Garam Lee* and James C. Bird | Boston University Daniel Attinger | Struo LLC Kenneth F. Martin Samira Shiri | University of Utah Abstract: Bloodstain pattern analysis uses the location, size, shape, and distribution of stains to identify potential mechanisms of a bloodletting event from the bloodstains detected at crime scenes. For instance, whether a certain circular stain was generated from dripping or another mechanism, such as a satellite droplet, is determined based upon the size of the stain. The current cutoff value for the smallest stain size from dripping has been suggested to be 3.9 mm in diameter. However, more recently, it has been demonstrated that blood impacting the same surface can cause varied stain sizes because of surface residues, which may affect the advancing and receding contact angles. Additionally, other factors such as the impact condition and the hydrophobicity of the surface can alter the size of the resulting stain as well. This presentation will revisit the minimum size of drip stains using human blood impacting multiple surfaces along with the application of various coatings. The data indicate that the cutoff for the minimum drip stain size is not always obvious. This research examined the role of contact angles, impact speed, and initial droplet volume resulting in the final stain size. The results demonstrate that drip stains are generally larger than the previously reported value. Furthermore, the hydrophobicity and low contact angle hysteresis of the surface can lead to a drip stain as small as 2 mm, not 3.9 mm as originally proposed.