when would you realize the danger?

this short video about pompeii is curiously intriguing. the disaster seemed to take much longer than i would have thought, especially since experiencing mt st helens (even from far away). and it makes me wonder ... at what point, time-wise, would a person have realized they needed to bail out and run away to escape what was happening. the husband would have figured it out -- he's pretty good about stuff like that. anyhow, if you have a quick 8 minutes, scroll down and watch the vid.