FRSC 309_ Presumptive tests and blood pattern analysis

Phenolphthalein

def: detection test in basic solution. most commonly used

Tetramethylbenzidine

def: acidic test to replace carcinogenic benzidine.

Combined PTMB Test

def: sensitive and specific for basic and acidic.

for bpa we look at 3 things

size, shape and distribution

sizing rules

• Force that causes the blood to break apart –

the greater the force the smaller the

droplets

• Distance that blood travels – the larger

drops have the ability to travel a greater

distance

This impact angle is determined by the ratio

between the width and length of the stain

distribution categories (5)

• passive

• contact

• projected

• arterial

• impact

passive

• Gravity alone

• large circular 0.05 ml

contact

• could be transfer, swipe, wipe

projected

• could be cast off (released from blood bearing object)or experiated (blown out)

arterial

• from artery, high volume.

impact

random distribution of smaller droplets.

• low, medium. and high energy

area of convergence

def: The area where the reverse vectors of several related spatter stains converge on a 2D surface is the  ____________?

area of origin

def: the three-dimensional space where a blood source was located when a blood-letting event occurred. Using the angle of impact and distance from the convergence point to calculate height.

The variations in combinations of blood volumes and forces acting on those volumes lead to recognizable classes of patterns.  This is what principle in Bloodstain Pattern Analysis?

 

The pattern diversity principle

Small droplets are released from the object over time and space, they land across surrounding surfaces and are deposited in linear orientations.

 

Cast offs

Stains created when blood is ejected in a stream under pressure or with velocity, most often encountered when an artery or the heart is breached.

Spurt

A radiating pattern of smaller circular or elliptical-shaped stains created when blood is broken up at a source by some force.

impact pattern

What are the two primary field tests for the presumptive presence of blood?

 

Phenolphthalein and leuco-malachite green

How long does it take for amido-black enhancement to take effect?

 

30 sec - 3 minutes

When calculating the impact angle of a stain the trigonometric function  used is

inverse sine