Basements. Parking decks. Rail right-of-way. Rural highways. Tunnels. The instant cell signal drops is the instant your reference book has to still work.
FireHazmat ships the entire 2024 ERG dataset bundled inside the app — every search, every isolation distance lookup, every Table 3 PAD calculation runs locally with zero network. The only feature that touches the internet is the optional weather chip on the Map screen, and it degrades gracefully to a dash if no signal — you can enter wind data manually and keep going.