The abrupt failure of Massachusetts’ 911 system on Tuesday was a stark example of the disastrous consequences that can occur when an emergency network that is supposed to be reliable is, without warning, suddenly unreliable.

The outage, lasting nearly two hours, prompted a scramble among emergency agencies as they directed the public to reach out directly to the local authorities at less-familiar phone numbers or, as a last resort, go in person to their local firehouse.

Last year, more than 3.2 million contacts were made to emergency call centers in Massachusetts. Calls to 911 fluctuate significantly through the day, but that comes out to an average of 367 calls an hour, an indication of just how impactful the outage on Tuesday may have been.

It was far from the first 911 outage to strike a large region. Several major failures in recent years have sent officials scrambling.

In June 2020, an equipment problem led to a vast T-Mobile outage across the United States during which 23,000 calls to 911 went unconnected. The company later agreed to pay a $19.5 million settlement.

In September of that year, a 911 provider was doing preparatory work to update its system and inadvertently created an outage that lasted an hour and 17 minutes across more than a dozen states.