After parking; B757 First Officer reports an air conditioning hose being ingested by the left engine. The hose was attached to a truck parked inside the safety zone.

Narrative

Upon taxi in to the gate we noticed an air conditioning truck positioned to our left near the jetway. I brought this to the Captains' attention and he acknowledged. I stated that it appeared to be a little close. We had a marshaller directing us in; a wing walker on the right side and a ramp agent near the nose wheel parking area just to the left of the lead in line. The captain continued in following the marshalers' directions. I mentioned that the truck appeared close to our path on the left side. The Captain slowed his taxi and paid particular attention to the truck as he continued in. The marshaller continued to guide us in while watching the truck. The wing walker was giving us the all clear signal and the ramp agent to our left was also waving us in. As the truck went out of my view on the left I asked the Captain once again how it was looking and he said it was outboard of the engine. Upon stopping on the assigned spot we kept the number one engine running while we waited on ground power to be connected. A few moments later we felt a vibration and the marshaller gave us the signal to shut the engine down. We shutdown the engine and found out we had ingested an air conditioning hose from the truck. We called maintenance and wrote up the incident in the log. We should have been more careful to make sure the truck was well clear of the taxi in area at the gate before proceeding in.