Nickel carbonyl is poisonous. It can be fatal if inhaled, swallowed, or absorbed through skin. Use water in flooding quantities as fog. A few whiffs of the vapor could cause death. If liquid or vapor penetrates fire fighter's protective gear it will cause fatality.
Vapor forms explosive mixtures with air.
Vapor explosion and poison hazard indoors, outdoors, or in sewers. Material is extremely dangerous and may explode. Remove all ignition sources. Ventilate area of spill. Atomize large quantities in a combustion chamber equipped with an effluent gas cleaning device.