Plunge Trips 'Circuit Breakers' Twice, Halting Trading

Stock traders were stopped in their tracks Monday after sellers twice tripped "circuit breakers" intended to prevent a market drop from turning into a rout.

It was the first time action has ever been halted in mid-session on the New York Stock Exchange and other markets for this reason.

The procedures were adopted after the 1987 market crash and updated last year. They are as follows:

*A 50-point drop in the Dow Jones industrial average means computerized program selling can take place only on an uptick - when the last price movement in a stock has been upward.

The opposite holds if the average has risen 50 points or more.

The restriction is removed if the industrial average recovers to within a 25-point move from the previous day's close.

*The "sidecar rule" is effective if the primary Standard & Poor's 500 stock index futures contract traded on the Chicago Mercantile Exchange falls 15 points from the previous day's close. The futures contract isn't allowed to fall further for 15 minutes.

*Trading is halted on all U.S. equity and futures markets for 30 minutes if the Dow Jones industrial average falls 350 points.

*Trading is suspended for an hour if the Dow loss hits 550 points.