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Safe Neon Processing

Operators must always know what they’re working with.

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Roughly 15 years ago, I began learning neon-tube manufacturing for artistic purposes. I’d been trained in high- and ultra-high-vacuum, laboratory practices. Then, as did many U.S. neonbenders, I read the book, Sam Miller‘s Neon Techniques, and I was amazed how signshops process “quick and dirty“ neon tubes, compared to laboratories’ “clean” techniques. Also, I learned, when you’re “bombarding” to clean the glass, you handle thousands of volts – at lethal levels.

So, before I set up my “garage artist studio,” I made sure I thoroughly learned how to set it up safely.

Having worked in labs with substances more hazardous than mercury, and having been respon¬sible for our research group’s safety when we used invisible, high-power lasers in open setups, I rehearsed Safety Rule No. 1: Ensure shop personnel always know exactly what they‘re dealing with and how to handle it safely, even in abnormal situations, to greatly reduce accidents.

No 24/7 workplace can be inherently safe, regardless of precautions. You can minimize, but not eliminate, accidents. Your shop design and setup should include safety features, and some of them are so important that, if you don’t have them, you should consider remodeling the shop.

Bombarding-transformer dangers

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Electrocution from a bombarding transformer causes most lethal, neon-shop accidents. A bombarding transformer can generate voltage that can “jump“ several inches, especially when the surface is humid or partially conductive (such as wood with nails or screws). However, direct curent rarely flows through the body, hand to hand, from two energized leads, unless you strike an arc to light a torch or cigarette.

Many bombarding transformers are secondary midpoint grounded or single-end grounded, where at least one bombarding lead has a high-voltage potential to ground. Thus, if an operator contacts (directly or indirectly) this lead, his body will conduct the current to ground (hand-to-foot contact). In contrast, if the bombarding transformer’s secondary coil is insulated, even accidentally grounding one lead by contacting the (ground-potential) operator won’t cause a lethal current to flow.

Thus, a good bombarding transformer’s secondary coil should be insulated from ground (and the transformer core) for at least twice the bombarder’s full, secondary voltage.

Even then, one end of the high voltage is more or less capacitively grounded and can cause arcing to ground. Thus, don’t rely on insulation of the bombarder’s secondary coil.

Vacuum-system dangers

Vacuum-system construction presents another bombarding-safety issue. Most U.S. shops use glass systems. During bombarding, a discharge may occur not only in the tube, but also through the tubulation back to the vacuum system (a flashback), which contains a gas that can become conductive when high voltage seeks ground potential. Though glass is an insulator, the next point of “ground potential” during a flashback is the operator, if he touches a stopcock from the outside. The current may arc through the stopcock packing/gaskets and trough through the operator.

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Thus, here’s a safety rule for glass systems: Never touch any part of the vacuum system while the bombarder is on.

If you must operate any part of the glass manifold, switch off the bombarder, then reach to the vacuum system, perform the task, step back and continue bombarding.

Some glass systems have pneumatically operated stopcocks. The remote pneumatic control isolates the operator from the stopcock, which enables safe operation while the bombarder is on. However, with only two positions, open or closed, maintaining correct bombarding pressure is difficult unless you open and close very quickly.

In many glass vacuum manifolds, a grounded, wire-mesh screen should “catch” accidental flashbacks and shield the electronic vacuum gauge. From my experience, depending on the pressure and type of gas in the manifold, flashbacks can reach up to 10 in. behind the screen.

Regarding flashbacks’ dangers, metal vacuum systems are much safer, when perfectly grounded. Even if a complete flashback occurs (when all current travels through the manifold instead of the tube), the metal parts in a perfectly grounded system can’t gain a lethal potential and will conduct a possible current to ground safely. Further, a flashback in a metal system doesn’t endanger the vacuum/filling gauges’ electronics if they’re several inches beyond the first metal flange.

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For this reason, my vacuum system is a perfectly grounded, all-metal system. Only the last few inches that connect to the tube are glass.

Around the table

There’s more to ground than just the vacuum system. In every commercial, high-voltage laboratory, all metal parts inside a high-voltage area that don’t intentionally carry high voltage must be bonded together and safely grounded. Bond all metal parts (even screw heads) together and ground them to prevent them from accidentally picking up high voltage.

Some shops put rubber mats on the floor in front of the bombarding table to provide “insulation” for the operator in case he contacts high voltage. Black, natural rubber (like tire rubber) isn’t an insulator, especially for elevated voltages, because it contains soot (carbon), which is conductive.

Also, many U.S. neon shops use a glass stick to push the dead-man switch to activate the bombarder, because glass provides insulation. This seems useless, because the operator is always on ground potential – he stands on the floor – as is the pushbutton switch. Instead, recess the pushbutton switch so it’s activated by pushing a rod through a hole. This prevents accidental activation (like leaning onto the switchboard). I don’t recommend using glass, because it can break and cause cuts.

A bombarder setup with a simple, on/off switch is unsafe. The “dead-man” pushbutton, having become momentarily an “on” switch, will de-energize the high voltage immediately when the operator pulls his hand back, either because he’s distracted or shocked. A foot switch isn’t safe, either. Most shops I’ve visited simply place a brick on it so the operator doesn’t have to put his foot on it.

Prevent accidental contact with high voltage by carefully planning and setting up the shop. A steel handrail should separate the bombarding area from the rest of the shop. Big windows should separate the pumping-system operators from the bombarding table. The bombarder must be activated only momentarily from the operator’s elevated chair position.

Some shops place grounded, wire-mesh cages around the bombarding table (the operator stands outside), and interlock switches de-energize the bombarder momentarily when the cage is opened. Few shops I’ve seen use a “light fence,” a 2-D, optical barrier in front of the bombarding table. When a person or object approaches the table, the bombarder control circuit is locked out.

Here another safety rule I‘ve described before: When the two bombarding leads aren’t used, short them by clipping them together. If someone hits the switch, no high voltage can be generated.

In addition to high voltage, the bombarding table provides other possible hazards, such as mercury spills. Construct the bombarding table so accidental spills can be cleaned up easily, quickly and completely. Don’t cover the bombarding table with fiberglass cloth or other fabric.

Instead, provide a smooth table surface and put a groove around the tabletop perimeter to collect droplets. Store and handle the mercury bottle in a dish filled with water so droplets will collect under water and can‘t contaminate the shop with vapor. Note that handling mercury-filled electrodes isn’t much safer than handling open mercury – the capsules can break and release their load. When cutting open misprocessed tubes, you‘re still dealing with open mercury. In my opinion, buying these electrodes only benefits the manufacturer.

My one last, but perhaps most important, safety rule is: Keep the entire bombarding area as clear as possible. Then, you can oversee the scenery all the time – and prevent accidents. Messes and high voltage don’t mix.

For further reading, I recommend the article, “A Hazard-Based Approach to Reduce the Risk of Shock,” which appeared in the September/October 2006 IAEI News.

In summary, neon and cold-cathode processing is safe for the operator and the environment if the operator knows his materials and how to deal with them safely. Never let routine replace attention to detail!

The author‘s all-metal vacuum system, having been completely grounded, is safe to touch even when the bombarder is on.

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