Security checkpoint gun seizures are at a three-year high for Denver International Airport, which sits third nationally for firearm recoveries.

Through the middle of December, 99 guns were confiscated by the Transportation Security Administration at DIA, eclipsing the 70 discovered at the airport in 2014 and 51 in 2013.

Only Dallas/Fort Worth International Airport and Hartsfield-Jackson Atlanta International Airport have surpassed seizures at Denver’s airport this year.

“I can’t speculate on why passengers continue to bring firearms to the checkpoint at DIA and airports across the nation,” said Carrie Harmon, a TSA spokeswoman.

Harmon said TSA works hard to communicate to passengers that firearms are not allowed, finding that most passengers caught with a weapon say they forgot the firearm was in their bags.

“These items are only allowed in checked bags, if declared to the airline and properly packed,” Harmon said. “Firearms must be packed in a locked, hard-sided container.”

Passengers found with a gun can face a civil penalty up to $11,000. The average penalty for a loaded firearm is $3,000, according to the TSA, and the average penalty for an unloaded firearm is $1,500.

Federal officials encourage passengers to check airline and TSA rules and restrictions before they head to the airport.

DIA ranked fifth nationally in firearm seizures in 2013 and 2014, according to TSA data.

So far this year, 2,633 guns have been seized at the nation’s airports. In 2014, the agency confiscated an average of six guns per day.

Denver security officials have also found other prohibited items on passengers, including an inert grenade discovered in September that prompted an evacuation.

Heath Montgomery, a spokesman for DIA, says Denver’s air hub is the fifth- busiest in the country and has the 17th most passengers of the world’s airports.

“Last year was a record-setter with 53.4 million passengers,” Montgomery added. “We are on track to possibly beat that this year.”

Jesse Paul: 303-954-1733, jpaul@denverpost.com or @JesseAPaul