Fire-fighting foam
When the CERN safety team and I heard the loud rumbling 25 meters underground, we weren't concerned. With no warning, it would have been frightening, but the rush of water through pipes overhead presaged a thrilling event. All of us on the second tier of the enormous CMS cavern waited through the noise for what seemed an incredibly long minute. Suddenly we were in a winter wonderland as white fluffy foam gushed from a dozen blowers along the ceiling. It was a deluge in which college foam-party fans could only dream to play.
In just two minutes, seven cubic meters of water were mixed with foaming liquid to create 5600 cubic meters of foam, enough to be knee-deep. The cavern's volume is 40,000 m3; however, the foam system is designed to fill 120,000 m3 since foam tends to collapse onto itself. If the CMS detector were installed, taking up most of the cavern, the foam would surge around the equipment to fill every nook.
With luck, this test will be the only time the foam is poured into the cavern—it is intended to put out any major fire that might start, but it would damage many of the fragile detectors of the experiment. And if, by accident, somebody is in the room when the system is activated, they needn't fear drowning. The foam is breathable; however, swimming lessons might be useful.
Carolyn Lee, CERN
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