WHAAAAAAAA??? Because of fungal spores, perhaps?
I haven't the faintest idea what was going through the mind of the idiot who wrote the reg. It is absolutely absurd. Let's say that it was due to fungal spores -- fungus in wet hay requires ambient temps to be above, oh, about 60F, and the hay needs time to "ferment" the sugars in the plant material -- like weeks.
The way the highway patrols and the US DOT is interpreting the rule is that hay carried on a truck in a rainstorm better be tarped, or they're going to cite any hay truck driver without a hazmat on his CDL for some pretty stiff fines.
Where rules, regulations and impact on business from regulatory law-making is concerned, the Bush administration has been a complete failure. There isn't a regulation that the Bush administration has rolled back and there's plenty more besides they've heaped on private industry, especially the truck, fuel and ag industry.
no combustible material.