Investigation of the Drying Times of Blood under different Environmental Conditions and on Different Fabrics. Transfer of Blood at Different Times of the drying process

PETER A. PARKINSON

Chief Crime Scene Examiner (INDECOM)

To investigate the effects of Temperature, Humidity, Wind Speed and Fabric Composition on the drying times of blood and assess the degree of blood transfer that occur during the drying process.

An assortment of fabrics, of different compositions and thicknesses, were collected and stained using two blood volumes and exposed to varying environmental conditions.  The conclusion reached was that Temperature, Humidity, Wind speed and Fabric thickness do have an effect on drying times.  An increase in temperature and Wind speed resulted in a decrease in drying times while an increase in fabric thickness and humidity extended the drying times of blood under similar conditions.

Transfer experimentation utilized three donor fabrics, 100% white cotton, 100% acrylic and 100% cotton (denim), which were blood stained using two blood volumes.  The fabrics were subjected to both Full and Low/Light force contact from the donor fabrics to the recipient fabric (100% Cotton) under different environmental conditions.  Transfer times onto the 100% white cotton were shorter than the drying times observed.  The intensities of the blood stains decreased from High to Low with time during the drying process.

The degree of transfer at High, Medium and Low intensities varied significantly between different materials and is dependent on the environmental conditions, fabric compositions, blood volumes, types of contact and the drying times observed for the respective donor fabrics.  These factors should be considered collectively and conservatively when assessing time frame of secondary blood transfer in casework.