Agreed.  Enlist the fire-fighter's aid if possible.  But that's counting on what has to be considered as exceptional courage on the fire-fighter's part. So, in case he isn't up to that challenge, I'd say, "Please don't worry, we're going to release you unharmed as soon as the truck is on site "putting out the fire".  That's a lot more than the official authorities are offering, by the way.

 Sure, fire-fighters are typically courageous to do what they do--but theirs is not moral courage--which is what would be required to oppose official rules to aid peaceful protesters defend themselves against a brutal police.

  Generally, all a fire-figher needs is physical courage.  His moral courage might be a disaster and he could still do very admirable work fighting fires.

"In such an environment it is not surprising that the ills of technology should seem curable only through the application of more technology..." John W Aldridge