No notch codes and too large for standard holder sounds like they are from a "film pack" which was a very popular method of loading film until after WWII. The film was actually the same base as roll film, thus thinner than cut film. It was also a little larger and required a different negative carrier for the enlarger.
Nitrate film will not have "Safety Film" encoded along the edge. Look through them. If any of the emulsions are beginning to bubble, I would burn them in a safe container. All others I would carry in a cooler as others have suggested. Although I know of no studies, I dare say that a large majority of problems with nitrate films happened in projectors, most of which used carbon arcs for light sources.