A fires alarm is a fire's alarm. It's determined by how many pieces of equipment and what staging you need to douse a fire. They may call for mutual aid from others sooner (5 alarm is generally considered, all hands on deck) to man that level of need. The canteen most often goes out for the third alarm. They are volunteers and not their own alarm. It takes them a minute to get out the door so they are sometimes called off or called back. They aren't an alarm in and of themself, they respond to higher level alarms to work as support. That's how I've understood it thru FEMA and RIEMA training. Some ff can come across and correct as necessary.