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Evaluation
of Fire Scene Contamination by Using Positive-Pressure Ventilation
Fans
Perry Michael
Koussiafes
Crime Laboratory Analyst
Fire and Arson Laboratory
State of Florida Fire Marshal
Havana, Florida
Introduction.......Materials
and Methods: Sample Preparation.......Materials
and Methods: Laboratory Instruments/Settings.......Materials
and Methods: On-scene Instrument and Structure.......Procedures.......Results.......Discussion.......References
Introduction
In most laboratories
measures are taken to prevent contamination and to verify the absence
of contamination. This paper addresses the contamination of a fire
scene before samples are selected. Specifically, this paper determines
if using a gasoline-powered positive-pressure ventilation fan could
contaminate a fire scene.
The purpose
of a positive-pressure ventilation fan is to help reduce smoke,
gases, and heat in a burning structure. This is accomplished by
placing the fan outside an opening, usually a doorway, of the structure
so that it forms a cone of air that effectively seals the opening.
This causes a rapid increase in the pressure in the structure. A
door or window on the other side of the structure is opened to allow
the escape of smoke and gases.
Most of the
articles in the literature consider positive-pressure ventilation
fans from the perspective of the fire fighter. This includes safety,
fire containment, exposure to hazardous materials, and search-and-rescue
efforts (Bolstad-Johnson et al. 2000; Gustin 1997; Gustin 1998;
Pressler 1997). Only one article was found that considered the possibility
of scene contamination by the exhaust of a positive-pressure ventilation
fan from a forensic perspective (Lang and Dixon 2000).
Materials
and Methods
Sample
Preparation
- 100 percent
cotton terry towels (D.C. May Corporation, Durham, North Carolina)
cut in 25-centimeter squares. This is a lightweight terrycloth
towel.
- Activated
carbon strip (Albrayco Laboratories, Incorporated, Cromwell, Connecticut)
cut to 21 millimeters by 5 millimeters
Samples were
tacked to a wood strip (121 centimeters long) to keep them from
being blown by the fan.
Laboratory
Instruments/Settings
- Gas chromatograph:
ThermoQuest Trace Gas Chromatograph (Thermo Finnigan, Austin,
Texas) with A200S autosampler
- Column:
Rtx-5MS (Restek, Bellefonte, Pennsylvania) 15M x 0.25 mm ID x
0.25um film thickness
- Carrier
gas: helium, 0.9 ml/minute
- Temperature
program: 50°C for 1 minute, ramp at 20°C per minute
to 300°C, hold for 2 minutes
- Detector:
Finnigan Trace Mass Spectrometer (Thermo Finnigan, Austin, Texas)
- Scan range:
Full Scan 40-400m/z
- Source
temperature: 200°C
- Gas chromatograph
interface temperature: 300°C
- Emission
current: 350 mV
- Software:
Xaminer 1.0, Xcaliber 1.0
On-scene
Instrument and Structure
- RamFan Turbo
Ventilator (RAMFAN Corporation, Spring Valley, California) powered
by a Honda GX160 5.5 horsepower gasoline engine
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Figure
1
Floor plan of structure. Sample locations
are marked as follows:
O = outside
L = living room
D = doorway
K = kitchen
Click to enlarge image.
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The
residential structure is diagrammed in Figure 1. The sample locations
are indicated by letters and correspond to Table
1 as follows:
- O = outside
samples, 2 meters from positive-pressure ventilation fan and in
the path of the engine exhaust of the fan
- L = living
room samples, 2 meters from front door
- D = doorway
samples, doorway from living room to kitchen
- K = kitchen
samples, 1.5 meters from rear door leading to small back porch
Procedures
The positive-pressure
ventilation fan was set up according to the standard-operating procedures
of the City of Marianna Fire Department, Marianna, Florida, with
the fan output blowing air into the doorway. The fan's engine exhaust
was vented to the left.
Samples for
Trial 1 were positioned and allowed to equilibrate for 20 minutes.
The first sample was taken from each of the sample locations as
a background. The positive-pressure ventilation fan was then operated
for 30 minutes, a common time span used at actual fire scenes. Samples
were collected from each sample location at time = 0 (immediately
after the fan was shut off), one hour, and two hours. Because investigators
do not typically take samples from a scene until at least four hours
after the fans have been shut off (Gunn 2002), this scenario should
have allowed every opportunity for any contamination that was going
to occur to still be present.
Trial 2 was
similar to Trial 1 with a deviation. In order to simulate a spill
a fire fighter might make while refueling the positive-pressure
ventilation fan at a fire scene, 250 milliliters of gasoline was
spilled on the side of the gas tank of the engine of the positive-pressure
ventilation fan and on the ground. The fan was then operated for
30 minutes, and the rest of the experiment was repeated.
An exhaust sample
was taken by holding an activated carbon strip approximately 30
centimeters from the exhaust of the gasoline engine of the positive-pressure
ventilation fan for two minutes. Additional exhaust samples were
taken by holding an activated carbon strip approximately 30 centimeters
from the exhaust of two vehicles, a 3-cylinder 1994 Geo Metro and
a 6-cylinder 1991 Chevrolet S-10 truck.
The towel samples
were collected and placed in airtight one-quart cans commonly used
for the collection of fire debris samples. The activated carbon
strips were collected directly into two milliliter autosampler vials
and sealed.
The towel samples
were prepared by passive headspace extraction (ASTM 2000). Carbon
disulfide (0.5 milliliters) was added to the activated carbon strip
samples. All samples were analyzed by gas chromatography-mass spectral
detection according to ASTM guidelines (ASTM 1994).
Results
Table
1 shows the results. All towel and activated carbon strip samples
from Trial 1 were determined to be negative for the presence of
gasoline. All the towel samples from Trial 2 were determined to
be negative for the presence of gasoline.
A
trace quantity of some of the early components of gasoline was observed
on the activated carbon strip samples taken from Trial 2, the trial
in which gasoline was spilled before operating the fan and collecting
the samples. This was not apparent from the total ion chromatogram
(Figure 2) but was visible in the extracted ion chromatogram (Figure
3). This trace amount consisted of some early alkanes and low levels
of toluene and xylenes. This is attributed to gasoline because of
the known origin of the samples. In actual casework this would not
be sufficient for a determination of gasoline or any other ignitable
liquid and would be reported as negative.
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Figure
2 Total ion chromatograms of the activated carbon strip
at time = 0.
A = outside
B = living room
C = doorway
D = kitchen
Click to enlarge image. |
Figure
3 Extracted ion chromatograms of the activated carbon
strip at time = 0, m/z 57.0, 91.0, 105.0, 134.0, 142.0,
A = outside
B = living room
C = doorway
D = kitchen
Click to enlarge image.
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Discussion
The activated
carbon strips were used to maximize the detection of contamination
at fire scenes. Samples taken from fire scenes might contain matrices
that strongly adsorb the organic compounds present in most ignitable
liquids. However, it is unlikely that these materials would provide
better adsorption than an activated carbon strip that is designed
to adsorb organic compounds.
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Figure
4 Extracted ion chromatograms, m/z 57.0, 91.0, 105.0,
134.0, 142.0. A = activated carbon strip located outside at
T = 0,
B = exhaust from positive-pressure ventilation fan
C = actual case sample
D = 50% weathered gasoline
Click to enlarge image. |
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Figure
5 Extracted ion chromatograms, m/z 57.0, 91.0, 105.0,
134.0, 142.0. A = activated carbon strip located outside at
T = 0
B = exhaust from 1984 Geo Metro
C = exhaust from 1991 Chevy truck
D = 50% weathered gasoline
Click to enlarge image. |
The
trace levels of contamination found on the activated carbon strips
compare favorably to the exhaust collected from the positive-pressure
ventilation fan (Figure 4: A and B). The trace levels of contamination
do not compare favorably to an extracted ion chromatogram of an
actual case sample determined to be positive for the presence of
gasoline (Figure 4: C).
Actual case
samples tend to be depleted of the early, more volatile components
of gasoline and possess a greater concentration of the later components
of gasoline. Actual case samples compare more favorably to gasoline
that has been weathered to 50 percent of its original volume, thus
eliminating most of the early components (Figures 4: C and D). This
is quite different than the exhaust and trace levels of contamination
seen in this experiment.
The
trace levels of contamination found on the activated carbon strips
also compare favorably to the exhaust collected from two vehicles
(Figure 5: A, B, and C). None of these compared favorably to gasoline
that has been weathered to 50 percent of its original volume (Figure
5: A, B, C, and D). This would indicate that vehicles or other power
equipment left running near the scene would not have a significant
impact on the detection of gasoline at a fire scene.
The results
from this experiment demonstrated that exhaust from a gasoline engine-powered
positive-pressure ventilation fan is not sufficient to contaminate
samples taken from a fire scene. Only when gasoline was spilled,
providing a greater concentration of gasoline vapors in the air
to be pulled through the fan, was any trace-level contamination
observed. It is unlikely that one would be able to verify whether
such contamination had taken place in actual casework. Further,
the contamination that might occur from gasoline-powered engines
of different types is not similar to what would be expected from
gasoline recovered from an accelerated fire.
This work was
designed to continue and complement that begun by Lang and Dixon
in 2000. Whereas no fire scenes are identical and exact replication
of any actual scene is impossible, by adding to the variety of structures
and conditions tested, it is hoped that reasonable assumptions may
be drawn regarding the potential contamination issues of positive-pressure
ventilation fans.
The author acknowledges
the assistance of the City of Marianna Fire Department, Marianna,
Florida.
References
ASTM. Standard
Guide for Ignitable Liquid Residues in Extracts from Fire Debris
Samples by Gas Chromatography-Mass Spectrometry, ASTM-E1618-94,
1994.
ASTM. Standard
Practice for Separation of Ignitable Liquid Residues from Fire Debris
Samples by Passive Headspace Concentration with Activated Charcoal,
ASTM-E412-00, 2000.
Bolstad-Johnson,
D. M., Burgess, J. L., Crutchfield, C. D., Storment, S., Gerkin,
R., and Wilson, J. R. Characterization of firefighter exposures
during fire overhaul, Journal of the American Industrial Hygiene
Association (2000) 61:636-641.
Gunn, J. Florida
State Fire Marshal, Personal communication, April 2002.
Gustin, B. Fog
streams and PPV: Their effects on two fires, Fire Engineering
(1997) 150(11):49-54.
Gustin, B. Search
and rescue in single-family dwellings: Part 1, Fire Engineering
(1998) 151(8):73-82.
Lang, T. and
Dixon, B. M. The possible contamination of fire scenes by the use
of positive pressure ventilation fans, Journal of the Canadian
Society of Forensic Science (2000) 33(2):55-60.
Pressler, B.
More two-minute drills, Fire Engineering (1997) 150(5):26-29.
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