Query on second hand smoke [View All]

Okay, I've been observing the latest iteration of the perennial smoking ban threads, and I have a serious question: How do we know how many people die each year from second hand smoke?

It's not like this scenario: Ambulance screams up to emergency room, paramedics wheel in woman on a stretcher in severe respiratory distress, doc asks what happened and paramedic responds: "It was terrible, doc. She was just walking down the street and passed an office building doorway and was struck down by a cloud of second hand smoke."

I am assuming it is more like this: XXX number of people die of lung cancer or emphysema beyond what is statistically expected and a certain percentage is attributed to second hand smoke.

How do we know these deaths attributed to second hand smoke are not actually caused by decades of sucking in bus exhaust or power plant emissions?

How de we separate out second hand smoke from other environmental contaminants?

How much second hand smoke kills you? One exposure? One hundred exposures? One hundred thousand?

Answers please. I'll check back in awhile; I'm going out for a smoke.