What Army regulations address active duty members being allowed to volunteer as firefighters while off-duty?

Is you in the Army or simply jiving RP? Too many things in your post cause me to wonder - who is you - where are you?

(Join to see) I had a few Soldiers that had the same issue. Before I signed anything I personally visited the locations, talked to supervisors, and most importantly I made sure Safety was the priority. We did this in case there was an accident. A line of duty investigation will be conducted and you may or may not be covered by the military. So I'd recommend a COA with you writing a succinct memo to your chain of command. Include the duty position, work hours, normal day to day activities, list all risks and your mitigation plan. Last, this volunteer position will not in any way affect your military position. You are basically writing a memo that your commander can use because surely he/she will get an opinion from JAG and their rater.

To answer your question, your Commander has to sign a memo approving you being a firefighter. There are no regulations outlining this. If your supervisor doesn’t approve of it, use the open door policy.