Noise cancellation headphones can actually cope very well with this sort of situation, because they completely control the sound in a way a PA system can't.
The microphone allows the headphones to pick up the noise which would enter your ear and play it back out of phase. It does work best with constant sounds, such as the background noise on an aeroplane or road noise etc., but it successfully works to a greater or lesser degree across a wide range of frequencies.
From ocertain's review on Amazon:
they are better at cancelling some types of noise than others. With the noise cancellation engaged and no music playing, on one side of the scale - the whoosh of the building's climate control system disappears completely. On the opposite side - nearby voices, including an office-mate with a "public speaker's voice", are still there but sound very far away. If I apply a low volume of music to the headphones with the noise-cancellation engaged, I'm completely isolated from the surrounding din. Nirvana.
Additionally, the headphones attenuate the sound considerably so the out of phase sound doesn't have to be at a high level.