I saw a air powered circular saw today at a thrift store. looked well made. Made in USA all heavy Al castings. I suppose it would not spark at motor brushes but sawdust and static might still be a fire hazard. I guess it would work underwater. But who needs one. At a guess made in the 1960's or earlier.
PS: looked like a 7 1/4" blade as a guess. 3/4" supply reduced down to 1/2' pipe. must use a lot of air!