More was learned about the outage's costs as well.
The team of U.S. and Canadian investigators, headed by Energy Secretary Spencer Abraham and Canada's Minister of Natural Resources Herb Dhaliwal, will take over several separate probes already underway across the region.
Officials close to the investigation have said an interim report on last week's blackout could be released by mid-September. But a final report may be months away.
"We've already had investigators sent out into the field," Abraham told the CBS News Early Show, "and we're going to move as fast as we can. We're also not going to jump the gun."
Experts studying the outage point to a series of small failures that may have combined to unleash a huge wave of destructive electricity.
Four otherwise innocuous events occurred Thursday afternoon on the northeast Ohio power grid owned by FirstEnergy Corp. They include unexplained voltage swings that the company said brought down a coal-fired generator, a pair of power line outages — one caused by a tree — and the failure of an automated warning system.
In other developments:
As disasters go, the blackout won't make the Top 10 and probably not even the Top 20 in terms of insured property losses, according to Insurance Services Office Inc., a Jersey City, N.J.-based advisory company.
It is expected to fall far short of the $2.2 billion price tag for the April 2001 tornadoes in the Midwest and South and the winter 1993 storm in the Northeast, which tied for No. 9. The costliest disaster on the list was the Sept. 11, 2001, terrorist attacks at $20.7 billion,
"It is a minor nuisance, as opposed to a major disaster," said David Wyss, chief economist at Standard & Poors.
Indeed, the U.S. economy generates more than $1 billion in economic activity every hour, on average. Even a $6 billion price tag would represent only about one twentieth of one percent of annual national output.
State and local governments, particularly in New York, took the biggest hit from the blackout.
New York City comptroller's office estimated that losses topped $1 billion, including $800 million in lost gross city product — half of that in the first 24 hours. The figure also includes $250 million in frozen and perishable foods that had to be dumped, spokesman Michael Egbert said.
Michigan officials remained uncertain of the extent of the effect there, but economists estimated that it will be in the hundreds of millions of dollars. In hard-hit Cleveland, officials hoped to release cost estimates by Wednesday morning.
The airline industry, which lost several days of travel, was in the midst of assessing the damage. Officials declined to comment on costs, but Ray Neidl, who follows airlines for Blaylock & Partners, estimated the loss at $10 million to $20 million, "similar to what a very bad snowstorm would be."
Experts say investigators may not find a single event that triggered the cascade of shutdowns. None of the individual glitches would be enough to kill a city's lights on a normal day, and the grid is designed to work around one or two failures, but not more, Stauffer said.
Akron-based FirstEnergy was beset by at least three collapses Thursday.
The company said unexplained voltage swings knocked out a generator in its Eastlake plant. Later, a high-voltage power line tripped off. Soon after, another power line, heated by the extra voltage it absorbed from previous failures, drooped into a tree and shorted.
The big questions that need answering, Stauffer said, are the reasons behind intra-grid failures that allowed the blackout to spread like a computer virus from FirstEnergy's lines around Cleveland into the neighboring utility network in Michigan.
After darkening Detroit, the plague spread into Ontario, darkening Toronto, and then south into New York state, where it surged the length of the Empire State, finally toppling the mighty grid that feeds New York City.
Amid such debacles, many things worked as they should have, Stauffer said. Power networks that lock into FirstEnergy — including those operated by PJM Interconnection and American Electric Power — did seal themselves off from the storm, saving Boston, Philadelphia, Pittsburgh, Columbus, Ohio, and other cities from the same fate.
Ultimately, Abraham said, the probe of the blackout will uncover as much about overall problems with the nation's grid as it does about the specific causes of last week's blackout. The conclusion is likely to be that more money must be invested.
"At the end of the day, the companies and the users are going have to obviously pay that bill," he told the Early Show.