I was fairly close to the fireworks, I'd say the setup was about 200 metres away.
The bonus of working at 18mm is that you're just poingting your camera and guessing anyways this way you can just catch a good one and crop out the rest later. Event at 18mm it was hard to get a full burst in the frame.
Bulb is a shutter speed setting that allows you to control the length of time the shutter is closed by holding down the button. You can have shutter speeds of a second up to all night if you lock your cable release.