Jim McNulty and Chris Wood were two of three hostages held in the Silver Spring, Md. building Sept. 1. A security guard was also held hostage.
McNulty said on the show that he was confused at first when he walked into the lobby and saw a man with a gun.
"I start thinking, 'Are we doing a production here? Why would somebody be showing a gun?' until the man pointed at me, 'On the ground. On the ground,"' said McNulty.
The suspect, /*James Jae Lee*/, 43, was shot dead by police after a standoff. The gunman had a longstanding grudge against the /*Discovery Channel*/.
"I just start praying Hail Mary after Hail Mary," McNulty said. "I lost track of how many I said."
Wood said his cell phone kept going off, and at one point he was able to send an email to his boss.
When the standoff was over, and it was time to leave, Wood said, "I just turned and ran the fastest I think I've ever run."
Nearly 2,000 people work in the building, but no one got hurt because most of them were able to leave the building before the standoff ended.
The Associated Press contributed to this report