Reprinted from the ACJ - May, 1993
Bring up the subject of gas tank repair in a group of repairmen and you will get as many differing opinions as there are folks in the room. "Fix 'em" -- "Replace 'em"-- and so on. But one thing everyone there will have in common is a story of someone they know or have heard of that has got into trouble due to gas tank repair.
Sometimes it is just a story about some guy who after numerous attempts at standard repair, several coating tries and one or two voodoo rituals still ends up buying a new tank and taking his lumps on the wasted labor. That predicament is a matter of having and using the proper technique, experience and talent. These things I lack, so I won't offer any helpful advice for that war story.
But sadly, the story more often is about someone who was badly injured in a gas tank repair mishap. Gas tank repair is a profitable but tricky business. Certain safety requirements are necessary and this month we will discuss a few of the precautions.
Generally speaking, the repair of a metal gas tank can be accomplished two ways. One is to solder the leaking seam or solder a patch over the puncture. The other method is to coat the tank with a sealer.
It should be obvious that anytime you put a torch to a gas tank, the potential for disaster exists. I won't spend time discussing this hazard, as important as it is, so we can spend a little more time on the hazards that gas tank sealers present. Keep in mind that the same principles discussed apply for gas fumes in a tank.
Sealers come in two general types: solvent-based systems that contain a plastic or resin dissolved in a liquid, and two-part epoxy type systems in which part A and B are mixed and a chemical reaction hardens the material. Both systems have advantages and drawbacks.
I would like to hold off on discussing the epoxy type of coatings for a future article where we will look at epoxy safety in general. That leaves us with the dissolved resin type of coatings.
The idea behind these type of systems is simple and very effective. A resin, usually a plastic or vinyl, is dissolved in a highly volatile solvent, one that evaporates rapidly and completely. When the solvent evaporates, what is left is a nice, even layer of plastic that coats the tank, is impervious to gas, is flexible and adheres well to the tank. The small holes are sealed and the customer drives away happy, ignorant of the incredible bravery displayed by the conquering repairman (I just thought I would throw a little ego boost in there).
The resin used in these coatings is usually non-toxic, not corrosive, and more or less harmless. So where is the danger? As with a poorly running furnace, radon and Mexican food, the danger is in the unseen vapor. The solvents used in these coatings vary, but most are very volatile organic liquids. Methyl ethyl ketone (MEK) or acetone are the most popular.
From a health aspect, these solvents are not incredibly nasty. They are only mildly toxic when ingested or inhaled, can cause dry skin due to extraction of the oils, are moderately irritating when the fumes get in your eyes and have few documented long-term, chronic health effects.
The worst health-related concern is asphyxiation due to the evaporating fumes pushing the oxygen out of a closed space, like a small room. Thus the famous "use in a well-ventilated area" warning we have all seen and ignored at times.
This concern for fume concentrations gets at the heart of the hazard: fire and explosion! The low flash point and the speedy evaporation required in the product sets up a potential fire hazard radiator shops are not accustomed to dealing with. The flash point of MEK is 22° F (-6º C). Thus an open can of liner above 22° F (-6º C) can give off enough fumes to burn. If and when these fumes build up to what is called the lower explosive limit (LEL) the air-vapor relationship is proper for explosion.
Think of the closed room as a very large cylinder filled with the proper gas-air mixture. Add a spark and watch the piston (you or anything else in the room) fly. The LEL for MEK and Acetone is approximately 2 percent. Two percent of solvent fumes and an explosion potential exists. Definitely "use in a well-ventilated area."
That spark we mentioned could be obvious, like a cigarette or torch. It could be more sneaky as well, like the ignition system of a running car, the pilot light of the furnace or water heater, or even the static electricity shock you get while walking across the carpeting and touching the door knob.
Now that we are knowledgeable of the vapor concentrations, another sinister aspect of these solvents comes into play. The fumes given off are heavier than air, almost twice as heavy. So as they evaporate, they creep out of the tank, off the workbench and settle on the floor. They then spread out around the floor of the room. Unknown to the unsuspecting worker, the level on the floor may well be above 2 percent as it oozes toward the space heater way over in the corner of the shop. Sounds like a bad horror movie.
It can't be emphasized enough that good ventilation, air circulation, and elimination of flame and spark sources is paramount to the safe use of fuel tank liners. A fume hood would be best, possibly in a separate room set up with an explosion-proof electrical supply, used solely for tank repair. Also make sure all the technicians working with the material are trained and knowledgeable in these safety practices.
The future of gas tank repair may be growing or it may be shrinking depending on who you talk to, but a sizeable market is out there right now. By the safe use of the products available you can guarantee your future will be growing -- bringing more customers, more work, more profits and more time for discussing subjects like sports and politics and not about the guy whose latest gas tank repair was his last.
The above article was written by David M. Brown, Chief Engineer of Johnson Manufacturing Company, Inc. and is published by JOHNSON with the expressed approval of the National Automotive Radiator Service Association and the Automotive Cooling Journal. Other reproduction or distribution of this information is forbidden without the written consent of JOHNSON and NARSA/ACJ. All rights reserved.
JOHNSON MANUFACTURING COMPANY
114 Lost Grove Road / PO Box 96 / Princeton, Iowa 52768-0096
Phone 563-289-5123 or Fax 563-289-3825