The August 2003 blackout began on August 14, 2003, a few minutes after 4:00 p.m. Eastern Daylight Time, and cut electricity to an estimated 50 million people and 61,800 megawatts of load in eight U.S. states and the province of Ontario. The joint U.S.-Canada Power System Outage Task Force traced the start of the failure to northern Ohio, not to Ontario. In Toronto the lights, subway, traffic signals and elevators stopped within minutes.
Timeline of August 14, 2003
The Task Force final report (Chapters 4 to 6) reconstructs the afternoon in Eastern Daylight Time (EDT). Most of the early steps happened in the control area of FirstEnergy, an Ohio utility, hours before Ontario was affected.
| Time (EDT) | Event in the Task Force report |
|---|---|
| 12:15 p.m. | Inaccurate input data leaves a monitoring tool of the Midwest operator MISO ineffective. |
| 1:31 p.m. | The Eastlake 5 generating unit near Cleveland trips and shuts down. |
| Shortly after 2:14 p.m. | The alarm and logging system in the FirstEnergy control room fails and is not restored before the blackout. |
| 3:05 p.m. | The Harding-Chamberlin 345-kilovolt line trips after touching a tree. The Hanna-Juniper line follows at 3:32 p.m. and the Star-South Canton line at 3:41 p.m. |
| 4:05:57 p.m. | The overloaded Sammis-Star 345-kilovolt line trips. The report calls this the event that started the uncontrollable cascade. |
| 4:10 to 4:13 p.m. | Thousands of line and generator trips spread through the Northeast and Ontario. |
| 4:11:58 p.m. | Ontario frequency collapses and a widespread shutdown follows, with 22,500 megawatts of Ontario load lost, including Toronto, Hamilton and Ottawa. |
What caused the failure
The report groups the causes into four categories: inadequate system understanding, inadequate situational awareness, inadequate tree trimming, and inadequate support from the regional reliability coordinator. The tree finding is the most concrete. The report says three FirstEnergy 345-kilovolt lines failed between 3:05 p.m. and 3:41 p.m. because they sagged into overgrown trees, even though each carried a current below its rating.
The control room at FirstEnergy had lost its alarm system, so operators did not see that the network was weakening. The report states that by about 3:46 p.m. the only way to avert the blackout would have been to drop at least 1,500 megawatts of load around Cleveland and Akron, and that no such step was taken. It also found that reactive power supply in the area had been inadequate for several years and that the regional reliability council had not identified this weakness. The investigators listed seven violations of the voluntary reliability standards administered by the North American Electric Reliability Council (NERC) and noted that the causes resembled those of earlier major outages.
How the cascade reached Ontario
After the Sammis-Star line tripped, power flows looked for other paths. Ontario sat on one of them. According to the report, Ohio, Michigan, New York and Ontario were scheduled net importers of power that afternoon, and large swings pulsed around Lake Erie as lines tripped. At 4:11:10 p.m. three lines west of Niagara tripped a second time and most of Ontario separated from New York. Ontario frequency fell to 56 hertz by 4:11:57 p.m., the last ties to Michigan opened, and the province’s system shut down within seconds.
The Independent Electricity System Operator (IESO) describes the result in provincial terms. Nearly all service east of Wawa was lost, apart from small pockets. Protective equipment separated the grid at Wawa and kept the northwest supplied. Cornwall stayed on power from Quebec, and the Niagara area isolated itself, with the Sir Adam Beck generating station helping to restart the system.
Toronto during the outage
The Toronto Transit Commission (TTC) records that power was lost at 4:13 p.m. About 30 subway trains were stranded in tunnels and about 160 streetcars on streets and in stations. All passengers were evacuated over several hours with no injuries reported. On August 15 the TTC announced that the subway would stay closed until it could count on a stable supply, and it explained that trains, signals, lighting, communications and ventilation all need uninterrupted full power.
The TTC chronology records that on August 15 Toronto Hydro reported that the city was receiving 80 percent of its electricity supply but that only 50 percent of residential areas had power, and rotating outages were in effect. The same chronology notes that Toronto Fire Services completed 110 elevator rescues. The CNE opening was postponed (see the article on the Canadian National Exhibition). A Globe and Mail headline of August 15, 2003, quoted by the Toronto Public Library, reports that Mayor Mel Lastman triggered the city emergency plan. On Sunday, August 17, the TTC announced that full service would run the next day, with Toronto Hydro feeding the 40 substations that power the subway without interruption. The first southbound train left Finch Station at 6 a.m. on Monday, August 18. The utility’s wider history is covered in the article on Toronto Hydro.
Nuclear plants and restoration
Eleven Ontario nuclear units were delivering power when the disturbance hit: four at Bruce B, four at Darlington and three at Pickering B. Seven shut down (one at Bruce B, three at Darlington and three at Pickering B). Four disconnected from the grid but stayed ready to supply it. The Task Force nuclear group found no evidence that the plants triggered the outage, and the plants were kept in a safe shutdown condition. Three Bruce B units and one Darlington unit were back on the grid within six hours. The other three Darlington units returned on August 17 and 18, and three Pickering B units and one Bruce B unit returned between August 22 and 25. Off-site power was unavailable for roughly three hours at Bruce B and nine hours at Pickering A.
The IESO directed restoration in three stages: generators first, then high-voltage lines and critical customers, then local distribution companies. It says the system was restored within 30 hours, and that daily appeals cut peak demand by 15 to 20 percent until the appeal ended at 8:00 p.m. on August 22.
The provincial emergency
Premier Ernie Eves signed a Provincial Declaration of Emergency under the Emergency Management Act, dated August 14, 2003 at 9:00 p.m. in Toronto and covering the whole province, as printed in the Ontario Gazette of August 23, 2003. A notice in the Gazette of September 13, 2003 records that he terminated the declaration on August 22, 2003 at 8 p.m.
Cost, findings and recommendations
The report puts the Canadian cost at a 0.7 percent drop in gross domestic product for August, 18.9 million work hours lost, and a reduction of $2.3 billion CAD in Ontario manufacturing shipments. U.S. cost estimates ranged from $4 billion to $10 billion USD. The two governments created the Task Force on August 15, 2003. It issued an interim report on November 19, 2003 and a final report, released on April 5, 2004, with 46 recommendations. It also held a public meeting in Toronto in December 2003. The single most important recommendation was to make compliance with reliability standards mandatory and enforceable.
Figures that sources report differently
- Time of the Ontario collapse: the Task Force gives 4:11:58 p.m. for the Ontario shutdown, the IESO gives 4:11 p.m. as the start, the TTC records 4:13 p.m., and the Toronto Public Library blog notes that the Globe and Mail used 4:15 p.m. for Toronto.
- Length of restoration: the IESO says the Ontario system was restored within 30 hours. The Task Force says parts of Ontario had rolling blackouts for more than a week. The Toronto Public Library blog says restoration took nine days.
Common questions
What caused the 2003 blackout?
The Task Force found that overgrown trees, a failed alarm system at FirstEnergy and weak monitoring by regional operators let line failures in Ohio spread into a cascade. The report says the blackout could have been prevented.
Did the blackout start in Toronto or Ontario?
No. The first failures were in northern Ohio. Ontario lost power about six minutes after the Sammis-Star line tripped.
How long did Toronto’s subway stay closed?
The TTC closed the subway on August 14 and planned to reopen it with the first train on the morning of Monday, August 18, according to its history page.
When did Ontario’s state of emergency end?
The Ontario Gazette records the declaration at 9:00 p.m. on August 14, 2003 and its termination at 8 p.m. on August 22, 2003.
Related reading
- History of the utility that serves Toronto customers
- How the subway and streetcar network grew
- The SARS outbreak of the same year
- The fair whose 2003 opening was postponed
- Overview of Toronto’s history
Last verified: October 2026
Sources
- U.S.-Canada Power System Outage Task Force, Final Report on the August 14, 2003 Blackout in the United States and Canada: Causes and Recommendations, April 2004, U.S. Department of Energy
- Natural Resources Canada with the U.S. Department of Energy, “Canada-U.S. Task Force presents final report on blackout of August 2003,” news release, April 5, 2004, Government of Canada archive
- Independent Electricity System Operator, Blackout 2003
- Ontario Gazette, volume 136, issue 34, August 23, 2003 (Provincial Declaration of Emergency), Government of Ontario
- Ontario Gazette, volume 136, issue 37, September 13, 2003 (termination of the declaration), Government of Ontario
- Toronto Transit Commission, “The blackout of 2003”, Back Track
- Toronto Public Library, Local History and Genealogy blog, “Remembering the 2003 Northeastern Blackout in Toronto” August 2018
Cite this page
APA: History of Toronto. (2026, October 23). The August 2003 Blackout in Toronto and Ontario. https://historyoftoronto.ca/blog/blackout-2003-toronto
MLA: “The August 2003 Blackout in Toronto and Ontario.” History of Toronto, 23 Oct. 2026, https://historyoftoronto.ca/blog/blackout-2003-toronto. Accessed .
Chicago: History of Toronto. “The August 2003 Blackout in Toronto and Ontario.” Last modified October 23, 2026. https://historyoftoronto.ca/blog/blackout-2003-toronto.
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