OSHA 1910.156 and NFPA 600 are the minimum standard for fire brigades. NFPA 600 is more detailed than OSHA. Should I be following both? If not what are my liability concerns?

OSHA’s standard is the minimum requirement. OSHA hasn’t adopted NFPA 600 by reference. So, from an OSHA lens, the minimum requirements to follow are 1910.156. Your local city or state jurisdiction may have adopted NFPA 600. If so, you’ll also need to follow it. Following a more stringent requirement such as NFPA 600 is okay from an OSHA compliance stance. If your local jurisdiction doesn’t adopt NFPA 600, following 1910.156 would be fine. You should also double-check your commercial insurance policy to verify if it specifies a preference for what to follow.