ONE EFFECT of the post-derecho uproar over power outages three weeks ago was to divert attention from an equally serious infrastructure meltdown: the collapse of emergency 911 service in most of Northern Virginia. Following the violent storm on June 29, some 2.3 million people lost access, for at least seven hours, to the nation’s most widely recognized telephone number, which in Northern Virginia is administered by Verizon; for some of them, it was not restored for several days.

Incredibly, the lesson for Northern Virginians was that they can rely on emergency 911 service — except in an actual widespread emergency, when a critical mass of people need it most. As one official told us, “It was like the Titanic sinking and nobody rang the bell.”

The result was tragi-comedy on a regional scale. Local officials, desperate to get the word out, resorted to traditional and social media — which in turn were not accessible to many people who lost power and cellphone service. In case of emergency, residents were advised to flag down passing police cars (if they could find one) or walk to the nearest fire station (in the blazing heat). Why not smoke signals?

The 911 breakdown seems inexplicable; it is certainly inexcusable. Simultaneous investigations are now underway at the Federal Communications Commission, Virginia’s utility-regulating State Corporation Commission and the Metropolitan Council of Governments. Verizon, which is conducting its own inquiry, owes the public as well as the regulators some answers.

Chief among the questions are how this could happen and what is being done to ensure that crash-proof and redundant backups are in place in the future.

Unfortunately, Verizon’s record of accountability, in Northern Virginia and elsewhere, is not encouraging. Last year, authorities in Maryland, where Verizon is the sole 911 service provider, said that the company had failed to notify emergency call centers in Montgomery and Prince George’s counties four times when service failed. In the worst instance, during a snowstorm in January 2011 that left commuters stranded for hours, some 10,000 calls to 911 failed to go through.

The failure to coordinate with local officials in Maryland should have sounded alarms for Verizon, but judging from its performance in the most recent major outage, it’s not clear that the company took corrective action. The storm knocked out power at several of Verizon’s 911 hubs; at one in Arlington, a backup generator failed to kick in, for reasons that remain unexplained.

Despite that, Verizon did not notify local officials in Northern Virginia until the next morning, nearly 12 hours later. Why not? And why was 911 service still impaired for some people more than 48 hours after the storm had passed?

In general, the company seems to have shirked its responsibility to keep local governments, and therefore the public, in the loop. Northern Virginia officials have asked Verizon to develop procedures to notify local governments quickly in the event of any interruption in 911 service and provide them with timely information in emergencies. Officials have also asked the company to carry out twice-yearly drills simulating steps to be taken in coordination with local jurisdictions in 911 outages. Those seem like reasonable minimum steps for Verizon to take immediately.