Final answer:
Probationary firefighters must complete their probationary period before being eligible to work the extra board, as this time is critical for training and assessment.
Step-by-step explanation:
Probationary firefighters will not be eligible to work the extra board until they have completed their probationary period. The probationary period is a designated span of time given to new recruits to demonstrate that they can effectively perform the duties of a firefighter. It often involves rigorous training, evaluations, and an expectation of learning and adhering to the department's protocols and ethics.