The fire started 150 meters inside the Stubberud tunnel in a large battery. All 24 workers were evacuated after they went into safety shelters.

Aftenposten writes that the Stubberud tunnel is the main rig area for the 11 kilometer long Rentvann water tunnel in Oslo.

https://www.aftenposten.no/oslo/i/P46o1X/24-personer-ble-evakuert-da-det-broet-ut-brann-i-en-tunnel-paa-alnabru-i-oslo