It seems to me that "toxicity class" is a generic thing, as opposed to the specific name "Toxicity Class 1", etc.
Per WP:MOSCAPS ("Wikipedia avoids unnecessary capitalization") and WP:TITLE, this is a generic, common term, not a propriety or commercial term, so the article title should be downcased. In addition, WP:MOSCAPS says that a compound item should not be upcased just because it is abbreviated with caps. Lowercase will match the formatting of related article titles. Tony(talk) 10:07, 31 March 2015 (UTC)
The above discussion is preserved as an archive of the proposal. Please do not modify it. Subsequent comments should be made in a new section on this talk page. No further edits should be made to this section.