Norwich — Firetrucks from nearly two dozen paid and volunteer fire departments and other emergency responders will converge on downtown Norwich on Sunday morning in what will appear to be a major fire at the giant historic mill complex at the junction of Franklin, Willow and Chestnut streets.

Instead, it will be one of the largest known fire drills in the city's history, Fire Chief Kenneth Scandariato said, to prepare for a general alarm blaze at the urban mill complex that could threaten numerous surrounding residential buildings.

It's a plan that has been in the works for two years, and Scandariato hopes will never have to be put to use.

The drill will start at 9 a.m. and run for about 90 minutes.

Mainly, it will test and practice the positioning of firetrucks from the Norwich departments, the tower trucks from the Mashantucket and Mohegan tribal departments and several other support vehicles, Scandariato said.

Trucks will be arranged and repositioned according to varying scenarios coordinated by the command team. Communications also will be tested.

Scandariato said no fire hoses will be laid out or used Sunday, but that plan also is envisioned, with extra pumper trucks to be deployed, and if necessary, hoses strung out from Norwich Harbor to the mill complex.

In the early planning for a potential major fire at the mill, city fire and Norwich Public Utilities officials determined that the downtown water supply would not be adequate.

NPU already has made hydrant modifications to boost the water supply for downtown firefighting, Scandariato said.

The mostly vacant, 216,000-square-foot F-shaped mill complex was identified as the top “target hazard” in the urban downtown area, Scandariato said.

The four-story brick main building is attached to two other buildings, one a wood-framed structure.

Streets are narrow and rear courtyards even narrower, restricting access by firetrucks.

The chief met numerous times with owner Maurice Mozinia of Franklin St. LLC, who agreed to remove “tons of combustible materials” stored in the mill.

Still, a large fire would pose a major threat to the Artspace apartment complex across Willow Street, the closest residential building, along with many other buildings on Franklin and Chestnut streets.

So the plan worked out by the city paid and volunteer fire departments, the Uncas Health District, Norwich Emergency Management Department and other agencies is a “surround and drown” tactic to preserve the neighboring structures.

Nearby residents would be evacuated to safe areas — although evacuations are not part of Sunday's drill.

“This drill is primarily a staging drill to show everyone where they need to be and put it in the minds of the first responders that they have to go to this hydrant or location or that hydrant or location,” Scandariato said. “It's been a two-year process to identify a hazard and develop an attack plan for positioning apparatus and developing attack plan.”

c.bessette@theday.com

Twitter: @Bessettetheday