It's well known that some people find the presence of the in- prefix in inflammable to be confusing, and as a result, the form flammable has become more common over time.
Although the spelling "imflammable" doesn't seem to have ever been at all common relative to either inflammable or flammable, it does seem to have had some use. (See the Google Ngram Viewer; also, to show that these are not just OCR errors, here are a couple of specific examples from Google Books: The Iron Age, 1906; Automatic telephone systems, 1907).
If I had come across "imflammable" before today, I would have thought of it as an accidental or ignorant spelling error. But I just learned from Hot Licks that it was at one point used intentionally as an alternative to "inflammable":
Back ca 1960 there was a hubbub in the US shipping and transportation arena because many people took "inflammable" (as used on, eg, tanker trucks) to mean "non-flammable". So "imflammable" was promoted as an alternative less likely to be subject to this confusion, and for a few years you'd see "imflammable" on tanker trucks, et al.
When I Googled "imflammable" to try to find more information about this, I came across a forum post from 2001 by someone who thought of "inflammable" and "imflammable" as antonyms, and said
A lot of engineers will agree that the word "Imflammable" (with an M) means "easy to burn", while "inflammable" (with an N) is supposed to mean "not flammable".
(h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition, A Conversation for Oddities of English, by MSL)
I find it interesting that this person associates the spelling with engineers. It could just be a common misspelling (engineers aren't exactly known for having perfect spelling skills), but I wonder if any engineering organization ever used "imflammable" as an official spelling. I find it somewhat reminiscent of the unetymological use of "-or" in profession names like "weldor" that was apparently promoted at one time.
Can anyone share more information about the use of this spelling, and any possible "offical" status it may have had at any point?
Best Answer
I'm not persuaded that the instances of imflammable over the years are the result of a conscious effort to establish a less confusing variant of inflammable—as opposed to being a longstanding variant with no pretensions to reducing the number if incidents of accidental flash fires.
'Imflammable' as a less easily misunderstood variant of 'inflammable'
Truth to tell, I couldn't find much direct information on this subject, except a comment that appeared in various publications of the American Society for Testing and Materials Solutions between 1960 and 1983 urging people to stop using imflammable and other variant spellings—presumably because these variants were only filling the room with smoke. From American Society for Testing Materials, ASTM Standards on Textile Materials: (with Related Information) (1960):
In short, the only member of the inflammable family of words to survive the comprehensibility conflagration resulting from efforts to avoid confusing people as to the meaning of inflammable was the word flammable.
An earlier note to similar effect appears in George Haven, Industrial Fabrics: A Handbook for Engineers, Purchasing Agents and Salesmen (1949) [combined snippets], which itself drew from the A.S.T.M. Standards of 1947:
At this stage, it seems that the ASTM was still plumping for nonflammable to be adopted as the standard way of saying "not inflammable"; but by 1960 the organization appears to have thrown the sponge into the bucket on that idea.
But if imflammable was already under a dark cloud—and indeed being recommended for excommunication—in 1947, when and by whom was it being promoted as a way forward for people trying to avoid the ambiguity of inflammable?
Multiple 19th-century instances of 'imflammable' in the same article
There are a couple of instances from the nineteenth century in which imflammable appears twice on the same page, lessening the possibility that its occurrence was a simple typo, but perhaps increasing the possibility that it was written by someone who didn't know how to spell inflammable. From a letter to the editor of The Belfast Monthly Magazine (September 1809):
From "The Texas & Pacific Railway Co. v. Levi & Bro.," in The Texas Law Reporter (1883):
From "Is Fine Wood Dust Explosive?" in The Wood-Worker (August 1887):
And from a rule change enacted on September 2, 1896, in Votes and Proceedings of the Legislative Assembly [of New South Wales] During the Session of 1896 (1896):
Presumably the 1809 instance of imflammable did not represent an effort to avoid having readers misunderstand the meaning of inflammable—but it is hard to tell whether that sort of thinking might have had some influence on the three instances from 1883–1896, a period when the spelling simplification movement and other efforts at orthographic rationality were increasingly popular. I have not, however, been able to find a manifesto on behalf of imflammable as a spelling less likely than inflammable to lead to tragic misinterpretation.
Conclusions
Twentieth-century publications that show strong signs of having intentionally used imflammable (because it appears more than once in the article) include Telephone Cables (1906), Engineering and Mining Journal (February 18, 1911), American Municipalities (November 1916), Mining Magazine (1921—using the word non-imflammable twice), and Ice and Refrigeration (July 1922). The only multiple instances of imflammable that I've been able to locate in a book published after 1922, however, are from Scientific Research Abstracts in Republic of China (1989), a source that may very well have used that spelling twice in the same paragraph without realizing that it was odd.
Just because I didn't find a contemporaneous argument touting imflammable as a safer spelling than inflammable doesn't mean that no one was making that argument—1n the 1880s, the 1910s, the 1920s, or later. But until I see such an article from that era, I remain skeptical that any such argument underlies the more frequent usage of imflammable during those decades.