SAFETY COMES FIRST!
By John Preston
We've got information on gasoline in plastic tanks, CO-2 charger safety, and fires in plastic. Most important: careless use of some of the new two-part polyurethane paints can cause death or serious injury—fast!
Gasoline and Plastic Fuel Tanks
This month we have a little something for everybody. For starters, more on the incompatibility of gasoline and some plastic fuel tanks. Although in a test we conducted last summer using a gasoline-filled Sullivan tank we experienced no leakage, such was not the case for Frank Vidmar of Orlando, FL. Frank writes:
"After installing a Quadra engine in the Pitts, I used the Sullivan tank that was installed inside the fuselage. After several flights, and much to my dismay, I discovered a gasoline leak inside the fuselage which dissolved a portion of the fuselage. (Foam in gasoline acts like an Alka-Seltzer in water.)
"On disassembly, I discovered that the silicone tubing and the rubber cork in the tank had swelled up, causing the tank to leak. It occurred to me, also, that with the fuselage full of gasoline fumes, I had a bomb on my hands."
We also talked with a fellow club member last month who had a similar experience. In that case the swelling of the rubber stopper was sufficient to split the tank open at the neck. The moral of this story: do not use gasoline in the old-style Sullivan tanks. When Sullivan switches to Buna-N rubber for the stoppers, you can again use them for both conventional fuel and gasoline.
Meanwhile, as Frank pointed out: "To remedy the situation, I repaired the Pitts, and installed a Kraft tank under the cowl, external to the fuselage. Since that time, I have had no problems. The Kraft tank is completely compatible with gasoline, because it does not have a rubber stopper, and it comes supplied with neoprene tubing. Byron was quite correct in warning their customers."
CO-2 Charger Safety (Small Models / FF Scale)
A tip for fliers of smaller models, mostly FF Scale types: Earl Van Gorder (author of the "Flyin' Things for Fledglings" column in Flying Models magazine) provided a solution for problems experienced by several modelers using Shark CO-2 motors. Several months ago we related incidents of chargers blowing apart in hot weather, apparently due to insufficient thread engagement when the CO-2 cylinder is pierced. Earl's letter states:
"I came upon this same problem last May as a result of an article in Max-Fax, the newsletter of the Washington, DC Maxecuters. Stew Myers of the Washington club had related his problem with an errant Shark charger letting go and just missing the head of a fellow modeler. He did further experiments, and found that the charger let go every time — on the day he tried it, the temperature was 90°F. Stew did some calculations, and determined that the pressure of the CO-2 at this temperature was 1,250 psi... and this is too much for the Shark charger."
Of course, the Telco, Brown, and the new Modella chargers each have a surrounding mechanical housing, and are not dependent on threads to hold in the pressure.
The good news: the Shark engine can be charged with the Telco charger. I tried this to make sure, and the Telco charger works fine on the Shark. When I wrote this for my FM column, I included that fact (about the Telco charger), and thought you might want to know it, since you apparently were not aware.
Thank you, Earl. Even though Stew and I are almost neighbors (not quite, because Stew lives on the wrong side of the river!), I was not aware that the Telco charger could be used with the Shark motor.
Hazards of Two-Part Polyurethane Paints (DuPont Imron)
Much has been said about the hazards of some hobby paints. In a previous column I stated that we generally spray outdoors to avoid inhaling noxious fumes. However, even that can be unsafe for modelers who use the latest two-part polyurethane finishes, such as DuPont Imron.
In the June issue of Flying Models, Bob Hoeckele devoted his editorial to the hazard of using Imron without proper equipment. This editorial was brought to our attention by John Jones of Houston, TX. We thank Flying Models for permitting us to quote from their editorial:
"DuPont's literature describes Imron as the 'wet look that lasts,' and that it does. It is a two-part curable polyurethane coating that is available in about 1,000 colors, cures amazingly fast, and gives a high-gloss finish with just one or two coats. It is also absolutely impervious to everything, including pure nitromethane. Sounds like just the stuff for a model airplane or boat, doesn't it? It does and it is, if you hire someone to spray it on and don't breathe any of it. That doesn't only mean an old rag wrapped around your face, either. It means an air-fed respirator and all of the other protective gear that a careful professional finisher uses.
"You see, Imron contains something called poly-isocyanates. Some other two-part polyurethanes use toluene diisocyanate (TDI), but Imron uses aliphatic light-stable poly-isocyanates. What these are is not as important to understand as much as what they can do to you. For instance, in the Dangerous Properties of Industrial Materials, published by Van Nostrand Reinhold Co., where a 3 is a high toxic-hazard rating and is defined as possibly causing death or permanent injury after very short exposure to small quantities, toluene diisocyanate rates a 3 under irritant, inhalation and allergen. It says that it is capable of producing severe dermatitis and bronchial spasm. It also never leaves your system after it is absorbed. It is cumulative, and it also sensitizes you. That means that, even if many years pass since you have breathed it, a small whiff of it could cause you to have an attack.
"Being a modeler means that we use things in cans and jars all the time that have warnings on the labels. After awhile, we don't even read them anymore, and tend to ignore those new products that we get. Imron carries all the proper warnings; in fact, it even says, 'For industrial use only by professional, trained personnel. Not for sale to or use by the general public.' But, if a modeler wants something, he'll get it, even though Imron costs about $40 per gallon. The reasons for writing this include reports that a lot of modelers seem to have gotten some. In researching this, we also contacted some mask manufacturers, including Binks. They did not recommend any of their lower-priced masks for use with the two-part polyurethanes. The only thing that should be used is an air-fed respirator. It seems that when you can smell the isocyanate, you are already about 200% past tolerable levels.
"What we are saying is that we want our readers around to buy FM and to enjoy their hobby. If not used properly, Imron could very well shorten that time. A DuPont spokesman told us that 'Imron is only to be used by trained, professional painting personnel with appropriate equipment. If DuPont thought that it was appropriate for finishing models, they certainly would try to sell it to you.' — Bob Hoeckele. (Note: Emphasis added by editor. RBM.)"
So there you have it. Even though you may want the best finish on the block (or in the club), avoid using Imron unless you are a professional painter and know how to handle an air-fed respirator.
Fires and Molten Plastic — Torch Safety
To wind up this month's column, a suggestion from John Hunton, a fellow club member who works for a firm that builds R/Cs. While the incident he describes happened at work, it could just as easily happen in your home workshop.
"An incident occurred to me at work yesterday that might find a place in your files for warning others.
"I was using a propane torch to heat and remove an engine backplate from a tapered shaft. Being engrossed in what I was doing, I sat the torch down on the bench, inadvertently aimed toward the MonoKote-covered vertical stabilizer of an RPV. The tail caught fire, and the burned area quickly spread to a diameter of two to three inches.
"My reaction was to blow the flame out quickly, before things got out of hand. The flame went out quickly, but there was a ring of molten plastic around the hole that flew back into my face. The plastic gave its heat to my skin, and each droplet solidified and stuck. This was a painful experience. Luckily no plastic got into my eyes.
"Suggestion: Keep small fire extinguishers readily available. Do not blow out burning plastic."
Final Note
By the time you read this column, the flying season (for those in the more northerly parts of the U.S.) may be over. Now that you have time on your hands, why not sit down and drop us a line?
John Preston 7012 Elvira Court Falls Church, VA 22042
SAFE FLYING IS NO ACCIDENT
Transcribed from original scans by AI. Minor OCR errors may remain.
