Alexandra Badzak stands in the entrance tunnel to the Diefenbunker, which will be divided to create two separate exits. (Kate Porter/CBC)

Ottawa's underground Cold War museum will be able to accommodate hundreds more visitors at once following an upgrade set to begin this fall.

All three levels of government have now committed $1.2 million toward the Diefenbunker's $1.5-million infrastructure project, including provincial money announced earlier in August.

The facility, now designated as a National Historic Site, was commissioned under then prime minister John Diefenbaker and built between 1959 and 1961 in the village of Carp as a secret shelter for Canadian government leaders in case of a nuclear attack. The bunker's four storeys are buried under a grassy hill in what is now part of Ottawa's western outskirts.

Even though the building was designed to house 500 people for 30 days, only 60 visitors are currently allowed inside at one time and only while led by a tour guide because the facility doesn't meet building code regulations.

One problem is all visitors must enter and exit through a single tunnel, said Alexandra Badzak, executive director of the museum.

"Most public facilities require a secondary exit," she said.

That forces the non-profit museum to turn away visitors and events that could provide revenue.

"We've had numerous requests for conferences, annual general meetings, that sort of thing, and we just can't accommodate them until we can … remove that capacity limitation," Badzak said.

The renovation project will include safety upgrades including:

• Divide the main entrance tunnel in half, officially resulting in two tunnels.
• Add sprinklers and a generator.
• Upgrade doors.

Once the upgrade is complete, the building will once again be able to accommodate 500 people at once.

Visitors will be able to tour the maze of government offices, meeting rooms and living quarters without a guide and the museum will be able to rent out its facilities for larger events such as weddings.

"We're looking at a lot more corporate retreats or high school programming where people get to play roles of the various people who would have come to the bunker in a lockdown situation, and pose ethical questions for them to work their way through."

Badzak is hiring several new staff to help develop audio guides, school programs, and rental ideas.