PROVIDENCE — At 8 a.m. Tuesday, the Fire Department will switch over for good to the 800 MHz radio frequency. That means it will be using a new digital microwave communications system that promises to keep first responders in close contact throughout any local, regional or statewide emergency.

Although the department has been testing the digital system for months and officials are confident of success, the city Department of Communications will keep its current VHF system running as a backup until about mid-September –– just in case.

Until the construction of the digital system, the Police Department relied on an ultra-high-frequency, or UHF, system and the Fire Department on a very high-frequency, or VHF, system. Both were dependent on leased telephone lines. The police went wireless and digital in July 2008.

The police had a small taste of the improvement in late winter, recalled William Trinque, city director of communications, when a glitch in the new system caused the police to lose communications for a few minutes. To maintain communication, they were able to take advantage of the flexibility and redundancy of the new setup by quickly switching over to the statewide digital network.

“It worked perfect,” Trinque said.

The problem turned out to be a neglected battery in a microwave tower, according to Joseph McGarry, deputy director of communications. When the backup battery ran out of energy, the signal from the tower was interrupted. The problem has been corrected.

Every frontline and reserve fire truck and rescue truck has a digital mobile radio, with a portable radio available at each manned position on a truck. In addition, according to McGarry, each fire truck has a repeater, which is a piece of equipment that boosts the signal to better penetrate buildings.

The city Department of Public Works is tied into the digital system, and ultimately the Parks Department and Water Supply Board will be, too.

One of the steps taken to prevent a repeat of the “December Debacle” was to give the School Department a digital radio for officials to keep an open line to First Student, the school bus contractor, according to Trinque.

The December Debacle occurred on Dec. 13, 2007, when several circumstances, including an underestimated snowstorm and inattention by key officials, combined to gridlock traffic in and around the city. Young children were stranded on school buses until late at night.

During the snowstorm, school officials complained, they lost touch with First Student when the company’s phone lines became clogged. The communications breakdown contributed to the debacle, an investigatory committee concluded.

One of the advantages of the digital system on the 800 MHz frequency is its statewide reach — much broader than the antiquated intercity radio. As a test, Trinque said, he took a portable radio with him on a fishing trip to Block Island and was able to easily call McGarry in Providence with crystal clear results.

If there is more than one emergency at the same time, first responders are supposed to be able to easily manage by using the multiple “talk groups” of the digital system. The intercity radio had only one channel, so there was a bottleneck.

“One of the nice features of this system,” McGarry said, “is that it is really three independent [regional] systems.” If any one part fails, communication can be maintained by using the other parts across the state.

Although state agencies and all municipalities have the necessary digital equipment in hand, there are important communication and training protocols to be written and imparted to everyone concerned, McGarry pointed out.

There will be “a hailing channel for everybody,” but before meaningful communication can occur, he said, all must agree on the language and terminology and on the standard operating procedures, or SOPs, to be used.

gsmith@projo.com