The pronoun that takes the place of the singular noun 'fire crew' is it.
There is a tendency to use the pronouns 'they' and 'them' when referring to one crew or one team as representing the members of the crew or team rather than the crew or the team as a single unit. However, although technically incorrect, it is commonly used in informal language.
Correct: The fire team was called. It arrived in minutes.
Informal: The fire team was called. They arrived in minutes.
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