Centaur Analytics Provides Precision Fumigation to Agribusiness And Is First AgTech Company Focused on Post-Harvest Precision Condition Monitoring.

1. COGNITIVE PEST
MANAGEMENT
Phosphine fumigations
Centaur Analytics

3. TABLE OF CONTENTS
PHOSPHINE AND IT’S CHALLENGES ..........................1
Monitoring ...............................................................................1
Safety issues............................................................................2
Leakage ..................................................................................3
Degassing rates of phosphine formulations ....................................4
Sorption ..................................................................................5
THE SOLUTION.........................................................7
Prescriptive Fumigation..............................................................7
Calculation of phosphine dosage.............................................8
Precision Fumigation..................................................................9
Phosphine fumigation of shredded tobacco ............................. 10
Silo fumigation.................................................................. 13
THE BENEFITS........................................................16
ABOUT CENTAUR....................................................17

4. PHOSPHINE AND IT’S
CHALLENGES
Phosphine (PH3) is the single most relied-upon fumigant to control grain
pests due to its inexpensiveness, ease of application and universal
acceptance as a residue-free treatment. However, there are several
factors that occasionally prevent phosphine fumigations to be
successful. For instance, leaky storage structures (e.g. crop silos) make
it difficult to maintain the proper phosphine concentrations. Impatience
or inefficient quality assurance methods lead to treatment durations
which are too short to be effective.
Interestingly, the application of pest control fumigants is done with
decades-old monitoring technology, and frequently without monitoring
at all. Fumigant dosage is seldom correlated to the product being
treated, the actual storage micro-climate, and the encountered types of
warehouse insects.
Improper use leaves the treated commodity susceptible to insects,
increasing the possibility of spoilage, but is also known to lead to
tolerant strains among key stored product insects throughout the world
(Mau et al., 2012).
Let’s first consider the challenges that fumigators face daily, with
reference to scientific data.
MONITORING
Traditional methods of grain monitoring systems employ sensors that
are hard-wired into the storage structure. Multiplexed signal
conditioning is performed outside the structure with the data
transmitted to a display and storage device. Advances in technology led

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to their replacement by wireless sensors that are still facing challenges
(e.g. communication range, durability under hostile environments).
Particularly, for fumigation applications, toxic gas sensors luck in
progress since they are big, cumbersome, have low sample frequency
and often involve human interaction making them prone to human error.
Additionally, phosphine is not distributed uniformly (please see next
section) throughout the stored product and accessible sampling areas
do not cover all the points of interest (e.g. at the back of a shipping
container).
SAFETY ISSUES
Phosphine is toxic to humans and can be absorbed into the body by
inhalation. According to the 2009 U.S. National Institute for
Occupational Safety and Health (NIOSH) pocket guide, and U.S.
Occupational Safety and Health Administration (OSHA) regulation, the
8 hour average respiratory exposure should not exceed 0.3 ppm. NIOSH
recommends that the short term respiratory exposure to phosphine gas
should not exceed 1 ppm. The Immediately Dangerous to Life or Health
level is 50 ppm.
Trained users with protective gear (Figure 1) enter/approach fumigated
areas in order to monitor phosphine levels, exposing themselves to
hazard environments. Additionally, residual toxic gases should be
monitored accurately, to ensure personnel safety while unloading cargo
from containers, warehouses and silos.

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Figure 1: Full face mask suitable for phosphine environments (source:
https://commons.wikimedia.org/wiki/File:Draeger-Apeks_Panorama_full-
face_mask_P4290089.JPG)
LEAKAGE
Loss of phosphine from an imperfectly-sealed structure is easily and
intuitively visualized, and probably involves diffusion mechanisms
driven by the large difference in fumigant concentration between the
interstitial air and ambient air. Air currents caused by temperature
gradients within the grain mass may also cause the fumigant gas to
escape. Wind often causes fumigant to rapidly escape from structures
(Reed and Pan, 2000). Figure 2 presents the observed phosphine
concentrations in unsealed bins for two test cases. Leakages are one of
the most important factors during a fumigation and a fumigator should
be able not only to identify its existence but also to quantify its effect.

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Figure 2: Observed mean phosphine concentrations in unsealed bins for two test
cases (Reed and Pan, 2000)
DEGASSING RATES OF PHOSPHINE FORMULATIONS
It is common to notice incomplete decomposition of phosphine
formulations (e.g. aluminum phosphide tablets) especially in short
fumigations of exposure time under dry conditions. Scientific studies
show that there is a strong correlation between the degassing rate and
air temperature and relative humidity. For example, Xianchang (1994)
found that decomposition times of AlP tablets ranged from 36 to 204
hours. Figure 3 presents the importance of air temperature and relative
humidity and how improper calculation of the degassing rates could lead
a fumigation to failure.

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Figure 3: Decomposition rate of Aluminum Phosphide tablets for two sets of
temperature and humidity (Xian…1994)
SORPTION
During fumigation, the gas concentration within the enclosure depletes,
mainly owing to sorption of the fumigant by the commodity and leakage.
As the sorptive capacities of food commodities vary, commodity sorption
can be a major factor in determining whether a lethal concentration of
fumigant is achieved under sufficiently airtight conditions. Sorption of
fumigants is known to be influenced by a given commodity’s previous
fumigation history, moisture content, temperature, particle size and
composition, exposure period and dose (Reddy et al., 2007). According
to the scientific study of Reddy et al. (2007), the terminal gas
concentration data (some of them are presented in Table 1) indicated

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the need to adjust phosphine dose regimes for food commodities
according to their phosphine-holding capacity.
Table 1. Terminal phosphine concentrations in the free space of 300 g
food commodities dosed at 2 g phosphine m-3 for 7 days at 25 oC (Reddy
et al., 2007).
COMMODITY
PHOSPHINE
CONCENTRATION
(PPM) AT THE
END OF 7 DAYS
SORPTION
(%)
empty chamber
(reference)
1049 -
wheat 850 19.0
dried dates 686 34.6
sesame seeds 442 57.9
paddy rice 578 72.3

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THE SOLUTION
The behavior of phosphine gas during a fumigation is complicated since
it’s affected by the multi-variable system of commodity, weather
conditions, gas-tightness (see previous section) and insect tolerance.
Even with the assistance of fumigation protocols and guides, a
successful fumigation is not a trivial task. Phosphine fumigations pose
challenges which can be tackled only with a combination of cutting-edge
technology sensors and accompanied cognitive software tools.
PRESCRIPTIVE FUMIGATION
Fumigators planning a treatment, typically base their dosage on one of
the following options:
 Fumigation protocols (e.g. Coresta) that set a target concentration
for a specific exposure time
 Guidelines that propose a specific dosage
 User defined dosage which is an outcome of personal experience
Unfortunately, none of the above option incorporate all the complex
phenomena that were described above.
To overcome the issue, Centaur has developed a computational
algorithm with advanced prediction capabilities. The algorithm can
predict the right amount of phosphine dosage and informs the user for
the date of successful completion.
The algorithm takes as input the following parameters:
 storage geometry
 stored commodity (sorption is automatically calculated)
 fumigant physical form (pellets, tablets, etc.)
 fumigant chemical composition (Mg3P2, AlP)

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 storage micro-climate (temperature, relative humidity)
 expected leakage (none, low, high)
afterwards, it solves a system of partial differential equations and yields
an accurate result in a matter of seconds (see below for a real-life
scenario).
Calculation of phosphine dosage
A 20’ shipping container (Figure 4) is considered for fumigation.
Approximately 90% of the container is filled with wheat flour sacks. The
container is considered gas-tight, air temperature is 20 oC and air
relative humidity 70% r.h.. The desired concentration is 300 ppm for 6
days of exposure time and Mg3P2 plates are available for the fumigation.
Figure 4: 20 ft container filled with wheat flour sacks
The sophisticated algorithm proposes a dosage of 1.8 gr PH3 / m3,
meaning that 2 Mg3P2 plates (2.0 gr PH3 / m3) are sufficient.
Additionally, a graph (Figure 5) of phosphine concentration at the
farmost location of the container is produced, informing the user that it
takes almost a day for the concentration to reach the threshold of 300

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ppm meaning that the fumigation will be successful at the end of the 7th
day.
Figure 5: Time evolution of phosphine concentration at the farmost location of the
20’ container.
PRECISION FUMIGATION
During fumigations, there are some factors that influence the process
which are difficult to know beforehand. These parameters include among
others the air flow movements inside the storage caused by temperature
gradients or the increase on leakage due to strong winds.
For that reason, Centaur has developed a new computational tool to
perform precision fumigation simulations. The software is based on the
Computational Fluid Dynamics approach.

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Computational fluid dynamics (CFD) is a branch of fluid mechanics that
uses numerical analysis and data structures to solve and analyze
problems that involve fluid flows. Centaur’s dedicated computer servers
are used to perform the calculations required to simulate gas
movements in 3-dimensional (3-d) spaces and their interaction with
surfaces defined by boundary conditions.
Centaur’s CFD software can evaluate heat transfereffects originate from
the temperature differences between grain temperature and ambient
temperature as well as solar radiation. Additionally, it has an advanced
implementation of porous medium approach for accurately capture
phosphine movement inside the stored product. Furthermore, insect
mortality models are integrated, offering a 3-d visualization of the areas
with 99.9% insect mortality. It goes without saying that they’re insect
species specific (e.g. Rhyzopertha dominica).
Phosphine fumigation of shredded tobacco
Stack fumigation involves the tarping of goods or commodities under a
gas-proof tarp. The tarp is then sealed to the ground via a number of
methods to ensure the gas level is maintained under the tarp. In the
following real-life application, 99 carton boxes were filled with shredded
tobacco (Figure 6). Two Mg3P2 plates were placed at the end of the
stack and a PH3 gas sensor was placed at the center.
Centaur’s CFD software creates a computational interpretation of the
tobacco boxes (Figure 7) and then calculates useful parameters such as
phosphine movement, concentration and zones where there are no
living insects. Specifically, Figure 8 presents the spatial distribution of
phosphine concentration after 4 days of fumigation and areas (black
color) of 99.9% insect mortality. Furthermore, Figure 9 shows the time
evolution of PH3 concentration as recorded by the sensor in comparison
to the simulation data. Inarguably, Centaur’s CFD software yields
accurate results.

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Figure 6: A stack of 99 C-48 carton boxes filled with shredded tobacco.
Figure 7: The computational interpretation of the tobacco boxes, used for the CFD
simulations

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Figure 8: Spatial distribution of phosphine concentration after 4 days of fumigation
(top) and areas (black color) of 99.9% insect mortality (bottom). Video available here:
https://youtu.be/cik_Pgwr8h0

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Figure 9: Comparison of simulation results to sensor data
Silo fumigation
Another fumigation scenario concerns silos, particularly the ones that
are subject to weather changes. For example, the steel grain silos shown
in Figure 10, are exposed to weather conditions (Figure 11) that are not
constant and could influence the distribution of phosphine. Wheat grains
were fumigated using Aluminum Phosphide blankets placed on the
surface of the wheat grains.
Simulations (Figure 12) reveal that air moves downwards close to silo
walls and upwards in the silo core. The outcome is faster phosphine
diffusion on the silo boundaries and an obvious lag in the core region.

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Figure 10: Physical to computational model of a silo filled with wheat grains. For
presentation purposes a 45o slice is shown here.
Figure 11: Weather conditions (air temperature, relative humidity, solar radiation,
wind velocity) used as input for the silo CFD simulation

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Figure 12: Phosphine concentration and insect mortality zones spatial distribution.
There is also a video of the entire simulation available in the following link:
https://youtu.be/X-tHBMbtSq8

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THE BENEFITS
The predictive capabilities as well as the in-depth knowledge of the
phosphine distribution throughout a fumigation treatment offered by
Centaur’s platform brings unprecedented benefits to its users.
The economic benefits for the end users of Centaur’s platform include,
among others:
 Mitigation and prevention of crop spoilage
 cost reduction of the overall pest control application, avoiding
excessive chemicals (e.g. overdosing, need to repeat failed
fumigations) as well as excess labor
 improved quality of finished products (e.g. flour), traceability
and defensibility against quality claims from retailers
Concerning health and safety issues, Centaur’s procedure is 100% safe
for the operator as it can be administered remotely and provides the
means to detect and measure any leakages to the surroundings
(particularly important to ship fumigations (Nautical Institute, 2008))

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ABOUT CENTAUR
Centaur is a leading IoT solutions provider in the field of stored
agricultural product protection, developing and delivering proprietary
wireless sensors (Figure 13) that can transmit reliably from inside
containers, warehouses, silos, and can form ‘mesh’ networks for
efficiently dispatching their data to the cloud. Additionally, Centaur’s
data aggregation platform (Figure 14) and cognitive analytics services
apply computer simulation techniques and data analytics methods for
real-time monitoring of stored product conditions (e.g. temperature,
humidity, ethylene, CO, CO2 emissions) in order to determine the
quality, safe storage time and spoilage risk of the product being stored.
Centaur’s gas sensors detect the concentrations of fumigants (such as
phosphine) and the cloud software offers online guidance for safe and
efficient pest management. End users can now implement precision
fumigation and pest management and track stored product quality in
real-time with customized alerts and notifications (Figure 15).
Centaur's cloud-based solution provides traceability from farm to shelf,
end-to-end quality management and pest-free certification with
advanced digital means.

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Figure 13: Centaur’s wireless sensor
Figure 14: Screenshot of Centaur’s platform in mobile devices

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Figure 15: Monitoring a phosphine fumigation through the Centaur platform

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References
Mau YS, Collins PJ, Daglish GJ, Nayak MK, Ebert PR (2012) The rph2
Gene Is Responsible for High Level Resistance to Phosphine in
Independent Field Strains of Rhyzopertha dominica. PLoS ONE 7(3):
e34027
Nautical Institute, 2008, Fatality from fumigated cargo,
http://www.nautinst.org/en/forums/mars/mars-2008.cfm/200880
Reddy, V.P., Rajashekar, Y., Begum, K., Chandrappa Leelaja, B. and
Rajendran, S. (2007), The relation between phosphine sorption and
terminal gas concentrations in successful fumigation of food
commodities. Pest. Manag. Sci., 63: 96–103. doi:10.1002/ps.1298
Reed, C., Pan, H., (2000) Loss of phosphine from unsealed bins of wheat
at six combinations of grain temperature and grain moisture content,
Journal of Stored Products Research, Vol. 36 (3), pp. 263-279
Xianchang, T. (1994), Evolution of phosphine from aluminium phosphide
formulations at various temperatures and humidities. E. Highley, E.J.
Wright, H.J. Banks, B.R. Champ (Eds.), Stored Products Protection.
Proceedings of the 6th International Working Conference on Stored-
product Protection, 17-23 April 1994, Canberra, Australia, CAB
International, Wallingford, UK (1994), pp. 201-203