I have no doubt a pound of BP igniting inside a house is bad news, but deadly? I've lit off as much as 1/2 a pound, and it just makes a big WOOF and satisfying mushroom cloud. There is no doubt a quart of gasoline ignited in a house could start the whole place on fire.
If you can pump your own gas, you can handle black powder. The only reason both BP and smokeless powders are charged a hazmat fee for shipping, is that when burning in a large quantity, say 100 pounds in a truck, it never ends well. I don't drive around with 50 pounds of powder in my car, and I don't handle more than a pound of powder at a time. Outside of an open flame or spark, BP won't just spontaneously ignite. Maybe if you left it in the oven? BP is stored in plastic bottles, previously steel cans. Why would a plastic and steel powder measure cause problems?
Let me put it this way. If the plastic bottle it's stored in isn't melting, there is no danger of the BP inside igniting.