The Federal Communications Commission has opened an inquiry into what prevented Verizon’s Northern Virginia customers from getting through to several 911 emergency centers after the brutal June 29 storms.

The review of Verizon’s performance is included in a broad inquiry into service problems at about a dozen carriers from Ohio to Virginia that handle calls for 911 call centers. The review will also look at the loss of customers’ telephone service.

Problems in Northern Virginia and West Virginia were “systemic,” the FCC said in its notice, while there were isolated breakdowns in Ohio, Kentucky, Indiana and Pennsylvania.

The overall effect was the partial or complete shutdown of a “significant number” of 911 systems and communications services, the FCC said.

Verizon has said that some of the Northern Virginia problem tracks to the failure of one of two generators at an office in Arlington County that provide backup power for 911 service in the heavily populated urban and suburban areas. But Verizon continues to investigate other mechanical and equipment failures, the company has said.

The FCC said it is seeking to find the cause of the outages, the effect on 911 systems and the impact on residents, along with assessing the reliability and resiliency of emergency systems. On Thursday, David Turetsky, bureau chief of the FCC’s Public Safety and Homeland Security Bureau, is expected to give a status report on the 911 outages in a regularly scheduled monthly meeting of the commission.

Verizon and local public safety officials have disagreed about the extent and duration of the 911 failures. Verizon has said outages lasted through June 30 in an area that would include 1.5 million people in Fairfax and Prince William counties and Manassas and Manassas Park.

Local 911 officials said outages extended to July 3, before both caller phone numbers and corresponding addresses reliably showed up in Arlington, parts of Alexandria and other areas of the region. That would increase the affected population to 2.3 million.

Local officials also questioned how promptly Verizon notified them of downed 911 center service.

The FCC requires companies to notify it within two hours of discovering a significant network outage, and Verizon did so, said spokesman Harry Mitchell. Information in the report to the FCC is regarded as confidential and there is a process for filing a full accounting of the reasons behind outages.

As the 911 outages extended into the Washington area and parts of West Virginia, the FCC enhanced its live monitoring. It activated a voluntary disaster reporting system that lasted from about 5 p.m. June 30 through July 3, with a few pockets still under heightened review until July 4. Under the added review, the FCC called out daily to companies to check where they stood with outages and repairs.