BANGOR, Maine — It’s hard to imagine a worse occurrence. A commercial airliner on approach to Bangor International Airport breaks up in the air scattering debris over a 5-mile area of Bangor and Brewer.

That’s the scenario for a planned exercise Thursday to determine how various emergency and governmental agencies would cooperate to deal with such a disaster.

According to Bangor Fire Chief Tom Higgins, nearly 200 emergency responders and officials from across the region will participate in the event scheduled for 8 a.m. to 4 p.m. at the Cross Insurance Center.

Sponsored by the U.S. Department of Homeland Security and the National Transportation Safety Board, the exercise is a tabletop exercise, meaning no actual emergency equipment or personnel will be deployed.

Instead, responders will talk through the scenario, making decisions about command structure, resources and how various agencies across the region can cooperate to deliver a timely and effective response over such a large area.

With participants including the Maine Emergency Management Agency, the Penobscot Emergency Management Agency, the U.S. military, and the Maine Department of Transportation, Higgins said the exercise is the largest such gathering he knows of.

“One of the goals is to examine our ability to deliver the required response,” he said.

The scenario will assume pieces of the aircraft land in Bangor, Brewer and possibly as far away as Hampden.

Higgins said he expects the exercise will show excellent cooperation between the various agencies that would respond to such a disaster. The exercise will be closed to the public.

Follow Evan Belanger on Twitter at @evanbelanger.