Chapter 4: Using the System
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Fuming Procedure
NOTE: The quality and durability of fingerprints developed by the CApture
can be affected by many variables, among them are:
The initial quality of the latent print
The surface the print is on
The air temperature during fuming
The relative humidity during fuming
The quantity, quality, and formulation of the CA used
The temperature of the CA during fuming
The length of time the CA fumes are released
Because of all of these variables, it is impractical to try to develop a single
methodology that will produce optimal results under all conditions.
If you
are unsure of the operating parameters you should use in a
particular circumstance, you should try one or more “trial runs” of
control prints before fuming the evidence.
Adjusting Humidity Levels in the CApture Portable
Fuming System
The humidity level when CA fuming is critical to the quality of print
development. Recent scientific tests have determined that the optimum
range of relative humidity for the development of fingerprints is 70%-90%
with the most high quality marks developing when relative humidity is
approximately 80%.
3
It has been determined by calculation and proven by in-house testing that
one drop of water will raise relative humidity level within the CApture
Fuming Chamber by approximately 2%.
4
When using the CApture, determine the current humidity level and the
amount of humidity that needs to be added in order to reach an 80%
humidity level. If humidity levels need to be increased determine the
number of water drops to add according to the following chart.
NOTE: Never use the CApture if condensation is present on the clear
chamber or on the evidence. The CA fumes will polymerize on the
condensate, reducing the clarity of the chamber, and obscuring any
fingerprints on materials being fumed. When using the CApture
repeatedly, allow adequate ventilation after each run to prevent the
buildup of humidity in the chamber.
3
Paine M, Bandey, HL, Bleay SM, Wilson H., The effect of relative humidity on the effectiveness
of the cyanoacrylate fuming process for fingermark development and on the microstructure of the
developed marks. Forensic Science International 2011 Jun 29.
4
The humidity testing was done at 75°F and an elevation of 885 ft.
