Concentration of a material in the air that kills 50% of the test animals when administered as a single exposure in a specific time period (usually 1 hour); a common measure of acute toxicity of vapors, dusts, mists and gases. Note that lethal concentration values are used when the route of administration is by inhalation. LC values are often expressed as parts of material per million parts of air (ppm). Compare "lethal dose 50".