I know this won't be to the scale most members here need to worry about, but for pellet stove users or those who store a ton or more, possibly so. I have half a skid of heating pellets in my basement that need to be relocated at the very least. This link addresses a few casualties in Europe even in private homes due to carbon monoxide poisoning. Apparently it's a known issue where pellets are produced and other saw mills, though I've never heard of it. https://academic.oup.com/annweh/article/56/7/755/172902 Knowing there are almost no regulations in place to govern pellet production, specifically about aging them, it's something to keep in mind if you store a good amount of pellets in a small enclosed space.