I have similar barrels on my layout - shape is different, but they are red and about the same size.
I don't know what Larry's barrels are, but the red ones I have are from an HO trestle bridge kit. Maybe Campbell or Alexander. The red barrels were placed along the top of the bridge in set outs and filled with water (or sand depending on area and RR) so if the embers from the loco landed on the bridge, the train crew could put them out.
I would bet that many HO details companies also sold bags with barrels. The ones designed for use as fire barrels would have come painted red.