I agree, it was probably not intended to kill anyone. I don't agree that it couldn't have. People could have been trampled during evacuation, someone could have already had respiratory ailments, etc.
Motive aside, even if it could have killed ten people by downplaying that risk the terrorists lose.
It's kind of like how sending suicide bombers to Israel is pretty much futile. The populace knows that unless they come by the hundreds of thousands it's not a risk worth being scared of. You can't terrorize people who don't think you're scary.
