Safe for cars/bikes, or the passengers vs the bicyclist?

Hail comes to mind. Lightning possibly (I believe cars are much better insulated against lighting strikes). High winds could easily push bikes around / knock them over where cars just keep going.

We drove our van through a forest fire (Cedar Creek Fire - a BIG one) and got a bit of smoke, but otherwise, just fine. No way would I have attempted that on a bike - the increased aerobic activity alone (to say nothing of embers / ashes / etc) would have probably caused crazy amounts of smoke inhalation / death.

And there is a reason drivers hate SOME bikers - here in CA, many simply refuse to follow the rules of the road. My light turns green, and 5 seconds later, some biker comes rolling along in the perpendicular direction - I almost hit him. This kind of stuff happens over and over. I am very fond of bikers when they follow the rules - I bike sometimes too.

>No way would I have attempted that on a bike - the increased aerobic activity alone (to say nothing of embers / ashes / etc) would have probably caused crazy amounts of smoke inhalation / death.

Riding a bicycle while wearing an unpowered respirator/face mask is surprisingly easy, especially if it has an exhalation value. It does restrict breathing somewhat, but breathing isn't usually the bottleneck when you're cycling. This might even be the optimal way to escape a fire if the roads are congested.