The new levels were approved late Thursday by the agency.The commission said in a statement the new trigger levels better reflect the original intent of the circuit breakers -- "that they only be triggered during a severe one day decline of historic proportions."

They are called circuit breakers because they are designed to gradually inhibit trading during market declines, first curbing New York Stock Exchange programme trades and eventually halting all US equity, options and futures activity. The new trigger levels will be converted into point values at the beginningof each calendar quarter using the average closing value of the Dow for the previous month.