Most electrode cleaning solutions are a blend of enzymes and a mild acid catalyst. They're designed to breakdown proteins and membranes that form on the sensor surface over time.
It's classified as non-hazardous because it won't quickly react with other substances to cause harmful vapors or flame in transport or storage. The enzymes (pepsins) won't create too much heat and the acid content is typically > 0.01%
Since it's non-hazardous, and given the reactions going on in mash, boil and fermentation, I'd consider it a non-issue.