Poultry may need to be culled in the event of an outbreak of disease. Gassing has advantages over mechanical and electrical methods or overdoses of anaesthetics because large numbers can be killed simultaneously and little or no handling of the birds is required. However, gaseous killing methods may have welfare implications for the birds, which may find various gases more or less aversive, may undergo respiratory distress and/or experience convulsions, and may remain conscious for a considerable time before they die. In addition, the gases used may present health and safety risks to human operators, and be difficult to supply and deliver.