According to FDNY Arson Training Bulletin, when does lividity typically start to develop?

Lividity, also known as hypostasis, is a postmortem change that refers to the pooling of blood in the lowest parts of the body due to gravity after the heart has stopped beating. This process begins shortly after death as the circulation ceases and blood begins to settle in the more dependent areas of the body. Typically, lividity starts to become noticeable around one to two hours after death. At this point, the skin may show a purplish discoloration where the blood has pooled, making it an important indicator for forensic investigations.

The timing of lividity is critical as it can help determine the time of death, which is invaluable in arson investigations and other criminal cases. Understanding this process aids fire marshals and investigators in assessing the circumstances surrounding a death in a fire scenario, helping to distinguish between potential causes.