Q:

A major incident was declared

A major incident was declared when winds caused two fires to merge near communication masts on Saturday.
From BBC.com
How should we interpret the main clause that a major incident was declared? Does it mean when winds caused fires and at that time somebody declared an incident or the major incident here is exactly the fire incident?
https://www.bbc.co.uk/news/uk-england-lancashire-44676707

A:

It is part of the procedure of the Fire Brigade. 
A small fire will be put out by the local fire brigade. But if the fire becomes more serious the local fire chief will decide to call it a "major incident" and get external help and support.
In this case, there were two small fires. The winds changed and the two small fires joined up to become one large fire. This fire was near some "communication masts". The local fire chief realised that his firefighters couldn't put out the fire alone, so he called the fire a "major incident" and got help from other firefighters.
As the reporter doesn't know who the fire chief is, the reporter uses the passive voice.

