High acute toxicity; possible human carcinogen (OSHA "select carcinogen"); highly flammable.

The acute toxicity of nickel carbonyl by inhalation is high. Acute toxic effects occur in two stages, immediate and delayed. Headache, dizziness, shortness of breath, vomiting, and nausea are the initial symptoms of overexposure; the delayed effects (10 to 36 h) consist of chest pain, coughing, shortness of breath, bluish discoloration of the skin, and in severe cases, delirium, convulsions, and death. Recovery is protracted and characterized by fatigue on slight exertion. Nickel carbonyl is not regarded as having adequate warning properties.

Repeated or prolonged exposure to nickel carbonyl has been associated with an increased incidence of cancer of the lungs and sinuses. Nickel carbonyl is listed by IARC in Group 2B ("possible human carcinogen"), is listed by NTP as "reasonably anticipated to be a carcinogen," and is classified as a "select carcinogen'' under the criteria of the OSHA Laboratory Standard.

Nickel carbonyl is a highly flammable liquid (NFPA rating = 3) that may ignite spontaneously and explodes when heated above 60 °C. Its lower flammable limit in air is 2% by