As bad as it's been, the stock market freefall would have to get even worse for some built-in safety nets to kick in.
They're called "circuit breakers," and they were implemented after the stock market crashed in the late 1980s to force a halt to frenzied selling.
The Dow Jones industrial average would have to fall 1,100 points in a day to trigger the first halt. If that point is reached before 2 p.m., the market would shut down for an hour. If the threshold is breached between 2 p.m. and 2:30 p.m., the halt will last 30 minutes. No trading stops will take place if the plunge occurs after 2:30 p.m.
There are also breakers for drops of 2,200 and 3,350 points. In the worst case, the market would close for the day.
The rules would also halt trading on the major securities and futures exchanges in a coordinated cross-market halt.