Absolutely. And then someone grabs the authorities, they ascertain that access to the fire hydrant is necessary, and they remove the block. Or, they ascertain that access to the hydrant would result in harm (e.g., the people who want access want to damage it, or use it improperly), and allow the block to stay in place/remove the hydrant. Both the alarm and hydrant block are temporary emergency measures to prevent lasting injury should the relief not be granted immediately. They are only there until an authoritative decision is made.
Should a single person be able to block the decision of the top ranking fire-fighter. That fire-fighter may be good, or may be in the job because he likes things to burn.