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THE EFFECTS OF ULTRA LOW TEMPERATURE ON RECON MEDICAL GEN 4 TRAUMA TOURNIQUET TENSILE STRENGTH
Asher Holland Project Engineer
Recon Medical, LLC
ABSTRACT In this study we analyze the effects of Ultra-Low
Temperature Environment (ULTE) on Recon Medical
Generation 4 (GEN 4) trauma tourniquet (TQ) tensile strength.
Analysis was compiled by placing 10 tourniquets in a closed
environment with 14.02 pounds of dry ice for 19 hours and
comparing to a control group at ambient temperature.
Tourniquets were individually removed from the ULTE and
immediately tensile strength tested using destructive testing
equipment aptly named Recon Ripper (see figure 1). The
resultant average ultimate tensile strength of the tourniquets
tested post-ULTE was 2637.0 pound-force (lbf). By comparing
this average tensile strength to the average ultimate tensile
strength of tourniquets stored at ambient temperature, which was
2540.0 lbf, we see a 3.8% increase in tensile strength in
tourniquets after being stored in an ULTE. This data proves
Recon Medical GEN 4 trauma tourniquets perform exceptionally
well after prolonged exposure in a controlled ULTE.
The effects of submerging tourniquets in water and then
placing in a closed environment with dry ice for 19 hours was
also considered. Tourniquets were similarly individually
removed from ULTE and immediately tensile strength tested.
Results were inconclusive as ice build-up in hook and loop
fastener caused premature failure. Fortunately, this failure mode
can be prevented by properly staging tourniquet.
INTRODUCTION The components that make up the Recon Medical GEN 4
tourniquet are comprised of a buckle made of nylon injection
molding with a 6061-T6 aluminum core, nylon webbing, nylon
hook and loop fastener, and Kevlar® stitching, all of which are
under massive tension during tourniquet application. However,
unique to Recon Medical tourniquets, this tension is supported
by a “floating”, high-strength strap design in combination with
an aluminum core buckle.
Trauma tourniquets are primarily carried on the outer
garments of military personal who are sometimes required to
operate in extreme, low temperature environments. Not only is
the temperature low, but conditions may even be harsh (i.e. snow,
ice, freezing rain). Ultra-low temperatures and harsh conditions
can have a significant impact on strength of materials as well as
ice build-up can cause tourniquet to not function properly.
Furthermore, abrasion against rocks and other hard surfaces is
likely on exterior of personal equipment. What happens to a
tourniquet when it has been carried by personal in a harsh, ULTE
for an extended period, and is then applied to a trauma patient?
Will the plastic injection molding shatter? Will the strength of
the nylon webbing be compromised and the tourniquet rip before
occlusion to the wound? Will ice build and prevent the tourniquet
from functioning? These are the questions this experiment was
designed to answer.
Figure 1: Recon Ripper
EXPERIMENTAL METHODS A total of 13 tourniquets were placed in a Yeti Tundra 75
hard cooler with 14.02 pounds of dry ice. 3 of the 13 tourniquets
were submerged in water for a total of 30 minutes immediately
prior to placement in cooler. The 3 tourniquets submerged in
water were isolated from other tourniquets in cooler. The
tourniquets were then left overnight in a climate-controlled
room. The following morning the cooler was taken to the testing
facility for tensile strength testing. The tourniquets spent at total
of 19 hours in cooler.
Prior to testing tourniquets in cooler, 3 additional
tourniquets at ambient temperature were tensile strength tested
to settle the control group, as seen in table 1.
A quantity of 10 tourniquets were then individually removed
from cooler and placed on the Recon Ripper. An infrared
thermometer was used to record the temperature of the
tourniquet immediately before beginning tensile test. The nylon
webbing between the buckle and the plate was targeted for
tourniquet temperature measurement. This portion of the
tourniquet can be seen in figure 2 below.
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Each individual tourniquet temperature was recorded in
Table 2. The tensile strength test procedure was then executed,
and the ultimate tensile strength results were recorded in Table
2. See appendix, figure 7 for visual of typical failure.
Lastly, the 3 tourniquets that were submerged in water for
30 minutes were tested. Prior to tensile strength testing, the 3
tourniquets had to be forcibly removed from dry ice. Regardless
of extensive ice build-up (see appendix, figure 4), tourniquets
were successfully engaged, and tensile strength tested, and
results can be seen in Table 3.
Figure 2: Temperature Assessment Zone
DATA Table 1 presents tensile strength test data of tourniquets at
ambient temperature. Table 2 presents tensile strength test data
of tourniquets after prolonged ULTE exposure. Table 3 presents
tensile strength test data from tourniquets submerged in water
and then placed in ULTE. Equation 1 was used to determine
overall performance change when comparing ambient to ULT
tourniquet tensile strength
Table 1. Tensile Strength at Ambient Temperature
Sample Ambient
Temp (°F) TQ Temp
(°F) Ultimate Tensile Strength (LBF)
1 75.5 76.2 2570
2 75.5 76.8 2695
3 75.5 74.2 2355
AVG 75.5 75.7 2540.0
Table 2. Tensile Strength Post-ULTE
Sample Ambient
Temp (°F) TQ Temp
(°F) Ultimate Tensile Strength (LBF)
1 75.5 20.2 2860
2 75.5 18.2 2660
3 75.5 18.5 2705
4 75.5 14.4 2700
5 75.5 11.0 2720
6 75.5 9.9 2750
7 75.5 23.2 2460
8 75.5 14.6 2410
9 75.5 22.7 2745
10 75.5 14.6 2360
AVG 75.5 16.7 2637.0
Table 3. Tensile Strength Post-water soak and Post-ULTE
Sample Break Force (lbf)
1 2060* 2 2195* 3 1510*
* Failure due to ice build-up
Eq. 1 – Difference in strength by temperature
𝑆𝑡𝑟𝑒𝑛𝑔𝑡ℎ 𝑐ℎ𝑎𝑛𝑔𝑒 =𝑈𝐿𝑇 𝑎𝑣𝑔 − 𝐴𝑚𝑏𝑖𝑒𝑛𝑡 𝑎𝑣𝑔
𝐴𝑚𝑏𝑖𝑒𝑛𝑡 𝑎𝑣𝑔𝑥100
% 𝐼𝑛𝑐𝑟𝑒𝑎𝑠𝑒 =2637.0 − 2540.0
2540.0𝑥100
% 𝐼𝑛𝑐𝑟𝑒𝑎𝑠𝑒 = 3.8%
RESULTS
Control tourniquets tested at ambient air temperature had an
average tensile strength of 2540.0 lbf.
Tourniquets tested post-ULTE, or -109.3 °F, for 19 hours
had an average tensile strength of 2637.0 lbf.
Tourniquets submerged in water and then stored in ULTE
for 19 hours returned inconclusive results due to ice build-up.
As seen in Eq. 1, tourniquets revealed a 3.8% increase in
ultimate tensile strength after being exposed to ULTE.
A special condition was imposed on 1 tourniquet from the
set of 3 submerged in water. After removal from dry ice and prior
to tensile strength testing, a large impact force was repeatedly
imposed on tourniquet using a metal rod. The purpose was to
simulate abrasion from being worn on external personal
equipment and determine whether abrasion would have an effect
on tensile strength. The results were inconclusive as tourniquet
failed tensile strength test prematurely due to ice build-up.
DISCUSSION
Dry ice is the solid form of carbon dioxide. Carbon dioxide
naturally occurs in our atmosphere as a gas, but it can be
solidified into hard, white blocks with an extremely low surface
temperature. Rather than melting due to heat, dry ice slowly
reverts to a gaseous carbon dioxide form through a process called
sublimation. A block of dry ice maintains a surface temperature
of -109.3 °F, or -78.5 ℃. Although the surface temperature for
dry ice far exceeds any expected tourniquet operating
environment, it was not feasible to invest in a laboratory freezer
for this experiment. Therefore, dry ice was chosen as the agent
for achieving an ULTE.
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Several variables are introduced when using dry ice such as
having no control over the rate at which the dry ice sublimates.
There is also no way to ensure uniform cooling of the
tourniquets. Recording the temperature using an infrared
thermometer immediately after removal from cooler and before
tensile testing was an effort to gain greater insight into the
effectiveness of the dry ice. As seen in Table 2, column “TQ
Temp”, the average tourniquet temperature was 16.7 °F. This is
significantly warmer than the actual temperature of dry ice and
is likely due to varying thermal conductivity, or rate at which
heat is transferred, in tourniquet components.
Variation occurred also in individual tourniquet temperature
readings, again seen in Table 2, column “TQ Temp.” This
variation is due to several limiting factors in infrared
thermometer operation. The accuracy and resolution of the
Etekcity Lasergrip 1080 infrared thermometer is ±2% and 0.1°F,
respectively. An infrared thermometer accuracy is affected by
distance from surface being measured and consideration was
given to this variable but measuring from the exact same distance
was not feasible in this experiment. Surface emissivity is also
important to consider in no-contact temperature readings and the
emissivity of the nylon webbing is not known. Further research
to determine the emissivity could contribute to a more repeatable
and accurate temperature reading.
The Yeti cooler used to contain the 14.02 pounds of dry ice
and tourniquets is not a true closed environment. The tourniquets
were positioned on the bottom of the cooler beneath the dry ice
per dry ice manufacturer recommendation. Although Yeti coolers
are high grade insulators, they are not able to prevent warm
ambient air from entering ULTE. The performance specifications
for the Yeti cooler used are not available from the manufacturer.
This could have also caused variation in tourniquet temperature.
The 19 hours tourniquets spent in ULTE may not have been
an adequate time duration for tourniquets to reach a uniform
temperature. Further considering the material properties of each
component of the tourniquet in future experiments may give a
more accurate time duration necessary for tourniquets to reach a
uniform temperature.
The time each tourniquet is in transition from cooler to
tensile strength test varies due to experiment methods. The
ambient air was an average of 75.5°F. The rate at which the
tourniquets absorb heat and return to ambient temperature is not
known but assumed to be a very fast rate given the temperature
differential between that of dry ice and ambient air. Performing
the ultimate tensile strength testing in a climate-controlled
environment and limiting time to transfer would reduce the
opportunity for heat absorption in the sample.
Secondary testing involving tourniquets submerged in water
was also completed. As mentioned previously, tourniquets were
submerged for 30 minutes and then placed in cooler with dry ice.
Upon removal the temperature was not measured prior to tensile
strength testing as temperature and its effect on tensile strength
was not the focus. Rather the effects of water and potential for
ice build-up and its effect on tensile strength were of interest.
As you can see in Table 3, the tensile strength of the
tourniquet was negatively impacted by submerging in water. The
failure mode was abnormal and in fact due to extensive ice build-
up in the single-component hook and loop material on the
tourniquet strap (see appendix, figure 3). This ice build-up
prevented the hook and loop from properly securing and
therefore delaminated at the break force listed in table 3 (see
appendix, figures 5 and 6). Fortunately, this failure mode can be
prevented by staging tourniquet before stowing on person. By
adhering terminating end of tourniquet to itself, water intrusion
and furthermore ice build-up is effectively reduced. Further
research is necessary to confirm properly prepped tourniquets
submerged in water would exhibit a tensile strength comparable
to results in tables 1 and 2.
Lastly, the single tourniquet repeatedly impacted with a
metal bar visually maintained structural integrity significantly
well (see appendix, figure 8) and did not fail tensile strength test
due to damage incurred from impact forces. Instead, tourniquet
failed due to ice build-up. This is not surprising as primary
weight bearing components of tourniquet, the 1” wide nylon
webbing and the aluminum buckle core, are internal components
and are shielded from external factors. Therefore, it is reasonable
to assume abrasion against rocks and other hard surfaces pose
little risk to tourniquet tensile strength.
CONCLUSION The Recon Medical GEN 4 trauma tourniquet can withstand
up to 2200 pound-force, a 150% increase in strength over its
predecessor, the Generation 3. Significant improvements were
made with the GEN 4 including an aluminum buckle design - a
6061-T6 core with nylon overlay. Although the force required to
occlude blood flow varies greatly from person to person and
location of tourniquet application, there is little doubt that the
GEN 4 tourniquet has the capacity to sustain the force required
to stop the bleed and save lives – and now this same life-saving
technology can safely be recommended for use in harsh, extreme
cold and artic operational environments. This study confirms the
GEN 4 tourniquet performs exceptionally well at very low
temperatures, and by correctly staging the GEN 4 tourniquet you
can rest assured no ice build-up will prevent tourniquet from
operational success.
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APPENDIX
Figure 3: Hook and loop fastener ice build-up Figure 4: Extensive ice build-up upon removal
from cooler
Figure 5: Premature failure due to ice build-up
on single-component hook and loop fastener
Figure 6: Premature failure due to ice build-up
on single-component hook and loop fastener
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Figure 8: Impact force tourniquet prior to tensile
strength testing Figure 7: Typical Failure
