Division 2.3 (Gas poisonous by inhalation). A gas poisonous by inhalation (Division 2.3) means a material which is a gas at 20 °C (68 °F) or less and a pressure of 101.3 kPa (14.7 psi) (a material which has a boiling point of 20 °C (68 °F) or less at 101.3 kPa (14.7 psi)) and which:
Is known to be so toxic to humans as to pose a hazard to health during transportation, or
In the absence of adequate data on human toxicity, is presumed to be toxic to humans because when tested on laboratory animals it has an LC50 value of not more than 5000 ml/m 3 (see the Code of Federal Regulations Transportation (49) Part 173.116(a) for assignment of Hazard Zones A, B, C or D). LC50 values for mixtures may be determined using the formula in the Code of Federal Regulations Transportation (49) Part 173.133(b)(1)(i).