You won't brick it. You could always slap the thing in DFU mode and go from there if somehow the phone magically became "unusable" during an OTA update.
The OTA update isn't committed until it is downloaded and for this you need to be on Wifi w/ more than 50% battery. If something fails during the download, guess what, it won't be committed.
OTA updates are incremental, i.e. you don't receive an entire iOS image and instead just the things that have changed. If this worries you then by all means wait till you get home and do a full update via iTunes.