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When the Sensor is exposed to a hydrocarbon or
accelerant, the Analog Meter Display needle will defl ect
clockwise, followed by fl ashing red LEDs and repeating
audio tones. This response indicates the possible
presence of hydrocarbons/accelerants. If high
concentrations of a detected hydrocarbon/accelerant
are sensed, it may be necessary to clear the Sensor
using the Purge function (see Purge instructions below)
and scan the area of concern again. Another positive
reaction indicates the presence of a suspect material.
Collect a sample of debris for analysis.
For investigations where the Sensor responds to higher
levels of hydrocarbon/accelerant vapor, the needle
on the Analog Meter may fully defl ect to the highest
level on the scale. Model 950-ASH can be normalized
for these conditions by rotating the Detection Range
Control counterclockwise until the fl ashing Detection
Indicator LEDs and audio tones just stop. Upon further
investigation, when the audio tones and Detection
Indicator LEDs begin again, you are closer to higher
concentrations of hydrocarbon/accelerant vapor and
may have the opportunity to collect a sample.
PURGE
The Purge function is used to clear the Sensor after
exposure to high levels of hydrocarbon or acceler-
ant vapor. Remove the Model 950-ASH detector from
the contaminated vicinity and set the Purge control
to the ON position. The red Purge Indicator LED will
fl ash. While the Purge feature is in use, audible tones
and red Analog Meter LEDs will be observed. Allow
the Purge to remain ON until the red Purge indica-
tor LED stops fl ashing and glows red (this may take
approximately 20 seconds). Return the Purge switch to
the OFF position and reset the sensitivity and detection
threshold. Your 950-ASH is now ready to detect another
sample.
Note:
While the Purge feature is in use, the Sensor will not
detect the presence of hydrocarbons or accelerants.
Mute feature may be used during the Purge cycle to
silence the audio tones.
ULTRAVIOLET and WHITE LED ARRAYS
The LED features of your Model 950-ASH consist of
an array of eight long-wave ultraviolet (395 nm) LEDs
and an array of eight white LEDs. Each LED array is
controlled by a 3-position toggle switch located on the
Controls and Display Panel. The Ultraviolet and White
LED arrays function independently of each other and
cannot be used simultaneously.
It is desirable to use the ultraviolet LED array in as
little ambient light at the investigation scene as
possible. The ultraviolet LED array allows the
investigator to search for a fl uorescence or glow of
suspect material, potentially indicating the presence
of residual or trace amounts of hydrocarbons,
accelerants, or other questionable material. Hold the
ultraviolet LED array at an angle of approximately
45° and approximately ½” inch away to examine the
suspect material. During an investigation, if
fl uorescence of suspect debris is discovered, it should
be gathered and sent to a lab for analysis.
The white LED array feature is desirable for use as a
fl ashlight in dimly lit or low visibility environments.
When using this feature, a backlight will illuminate the
Analog Meter Display.
How Ultraviolet (UV) Light is Used
in Arson Investigations
UV light is used to detect information that is otherwise
invisible to the human eye and to uncover valuable
evidence that can be used to solve a fi re investigation.
UV light is used to identify the presence of hydrocar-
bons, accelerants, and to identify pour patterns.
UV light not only assists in identifying the presence
of accelerants but also in rapidly locating accelerant
residues and assists in locating the point of
origin of the fi re. The color in which accelerants glow
is aff ected by heat exposure. The longer an accel-
erant is exposed to heat (i.e. the origin), the more
diff erentiated its fl uorescence color will be from
other, less exposed areas. Evidence of accelerants is
absorbed in a fi re and is almost always invisible to
the naked eye. However, the area contaminated by
accelerants is easily discernible under UV light.
Volatile hydrocarbons such as gasoline, kerosene,
acetone, etc. fl uoresce when exposed to UV light. By
using UV light, investigators can accurately identify
locations where samples should be collected for
further laboratory analysis. UV light can also be helpful
in locating fragments of incendiary devices since
explosive wrappings are frequently fl uorescent.
Samples collected in cans and plastic evidence bags
can be heated in warm water to form condensation.
The latent accelerant residue rises to the surface and
can be seen under UV light.
UV light has been used to identify pour patterns,
the shape of an accelerant container, and pour trails
leading back to containers. UV light will indicate
