Major fires will involve complex communications and require understanding Incident Command terms to monitor the fires with ease. ScanCal only defines major fires by its complex communications and ICS structure. CalFire/USFS may declare a fire Major on its own terms.
As a fire progresses in size, intensity and threat to structures or subdivisions, the Incident Command will quickly expand its Operations Section to include multiple Divisions, multiple tac nets, etc. If a fire's offensive attack progresses past a 12 hour shift, a Command Team is typically established. Traffic between IC and Dispatch may grow signficant to dedicate a dispatcher just for that incident. That dispatcher will communicate with IC over a command net.
The first 12 hours of a quickly growing fire can be chaotic over the radio. It is important to pay attention. Requests for additional tacticals will come to the ECC; they will announce it back to IC only once. On air attack, if they start getting a lot of copters (rotary) over the incident, Air Attack may switch them to a victor frequency. Once the first 12 hours are over and an Incident Action Plan is established for the fire, a communications plan is established and you'll no longer hear new freqs mentioned over the air. Now it requires having someone on the inside of the incident to "leak" the plan out, or for scanner listeners near the fire to scan all possible tactical nets and report back what's active. The first 24-36 hours may keep the initial frequencies from day 1. However after 36 hours frequencies may switch to odd tacticals, NIFC channels, odd victor nets etc. to relieve the regular tacticals and return them back to the region for initial attack.
Incident Command System - Learn it. Understand it. Makes listening to a large fire much easier.
Communications on Major Fire - how various radio channels are assigned in a major fire.Parts of a Major Fire - Divisions, Flanks, Spots, Heels, Branch etc.
Strike Teams - strike team terminology explained
Divisions, Branches etc.
As a fire grows, the lines needed to contain the fire grow as well. Once a particular line gets too big for a single person to be in charge of, they will split it into different Divisions. Typically the Divisions start at the origin and go up from A along the left side and Z along the right side. (See parts of a major fire) If it gets even larger, they'll designate letters from the middle such as L, M, N etc. These will typically be opposite the fire from the origin, where it began. Each Division has a Division Supervisor in charge of the resources on their Division. Read up on ICS for more about Divisions etc. Each Division will typically have their own tactical frequency also.
Larger fires with multiple Divisions will eventually need to split into larger chunks, called Branches. A Branch Director will have multiple Divisions under him, which in turn has various resources and crews under the Division.
Summer lightning storms mean no sleep for weeks for the firefighters. As numerous storm cells travel through an area, a Lightning Coordination Area (LCA) will be established for that area in the CalFire Unit. (Forests activate a Lightning Plan). Recon flights will be established and a lot of resources move into the area in anticipation of a large number of fires. Fires are given names of 1-1, 3-2 etc. (one dash one) These names could be named by a branch or geographic area, or simply by storm series. Storm1 fire 4 or Area 2, fire 15 etc. Different Units will designate their names as they see fit. Priorities are set for each fire and resources do the best they can. Some fires may not have resources on them for 24-36 hours depending on the number of resources in the area. This is the most chaotic fire scanner traffic you will ever encounter due to the number of resources (and out of area resources) in such a small area, up to hundreds of fires, multiple frequencies involved that have equally important traffic, etc. To make matters worse, lightning storms tend to go across multiple neighboring areas, so all resources in the geographical area are stretched thin. This is the best time to have paper/pencil to jot down the numerous lat/lon coordinates of the fires as aircraft report them, including legal coordinates from lookouts etc. Topographic maps can be found here.