Why is Blue Foam on the Ceiling?
October 10, 2013 2:28 PM   Subscribe

Does anyone know the purpose of the light blue foam sprayed on the exposed ceiling beams at the Powell subway station in San Francisco? Is it acoustic? Rust prevention? Fire retardant? Decoration? Something else?
posted by Jeff Howard to Technology (7 answers total) 2 users marked this as a favorite
 
Your guess is correct. That material is a fire retardant applied to the structural steel. You can see a nearly identical photo with the same light blue color on the second page of Fire Protection of Structural Steel... ´┐╝For Dummies, STRUCTURE magazine, November 2005.
posted by RichardP at 2:48 PM on October 10, 2013 [2 favorites]


Interesting. Spray-Applied Fire Resistive Material (SFRM). Thanks RichardP.
posted by Jeff Howard at 3:02 PM on October 10, 2013


And the reason it's there is that in a fire, steel will get hot and lose its strength, so you need to insulate it even if it won't burn.
posted by Monday, stony Monday at 3:05 PM on October 10, 2013 [2 favorites]


Yeah. The alternative is to a cementitious coating is intumescent paint, which is an order of magnitude more expensive. So if you go into a building that has exposed steel beams, chances are that it was painted with intumescent paint -- which, when heated, expands to create a protective foam.
posted by suedehead at 3:49 PM on October 10, 2013 [2 favorites]


The alternative is to a cementitious coating is intumescent paint, which is an order of magnitude more expensive. So if you go into a building that has exposed steel beams, chances are that it was painted with intumescent paint -- which, when heated, expands to create a protective foam.

I think chances are slightly more favorable that a building without spray-on fireproofing just doesn't require a fire rating, which is actually quite common. Lots of retail big box stores and high-ceilinged spaces (more than 20 feet) of almost any use would fall into that category.
posted by LionIndex at 7:03 AM on October 11, 2013


You're probably right, LionIndex. Also, most probably varies by state/local fire code.
posted by suedehead at 2:00 PM on October 11, 2013


in a fire, steel will get hot and lose its strength, so you need to insulate it even if it won't burn

Of note, this was in fact the mechanism of collapse at the World Trade Center. The towers were constructed based on older code, but were in the process of being upgraded for fire resistance with SFRM. Unfortunately, the impact from the planes, and the consequent "springing" effect on the structure, meant that most of the foam was shaken off even where it had been applied. This left the structural elements vulnerable to the intense heat from the burning jet fuel and other combustible materials.

Specifically, 9/11 has had a real influence on the evolution of building codes for skyscrapers.
posted by dhartung at 5:07 PM on October 11, 2013 [1 favorite]


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