Quotes of the Day

A WIRED WORLD North America is crisscrossed by thousands of power-transmission lines linking generators and cities in a complex web designed to send power where it is needed

THE LAKE ERIE LOOP Investigators now think the crisis started with the failure of several transmission lines near Lake Erie. The clockwise flow of power around the lake was very suddenly sucked backward, destabilizing the flow of electricity

How Electricity Is Supposed to Flow ...
1 --Power plant --Generator

Electricity starts at the power plant, produced by a spinning generator driven by various means: a hydroelectric dam, a large diesel engine, a gas turbine or a steam turbine. The steam is created by burning coal, oil or natural gas or by a nuclear reactor

2 --Transmission substation

At a transmission substation, large transformers increase the voltage from thousands to hundreds of thousands of volts so the power can be shipped long distances

3 --Power substation

The electricity travels along high-voltage lines to a power substation. There, the power can be redirected to other high-power lines or stepped down to a lower voltage that is sent to neighborhood power lines

... AND HOW ONE FAILURE CAN SPREAD 4 --High-voltage transmission lines

Power grids are a delicate balance between supply and demand in which sudden fluctuations can cause portions to fail. If, for example, a transmission line breaks, the system is designed to isolate the problem and disconnect it from the grid

5 --Transmission substation

In last week's case, control mechanisms — computers, circuit breakers and switches — failed to contain the problem quickly, causing rapid fluctuations at substations elsewhere in the grid, tripping more shutdown mechanisms

6 --Generator --Power plant

The problem spread fast back to generating plants that then were producing too much or too little electricity, causing more shutdowns. Eventually, the problem was contained, preventing a blackout that could have spread as widely as the entire eastern half of the U.S.

POWERFUL NUMBERS The biggest blackout in North American history set all sorts of records

50 million people in the U.S. and Canada affected

8 states and 2 Canadian provinces experienced power failures

3 deaths attributed to the blackout

22 U.S. and Canadian nuclear plants shut down

10 major airports shut down

700 flights canceled nationwide

850 arrests on the night of the blackout in New York City compared with 950 on a typical night)

23 cases of looting reported in Ottawa

7,600 gal. (29,000 liters) of drinking water distributed by the National Guard in Cleveland after the city's four main pumping stations failed

350,000 people on the New York City subway when the power went out. Nineteen trains were in underwater tunnels

Sources: North American Electric Reliability Council; Department of Energy; ESRI; AP; Philadelphia Inquirer; New York Times; How Stuff Works

• Missy Adams