Basics of Blood Spatter

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Basics of Blood Spatter
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Physical Properties of Blood

• 1. Blood acts like any other fluid
• Surface tension the property of liquid molecules
  to combine so as to present the smallest surface
  area possible
• Falling drops of blood are spheres- not teardrop

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Physical Properties of Blood

• 2. Properties of blood drops
• A. Relatively constant volume .05 ml (20 drops
  to the milliliter)
• B. Relatively constant diameter (12-15mm)
• C. Terminal velocity25 ft. per second

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Stain Size vs. Distance

• 1. Up to about four feet, as target to source
  distance increases, spot size will increase
  (assuming a smooth, hard surface)
• 2. After about four feet, there is no change in
  spot size (assuming smooth, hard surface)

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Stain Size vs. Distance

• 3. Surface texture is more important in
  determining ultimate spot size and shape than
  distance.
• A. smooth, hard surfaces produce circular spots
• B. Irregular surfaces cause drop to burst,
  leaving irregular spot size and shape

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Spot Shape vs. Horizontal Motion

• 1. Drops striking surfaces at less than 90
  degrees will produce pear-shaped spots
• A. Pointy end of spot will point in the original
  direction of travel of the blood.
• B. The smaller the angle of impact, the longer
  and skinnier the resulting spot.

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Spot Shape vs. Horizontal Motion

• 2. Angle of impact can be calculated by dividing
  the width of the spot by the length. Result is
  the sine of the angle of impact (W/L sine angle)

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Effect of Added Energy

• 1. Adding energy to a blood source will break the
  blood drops into smaller drops.

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Effect of Added Energy

• 2. Types of drops
• A. Low Level velocity gravity up to about
  5ft./second produces spots of ¼ or larger-
  cast-off or dripped blood

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Effect of Added Energy

• 2. Types of Drops
• B. Medium Velocity more than 5ft./sec up to
  about 100 ft/sec- spots produced are 1/8 or
  smaller- beatings, stabbings

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Effect of Added Energy

• 2. Types of drops
• C. High Velocity over 100 ft/sec- spots are so
  small they appear to be an aerosol, or mist-like-
  gunshot wounds, auto collisions

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Other Types of Spatter

• 1. Cast off
• 2. Transfer
• 3. Projected