Q. We are using a vibratory finishing compound that has been satisfactory for more than 20 years. Recently, a potential new vendor pointed out that it contains sodium nitrite; this is clearly stated on the product Material Safety Data Sheet. He said we are violating the law in using it. We checked with our supplier, who said that mass finishing compounds are basically cleaners and, as such, are not banned by regulations concerning sodium nitrite. Our system operator was present in meetings when we discussed changing compounds, and he is concerned about any health risk. Furthermore, he said his wife has expressed concern about the fragrances used in the compounds he works with. Are these valid concerns? J.P.
A. You have two distinctly different concerns here, and each deserves a complete answer. Let me start with the nitrite issue. The U.S. Environmental Protection Agency banned the combination of two ingredients in metal working fluids: amines and metal nitrites (including nitrites of lithium, sodium, potassium, rubidium, cesium and francium). This regulation is spelled out under 40CFR721. It results from studies showing that nitrosamines (known carcinogens) could be formed under certain conditions when these two ingredients are combined. This knowledge first became public with a bulletin published by the National Institute for Occupational Safety and Health in 1976. Regulatory restrictions soon followed defining metalworking fluid as “a liquid of any viscosity or color containing intentionally added water and used in metal machining operations for the purpose of cooling, lubricating, or rust inhibition” (40CFR721.3). Responsible manufacturers of metalworking liquids scrambled to develop alternative formulas.
The reason for using amine-nitrites was for corrosion control with ferrous metals. The two nitrites most commonly used were of sodium and potassium. They are very effective and very economical for this purpose. Good corrosion inhibiting is essential in cutting fluids, lubricants, washing fluids, grinding fluids and rust inhibitors. The cost of obtaining adequate corrosion control without the use of nitrite has approximately doubled.
Most manufacturers of manufacturing fluids interpret this restriction to apply to machining coolants, grinding coolants, rust inhibitors, lubricants and mass-finishing or parts-washing compounds. The fact that the regulation does not specifically list washing compounds has provided a loophole some manufacturers squeeze through to use nitrites in their washing and mass-finishing compounds. It is a small loophole, indeed, when we are talking about potential carcinogens!
Allow me to expand on the regulatory definition: 1) If you run a mass finishing machine without compound, will it get hot? Yes. Therefore, one function of the compound is cooling. 2) Do you expect the compound to protect your parts from corrosion? In most cases, yes. Therefore, the compound is a rust inhibitor. 3) Does mass finishing remove any metal from the parts? In most cases, yes. Therefore, it is grinding. 4) Do you expect your parts-washing compound to protect either the machine or workpieces from corrosion? Yes. Therefore, it is a rust inhibitor.
Clearly, mass finishing and washing compounds should not contain the combination of amines and nitrites. If you are using such a compound, you are exposing your company to severe penalties by EPA and/or the Occupational Safety and Health Administration. I strongly suggest you obtain a written certification from your supplier that his compounds do not contain amine-nitrites. The certification should be signed by an officer of the manufacturer of the compound, not just by its representative. I cannot overemphasize the importance of taking these precautions and/or changing vendors.
The second part of your question regards fragrances that may be present in your mass-finishing compounds. In general, fragrances can be either natural, such as essential oils, or synthetic, such as the majority of perfumes. (Chanel No. 5 was the first major perfume based on synthetic formulas.) The primary chemical difference pertains to the oil used in the fragrance. Synthetics typically use refined mineral oils, although some may use vegetable oils. Perhaps some mass finishing compounds include fragrances, but this is more likely to simply mask chemical odors for a more pleasant fragrance, and not to actually make a sweet-smelling product. Our finding over the years has been that operators do not enjoy working all day in a perfumed atmosphere.
Are these fragrances, if present, a health hazard? The answer is no, but I’ll take time to explain myself on that possibly controversial statement. There is a standard measure for the toxicity of a substance—LD50. Without getting overly involved in explaining that measurement, let me just say that it is an estimate of how much you would have to drink for it to kill you. Actually, it is how much you have to drink until you have just a 50-percent chance of survival. Having said that, let me say that you can drink enough of anything, including water, to do yourself in. Even highly toxic substances such as arsenic trioxide can be taken in small doses for medicinal purposes.
So what about fragrances? My experience with formulating compounds is that about 0.05 percent of a fragrance is all you want in metalworking compounds—in some, you may not need any. On that basis, for the fragrance in your compound to poison you, you will have to drink about eight pounds for each pound you weigh, in a single dose. So, if you weigh 180 lbs, the single dose that may do you in is about 170 gal. This is based on a typical synthetic fragrance; most essential oil fragrances (lemon oil, for instance) are more toxic, so you may just have to drink as few as 100 gal at one sitting. That is the straight stuff, right from the bottle, so to speak. If you prefer drinking it as diluted for mass finishing, let’s say 2 percent, you can multiply those quantities by 50 times.
These numbers are just based on the fragrance, and in a complete product there will be other ingredients to consider, but clearly even the most toxic fragrances create no realistic concern.