Use of Methyl Bromide (MeBr) has been banned in most developed countries since 2007. From January 1, 2015, it is not available anywhere as a fumigant for flourmills and other industries. Several fumigation alternatives have been tried around the world with heat treatment being one of them. But how good are these compared to good old MeBr? Can such alternatives be used for precise fumigation, i.e. a tightly controlled and monitored fumigation process?

1. M
ethyl Bromide has been
a good fumigant, but
not excellent since the
main disadvantage of gas
fumigants is that they need
airtight buildings. And in
the real world, very few
buildings are made airtight
or can become airtight with
proper sealing work. The majority of buildings will never hold
the gas, especially on a windy day or when there are significant
temperature differences between day and night.
The heat advantage
Heat treatment has been practiced worldwide for a few years
and is by now deemed a very effective replacement of MeBr
for structural fumigation. Insects die at temperatures above
50oC because the proteins in their bodies coagulate, their salt
equilibrium becomes damaged and they dry out. All insect stages
are affected and no resistance to heat has been observed in the lab
or in the field.
Electricity, gas, petrol and steam can be used to generate heat
for insect extermination. In our work, we have found out that
each type of heater has its plusses and minuses. Electrical heaters
(Photo one) are easy to use, easy to handle and efficient; but they
cannot be used to treat an empty concrete silo (you need a gas
heater for that, with a long ductwork). Gas heaters (Photo two)
need to be placed outside the building, so for high buildings you
may need to lift heaters by crane to the top floor. In most of the
cases, the use of special air ducts through available shafts enables
us to treat several floors and sections of a mill at the same time
(Photo three).
In comparing recycling of air (electrical heaters placed inside
the building) with introduction of new air (gas heaters placed
outside), we found out that the increase of pressure in the latter
case helps the hot air to enter cracks and crevices. In practice, the
merits of electrical and gas heaters can be combined, using both
types to treat large mills with speed and efficiency.
No sealing required
A main operational advantage of heat is that it does not need
any sealing at all. In fact, when new hot air is introduced in a
building we need to leave a top floor window partly open to avoid
the increase of internal pressure.
Heat treatment is fast
Proper cleaning of the mill area to be treated is needed, but
since no sealing is required preparation time is minimal. With
the right equipment, an experienced team will need slightly more
than 24 hours to treat a building. In Diagram one, temperatures
are plotted from various sensors inside a mill during a heat
treatment; as can be seen, lethal temperature levels are reached in
by Vasilis Sotiroudas, Food Scientist, Heat Treatment specialist, Agrospecom, Greece
Use of Methyl Bromide (MeBr) has been banned in
most developed countries since 2007. From January
1, 2015, it is not available anywhere as a fumigant
for flourmills and other industries. Several fumigation
alternatives have been tried around the world with
heat treatment being one of them. But how good
are these compared to good old MeBr? Can such
alternatives be used for precise fumigation, i.e. a
tightly controlled and monitored fumigation process?
precision fumigation with benefits
HEAT TREATMENT:
Photo 1: Heat treatment with
electrical heaters
46 | Milling and Grain
F

2. less than 12 hours. If these levels are maintained for about 12 to
16 hours, complete extermination of all insect stages (including
larvae and eggs) is guaranteed with high statistical probability.
Downtime for the mill is really short, especially since an area of a
large mill may be under treatment while an adjacent isolated area
remains operational.
Safety
Heat is totally safe for people and the environment. Workers can
work next door to a heat-treated area, or can even enter for a short
time an area during heat treatment. By contrast, gas fumigation
requires a safety zone around each building under treatment,
needs several hours of aeration and a professional gas inspection
before workers can enter.
Precision monitoring
With all gas fumigants from Methyl Bromide to Profume
you need several sampling points to measure concentration
precisely. You may have two, three, or even 10 sampling points
per floor if you are really well organised. With heat, you may
have for instance 10 temperature sensors per floor, but you can
also enter the building during the treatment and use an infrared
thermometer to check literally thousand points per floor. This
means unparalleled precision!
Our team is performing a large number of heat treatments each
season, most of them in flourmills and food processing factories.
For precision monitoring and effective remote supervision, we are
using the therminate.com solution that we have jointly developed
Photo 2: Heat treatment
of a mill using gas heaters
externally
Diagram 1: Lethal temperatures are reached in about 12 hours
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June 2015 | 47
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3. with Centaur Technologies (Volos, Greece).
This is a cloud-based service that allows remote monitoring
of heat treatments from a smartphone or computer (Photo four).
Temperatures are collected from wireless sensors that provide
good coverage even inside concrete buildings and silos, and
connect to the therminate.com cloud system via a wireless
gateway. Treatment durations and kill statistics are reported, and
alarms are issued whenever something requires attention (e.g. a
temperature level exceeding safe limits). This allows our team to
effortlessly and safely drive the process to eventual success.
A heat treatment with good equipment and an experienced team
can never be a failure. But assuming a corner of a building is left
under-treated, for whatever reason, you may extend the treatment
in that corner only to cure the problem. The unique advantages
of multi-point monitoring, along with the option to perform
incremental or extended treatments, give heat treatment its highly
precise character.
References available on request
Photo 3: Special ductwork to
heat treat the upper floors
of a mill
Photo 4: Monitoring heat treatment on a smartphone
48 | Milling and Grain
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