Non-Electronic Oxygen Concentrator Test
April 21, 2008
Non-Electronic Oxygen Concentrator Test
BME 262: Design for the Developing World
Matthew Burke
Andrew Dang
Geoffrey Southmayd
Table of Contents
1
Abstract ................................................................................................................1
2
Background ...........................................................................................................2
3
Completed Work ...................................................................................................4
3.1
3.2
3.3
3.4
4
4.1
4.2
4.3
Pressure/Volume Measurement of Dissolved O2 Concentration ..............................................5
Temperature Measurement of O2 Concentration ............................................................................7
Spectroscopic Measurement of O2 Concentration ...........................................................................9
Final Design: Combustion Rate Measurement of O2 Concentration...................................... 10
Future Work ........................................................................................................ 18
Improve Gas Container ............................................................................................................................ 18
Improve Seal Between Container and Test Surface ..................................................................... 18
Binary Test .................................................................................................................................................... 19
5
Schedule ............................................................................................................. 20
6
Budget ................................................................................................................ 21
6.1
6.2
7
7.1
7.2
Prototyping Budget ................................................................................................................................... 21
Bulk Manufacturing Budget ................................................................................................................... 21
Facilities and Personnel ....................................................................................... 22
Facilities ......................................................................................................................................................... 22
Personnel....................................................................................................................................................... 22
8
Bibliography ........................................................................................................ 23
9
Appendix ............................................................................................................ 25
9.1
9.2
9.3
9.4
9.5
9.6
Intellectual Property and Literature Analysis................................................................................ 25
Standards Analysis .................................................................................................................................... 33
Regulatory Analysis .................................................................................................................................. 35
Specifications ............................................................................................................................................... 39
Experimental Data & Look-Up Table ................................................................................................. 40
Parts List, Instructions, and Pictograms ........................................................................................... 41
Non-Electronic Oxygen Concentrator Test
April 21, 2008
1
Abstract
Oxygen is considered an important prophylactic and life-saving aid for medical
patients when administered during procedures requiring anesthesia, as well as
during patient recovery. In the developing world, hospitals often struggle to
provide oxygen to their patients due to a lack of funding. In addition to these
financial problems, delivering oxygen in cylinders is challenging due to poor road
systems in developing countries. As a result, supplying developing world hospitals
with oxygen in cylinders remains difficult.
The use of oxygen concentrators has provided some relief to the problem of
delivering oxygen cylinders to developing world hospitals. Concentrators provide
an in-house method of producing oxygen from ambient air. This occurs by passing
compressed air over nitrogen-absorbing zeolite crystals, which increases the
concentration of oxygen in the compressed air. With repeated use, however, these
oxygen concentrators become less accurate, but the cost of maintenance is often too
great for the hospital to afford, and as a result, the device may provide patients with
oxygen at undesired concentrations. Most often, problems with the concentrator
are only observed once a patient becomes hypoxic. A test is needed to verify that
the concentrator is delivering oxygen at the desired concentration.
We plan to design a non-electronic device for measuring the oxygen levels delivered
from concentrators in developing world hospitals. The device will utilize an
important property of oxygen: combustion is accelerated in the presence of oxygen
gas. Specifically, the device will allow the user to measure the rate of burning of a
paper match and with that data “look up” the percentage of oxygen present in the air
outputted by the concentrator in question.
The device is simple to assemble and use, and a kit will be provided to hospitals to
ensure that results can be standardized. Maintenance for the device will occur in
the hospital using resources readily available to technicians and doctors. To reduce
cost below existing oxygen concentration tests, the accuracy of the reported output
to the user was decreased to indicate only clinically relevant concentration
intervals. However, under test conditions we were able to achieve prediction
accuracy of ±5%. We believe that the resulting device provides a maintainable,
reliable, and cost effective method of testing hospital oxygen concentrators in the
developing world.
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2
Background
The need for an inexpensive yet reliable method to measure oxygen concentration is
the basis for our project. Such a method is required because oxygen concentrators
used in developing countries are assumed to deliver 90-95% concentrated oxygen,
when many times the actual concentration is much less. As an example, Bill Teninty
states that on a recent trip to Indonesia, he tested what a hospital there called a
“new” oxygen concentrator and the output he measured was 29-30.5% oxygen, well
below the necessary level. (Teninty, 2008)
Mission hospitals in developing countries have used oxygen concentrators since the
1980s. (Teninty, 2008) The devices are used in developing world hospitals
primarily because oxygen cylinders are too expensive and require too much
management (e.g. cylinder refill and replacement) to be affordable (Perrelet, 2004).
Instead of using cylinders as a source of pre-concentrated oxygen, oxygen
concentrators work by passing compressed atmospheric air through one of two
canisters containing zeolite granules. The higher pressure inherent in the
compressed air of the canister causes nitrogen to bind to zeolite granules in the
filtering canister, allowing output of product with higher oxygen concentration. The
pressure is then returned to normal in the first canister, and flow of compressed air
is switched into the second canister. Returning the pressure to normal in the first
canister allows the bound nitrogen to unbind from the zeolite granules, while the
second canister goes through the same process with the compressed air as
described before. A constant supply of concentrated oxygen can thus be delivered
by continuously cycling the flow of compressed air between the two canisters.
(Eltringham, 1992)
The World Health Organization has provided specifications for oxygen
concentrators used in developing countries. However, the proper performance of
concentrators depends on a steady supply of electricity and required maintenance
that many rural hospitals lack. (Dyke, 1994) As evidenced by Teninty’s visit to
Indonesia, a faulty concentrator was unknowingly assumed as working properly.
Therefore, an inexpensive, reliable test of oxygen concentration would decrease the
chances that a poorly performing concentrator is used for patient care.
Numerous technologies currently exist for measuring oxygen concentration. The
zirconia oxygen sensor is used in many industries to measure oxygen
concentrations in gas and liquid mixtures. The zirconia electrolyte used in this type
of sensor becomes conductive to oxygen ions at high temperatures—300°C-600°C.
Higher concentrations of oxygen correspond to greater charge flow, which can be
measured as a voltage (Hradek, 1991).
Oxygen can be measured chemically using Azide-Winkler titration. This method
uses a series of corrosive reagents such as manganese sulfate, sulfuric acid, and
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sodium thiosulfate, to titrate a liquid containing dissolved oxygen, thereby
measuring oxygen concentration. (Chapter 4…, 2007)
Electrodes are also used to measure oxygen concentration. The Clark method
utilizes the reduction of oxygen at platinum electrodes to generate current and
measure oxygen concentration. The electrode is constructed using a thin, organic
membrane to cover a layer of electrolyte and a cathode-anode pair that have a fixed
voltage, allowing only oxygen to be reduced. (Clark, 2003)
Oxygen concentration can also be measured optically. An optical fiber oxygen
sensor utilizes a chemical film that covers the tip of an optical fiber. The film is
photoluminescent, and its emissions are quenched when exposed to oxygen. Less
luminescence means more oxygen is present. (Rosenzweig, 1995)
The paramagnetic oxygen sensor is yet another method of measuring oxygen
concentration. This device uses a dumbbell-shaped vessel filled with inert gas that
is suspended on a platinum wire in a non-uniform magnetic field. As oxygen is
passed through the system, oxygen molecules move towards the stronger section of
the magnetic field, resulting in a displacement of the dumbbell that corresponds to
the oxygen concentration. (Alpha Omega, 2006).
Though there are many technologies available, none have been successfully
implemented as a cheap, reliable method for testing oxygen concentrator levels in a
developing world hospital. The current project seeks find a solution to that
problem.
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3
Completed Work
Three design alternatives were explored with the goal of arriving at the most
effective and practical. Because of the nature of the problem—oxygen is an
odorless, colorless gas—we focused our search on exploiting a measureable
property of oxygen, or on an interaction between oxygen and another substance.
Our end goal was to create a simple, novel method for indirectly measuring oxygen
concentration in an air sample of unknown quality.
There are several properties of oxygen that we believed might prove useful in its
measurement. The following design matrix evaluates the merits of several oxygen
measurement techniques that take advantage of properties including
paramagnetism, combustion, solubility, and chemical reaction. They are examined
based on five design goals important to the success of this project: reliability, ease of
use, ease of maintenance, cost, and performance.
Alternatives
Spectral Flame
Burn Rate
Flame Temp.
Fluorescence w/
Aerogel
Fluorescenece
w/ Fiber Optics
Dissolved O2
Volume
Tube Pressure
Titration
Paramagnetism
Reaction w/ NO
Reliability
(100)
5/500
8/700
6/600
8/800
Maintenance
(100)
8/800
8/800
8/800
4/400
Goals
Ease of Use
(80)
9/720
8/640
9/720
5/400
8/800
6/600
6/480
5/200
7/140
2220
7/700
9/900
10/800
6/240
6/120
2760
7/700
8/800
9/900
7/700
9/900
4/400
6/600
4/400
9/720
4/320
7/560
4/320
5/200
3/120
3/120
3/120
7/140
8/160
9/180
8/160
2660
1800
2360
1700
Cost
(40)
9/360
9/360
8/320
3/40
Performance
(20)
4/80
6/120
5/100
7/140
Total
2460
2620
2540
1780
Table 1: Design Matrix
Based on their individual scores, we chose to pursue flame analysis (which includes
both burn rate and spectral/temperature analysis), and dissolved O2 analysis.
Testing was performed on these alternatives, and it was found that only the burn
rate analysis yielded promising results. The results of testing for each alternative
will be discussed in brief before a detailed analysis of the final design choice is
presented.
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3.1
Pressure/Volume Measurement of Dissolved O2 Concentration
This proposed method of measuring oxygen concentration relied on the physical
properties of liquids and gases and the ideal gas law for determining concentration
given pressure and volume. It depends on the following hypothesis: for higher
oxygen concentrations, more gas will dissolve in water because oxygen has a higher
solubility in water than the other gases that comprise room air.
Oxygen is bubbled through a fixed quantity of water (H2O) for a fixed period of time.
Both of these parameters (volume of water and bubbling time) were investigated
during testing to find the optimal combination. We found that due to the time
consuming process of boiling water, using smaller quantities was more practical.
The operating procedure will be as follows:
1. Fill Erlenmeyer flask with specified amount of water.
2. Bubble oxygen through water for specified period of time.
3. Stopper flask and connect output tube running from Erlenmeyer flask to
eudiometer.
4. Engage heat source and bring water to a boil.
5. Read off volume from eudiometer when water reaches a boil (i.e. the
solubility of oxygen is considered zero).
Experimental Set-Up:
Figure 1: Complete set-up for volume measurement method
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3.1.2 Testing Results
Investigation of Bubbling Time:
Trial 1
Bubbling Time (air only)
Trial 2
Trial 3
None
30 sec
5 min
74
74
74
200
200
200
66
59.6
65
Initial Water Temp. (C)
Water Volume (mL)
Volume of Gas Released (mL)
Table 2: Investigation of Bubbling Time Data for Room Air (21% O2)
As can be seen by the results shown in Table 2, there does not appear to be any
relationship between boiling time and the amount of gas released during boiling for
room air.
Trial 1
Bubbling Time (100% O2)
Initial Water Temp. (C)
Water Volume (mL)
Volume of Gas Released (mL)
Trial 2
Trial 3
None
2 sec
30 sec
65
65
65
200
200
200
26
66
60
Table 3: Investigation of Bubbling Time Data for 100% O2
In this experiment, there appeared to be an encouraging result in Trial 1. Ideally,
with no bubbling, the gas released should be much less than that released when
bubbling is applied. However, this result was not replicated and was determined to
be an anomaly. There was no significant difference between Trials 2 and 3 when
bubbling time was increased from 2 seconds to 30 seconds, which implies that the
water is becoming saturated with oxygen very quickly (i.e. < 2 sec). If this is indeed
the case, this method may not be practical for clinical use because it will be
impossible to achieve a gradient of dissolved oxygen for different gaseous
concentrations.
Because it is known that solubility of oxygen in water increases as the water
temperature approaches 0°C, we investigated whether decreasing the temperature
of the water before bubbling would affect our results. However, decreasing the
temperature to 1°C had no effect on the volume of gas released during boiling. This
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is an indication that the boiling method may not be indicative of dissolved oxygen
content at all.
Investigation of Oxygen Concentration:
Trial 1
O2 Concentration
Bubbling Time
Water Volume (mL)
Volume of Gas Released (mL)
Trial 2
Trial 3
21%
21%
100%
30 sec
30 sec
30 sec
200
200
200
59
59.6
60
Table 4: Investigation of Oxygen Concentration Data
This phase of testing was designed to determine whether we could distinguish
between room air (21% oxygen) and 100% oxygen, the largest range we would
need to differentiate using this method. Unfortunately, there appeared to be no
difference in the volume of gas released when using 100% oxygen as compared to
room air. This is another indication that this method may not be reliable and in fact
impractical in achieving our design goals.
In conclusion, there may be many factors that inhibited successful implementation
of this idea, but regardless, the pressure/volume method of measuring oxygen
concentration was deemed a failure due to lack of repeatability.
3.2
Temperature Measurement of O2 Concentration
Oxygen supports combustion, and changes the characteristics of a flame depending
on its concentration in air (i.e. color of the flame, intensity of burning). For this
method, we were interested in investigating the adiabatic flame temperature of a
fuel at constant pressure. Adiabatic flame temperature is the temperature achieved
during combustion of a fuel with no heat transfer or changes in kinetic or potential
energy. (Engineering Toolbox, 2005)
Other characteristics of a flame were also analyzed in later experiments, such as
spectral band emission, flame size, and flame shape.
3.2.1 Testing Results
The first step in the flame experiments was determining what type of fuel source(s)
to use to generate a flame. Cotton, newspaper, wood on a match stick, and natural
gas (from a research lab) were investigated for ability to generate measurable
flames. Both cotton and newspaper did not produce measurable flames when
ignited with a grill lighter. Instead, they both “cindered” as they burned, therefore
we decided not to use cotton and newspaper as fuel sources. We considered using a
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gas source (natural gas from lab, butane, propane) but professionals
(anesthesiologist at Duke Hospital, an M.D. /Ph.D. in a Duke research lab, and the lab
manager in the Physics Department at Duke University) recommended against
testing gas-fueled flames (e.g. Bunsen burner) with 100% oxygen due to safety
concerns.
Temperature (near or in the flame):

PROPOSED IDEA: By using an infrared thermometer and a closed
environment, a correlation could be determined between adiabatic flame
temperature and oxygen concentration.

TESTING RESULTS: The infrared thermometer used was a Sixth Sense
LaserTemp100 IR thermometer with a range of -58 to 932F.
The IR thermometer measures surface temperature of whatever object the mounted
laser is pointed at. We attempted to measure the temperature of a match flame
(Diamond brand matches), but found that the flame was too small and fluctuated too
rapidly to get an accurate reading. We did not test a Bunsen burner flame (natural
gas fuel) because of multiple warnings from professionals about the dangers of
using 100% oxygen with flames from any sort of gas burner. Because of the
inaccuracies and inherent danger, we concluded that flame temperature analysis
would not be a suitable method for measuring oxygen concentration.
Figure 2: Measurement of Flame Temperature using IR Thermometer
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3.3
Spectroscopic Measurement of O2 Concentration
Because oxygen accelerates combustion, we hypothesized that the increased
presence of oxygen might also alter the spectral bands of a flame.
3.3.1 Testing Results
Spectral/optical bands:


PROPOSED IDEA: The spectral band emission of a flame is like a
fingerprint that changes depending on the substances being combusted.
In this case, visual analysis of spectral bands from a flame (using a prism
to separate wavelengths) would be correlated with different oxygen
concentration.
TESTING RESULTS: Three different methods were used in the attempt to
generate spectral bands from a match’s flame. The first was an
equilateral prism placed in between the flame and a white background
wall in a dark room. Spectral bands were not observed at all with this
method.
The second method used was the creation of a “homemade” spectroscope crafted
out of a narrow cookie box, paper, tape, and diffraction grating film. Spectral bands
were observed in the device when the slit of the device was pointed at a bright and
steady light source, such as a fluorescent light bulb, which indicated that the device
was working. However, when the device was used with a match flame, spectral
bands were not observed. This is most likely because the flame’s intensity was not
strong enough to produce bands in the device.
Figure 3: Homemade Spectroscope
To see if lack of viewable spectral bands was a problem with the device itself, an
analog spectroscope was borrowed from the Physics Department at Duke
University. Once again, the analog spectroscope produced spectral bands when
viewing white light, from a fluorescent bulb, but no bands were viewed when
observing the flame from a match. We concluded from these results that spectral
band observation of flames would not be a viable method for measuring oxygen
concentration.
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3.4
Final Design: Combustion Rate Measurement of O2 Concentration
The final method of measuring oxygen concentration investigated was to analyze
the burn rate of a match exposed to air from a concentrator. A container of known
volume (in this case a 250 mL glass beaker) is filled underwater with air from the
concentrator—water is used to ensure that air from the concentrator fills the entire
volume of the container without mixing with room air. A match is placed in a small
piece of putty to secure it upright on the test surface. The beaker is covered on the
open end with aluminum foil and a small hole is cut in the center to allow placement
over the match. As the beaker is moved down over the match, a timer is started.
The method depends on measuring the time it takes for a flame traveling along the
length of a match to either: reach the bottom of the match, or to cease forward
progress along the match. Our design is not a completely closed system, so we
cannot measure the time it takes for the flame to extinguish. This is because once
the oxygen inside the container is depleted, the flame “sucks in” room air through
small gaps between the container and the test surface, causing the match to cinder
for a prolonged period before finally extinguishing completely. The time is recorded
and the length that the flame burned along the match is measured. This procedure
is repeated five times to eliminate random error, and the times/lengths are
averaged. Finally, a look-up table is utilized to read off the oxygen concentration
from the average burn time and average burn length. The testing process for this
design will be discussed in detail later in this section.
3.4.1 First Attempt: Wood Matches and Open-Ended Beaker
The first attempt at predicting oxygen concentration with burn rate analysis utilized
similar materials, but was not as reliable as the final design. Rather than covering
the mouth of the beaker with foil, it was left open. And, instead of using putty to
secure the match, a metal spring clip was employed. We performed 50 trials each at
oxygen concentrations of 100%, 80%, 60%, 40%, and 21%. It is important to note
that during testing, we did not have access to pre-mixed gas at intermediate
concentrations. We procured an oxygen cylinder that contained 100% oxygen, and
used a basic algebraic formula to calculate how much pure oxygen needed to be
combined with room air to create gas containing 80%, 60%, and 40% oxygen.
0.21(V  x)  x 
P 100  



V
In the relation above, P is the desired oxygen percentage; V is the volume of the
container (250 mL beaker for our tests); and x is the volume of pure 100% oxygen
needed. Generally, 
we solved this equation for x at the percentages we desired for
the known volume of the beaker.
The data for this experimental setup is summarized in Table 6, and the plot in Figure
4 shows the analytical fit to the data as well as 99% confidence intervals calculated
based on the standard deviation.
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Oxygen Percentage
100%
80%
60%
40%
21%
Average Rate (cm/s)
2.02
1.23
0.70
0.37
0.12
Standard Deviation
0.18
0.11
0.10
0.01
0.01
99% Confidence Interval
0.15
0.09
0.08
0.01
0.01
Table 6: Results of Testing with Method 1
Figure 4: Power Law Fit of Testing Data with Method 1
The plot above shows a power law fit with an R2 of 0.996, which is very high. The
confidence bars confirm that this method does indeed allow discrimination of
oxygen percentages that differ by 20%.
Although the data presented above appear promising, it was determined through
blind trials (using people unfamiliar with the procedure) that the open-mouth
beaker introduces too much error for the method to be effective. In other words,
there was a sharp learning curve for individuals performing the test that greatly
decreased their accuracy. Specifically, the method assumes that some volume of
oxygen will be lost out the bottom of the beaker in each trial. However, it also
assumes that this volume will be constant for each tester. It became clear that a
method that depends so strongly on human error for its function was not a viable
option.
Further, we discovered that wooden matches are not manufactured to be the same
size and shape. Some matchsticks were thicker than others, which affects the burn
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rate—a fact that serves to compound the human error described before. Also,
match composition varies between matches as well. Wood that contains more pitch
(resin) burns at a faster rate than wood with less. Therefore, we found it difficult to
standardize our results across all wood matches of the same brand, let alone all
wood matches.
3.2
Second Attempt: Covered Beaker and Wooden Dowels
An alternative method was needed. We attempted to solve the gas leakage problem
by covering the open end of the beaker with aluminum foil and cutting a small hole
for the match to fit through. This greatly decreased the amount of gas that escaped
from the beaker in our trials. Unfortunately, the system worked almost too well.
The wooden matches flashed completely into flame in well under a second—too
short a time to be measured. This occurred at concentrations of both 100% and
80%, effectively preventing us from achieving our specification of ±20% accuracy.
Recognizing that the aluminum foil provided optimal retention of gas and was much
easier to use than the previous setup, we attempted to find a material that would
burn slow enough to be measured when exposed to high oxygen concentrations.
Cylindrical wooden dowels were chosen (r = .3 mm, h = 5 mm) as the next test
material. These did indeed burn slow enough to be practical. However, a similar
problem was encountered as with wood matches. The grain and composition of the
dowels varied greatly from piece to piece. Reproducible results were thus not
attainable.
3.3
Third Attempt: Covered Beaker and Paper Matches
Paper matches were avoided in original testing because we assumed they would
yield less consistent results than wood matches. However, further testing proved
this assumption incorrect. In fact, paper matches were more reliable than wood for
several reasons. First, they are completely manufactured, so each match is identical
to every other match (brand dependent). Second, we found that although wood
matches burned too quickly under 100% oxygen with a covered container, paper
matches did not. Rather, paper matches burned at a measurable rate of
approximately two seconds under these conditions. Finally, paper matches are
even cheaper than wood matches, costing only $1.44 for 1500 matches.
These three observations made paper matches the material of choice for our final
design. Testing was performed in much the same way as in the first attempt—
however, due to the very consistent results we obtained after 25 trials for lower
concentrations (as opposed to the 50 performed before), we determined that
additional trials were not necessary. Table 7 summarizes the results from this
round of testing. Notice that the standard deviations of the averages are extremely
small. This implies that taking the average of five trials as the measured burn rate
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effectively eliminates whatever inherent error remains in the method.
complete data tables can be found in Appendix 9.5.
Oxygen Percentage
100%
80%
60%
40%
21%
Average Rate (cm/s)
1.48
0.87
0.46
0.28
0.10
Standard Deviation
0.04
0.05
0.01
0.01
0.01
99% Confidence Interval
0.02
0.03
0.01
0.00
0.00
The
Table 7: Results of Testing with Final Method
Figure 5 below shows the exponential fit to the burn rate data. A correlation
coefficient of 0.981 indicates a good fit. The error bars are too small to be visible on
the plot, which is an indication of how accurate this method is from trial to trial.
Figure 5: Exponential Fit of Burn Rate Data - Final Method
In order to construct a look-up table for easy use by hospital technicians without
access to scientific calculators, we back-solved the fit to yield concentration in the
following manner, where x is oxygen concentration and y is the measured burn rate.
y  0.061e 3.264x
ln y  3.264 x  ln( 0.061)
x  0.306  ln y  0.857

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The following provides a detailed description of the testing procedure followed to
obtain the plot above.
1. Place a dime-sized amount of adhesive putty in a mound on the table.
2. Cover the mouth of a 250 mL beaker with foil. Tape around the edges of the
foil to keep it sealed and secure. Cut a small hole in the center of the foil
approximately 1 – 2 cm in diameter. The hole should be able to fit over the
match and mound of putty.
3. Stick a paper match about 2 mm into the putty so that it is standing upright.
If testing 21% oxygen (room air): fill the beaker with water and then
completely empty it to fill the entire volume with room air, then skip to step
5. If testing oxygen concentrations from 40-100%: submerge the 250 ml
beaker under water. Invert the beaker, and then fill it as follows:
a. 100% oxygen: fill the entire beaker with gas from the 100% oxygen
cylinder.
b. 80%: fill the beaker to 187ml with 100% oxygen and allow room air
to bubble in the remaining gas volume.
c. 60%: fill the beaker to 125ml with 100% oxygen and allow room air
to bubble in the remaining gas volume.
d. 40%: fill the beaker to 60ml with 100% oxygen and allow room air to
bubble in the remaining gas volume.
4. Carefully remove the beaker from the water after sliding a piece of aluminum
foil over the hole in the mouth of the beaker to keep most of the gas from
leaking out. If following from steps 3b, 3c, or 3d, the rest of the beaker is
filled with room air (assumed 21% oxygen) by carefully letting water drain
out.
5. Bring the beaker over near the match while maintaining the foil seal.
6. Have a 2nd person light the match.
7. After the initial flare up from the sulfur on the match head, quickly place the
beaker over the top of the match. Slide the beaker directly from the foil to
the flame with as little upward vertical movement as possible (vertical
movement causes gas to leak out of the beaker).
8. The 2nd person begins timing once the beaker has been set down. Stop the
timer when the flame reaches the bottom of the match or when the flame
stops its progress moving down the match.
9. Measure and record the distance burned as well as time to burn along the
match.
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10. Repeat steps 1-9 for 25 times for each oxygen concentration.
11. For each oxygen concentration level dataset, calculate the burn rate for each
trial (divide burn length by burn time) and then find the average of each set
of five trials. Standard deviation and 99% confidence interval were
calculated from the averaged data. The total average combustion rate for
each oxygen concentration level can be plotted and fitted to form a rateconcentration curve and equation.
3.4
Unknown Concentrations and Blind Trials
The final phase of testing performed was to recruit volunteers unfamiliar with the
test procedure and determine whether or not they could replicate our results. Some
trials were performed on pure 100% oxygen, however in others, volunteers were
instructed to fill the beaker to a specified volume with oxygen and the rest with
room air (this produced unknown intermediate concentrations). The following
table summarizes the results obtained by eight teams of two volunteers.
Table 8: Results of Blind Trials
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Volunteers were able to predict oxygen concentrations (using our previously
determined exponential fit) with an average error of ±5%, well within our original
specification.
The results presented in Table 8 are encouraging; they demonstrate that users of
this test can learn the technique within five trials and still predict very accurately
the concentration of oxygen in an unknown sample of gas.
A detailed parts list for our testing and instructions for the end-user are included in
Appendix 9.6. Also included is a pictogram version of the instruction manual to be
used by non-English speaking individuals or as a supplement to the written
instructions.
3.5
Limitations
There are several limitations to the design described above. First, although efforts
were made to seal the bottom of the beaker with foil, some leakage inevitably occurs
when removing the beaker from the water. The process of filling the container
underwater seems to be the simplest method of reducing contamination by room air
and ensuring that as much of the gas inside the container during testing as possible
came out of the concentrator. We experimented with filling the beaker out of water.
Since we knew the flow rate of oxygen out of the cylinder, we could estimate how
long the gas needed to be running to completely fill the beaker. However, because
oxygen is odorless and colorless, there is no way to tell when the container is
entirely full. Worse, pure oxygen will not usually totally displace the room air that
was originally inside the beaker—some mixing will occur.
Second, because of the presence of water on the container after it is removed, there
were a few instances of drips coming into contact with the match and/or flame.
This usually invalidated the trial in question, but was observed rarely enough (1 in
25 trials) that it was not deemed a major issue.
Third, there is a slight learning curve that comes with this method. However,
because the final measurement is taken from the average of five trials, and because
users learned the technique in less than five trials during our experiments, the effect
of this should be negligible. Further, because we saw such good accuracy (5%) and
our specification was for 20%, there is some room for human error before the test
fails.
Fourth, since the table was developed for the specific setup we developed, some
materials must always remain constant. For this reason, our device will be sent to
developing world hospitals in kit form. The kit will include enough matches for 150
tests (1500 matches), a 250 mL glass beaker as a container, and 12 sticks of
adhesive putty. The rest of the materials (tape, bucket, foil, watch) should be locally
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available. Any digital watch or analog watch with a timer can be substituted for the
stopwatch used during testing.
The final limitation that we foresee is a general misinterpretation of instructions by
the user. This would become especially likely if the user does not speak English and
must rely on the pictogram instruction manual. While the procedure is relatively
simple in and of itself, the user must understand when to start and stop the timer—
otherwise the method loses its efficacy. Difficulty in understanding that the user
must stop the timer when forward progress ceases or the flame reaches the end of
the match, rather than when it extinguishes, may occur. Future work may be helpful
in eliminating this and other sources of error.
3.6
Summary and Conclusions
This project achieved all of the goals set for it at the beginning of the semester.
Namely, it met every design specification and provided performance far beyond
what was initially expected (see Appendix 9.4). Our hope is that others take up this
concept and work with it in the pursuit of our ultimate goal: impact. Because there
is no previous solution to the oxygen concentrator performance problem we
investigated, we believe this design has the potential to become widely utilized in
hospitals throughout the developing world. Ultimately, it may even save lives. As
graduating college seniors we are excited to have participated in creating a device
with such potential.
Finally, we wish to extend ourselves as resources to others working with our idea.
Please feel free to contact any of us to ask specific questions about our work.
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4
Future Work
Although the proposed design successfully meets the desired design specifications
for the project, improvements to the design could still be made. Such improvements
may involve choosing a different container in place of the 250 ml beaker, or finding
a new method of sealing the system while the match is burning. It may also be
useful to simplify the test to provide only basic high/low oxygen concentration
information.
4.1
Improve Gas Container
The use of a 250 ml beaker was useful for prototype testing, since a graduated
container was needed to mix different oxygen concentrations for data collection. In
the developing world, however, there will be no need for gas mixing, since the gas
emitted from the concentrator is already mixed to some (unknown) oxygen
concentration. Thus, a non-graduated container, such as a glass cup, may provide a
more inexpensive alternative to the beaker.
Glass Coca-Cola bottles, or even clear glass beer bottles, might be especially useful
substitutes. These containers are readily available in the developing world, and
would provide cheaper, more easily replaceable alternatives to the glass beaker. In
addition, the small mouth of the Coke or wine bottle would eliminate the need for
aluminum foil to cover the opening, since there would be only minimal area for gas
to escape. In addition, bottles with volumes larger than 250 ml could be used so
that the match would burn longer before depleting the available oxygen. This would
eliminate the often-difficult task of deciding when the forward progress of the flame
down the match has stopped, since more flames will be able to reach the bottom of
the match.
The choice of a new container will require additional testing to develop a new
calibration curve to fit the data.
4.2
Improve Seal Between Container and Test Surface
As the match burns inside the beaker, it draws in room air in an attempt to continue
combustion in the increasingly hypoxic environment of the container. As a result of
this addition of 21% oxygen, the burn rate of the match decreases. Our model
attempts to correct for this occurrence by stopping the timer when burn progress
down the match ceases, and not when the match is extinguished. This error could
be eliminated, however, by creating a tight seal around the base of the beaker to
ensure a closed system during trials. This would allow for timing until the match
goes out completely, which is far easier to determine.
A seal could be established by pressing the beaker down into a ring of putty circling
the match, or by placing the beaker into a shallow pan of water below an elevated
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match. This procedural change would likely improve the accuracy of the test
drastically, but due to time constraints, was not investigated in this analysis.
4.3
Binary Test
It is possible that oxygen concentrators experience all-or-nothing failure; that is, the
concentration of oxygen emitted immediately drops from the desired value towards
21%, rather than slowly declining over time. Instant failure could be due to the
zeolite crystals becoming wet due to excess humidity, for instance. In this case, a
test would only be necessary to distinguish between extreme high and low oxygen
concentrations.
The proposed design could easily be simplified to provide this binary concentration
determination. Observed burn rates in room air and 100% O2 differ by a factor of
almost 15, and so a rough estimate of concentration could be obtained simply by
watching the match burn. Rather than calculating burn rate and using a lookup
table to determine concentration, the medical technician could simply check
whether the match burns the length of the match within a certain amount of time
(say, 3 seconds). Implementing such a test would require a detailed analysis of most
common failure mechanisms of standard oxygen concentrators.
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5
Schedule
The following design schedule (Figure 11) was followed as closely as possible, with
small modifications being made as the process progressed.
Figure 6: Design Schedule
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6
Budget
6.1
Prototyping Budget
The prototyping budget outlines the cost of building three (3) working prototypes of
our design.
The following lists the costs incurred to build three prototypes of the combustion
rate measurement device.







250 mL Bomex Beaker (3): $7.80
Adhesive Putty (3 1-cm pieces): $0.38
Diamond Matches (30): $0.03
Aluminum Foil (3 ft2): $0.09
Electrical Tape (3 ft): $0.03
12” Ruler (3): $1.50
Plastic Bucket (3): $6.00
o TOTAL: $15.83
Therefore, a single prototype device costs roughly $5.27, well under our original
specification of $100.00. This budget does not take into consideration the cost of a
stopwatch. This is because a stopwatch is extremely expensive compared to all the
other materials used ($12.99 each). Ideally, the user would own a watch capable of
tracking times on the order of several seconds (digital, or analog with a timer). If
not, they should be able to find a co-worker who does. If it is deemed during
production that a stopwatch should be included in the kit, the cost of production will
increase significantly but still fall well below our specification.
6.2
Bulk Manufacturing Budget
The bulk-manufacturing budget estimates the cost of producing 500 units of each
device. Labor costs are neglected, as no pre-assembly is required to use our device.
These budgets were calculated assuming a 20% discount on materials for bulk
orders. Further, this budget only takes into account items to be included in the “kit”
that will be distributed to hospitals. Locally available items are thus not included in
the bulk-manufacturing budget below.



250 mL Bomex Beaker: $2.60
Adhesive Putty (12 sticks): $5.97
Diamond Matches (1500): $1.44
o TOTAL: $10.01
Approximate cost of 500 kits: $4,004.00
Miscellaneous items in both budgets such as travel, consultants, facilities, etc., were
found to be negligible.
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7
Facilities and Personnel
7.1
Facilities




7.2
Duke Engineering BME 261/262 design labs
Table saw, band saw, CAD, PIC, computers, other available/purchased
equipment and tools as needed
Duke University Hospital: access to oxygen concentrators and/or
compressed air.
Duke Chemistry Department Lab: use to build prototype
Personnel
Client: Bill Teninty

International Aid: Medical Equipment Training Manager
Faculty advisor: Dr. Robert Malkin

BME 261/262 design class professor and project advisor
Expert Consultants:


Richard Buck; UNC Biochemistry Department
Erno Lindner; University of Memphis
University Contacts


Dr. Allan Shang, M.D. Duke University Dept. of Anesthesia.
Dr. Keita Ikeda, Ph.D. Duke University Dept. of Anesthesia, Research.
Project team members:



Matt Burke;
Andrew Dang;
Geoff Southmayd;
matthew.burke@duke.edu
andrew.dang@duke.edu
geoffrey.southmayd@duke.edu
This team would like to acknowledge Dr. Ikeda for allowing us access to his lab, and
Dr. Shang for providing us oxygen—without which this project would have been
impossible. We would also like to thank Dr. Malkin for his support and guidance
throughout the project, and for sharing his vision of designing for the developing
world with us.
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8
Bibliography
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and vapors using controlled flames.” U.S. Patent 6780378. 24 Aug 2004.
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http://encyclopedia.airliquide.com/Encyclopedia.asp?GasID=48
American Chemical Society. (1999). Division of Chemical Education. Retrieved
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Acid:
http://jchemed.chem.wisc.edu/JCeSoft/CCA/CCA3/MAIN/RAINN1O2/PAGE1.HTM
Aquatic Ecosystems, Inc. (2007). Self-Priming Manual Siphon Pump. Retrieved
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Bales, R., & Conklin, M. (n.d.). University of Arizona. Retrieved February 4, 2008, from
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Blackie, J., Wu, P., & Naveh, D. (1999). Membrane Oxygenation of Mammalian Cell
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W. Noe, & F. Wurm, Animal Cell Technology: Products from Cells, Cells as Products
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“Chapter 4 - From the Field to the Lab: How to Measure Dissolved Oxygen”. A
Citizen's Guide to Understanding and Monitoring Lakes and Streams. 23 May 2007.
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Dow Corning. (2008). Rubber Physical and Chemical Properties. Retrieved February
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Dwyer Instruments, Inc. (2005). Measurement of Pressure with a Manometer.
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Dyke, T., Brown, N. “Hypoxia in childhood pneumonia: better detection and more
oxygen needed in developing countries.” BMJ (1994) 308:119-20.
http://www.bmj.com/cgi/content/full/308/6921/119.
Educate-yourself.org. (2006). Educate Yourself. Retrieved February 4, 2008, from
Ozone's Reaction with Common Chemicals: http://educateyourself.org/ozone/ozonereactionswithcommonchemicals29sep06.shtml#acids
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Engineering Toolbox. (2005). Adiabatic Flame Temperature. Retrieved February 5,
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http://www.engineeringtoolbox.com/adiabatic-flame-temperature-d_996.html
Elert, Glenn. “Melting Point of Glass.” 2002.
http://hypertextbook.com/facts/2002/SaiLee.shtml. 22 Feb. 2008.
Eltringham, Roger. “The Oxygen Concentrator.” Update in Anaesthesia (1992)1,6.
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Hradek, Richard W., Myers, William P., Alftine, David N., Cao, Tuan. “Oxygen
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Patent 5071453. 10 December 1991.
“Jet Engine.” Avarneg Inc. 2007. http://www.madehow.com/Volume-1/JetEngine.html. 22 Feb. 2008.
“Leland C. Clark.” The Hebrew University of Jerusalem, Institute of Chemistry. 17
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“Oxygen Sensor Types.” Alpha Omega Instruments. 2006. http://www.aoicorp.com/additional_information/oxygen_sensor_types/. 4 Feb. 2008.
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Perrelet, A., et. al. “The oxygen concentrator: an appropriate technology for treating
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9
Appendix
9.1
Intellectual Property and Literature Analysis
9.1.1 Patent Search
Patent Title: Oxygen detecting composition
Number: 6,703,245
Date: March 9, 2004
The oxygen detecting composition described in this patent has the ability to change
color depending on the availability of oxygen. This could be utilized as a quick test
of oxygen concentration if the color change could be set at a certain threshold of
oxygen concentration.
Patent Title: Method for measuring concentrations of gases and vapors using
controlled flames
Number: 6,780,378
Date: Aug 24, 2004
This patent describes a method of measuring select spectral bands emitted from a
controlled flame to determine the concentration of certain gases and vapors.
Application of this technology to calculate oxygen concentration is mentioned in the
patent. Adapting this technology could provide a novel method of measuring
concentration.
Patent Title: Optical paramagnetic/diamagnetic gas sensor
Number: 4,875,357
Date: Oct 24, 1989
The apparatus described utilizes the paramagnetic nature of certain gases to cause a
dislocation in a movable element as they are passed through a magnetized chamber.
Greater dislocation is correlated to greater concentration of tested gas. This
technology is a potential means of measuring oxygen concentration, since oxygen is
a paramagnetic gas.
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Patent Title: Oxygen indicator
Number: 5,358,876
Date: Oct 25, 1994
This patent describes the use of an organic compound, acid, and a dye to test the
presence of without water and in the presence of light. If this method could be
adapted in some way to indicate degree of oxygen content, it would prove useful to
the proposed project.
Patent Title: Device and method for determining oxygen concentration and
pressure in gases
Number: 5,885,843
Date: March 23, 1999
This patent describes a novel approach to photoluminescence-based oxygen
concentration detection. A silica aerogel diffusive medium allows oxygencontaining gas to diffuse easily through the porous network and quench
photoluminescent material infused into the aerogel. This process provides an
option for oxygen concentration detection in the current project.
Patent Title: Method and sensor for measuring oxygen concentration
Number: 5,043,286
Date: December 14, 1988
This patent describes a method for measuring oxygen concentration in a fluid. A
plastic film containing a luminescent substance that is quenched in the presence of
oxygen is exposed to the test fluid. The film is subjected to irradiation by light that
is strongly absorbed by the luminescent substance, and the time-dependent
emission intensity is measured. The luminescent substances used are metallo
derivatives of partially or fully fluorinated porphyrins. Although the actual
mechanism of luminescence and quenching is non-electronic, this method would
most likely require an electronic transducer to be effective, making it difficult to
apply to this project.
Patent Title: Method and arrangement for measuring the concentration of gases
Number: 4,003,707
Date: January 18, 1977
In this method for measuring the concentration of a gas, an indicator generates light
signals corresponding to the concentration of gases in a sample to be measured.
The apparatus includes a light transmissive surface upon which a beam of
monochromatic light is directed. The indicator reacts when illuminated by the
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incident light and has a resulting color characteristic that will show the
concentration of gases in the mixture. This apparatus seems too complicated for our
application, but the technology is useful in thinking about the problem.
Patent Title: Dissolved oxygen measurement instrument
Number: 4,330,385
Date: May 18, 1982
This patent describes an instrument for indirectly measuring the concentration of
dissolved oxygen in a liquid. Entrapped air is continuously circulated through the
enclosure and bubbled through the liquid. A sensor measures the oxygen
concentration of the air after it is bubbled through the liquid, which provides an
indirect measurement of the amount of oxygen that dissolved in the liquid. The
same type of design may be useful for our purposes, although the sensing element in
this case is electronic.
Patent Title: Ozone/ultraviolet water purifier
Number: 4,141,830
Date: February 27, 1979
This patent describes a method of purifying water by irradiating air with ultraviolet
light to convert some of the oxygen to ozone, and then bubbling this ozonated air
through water to purify it. This method may be useful for creating ozone and
dissolving it in a liquid should we choose to pursue that design concept.
Patent Title: Method for Measuring Oxygen Concentration
Number: 4,810,655
Date: March 7, 1989
This patent uses luminescent emission to determine oxygen concentration from a
test fluid. This fluid is passed over an oxygen-permeable matrix containing
phosphorescent molecules that fluoresce in response to a particular wavelength of
light. By measuring the change in intensity due to the addition of the test fluid to the
matrix, the oxygen concentration can be determined. This could provide a method
of testing the oxygen concentrators in a developing world hospital, if we could find a
reliable and inexpensive method of measuring fluorescence.
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Patent Title: Ozone Generating Device
Number: 4,857,277
Date: August 15, 1989
Ozone is generated by exposing ambient air to ultraviolet (UV) radiation. The
device has been designed with a series of two 90° bends to allow for airflow through
the system without exposing the user to any harmful UV radiation. This patent
would be useful as a method for safely creating ozone from the gas delivered by the
concentrator. The added reactivity of this ozone-rich gas could then be measured to
estimate the concentration of oxygen in the original sample.
Patent Title: Direct Readout Dissolved Gas
Number: 4,702,102
Date: October 27, 1987
This patent measures the percentage of gas dissolved in some liquid solvent. The
device includes a gas-permeable tube that is sealed on one end and has a pressure
sensor on the other. When the tube is immersed in the liquid, gas will either be
released or absorbed as the pressure inside the tube equilibrates to the external
aqueous environment. The resulting change in the pressure gage can then be used
to determine the percentage of gas dissolved in the liquid. This process would be
useful if we chose to bubble the gas from the concentrator through a solution before
measuring its concentration.
Patent Title: Colorimetric Oxygen Detection
Number: 3,545,930
Date: December 1970
This patent describes a method of determining the amount of oxygen in a sample by
reacting the gas with bis(cyclopentadienyl)titanium chloride, and observing a color
change in response to oxygen. This method could serve as an oxygen indicator test,
which could easily be read, like pH paper, by technicians in developing hospitals.
Patent Title: Oxygen Monitoring Device and Method
Number: 4,677,078
Date: June 30, 1987
This patent uses a manganese tertiary phosphine polymer film that experiences a
change in color intensity with varying oxygen levels. It provides measurements
“over an indefinite period of time and at a minimal cost.” This could potentially
provide a cost efficient oxygen sensor, although the ease of obtaining the necessary
film in a developing country may be a problem.
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9.1.2 Literature Search
Last name of 1st author: Broenkow
Title: Colorimetric Determination of Dissolved Oxygen at Low Concentrations
Journal: Limnology and Oceanography
Year Published: 1969
This journal article details a non-electronic, chemical means of measuring amount of
dissolved oxygen. The requirement of this method is that the dissolved oxygen is at
a low concentration. Our project could follow this path if we develop a means of
dissolving sampled air into a liquid and determine the amount of dissolved oxygen
in liquid as an indirect measure of oxygen concentration in the sample air.
Last name of 1st author: Perrelet
Title: The oxygen concentrator: an appropriate technology for treating hypoxaemic
children in developing countries
Journal: The International Journal of Tuberculosis and Lung Disease
Year Published: 2004
This article details a study of oxygen concentrator use by patients and personnel in
Ndioum Hospital, Senegal. The article is useful in providing insight and examples of
how patients and personnel potentially handle oxygen concentrator equipment.
The design of our project can take this behavior into account, particularly in terms
of structurally designing our project to be user and/or patient friendly.
Last name of 1st author: Eaton
Title: A novel colorimetric oxygen sensor: dye redox chemistry in a thin polymer
film
Journal: Sensors and Actuators
Year Published: 2002
The approach outlined in this article uses a redox reaction of 2,6dichloroindophenol, fructose, and base in a thin ethyl cellulose polymer film that is
colorless when there is a lack of oxygen. In the presence of oxygen, color changes to
a strong blue. The intensity of the color is stated to show “reasonable linearity” with
increasing partial pressures of oxygen, thereby making this a potential method to
implement in detecting oxygen concentration in our project.
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Last name of 1st author: Cox
Title: Detection of oxygen by fluorescence quenching
Journal: Applied Optics
Year Published: 1985
This paper details experiments using fluorescence quenching of an aromatic
hydrocarbon fluorescent compound in a silicone composite matrix. Measurement of
oxygen concentration is shown to be approximately linear when correlated with
fluorescence intensity. The paper provides experimental examples and reference
data in the case that we decide to use a form of fluorescence quenching
methodology in our project design.
Last name of 1st author: Chung
Title: Measurement of Dissolved Oxygen in Water using Glass-Encapsulated
Myoglobin
Journal: Analytical Chemistry
Year Published: 1995
This paper introduces the concept of using myoglobin, a biological molecule that
binds to oxygen, to measure oxygen concentration in a liquid. The absorbance of a
deoxyMb-containing gel is measured and was found to change linearly with time
and be directly proportional to the concentration of oxygen in the solution.
Although developing world hospitals most likely do not have the equipment to
measure absorbance easily, it may be possible to develop another method of
achieving the same measurement.
Last name of 1st author: Evans
Title: A Novel Luminescence-Based Colorimetric Oxygen Sensory with a “Traffic
Light” Response
Journal: Journal of Fluorescence
Year Published: 2006
The authors of this paper developed a dual-lumophore oxygen sensor that changes
color dramatically depending on oxygen concentration (red, yellow, and green).
Their approach enables the simple and quick determination of oxygen concentration
in a solution. The sensor requires the use of platinum, which may be too expensive
of a material for our application, but nonetheless the technology is very interesting.
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Last name of 1st author: Hitchman
Title: Measurement of Dissolved Oxygen
Journal: none (source is a book, 255 pp.)
Year Published: 1978
This text discuss the importance of dissolved oxygen measurements,
thermodynamic considerations, and the principles of many different kinds of
sensing methods including chemical, electrochemical, and polarographic. There is
also a detailed discussion of the Winkler method, colorimetry, radiometry,
manometry, volumetry, mass spectrometry, thermoconductivity, paramagnetism,
and gas chromatography. Solubility tables, convective flow and diffusion, and other
useful parameters are listed as well. This resource will provide a fundamental
background to the science of oxygen measurement.
Last name of 1st author: McEvoy
Title: Dissolved oxygen sensor based on fluorescence quenching of oxygen-sensitive
ruthenium complexes immobilized in sol–gel-derived porous silica coatings
Journal: The Analyst
Year Published: 1996
This article describes a fluorescent quenching method similar to ones described in
the papers above. However, it uses a ruthenium complex as its indicator molecule
and a blue LED as its light source. A photodiode is the measurement instrument.
This technique, although it uses some electronics, has applications to be a low-cost,
portable tool for measuring oxygen concentration in the developing world.
Last name of 1st author: Howie
Title: Beyond Good Intentions: Lessons on Equipment Donation from an African
Hospital
Journal: World Health Organization
Year Published: 2007
This article describes modes of failure of a group of oxygen concentrators donated
to a Gambian hospital. It provides important insight into how the concentrators
malfunction, and discusses how technicians and doctors use these devices in
developing world hospitals.
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Last name of 1st author: Solanki
Title: Oxygen Concentrator Malfunction
Journal: The Lancet
Year Published: 1990
This article is more of a case study documenting the malfunction of an oxygen
concentrator being used at home by a 55 year old woman. In this case, a drink had
been spilled on the device, causing it begin producing gas with oxygen
concentrations below desired levels. The article calls for the need for an “analyzer”
that can “warn the patient of poor oxygen concentration.” This article provides an
additional example of a malfunction that might occur in the concentrators being
used in developing world hospitals.
Last name of 1st author: Vanderkooi
Title: An Optical Method for Measurement of Dioxygen Concentration Based upon
Quenching of Phosphorescence
Journal: Journal of Biological Chemistry
Year Published: 1987
This article describes the oxygen-dependent quenching of phosphorescence used to
determine oxygen concentration. Our design may use a similar method of optical
oxygen sensing technology.
Last name of 1st author: Zhu
Title: Effects of Oxygen Concentration on Combustion of Aluminum in
Oxygen/Nitrogen Mixture Streams
Journal: Combustion and Flame
Year Published: 1998
In this article, the experimenters measure burning rate, temperature, and flame
structure of an oxide-coated piece of aluminum placed in a stream of oxygenated air.
Their finding show increases Al and AlO emissions with increasing oxygen
concentration, as well as increases in the burning rate of the aluminum that were
slightly dependent on the amount of oxygen present.
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9.2
Standards Analysis
ISO 7767:1997: Oxygen monitors for monitoring patient breathing mixtures –
Safety Requirements
Table 9: Standard Analysis
Name and # of Standard
ISO 7767:1997 Section 6.1 - Oxygen monitors
specified for use with flammable anaesthetic
agents shall be classified and marked as
CATEGORY APG EQUIPMENT and shall comply
with the requirements of APG EQUIPMENT in
IEC 601-1:1988.
ISO 7767:1997 Section 7.2 - Fire Prevention
In order to reduce the risk to patients, other
persons or the surroundings due to fire,
ignitable material, under normal and single
fault conditions, shall not, at the same time, be
subjected to conditions in which:
- the temperature of the material is raised
to its minimum ignition temperature, and
- an oxidant is present.
Why/how we will meet/not meet standard
N/A
ISO 7767:1997 Section 7.2 - Annex
In considering the ignitable material, particular
attention should be paid to materials which
may accumulate during prolonged use, e.g.
airborne particles of paper or cotton.
We will test to this standard by collecting
potential waste material (e.g. used/burnt
match sticks) and attempting to ignite the
waste with a match flame to quantify the
danger of such waste material.
ISO 7767:1997 Section 8.2 – Protection against
hazardous output
subsection 51.5 – The difference between the
mean oxygen reading and the oxygen level
shall be within ± 3% (V/V) over the range 15,
21, 40, 60, and 100% Oxygen (V/V) (Balance
nitrogen).
We will test for ± 20% accuracy instead of ±
3%. We will use a modification of the
suggestion stated in the standard: ISO
7767:1997 Section 8.2 - Annex
A simple, effective calibration method would
be
a) place the sensing area in 100%
(V/V) oxygen;
b) adjust the calibration control so
that the oxygen reading is 100%
(V/V) oxygen;
c) place the sensing area in room air
and verify that the oxygen reading
is 21% ± 3% (V/V) oxygen.
[change ± 3% to ± 20%!]
We will NOT meet this standard because the
basis of our flame combustion rate test
depends on igniting a match using oxygen as
the oxidant.
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ISO 7767:1997 Section 11.3 - Gas leakage and
sampling loss
ISO 7767:1997 Section 11.3.1 - Requirement:
the rate of leakage of a non-diverting oxygen
monitor shall not be greater than 20ml/min.
We plan to meet this standard. See 11.3.1.1
and 11.3.1.2 of ISO 7767:1997 for testing
apparatus and procedure
ISO 7767:1997 Section 11.4 - Connections
If an oxygen sensor is intended to be
connected to the breathing system through a
T-piece, the breathing system connection
ports of the T-piece shall be 15mm and/or
22mm conical connectors in accordance with
ISO-5356-1 or ISO 5356-2.
We plan to meet this standard. If we use a Tpiece, we will measure the diameters of our
connectors to match the values listed in the
standard.
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9.3
Regulatory Analysis
9.3.1 Device Classification:
Classification of this device was made using the classification system developed by
the Global Harmonization Taskforce. The device fit the necessary criteria of a Class
A device.
Table 10: Device Classification
Rule #
Response
Conclusions
1
The device is non-invasive, and does not touch the skin. Rules 2, 3,
and 4 do not apply.
Class A
2
The device is not intended for channeling or storing fluids or gases.
Does not apply
3
It is not intended for modifying biological or chemical composition
of fluids before infusion. It does not filter, centrifuge, or exchange
gas/heat.
Does not apply
4
It does not come into contact with injured skin, nor does it act as a
mechanical barrier.
Does not apply
5
It is non-invasive
Does not apply
6
It is not involved in surgical procedures.
Does not apply
7
It is non-invasive and non-surgical in nature.
Does not apply
8
It is not implantable and not used for surgery.
Does not apply
9
It is not utilized directly in patient care and therapy. It does not
administer or exchange energy with the patient.
Does not apply
10
It does not supply energy to be absorbed by patient. It will not be
used in vivo, will not measure vital signs.
Does not apply
11
Does not administer or remove substances from the body
Does not apply
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12
Rules 9, 10, 11 do not apply
Class A
13
It does not use ancillary medicinal products.
Does not apply
14
It does not incorporate animal cells or tissue.
Does not apply
15
Will not be utilized for sterilization of other deices.
Does not apply
16
It is not intended for use as a contraceptive.
Does not apply
9.3.2 Regulatory Pathways:
The regulatory pathways set forth by the Global Harmonization Taskforce (GHTF)
are necessary to ensure protection of public health and safety when using this
oxygen concentration test, as well as consumer trust in the product.
The GHTF regulatory pathway begins with documentation to verify that the device
conforms to the Essential Principles of Safety and Performance for Medial Devices,
SG1/N041:2005. The maintaining of a quality management system will be
unnecessary, since our manufacturing will be limited initially to 3 individual
devices. Thus, manufacturing practices need not be verified. Post-market
surveillance is also not needed, since this is beyond the scope of the class.
Documentation of adherence to SG1/N041 is contained in the Summary Technical
Documentation for Demonstrating Conformity to the Essential Principles of Safety and
Performance of Medical Devices (STED). This document is reviewed by the
Regulatory Authority (RA) to determine proper compliance. Technical documents
may be collected in a Declaration of Conformity, used to ensure compliance with
other GHTF regulations. Following this technical documentation, the oxygen test
must be registered by the RA before it is able to enter the market. A summary of
these steps is shown below in Table 11.
Table 11: GHTH Regulatory Pathway for Class “A” Device
#
Topic
Comments
1
Quality Management System
Not applicable
2
Post-Market Surveillance
Will not be possible.
Technical Documentation
Prepare STED if requested
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3
Declaration of Conformity
Prepare if requested
4
Registration
Provide Regulatory Authority with needed
registration information
Final completion of meeting regulatory requirements will likely take several
months. In addition, registration could also take up to a month to complete. We
estimate a period of 4-6 months to complete the regulatory pathway.
9.3.3 FDA Regulations:
This oxygen concentration test constitutes an unapproved medical device. The
export of such devices outside the United States is governed by Chapter VIII of the
Federal Food, Drug, and Cosmetic Act (FD&C Act), primarily in sections 801 and
802. This Act was modified in 1996 by the Public Law 104-134, the Food and Drug
Export Reform and Enhancement Act (FDERA), which modified sections 801 and
802 of the original document.
The device will be exported under section 801(e)(1) of the FD&C Act, which allows
for the export of adulterated medical devices without FDA approval. As a class I
medical device, 801 should be sufficient, and section 802 need not be considered.
Currently, there are not many other similar oxygen concentration tests, and thus
510(k) marketing clearance may need to be obtained before export. Further
research may result in the discovery of a similar concentration test, which would
allow for export without marketing clearance.
Table 12: FDA Regulatory Pathway for Export of Device
#
Topic
Comments
1
801(e)(1) Requirements
Keep documentation showing that device
meets requirements to obtain Certificate of
Exportability
2
501(k) Clearance
No documentation needed if equivalent,
FDA-approved devices are found.
3
Section 802 Requirements
Not necessary.
4
Foreign Law
Ensure device abides by laws of importing
country, and that device meets foreign
specifications.
5
Export
Export Device to Foreign Country
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Device I classification was determined using the DHHS General Device Classification
Questionnaire.



The device is not life-sustaining or life-supporting
It is not used in preventing the impairment of human health
It does not present unreasonable risk of injury to the user
Further testing will be needed to support safety estimations. Specifically, the risk of
combustion due to the close proximity of flame and compressed oxygen will be
explored.
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9.4
Specifications
Design Goals
1. Reliability
2. Ease of Maintenance
3. Ease of Operation
Design Feature
O2 Concentration
Specification
±20%
Test Results
±5.08%
Status
Pass
Cost
< $100
$17.66
Pass
Ease of Use
Able to be used by a standard medical
technician
within 15
minutes of reading instructions
Pass
Instructions
Printed in pictograms
Pass
Maintenance
Able to be maintained by standard
medical technician using in-house
tools.
Only required
maintenance:
cleaning beaker
Pass
Reliability
< 1% readings more than 20% from
actual gas concentration
0%
Pass
Assembly
On site in developing world hospital
Only Required
Assembly: Cover
beaker with foil
Pass
Speed of Operation
Reading obtained in < 20 minutes
~ 10 minutes
Pass
Electronics
None
None
Pass
Dimensions
Device should be portable from room
to room in a hospital
Weight
< 20 lbs
Pass
2 lbs
Pass
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9.5
Experimental Data & Look-Up Table
(See uploaded PDF’s)
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9.6
Parts List, Instructions, and Pictograms
9.6.1 Parts
Part
250 ml beaker
Adhesive putty
Paper matches (3.3
cm each)
Aluminum foil
Vinyl electrical tape
Stopwatch
Ruler
Manufacturer
Pyrex
Office Depot
Diamond
Reynolds Wrap
Tartan
Sportline
Wescott
Item number
Product #1000-250
49656
Model 220
Price
$4.50
$2 for 2oz.
$1.44 for 1500
matches
$0.09 for 0.33 m2
$0.95 for 1 roll
$12.99
$0.49
250 ml beaker
We chose to use a 250 ml beaker because it provided enough volume of oxygen so
that the flame could burn long enough to calculate combustion rate. Having a
known volume of 250 ml allowed us to standardize the volume of gas tested. The
beaker is also made of glass that withstands the flame’s heat while simultaneously
allowing visual observation of the flame.
Adhesive Putty
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Adhesive putty is utilized to hold the match steady and vertical during the
experiment. Furthermore, putty is flame-resistant and waterproof, two important
properties that made it ideal for our experimental procedure.
Diamond brand paper matches
We decided to use paper matches because when covered by a beaker infused with
100% oxygen, they burned slowly and consistently enough to record burn time.
These matches also had consistent length (3.3 cm), allowing for experimental
standardization.
Aluminum foil
A piece of aluminum foil with a small hole in the center was used to cover the mouth
of the beaker so that a minimal amount of gas was lost when transferred from the
bucket of water to the match. Foil was a good material for this purpose because of
its low cost, high availability, and flame-resistant properties.
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Vinyl Electrical Tape
Electrical tape was used to seal the edges of the aluminum foil onto the mouth of the
beaker. However, any heavy-duty tape may be substituted for this purpose (duct
tape, packing tape).
Stopwatch
A typical stopwatch was used to measure the time (in seconds) for the flame to burn
along the match. In practice, any digital watch or analog watch with a timer may be
used.
Bucket
A typical plastic bucket was used to contain the water used to submerge the beaker.
The bucket had a width and depth sufficient to completely submerge the beaker
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while allowing enough room for handling and to bubble oxygen from a tube through
the mouth of the beaker.
Ruler
A common metric ruler was used to measure the burn distance along the
matchstick.
9.6.2 Building Instructions
To prepare the beaker, cover the mouth of the beaker completely with a piece of
aluminum foil. Roll down or trim the edges of the aluminum foil so that there is
enough visibility into the beaker (this is important in order to be able to view the
match as it is burning within the beaker). Secure the aluminum foil to the mouth of
the beaker by wrapping electrical tape around the edges of the aluminum foil. Cut a
hole in the center of the aluminum foil with a diameter large enough to surround a
dime-sized mound of sticky-tack (this is the hole where the match and sticky-tack
will fit through).
9.6.3 Directions for Use
Our device measures oxygen concentration by determining the burn rate of a match
when exposed to gas from a concentrator. Procedure for using the device is as
follows:
1. Place a dime-sized amount of adhesive putty in a mound on the table.
2. Cover the mouth of a 250 ml beaker with foil. Tape around the edges of the foil to
keep it secure. Poke a small hole in the center of the foil. The hole should be able to
fit over the match and mound of putty.
3. Stick a paper match 2 mm into the putty so that it is standing upright. Submerge
a 250 ml beaker under water. The beaker should be filled as full of water as
possible, avoid leaving any air bubbles inside—tap against the side of the bucket
and swirl underwater to remove air bubbles. Invert the beaker, and then fill the
entire beaker with gas from the oxygen concentrator.
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4. Carefully remove the beaker from the water after sliding a piece of aluminum foil
over the hole in the mouth of the beaker to keep most of the gas from leaking out.
5. Bring the beaker over near the match while maintaining the foil seal.
6. Have a 2nd person light the match.
7. After the initial flare up from the sulfur on the match head, quickly place the
beaker over the top of the match. Slide the beaker directly from the foil to the flame
with as little vertical movement as possible (vertical movement causes gas to leak
out of the beaker).
8. The 2nd person begins timing immediately once the beaker has been set down.
Stop the timer when the flame reaches the bottom of the match or when the flame
stops its progress moving down the match. Important note: timing must be stopped
when forward progress stops, not when the flame extinguishes itself.
9. Measure and record the distance burned and time to burn along the match.
10. Repeat steps 3-9 for 5 trials. Calculate the average distance burned and average
burn time for the 5 trials. Look up where these two values intersect on the supplied
table to find the approximate oxygen concentration.
9.6.4 Pictogram Instructions
(See uploaded PDF)
45