It is incompatible or reactive with amines, oxidizers, acids, sodium hydroxide, calcium hydroxide, sodium carbonate, caustics, and ammonia. It is intensely poisonous even when mixed with air, and is highly toxic to all species in water. Synonyms are hydrocyanic acid, prussic acid, aero liquid HCN, carbon hydride nitride, formic anammonide, and formonitrile. Massive doses may cause sudden loss of consciousness, asphyxiation, and death from respiratory arrest. Unconsciousness can also be followed by violent convulsions, paralysis, protruding eyeballs with dilated and unreactive pupils, and foaming mouth.
Exposure can cause blindness and damage optic nerves and retina.
Other symptoms of hydrogen cyanide exposure in lesser concentrations include salivation, nausea, vomiting, hyperpnea, dyspnea, an irregular and weak pulse, anxiety, confusion, tachypnea, vertigo, giddiness, stiffness of the jaw, neurasthenia, breathlessness, bradycardia, arterial hypotonia, polycythemia, hepatic impairment, and thyroidal hypofunction. Chronic exposure to hydrogen cyanide gas can cause eye irritation, conjunctivitis, or superficial keratitis. Laetrile and amygdalin-containing fruit pits, in cherries, peaches, apricots, apples, and pears, have been implicated as causes of acute cyanide poisoning. People with chronic diseases of the kidneys, respiratory tract, skin, or thyroid are at greater risk of developing toxic cyanide effects.