A Vortex in Vegas: Advanced fire protection

Last month I was in Las Vegas attending the AUVSI unmanned-vehicle trade show to research an article. While there, I stayed at the Luxor Hotel. It's a pyramid-shaped building with hundreds of rooms arrayed around a cavernous atrium. From the outside, it looks like this:

Those who have walked around the atrium might recall this part of the ground floor near the hotel registration desk and escalator to the theater level. 

Tucked into this scene is a slightly odd structure, about twelve feet high. It looks like a stack of leftover blocks from the Egyptians' last pyramid. 

Here's a closer view. Can you guess why it's there?

Here's another view:

Why would faux limestone blocks have a big hole in a slanted face? Because it's the exhaust port for a very powerful fan. There are eight of them around the base of the atrium (diagram from Fire Protection Engineering, Summer 2000).

Together with other gear (such as smoke-detecting light beams emanating from the obelisk) the "vortex fans" are critical to controlling the movement of smoke in case of fire. 

(That's important because smoke is the principal hazard in most fires, as we know from disasters like the MGM Grand fire in Las Vegas. In that 1980 fire, out of 84 people who died, 82 succumbed to fumes and smoke, rather than flame.)

 Clark County's building department wouldn't have allowed the Luxor Hotel to open without the special arrangements, because standard smoke-handling methods wouldn't work for a giant atrium.

In a traditional building like an office building or an older hotel, each level can be pretty well isolated by careful attention to stairway doors, floor decks, and seals in elevator-lobby doorways. That makes smoke control straightforward: if the barriers hold, smoke can't rise from the fire floor to threaten people on floors above.

The situation is more challenging in tall buildings with cavernous atrium spaces. These have no barriers to smoke movement, so heated smoke can rise, cool and form a toxic, stagnant layer at the top of the space. Why not just install whopping big fans at the apex? It wouldn't be enough to protect guests in the upper levels because a dangerous smoke layer could still form and spread sideways into the rooms. Just raising the apex-fan horsepower would create hazards of its own. 

The solution proposed was this: eight high-capacity fans around the base of the atrium, aimed upward and diagonally, would set the atrium air moving in a vortex. That would confine the smoke into a spiraling column, keeping it away from the floors as it rose toward exhaust fans in the apex.

Clark County wanted a test to verify the computer model, so the hotel owners brought in Hollywood-type smoke generators and gas-fired space heaters to simulate hot smoke from a fire in the base of the atrium.

I'm told the smoke test at the Luxor worked well, with the fans keeping the smoke out of rooms in the upper floors. And kudos to whomever insisted on verifying the model results with a field test! I put little faith in computer models that aren't tested, and retested, against the real world.