Ask The Experts: Nitrites and Fragrances
16. March 2012
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.
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