'Manageable' fear a handy safety tool

Wed, 01/31/1996 - 7:00pm
Michael Lafferty

As fiber optics continues to spread throughout broadband communication plants, and new fiber equipment is beginning to feature higher power outputs, many safety and training professionals in the industry are re-energizing their fiber optic training efforts. Kevin Wilkes, director of field services for Integration Technologies, says that while fiber optic technology continues to change, fiber optic safety issues have not. In fact, he believes new technology only underscores the importance of long-term safety training that needs a healthy dose of fear to succeed.

"I think probably 99 percent of the concerns about safety involving fiber have not changed with technology," says Wilkes. "I think they've been amplified by higher launch powers and connectivity. But, the basis is still there for problems with the eyes.

"It's pretty straightforward.... Of course, there are other things to worry about. But they're pretty trivial compared to the eyes. You instill what I call 'manageable' fear. And, there's nothing wrong with that at all. Because too much comfort breeds carelessness."

Laser dangers are real

The word "laser" is an acronym for Light Amplification by Stimulated Emission of Radiation. The light we see is just a small portion of the entire electromagnetic spectrum (See Figure 1).

When light is amplified or intensified, the atoms in a chosen laser material are electrically stimulated into an excited state of high energy. When the selected laser material absorbs enough energy, it's triggered to produce an enormous burst of light.

The laser material used depends on the task a laser is expected to perform. Higher power laser outputs use such things as gas molecules or crystals doped with a variety of lasing materials. Those used in optical fiber applications are made from semiconductor materials that feature low voltage, high-speed operation. Because some lasers have inherent physical dangers, they have been classified into four major categories (see Figure 2). Telecommunications lasers fall into category three, typically.

Optical fiber lasers operate at 850, 1300 and 1550 nm wavelengths. They range from the lower part of the ultraviolet portion (1 × 1015 Hz) of the electromagnetic spectrum through the visible light section, to the upper part of the infrared portion (4.0 × 1014 Hz) of the spectrum.

Eye safety concerns are concentrated on those lasers that operate at the 850 and 1300 nm wavelengths. That's because these wavelengths are naturally focused by the eye onto the retina. The eye is opaque to the 1550 nm wavelength.

The problem occurs when lasers with either 850 or 1300 nm wavelengths pass through the cornea. As Wilkes notes, "If you give the eye the chance, it's going to try to make something out of the signal that's coming to it by amplifying it more and more." In fact, the cornea will amplify such beams approximately 100,000 times (105).

As a result, such beams, which are usually invisible, can burn retinal tissue. This damage, which usually results in permanent blind spots, is neither instantaneous, nor does it usually cause any immediate pain. The retinal damage occurs because the viewing time has exceeded the damage threshold. For wavelengths used in telecommunications, these threshold formulas are: 10 mW for 10 seconds and 5.6 mW for 100 seconds.

Tidy formulas breed carelessness

Engineers and technicians who work in telecommunications, by the very nature of the industry itself and the exacting sciences that define it, are usually very precise, tidy people. There are immutable laws and limits that, when broken or exceeded, will produce predictable results. And therein, says Wilkes, lies one of the biggest dangers in fiber optic safety.

"There are a tremendous (number) of misconceptions concerning fiber and light signals," remarks Wilkes. "A lot of systems you go into, there's some overkill on fiber safety, and then there are a lot who have no idea (about it). I've seen people stare right into the end of a fiber and say, 'Well, it's a class three laser; there's no worry.' It's really very scary."

Wilkes says in 1989, standard lasers had a launch power of about 2 mW. In those days, "We had a real 'heater' if we had maybe 5 or 6 dBm launch power, which is about 3 mW." Today, however, 10 mW has become the nominal standard. And Wilkes notes he's seen reports on units that will operate in the 200 mW range. Added to that, is the increased opportunity for danger because of the ever-increasing volume of fiber deployment.

"Now, we have a typical headend with maybe 100 termination points, maybe even 200," notes Wilkes. "So, there are a lot of places there that someone can go in and simply take a connection and take it apart and look right into it."

According to Wilkes, when you combine the more powerful equipment, and the increased opportunities for danger, along with a fiber professional's unshakable belief in scientific formulas, a good dose of fear will go a long way in promoting fiber optic safety.

"With the magnification we're using to look at fibers and the launch powers we have now, it's a real danger," states Wilkes. "If you look at the formula, 10 mW for 10 seconds is the damage threshold. So, what is it at 80 mW? A half second?

"If you promote comfort...that there is a time factor, and a distance factor, and a launch power factor, and an eye-loop get comfort you don't want...but there is no middle ground. You don't need to tell your people it's going to burn a hole in the back of their head. But, you definitely want to instill a little bit of fear....

"It's like I've always said: I don't want to know the formula. Because I don't want to count 'one Mississippi, two Mississippi' and stop looking.... The worst thing you can do is to tell somebody that it's not dangerous until you have looked at it a certain amount of time or at a certain amount of power, or whatever."

Damned if you do, damned if you don't

While the "don't look" rule is paramount, Wilkes is the first to admit handling fiber optics is not a job people do blindfolded just to be or in the past. "In the early days," says Wilkes, "when we did rotary mechanical (splices), I always worked with them active. But, I just never looked into it. I always looked at it from an angle, and I never had to worry... with that type of connection. But that's changing."

That change, he points out, can be seen in the increasing use of the metal-bodied twist and lock FC connectors and the plastic-bodied, push-in and click SC connectors. Both the FC and SC require someone to look into the connector and the fiber attached to it, "Otherwise, there's just no way of knowing whether it's cleaned or not," states Wilkes. "Cleaning in these connectors is incredibly critical, even if you get them right out of the box brand-new."

For that reason, Wilkes stresses a four-point plan, with a heavy emphasis on established procedures for handling fiber as far as viewing goes. First and foremost, says Wilkes, is for people to keep the "don't look" rule running through their minds like a mantra, from start to finish of every job. The second thing is to verify the equipment is turned off, locked out and/or tagged out "so no one can go into the headend or the CO and turn the laser on while you're out there working on it."

Next, he believes fiber workers should have a reliable power meter or finder's scope to confirm that the fiber is not transmitting. He notes that some fiber technicians have been using a cheap, over-the-counter device for testing home remote controls to accomplish this task. He strongly disagrees with this practice.

"I wouldn't dare use that as a tool to see if I'm dealing with an active fiber or not," declares Wilkes. "How exact can that device be, and do you want to trust your eyes to it? The answer is 'No, absolutely not,' especially with the higher launch powers and the greater number of connectors that folks are dealing with now."

He also recommends workers take advantage of protective lenses or goggles designed to attenuate (disperse) laser energy at key wavelengths. Lenses that block specific wavelengths usually offer better protection than broad spectrum glasses used to block a number of wavelengths.

Wilkes notes that while some companies are really gung-ho on protective lenses, others hesitate to enforce such a requirement. Their hesitancy is based on a fear that technicians will "become too comfortable," expecting the lenses "to fully protect them." But Wilkes prefers to err on the side of caution. "I don't think there's a lot of middle ground on protective eye wear," says Wilkes. "Ultimately, the best way is to use protective eye wear and keep hammering away at the policy of never, ever looking into the end of a fiber. It's double insurance."

The four-step plan, with its combination of using equipment and procedures, is of critical importance to Wilkes. "All these things should be used together, never one by itself," insists Wilkes. "My personal credo is 'Rely on the equipment for what it's supposed to do. But, back it up with no-fail procedures.'

"Procedures are a whole lot less likely to fail than equipment is, because you're responsible. You can't always be responsible for whether a particular piece of gear is going to work or not."



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