Washington (CNN) As the impeachment inquiry into President Donald Trump escalates on Capitol Hill, lawmakers are constantly looking at documents and interviewing key witnesses behind closed doors in a congressional secure room, or "SCIF."

House Republicans on Wednesday, as a protest, stormed the SCIF where Deputy Assistant Defense Secretary Laura Cooper was preparing to testify before the three House committees leading the inquiry. Some lawmakers even appeared to live-tweet from the SCIF once inside. The political stunt caused a five-hour delay of the hearing and angered Democrats. House Homeland Security Chairman Bennie Thompson of Mississippi requested House Sergeant-at-Arms Paul D. Irving investigate the "reckless action."

Here is what we know about the secured space that lawmakers have continuously convened in since House Speaker Nancy Pelosi launched a formal impeachment inquiry into the President in September.

What is a 'SCIF' and how is it created?

A sensitive compartmented information facility is a secured place where sensitive information can be viewed and discussed without the risk of spying. It can be any size or any place, including a closet or an entire building. The most commonly known SCIF is one of the most secured rooms within the White House -- The Situation Room. Among the intelligence community, SCIFs are accredited by the Office of the Director of National Intelligence and there are standards for determining what rooms are cleared for use as such. SCIFs have reinforced walls and electronic methods to prevent eavesdropping on classified conversations.

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