blood spatter!

Analysing blood stains and spatters can help forensic scientists determine how & where the crime was committed. Blood stains have different shapes and sizes. This is because of the different ways the stain is created (ie. angle of impact, direction, force of impact, etc.). They are very useful to an investigator and may be able to provide conclusively the:

• Movement and direction of persons or objects while they were shedding blood.
• Position of persons or objects during bloodshed.
• Movement of persons or objects after bloodshed.
• The mechanism or object used to create a specific pattern.
• The direction a stain was traveling when it was deposited.
• The area of origin of an impact pattern.
• The minimum number of impacts during an incident.
• The sequence of events.

All blood droplets fall as spheres, due to surface tension. When they impact on a surface, they form an elliptical or circular stain.

1. What is shape of blood splatter?
1. Splatter 1: Irregularly shaped, rounded edges. 
   Splatter 2: Mostly circular, series of smaller drops in the direction of the larger drop below. 
   Splatter 3: Circular, with ‘spiked’ edges. 
   
   
   Splatter 4: Elliptical shaped stains, with trails dripping downwards.
2. Describe any other characteristic of the splatter.
1. Splatter 1: Concentrated at the bottom, with smaller drops surrounding it.
   Splatter 2: Concentrated at the bottom left, mostly, with smaller drops surrounding it.
   Splatter 3: Larger, more ‘spread out’ (no concentrated areas). Series of small drops from the left, largest drop to the right.
   Splatter 4: Entire series of large splatters against a vertical surface. 
3. What are the factors that affect the shape of the blood splatter? Name as many as possible.
1. Direction of splatter
2. Angle of impact
3. Force of impact
4. Distance of impact (similar to force?)
5. Speed of blood dropping
4. Generate some hypotheses from the blood splatter patterns observed above.
1. The larger the impact of the splatter, the larger and less concentrated the stain. 
2. The greater the angle of impact, the more elongated the splatter (ie. Splatter 4).

Experiment 1

Aim: To investigate how the diameter of the blood stains vary with the height
Apparatus: Retort stand, dropper, metre rule, protractor, clipboard, paper, artificial blood (70ml hot water + 25 g flour + food colouring), newspaper.

Procedure:
1. Lay the floor with newspaper to

Setup of Experiment 1

prevent the blood from staining the floor.
2. Attach an A4 paper onto the clipboard and place it on the floor.
3. Place the dropper loosely between the clamp on the retort stand 10 cm above the paper as shown. DO NOT SQUEEZE YET !
4. Slowly tighten the clamp to allow only ONE drop of blood to drip onto the paper below.
5. Measure and record the diameter of the blood stain in the table below. (Is one measurement of the diameter enough?)
6. Label the blood stain as “A10”.
7. Repeat Step 4 and 5 to obtain another blood stain on another spot of the paper and label it “B10”.
8. Repeat steps 3 to step 6 by adjusting the vertical distance for 30 cm, 60 cm, 100cm, 150 cm and label them appropriately.
9. Plot a graph of average diameter of blood stain, d against vertical distance, s using "Numbers".

Height/cm	LA / mm	LB / mm	LAve / mm	WA / mm	WB / mm	WAve / mm
10	8	8	8	8	8	8
30	10	10	10	10	10	10
60	11	11	11	11	11	11
100	13	12	12.5	13	12	12.5
150	13	13	13	13	13	13

Experiment 2

Aim: Investigate how the shape of the blood stains vary with the angle of impact
Procedure:
1. Lay the floor with newspaper to prevent the blood from staining the floor.2. Attach an A4 paper onto the clipboard 

Setup of Experiment 2

place it on the floor.3. Place the dropper loosely between the clamp on the retort stand least 100 cm above the paper as shown.DO NOT SQUEEZE YET !4. Elevate the clipboard to 10° as shown.5. Slowly tighten the clamp to allow only ONE drop of blood to drip onto the paper.6. Measure and record the length, L and width, W of the blood stain in the table below.7. Label the blood stain as “P10”.8. Repeat Step 5 and 6 to obtain another blood stain on another spot of the paper and label it “Q10”9. Repeat steps 4 to step 8 by adjusting the vertical distance for 30°, 50°, 70° and label them appropriately.

Angle of elevation / °	LP / mm	LQ / mm	LAve / mm	WP / mm	WQ / mm	WAve / mm
10	12	13	12.5	13	14	13.5
30	12	12	12	15	15	15
50	10	10	10	18	18	18
70	23	24	23.5	7	6	6.5

Here are the graphs! (plotted using data collected in the tables)


Experiment 1

Experiment 2