SEA-TAC AIRPORT -- The essential tools for testing a luggage conveyor belt include1,600 bags of dog food and 160 jars of peanut butter, according to airport officials.

Of course, after you run the tests, you're stuck with the 1,600 bags of dog food and 160 jars of peanut butter.

Port officials spent $40,000 on 12 tons of dog food in order to test the reliability of its luggage conveyor system. To simulate how the conveyor would handle luggage, airport officials took sacks of dog food and put them in luggage.

The approach begs the question: why dog food?

"Well, it gives it some weight and substance as it goes down the chutes. And around corners, it acts like a normal bag," said Terry Dix, who tested the conveyor system.

Some bags were loaded with pieces of reinforcing steel. And 160 bags got 8-ounce jars of peanut butter.

"Peanut butter is a fluid and it will set off an alarm for explosives. It simulates an explosive," Dix said.

The X-ray machine spotted all the steel and peanut butter and shunted it aside for special inspection. Oh, and in case you're wondering, one in every four jars of peanut butter broke.

"It's a reliable system. It's nice to bags, but some bags will break," said Port of Seattle spokesperson Dana Egbert.

Bottom line: this is all about security, not so much about protecting your bag.

The $40,000 worth of dog food was bought with airport fees, not taxes.

"If you flew somewhere, probably a little bit of your cost came in for dog food," said airport spokesperson Terri Ann Betencourt. "Maybe a kibble."

The dog food won't be wasted; it will be donated to local animal shelters.