Death caused by hyperthermia. This questionable method has been developed as a last resort option in case of a large-scale outbreak of High Pathogen Avian Influenza in the UK. Even in EU Regulation EU 1099/2009 there is room for countries to use this kind of methods, when compliance is likely to affect human health or significantly slow down the process of eradication of a disease. (EU 1099/2009; article 18, under 3).
Hyperthermia means that the cause of death is overheating the shed of the birds. The normal core body (CB) temperature of a bird must remain within a narrow range around a mean value of 41.4°C if its welfare is to be safeguarded.
If the core body temperature rises above 45°C most poultry will die quickly. To ensure VSD is effective the temperature in the house must rise to 40°C or greater and remain at that level. Maintaining a relative humidity of at least 75% will help speed the onset of death through hyperthermia.
This DEFRA document provides procedures and instructions on using Ventilation Shutdown (VSD) as an emergency method of killing of poultry for disease control purposes.