Jeffrey D. Allred, Deseret News
File - University of Utah Health Care's new EC145 helicopter lands in Salt Lake City on Friday, Dec. 28, 2012. For the first time ever, the University of Utah plans to activate an extra medical helicopter and preposition it in Wyoming for the Great American Eclipse on Aug. 21, part of a major medical preparedness effort.

JACKSON, Wyoming — For the first time ever, the University of Utah plans to activate an extra medical helicopter and preposition it in Wyoming for the Great American Eclipse on Aug. 21.

It's part of a major effort to be ready for routine medical problems — and even a large-scale disaster — as millions of people may head for states where the solar eclipse will be total.

All across Wyoming, they're getting ready for an invasion. And in Idaho too. Roads might be jammed, possibly for days.

"Folks are going to have medical emergencies, and we've got to be able to get to them," said Idaho Falls Fire Chief Dave Hanneman, who is serving as incident commander for the eclipse.

Hanneman's command is designed to coordinate the response of numerous agencies in eastern Idaho. Planners are bracing for up to a half-million visitors just in that region.

"Roughly speaking, doubling the population for potentially four days," said Coleen Niemann, spokeswoman for Eastern Idaho Regional Medical Center.

The hospital serves a vast region, including Yellowstone and Grand Teton national parks. The medical center has banned any vacations by staff members from Aug. 19-22, the days surrounding the eclipse.

"We've never done that before, to my knowledge," Niemann said.

Across the Teton mountains in Jackson, Wyoming, officials at St. John's Medical Center decided not to schedule any appointments at their clinics on Aug. 21.

"We are bringing in the staff from all of those clinics to be on hand should we need extra doctors and nurses and other professionals," St. John's spokeswoman Karen Connelly said.

On the morning of Monday, Aug. 21, as the moon slides in front of the sun, the moon's shadow will race across the United States. Only in a narrow "path of totality" that slices through Idaho and Wyoming will viewers see a total solar eclipse.

In Utah, where it's only a partial eclipse, thousands may decide to drive north for a better view. No one knows how many will be on the move.

Over the years, law enforcement and medical agencies have practiced for various potential disasters, but they've never rehearsed a similar situation, Hanneman said.

"We've never really planned for something this big as a real event happening," he said.

The hospital in Jackson is working with the University of Utah, which will activate a spare AirMed helicopter. It will be prepositioned in Jackson with extra staff to fly round-the-clock if necessary.

"We've never done anything like this," said paramedic Cory Cox, outreach coordinator for AirMed. "We've prepositioned for special events before, but we've never brought in extra staff and an extra helicopter."

The special arrangement reflects concern that roads might be jammed in areas served by St. John's Medical Center.

"We want to be able to get to patients in the field to get them to care," Connelly said. "But also, if it becomes necessary to move them on to a larger care center for more definitive treatment, we want to be able to get them there quickly and safely."

The University of Utah helicopter will be prepositioned at a public safety helipad in Teton County.

"We are dedicated to that county and that hospital," Cox said. "Whatever they need, we will help them out."

One of the things that especially haunts some of the planners is the possibility that thousands of people from other states will flood into remote areas — and high-elevation places — with no experience or know-how about the various risks.

"Conduct around wildlife they might not be familiar with," Niemann said. "Fire safety they may not be familiar with."

In addition to relatively uncommon risks like snakebite, bear attacks and altitude sickness, there's concern that routine medical emergencies will occur in numbers much greater than normal.

"I'd say we're worried," Niemann said, "because it's not something we have history around."

One location of special concern is I-15 in the Idaho Falls area. Thousands of cars may crowd onto the freeway right after the eclipse and create a sprawling traffic jam in the southbound lanes.

"We think the interstate is going to be bumper to bumper," Hanneman said. "On Aug. 21, it's going to be very hot."

With so much potential for medical problems, ambulances will be prepositioned along the freeway. Two extra medical helicopters will be stationed in eastern Idaho. There's even a contingency plan to set up a triage tent outside on the grounds of the regional hospital.

"That is not for sure," Niemann said. "That will be only if patient load requires."

The Great American Eclipse might be a once-in-a-lifetime experience for sky-watchers, but it could be an epic test for medical responders.