Types of Bloodstain Patterns
Many books on the subject of Bloodstain Pattern Analysis will describe three velocity types: Low Velocity Impact Spatter (LVIS) Medium Velocity Impact Spatter (MVIS) and High Velocity Impact Spatter (HVIS). One should realize, however, that bloodstains can be quite complex and will tend to overlap each other. There is no defined demarcation point where each velocity begins or ends.
When considering velocity types, it should be understood that it doesn't represent the velocity at which blood droplets are traveling, but the amount of force which has been applied to a given blood source. Low Velocity has been stated to be at 0 (gravity) - 5 fps, Medium Velocity 5 - 25 fps and High Velocity 100 + fps. Low Velocity is usually associated with passive bleeding with larger blood droplets of 4mm and greater. Medium Velocity would be 1mm - 4mm in size and finally High Velocity would be associated with stains of 1mm or less.
The picture above illustrates that the amount of force applied to a given blood source will produce different sized stains.
The picture above illustrates the three velocity groups and the relative force applied.
Now keeping these size ranges in mind, it becomes apparent that there will be cases of overlapping stains, depending on the actions of the assailant and victim at the crime scene. Therefore, these ranges should (in my opinion) be used only as a guideline and not the absolute rule. For example, look at the picture at the bottom of this page which demonstrates a medium velocity event. There were hundreds if not thousands of stains of 1mm or less created here by smacking two boards together. Stains of that size are normally associated with high velocity. The bloodstain expert looks for the predominant size stains within a pattern to get an initial idea of what type of pattern they may be viewing. Through my experiments and basic training received it has become evident that caution must be used when examining bloodstain patterns. MVIS has been associated with blunt force trauma, i.e., beatings. HVIS of course leaves us with the use of guns; however, one may witness high velocity impact spatter from explosions and accidents involving high speed machinery.
Bloodstains and/or patterns have also been grouped into: Passive, Transfer and Projected stains. Each one of these will have subcategories. For example, in Passive you may find: clots, drips, blood flows and pools of blood. In Transfers you will find: Swipes (a bloody object coming into contact with a non-bloody surface) or Wipes (a non-bloody object coming into contact with a bloody surface) and pattern transfers, i.e., shoe-prints, hand-prints or perhaps a print of a weapon used. And finally in Projected you can find: Gushes, Arterial Spurting and Cast-Off Stains.
Here is an example of Passive bleeding (Low Velocity)
This stain pattern is the result of an attack from a (perceived to be) domestic cat. My wife suffered this injury to the back of her right calf after she had chased a neighborhood cat out of our garage. While returning to the front porch, the cat attacked by sinking its teeth into the back of her leg. Needless to say, my wife had a few choice words for the cat! It amazes me that she had the state of mind to take pictures of the stains. She has recovered from this with no complications (no rabies). This is a good example of passive bleeding (blood into blood). Notice all the satellite spatter emanating from the various 90 degree drops.
A few examples of Transfer patterns
A knife print
A bloody hand print (notice the areas where the blood is darkest, Capillary Action)
Bloody Shoe Print
Examples of Projected Patterns
Simulated arterial spurting with a syringe
Forward Spatter from a gunshot .22 cal into a bloody sponge (High Velocity)
Cast-Off stains from a knife (Medium Velocity)
What about diluted (altered) stains?
This picture in my opinion is why one has to be very cautious when determining whether a stain pattern is of a certain velocity group. Velocity is not the speed at which blood is traveling; it is the amount of force applied to a blood source. One of the characteristics a bloodstain analyst would look for is the predominant stain size. At first glance the analyst may see all the large spatter stains; but notice the numerous stains of 1mm and less in this pattern. This stain actually displays all sorts of stain sizes. So, is it HVIS or MVIS? There is no clear demarcation point between the velocity groups and as such will overlap. This pattern was created by smacking two boards together. How fast did I smack the boards together? Who knows, but it was fast enough to create stains smaller than 1mm in size. Had I not known how this stain was created, my opinion would have been MVIS. Why?...Because the predominant sized stains fall in this category and although there are very small stains of 1mm and less, it still lacks the very fine mist which is indicative of a high velocity event. However, one should keep in mind that you may not have this fine mist visually observable due to the fact that stains this size only travel up to approximately 4 feet. One might need to introduce Luminol to identify any hidden stain patterns.