where a laser user spent three days going through their entire system trying to figure out why the laser would not turn on. They eventually learned that the system was doing exactly what it was designed to do, which was to shut the laser down when the warning light stopped working. Finally, someone (OK, it was me) noticed that the exterior warning light was not illuminated.
The common positioning of lights above the door frame is not the most noticeable option. Ideally, the light should be to the side of the door, at eye height. In addition, if you are using a single red light, it is advisable to place a sign near
it to indicate what the light means when
it is illuminated.
The next evolutionary step in laser safety indicators following the little red light was the two- to three-light sign, which had three settings: safe, caution, and danger. Some of these signs had a mechanism to indicate that beams were accessible (that is, they were linked to a shutter). This approach lasted for decades before LEDs replaced standard iridescent bulbs. LEDs eliminated the need for
these signs to have fail-safe circuits.
Two additional indicator types developed later. The illuminated message became part of an interlock system display, and flat display screens were used to combine laser warning sign properties with laser status indication.
Some of these displays use programmable logic systems and can include graphics and features showing the status of individual lasers.
Some in-between approaches remain. One underused option is a scroll sign indicating laser status. The nice thing
about these signs is their dynamic nature. The message’s scrolling action catches
the eye and tends to be read, whereas
all static signs (for those who are honest with themselves) become essentially invisible over time.
The advantage of a flat screen is that it facilitates customized messages. The clearer and more detailed the information is, the more likely it will be that people will pay attention and make good decisions about safety and risk.
What about the future? Although I have seen neither of these ideas applied yet, I look forward to the implementation of hologram figures positioned outside laser labs and AI-equipped robots that talk to you if you wish to enter. I have seen robots interacting with people in department stores and at information stations. So, with minimal effort, robot sentries could be operational outside laser labs today. The use of holograms will take a little longer.
An indicator of laser risk status is important to laser safety because it communicates active hazards. If you are still using outdated methods, please consider updating your approach.
Hologram anyone?