That’s a volunteer program. This is inside the prison work and comes with physical and mental punishment if you refuse.
Oh no you seem to think I’m defending this so let’s break this down.
You can circumvent the normal prison labor system by volunteering to fight fires. This comes with perks and good time. Or you can exist in the normal prison labor system making products under threat of mental or physical abuse.
So joining the firefighters is also extremely coercive because it requires you to risk your life for your freedom, privileges, and keeping you away from the abusive labor system the other prisoners exist in.
None of this is good.
Not exactly “voluntary” in a meaningful way if the alternative is in-prison work or punishment.