Note: Descriptions are shown in the official language in which they were submitted.
CA 02786995 2012-07-12
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METHOD FOR VENTILATING A HEAVILY CLUTTERED ROOM
FIELD OF THE INVENTION
The present invention relates to a method for ventilating a heavily cluttered
room, as
well as a room provided with ventilation means performing ventilation
according to this
method. The invention also relates to air intakes suitable for implementing
the method.
The invention can be applied in the context of natural gas liquefaction, which
requires ventilation of heavily cluttered rooms (called LNG modules),
including under
particularly rigorous climate and environmental conditions (arctic region).
BACKGROUND OF THE INVENTION
A room containing a significant number of hazardous contaminant sources and
that is
heavily cluttered (by equipment, pipes, structures, etc.) must be ventilated
in order to
evacuate said contaminants. This ventilation, associated with other devices,
contributes to
improving safety conditions for personnel and equipment.
However, when wintry outside conditions, call arctic conditions, exist, it may
be very
difficult to ventilate the room, as it is directly impacted by rain, snow,
frost, ice and wind.
Furthermore, the personnel and the equipment must also be protected from these
différent
phenomena.
In order to ventilate a room under wintry outside climate conditions, it is
known to
use natural ventilation, which uses both the dynamics of the outside wind and
the variation
of the density of the air inside the room (natural draught) to renew the air
in the room.
However, this solution, which appears simple, is in reality difficult to
implement, given the
outside climate conditions. In fact, outside a well-defined wind speed range,
the air flows
inside the building are unacceptably disrupted. Furthermore, since the
effectiveness of
natural ventilation also depends on the clutter in said room, the dilution
effect contributed by
the natural ventilation on the contaminants is mediocre for heavily cluttered
rooms.
Additionally, pressure losses are significant when the clutter of the room is
heterogeneous
(for example, heightwise), and it is impossible to capture contaminants in the
area close to a
piece of equipment, opposite the airflow striking that equipment (vacuum and
aeraulic
turbulence zone). As a result, natural ventilation does not make it possible
to provide
controlled security in all situations.
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A second solution, mechanical ventilation, is also known. Mechanical
ventilation
uses fans to provide (and possibly heat) the air blown into the room and then
remove it.
However, this solution requires providing a technical room dedicated to the
aerothermodynamic equipment, the surface area of which typically represents
between 50
and 70% of the area of the room to be ventilated for a LNG module.
Furthermore, this
solution requires the presence of air transport sheaths in the room to be
ventilated. These air
transport sheaths are generally very large and extremely restrictive for
positioning the
equipment in the room, in particular when the room is heavily cluttered. As a
result,
mechanical ventilation is difficult to implement and is costly in terms of
investment (land,
machines, etc.) and operation (heating a large volume of air).
There is therefore a real need to develop a method for ventilating a room, and
in
particular a heavily cluttered room, that can operate correctly under wintry
conditions, that is
more reliable, simpler, and less expensive to implement and use than the
existing methods.
BRIEF DESCRIPTION OF THE INVENTION
The invention first relates to a room comprising an inner space delimited by
an upper
wall, a lower wall and side walis, said room being provided with a ventilation
means, the
ventilation means including:
- a means for extracting air from the inner space towards the outside of the
room,
arranged on one side wall; and
- air intakes on the other side walls.
According to one embodiment, the ventilation means also comprises one or more
fans in the inner space, said fans preferably being located near a side wall
facing the side
wall provided with the air extracting means, and said fans more particularly
preferably
comprising:
- one or more fans situated close to the lower wall and oriented so as to move
air
toward the upper wall; and
- one or more fans situated close to the upper wall and oriented so as to move
air
toward the side wall provided with the air extracting means.
According to one embodiment, the side wall provided with the air extracting
means
comprises two end portions situated close to respective adjacent side walls,
and a central
portion between the two end portions, the air extracting means being
distributed on the side
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wall so that the air extraction capacity per surface unit in the central
portion is greater than
the air extraction capacity per surface unit in the end portions.
According to one embodiment, the room has no heating means for the inner
space.
According to one embodiment, the room is a natural gas liquefaction module.
The invention also relates to a method for ventilating a room comprising an
inner
space delimited by an upper wall, a lower wall and side walls, said method
including the
extraction of air from the inner space to the outside of the room by an air
extraction means
arranged on one side wall, and the entry of air via air intakes arranged on
the other side
walls.
According to one embodiment, the method also includes moving air in the inner
space using one or more fans positioned in the inner space, said air movement
preferably
being done close to a side wall facing the side wall provided with the air
extraction means,
and said air movement more particularly preferably comprising:
- moving air from bottom to top close to the lower wall and the side wall
facing the
side wall provided with the air extraction means;
- moving air toward the side wall provided with the air extraction means close
to
the upper wall and the side wall facing the side wall provided with the air
extraction means.
According to one embodiment, the ratio of the air flow extracted on the
surface of the
side wall provided with the air extraction means is less than or equal to 0.5
m/s, preferably
less than or equal to 0.3 m/s, still more preferably less than or equal to 0.2
m/s.
According to one embodiment of the method, the room is a natural gas
liquefaction
module.
The invention further relates to an air intake comprising:
- an air injection grid adapted to be positioned in an opening formed in a
wall;
- an enclosure adapted to be fastened on one side of the wall and
communicating
with the air injection grid;
- an air entry conduit adapted to be fastened to the wall and communicating
with
the enclosure by a protective grid, the air entry conduit having a section
smaller
than the section of the enclosure along a plane perpendicular to the air
injection
grid.
According to one embodiment, the section of the air injection grid available
for the
passage of air on the enclosure side is larger than the section of the air
injection grid
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available for the passage of air on the side opposite the enclosure and/or the
air injection grid
is provided with a heating means.
According to one embodiment, the air entry conduit is provided with baffles
and
possibly drains, the baffles preferably being provided with heating means, and
the baffles
preferably having a surface oriented toward the enclosure and a surface
oriented opposite the
enclosure, the surface oriented toward the enclosure being less rough than the
surface
oriented opposite the enclosure.
According to one embodiment of the room according to the invention, the air
intakes
are as described above.
The present invention makes it possible to overcome the drawbacks of the state
of the
art. It more particularly provides a method for ventilating a room, and in
particular a heavily
cluttered room, that can operate correctly under wintry conditions, which is
more reliable,
simpler and less expensive to implement and operate than the existing methods.
This is accomplished owing to a ventilation means operating only for air
extraction
(from the inside to the outside of the room), the air entry in the room being
ensured by
passive devices (air intakes), i.e. without mechanical air blowing (from
outside the room to
the inside thereof).
According to certain particular embodiments, the invention also has one or
preferably
more of the advantageous features listed below.
- The dilution of the contaminants is controlled irrespective of the outside
conditions, and even at a high level of clutter, and thus the security of the
facility
is ensured.
- The invention makes it possible to achieve surface area savings in technical
rooms and energy consumption savings relative to traditional mechanical
ventilation.
- The work of the personnel is made easier because the invention allows a
laminar
state of the flow of air in the room.
- The invention makes it possible to dispense with any general heating of the
inner
space of the room. In fact, the speed of the air being low, the sensation of
cold for
personnel remains moderate. More specifically, a low airflow rate means a low
convection exchange between the occupant and the air of the room, and
therefore
a feeling of comfort and "warmth" relative to the outside. It is therefore
possible
to provide only localized (extra) heating for certain maintenance operations
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requiring specific comfort. The energy savings achieved by doing away with
general heating of the room are considerable.
The invention provides an improved air intake relative to the air intakes of
the
state of the art. The air intake according to the invention makes it possible
to
5 greatly limit the risks of taking in ice or of snow blockage. The air intake
according to the invention is advantageously used in the context of the
ventilation
method according to the invention, but it can also be used in the context of
another ventilation method.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 diagrammatically illustrates a room according to one embodiment of
the
invention, in horizontal cross-section.
Figure 2 diagrammatically illustrates a room according to one embodiment of
the
invention, in vertical cross-section.
Figure 3 diagrammatically illustrates the side wall 3 of the room of figures 1
and 2.
Figure 4 diagrammatically shows one embodiment of an air intake according to
the
invention, in cross-section.
DETAILED DESCRIPTION OF THE INVENTION
The invention will now be described in more detail and non-limitingly in the
following description.
Room according to the invention and ventilation method according to the
invention
In reference to figures 1 to 3, the room to be ventilated according to the
invention
comprises an upper wall 6 (roof), a lower wall 7 (floor), and side walls 2a,
2b, 3, 4. In
general, the room is parallelepiped, and there are then four side walls 2a,
2b, 3, 4. An inner
space 5 is defined by the set of walls 2a, 2b, 3, 4, 6, 7.
The inner space 5 generally contains industrial equipment.
According to one preferred embodiment, the room is a natural gas liquefaction
module, i.e. a hangar containing part of the equipment necessary to produce
liquefied natural
gas from raw natural gas. However, the invention can also be applied to other
fields, for
example in the oil, mining, chemical, pharmaceutical, or other industries.
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According to the invention, the room is ventilated by a ventilation means that
comprises:
- a means for extracting air 1; and
- air intakes.
The air extracting means 1 consists of a plurality of fans 15 positioned on a
side wall
3, suitable for extracting air from the inner space 5 toward the outside of
the room
uniformly, i.e. with a laminar state airflow.
In the context of this application, "air intakes" are "passive" devices
allowing air to
pass through a wall. In other words, the air intakes in the context of the
present invention do
not have a mechanical rotary machine (fan).
The invention provides that air intakes are formed in the side walls 2a, 2b, 4
separate
from the side wall 3, which comprises the air extracting means 1. In other
words, according
to the invention, a single side wall comprises the air extracting means, while
the other side
walls have no active air movement means (i.e. active means for extracting air
or injecting
air) such as fans. The room is supplied with air, through the aforementioned
air intakes, via
an air vacuum in the room created by the air extracting means 1, and does not
involve the
action of fans on either side of said air intakes.
The air extracting means 1 according to the invention allows a laminar air
movement
in the entire inner space 5, under the combined effect of the natural
convection of the air and
the forced convection caused by the vacuum existing at the side wall 3
provided with the air
extracting means 1.
Given that the clutter of the room by the equipment generally varies
heightwise (the
lower portion of the room most often being more cluttered than the top portion
of the room),
and given that the possible contaminants may comprise light contaminants and
heavy
contaminants, it is advantageous to do the modeling by stratification, i.e. to
vertically cut the
inner space 5 into successive layers 10, 11, 12, so as to determine the power
and
implantation of the fans making it possible to obtain satisfactory ventilation
in each layer 10,
11, 12.
The inner space 5 is cut vertically into successive layers 10, 11, 12, the
power and
implantation of the air extracting means 1 on the side wall 3 being adapted to
the ventilation
in each layer, the flow of air having a laminar state. In other words, the
room has a wall (or
barrier) supporting the fans to extract the air from several aeraulic layers,
with différent fan
rates for each zone so as to have stratification of the layers of air and a
laminar flow.
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Typically, the equivalent speed of the air in the room, which is defined as
the ratio of
the airflow rate extracted on the surface of the side wall 3 provided with the
air extracting
means 1, is less than or equal to 0.5 m/s, preferably less than or equal to
0.3 m/s, still more
preferably less than or equal to 0.2 m/s." This air speed must be as low as
possible so as to
minimize the turbulence (system effects) due to the presence of equipment in
the room.
Furthermore, the equivalent air speed in each layer 10, 11, 12 defined by a
vertical
cut of the room corresponds to the ratio of the airflow rate extracted from
the stratified area
divided by the surface projected on the side wall 3 provided with the air
extracting means 1.
Thus, in a lower portion of the room (relative to the vertical direction), and
for example in a
lower half of the room, the equivalent air speed is preferably less than or
equal to 0.3 m/s,
more particularly preferably less than or equal to 0.2 m/s (or even less than
or equal to 0.15
m/s).
Due to these low speeds, the pressure losses are minimal in the room, even in
the
presence of heavy clutter, and the airflow is laminar in the entire inner
space 5.
Preferably, the ventilation in the room is completed by one or more fans 8, 9
situated
in the inner space 5, so as on the one hand to eliminate dead areas in the
inner space 5 (areas
where the convection of the air is practically nonexistent) and on the other
hand to orient the
airflows correctly. Thus, these fans 8, 9 are preferably situated close to the
side wall 4 facing
(opposite) the side wall 3 provided with the air extracting means 1. In one
embodiment, the
distance from the fans 8, 9 to the side wall 4 is smaller than or equal to
50%, for example
smaller than or equal to 40%, or smaller than or equal to 30%, or smaller than
or equal to
20%, the distance between said side wall 4 and the opposite side wall 3
provided with the air
extracting means 1.
Particularly advantageously, one thus provides:
- one or more fans 9 situated close to the lower wall 7 and oriented so as to
move
the air from bottom to top;
- one or more fans 8 situated close to the upper wall 6 and oriented so as to
move
the air toward the upper portion of the side wall 3 provided with the air
extracting
means 1.
In one embodiment, the distance from the fans 9 to the lower wall 7 is smaller
than or
equal to 50%, for example smaller than or equal to 40%, or smaller than or
equal to 30%, of
the distance between said lower wall 7 and the upper wall 6; and the distance
from the fans 8
to the upper wall 6 is smaller than or equal to 50%, for example smaller than
or equal to
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40%, or smaller than or equal to 30%, of the distance between said upper wall
6 and the
lower wall 7.
In this way, the dead areas located close to the side wall 4 facing the side
wall 3,
provided with the air extracting means 1, are eliminated.
The air extracting means 1 present on the side wall 3 can be fans 15 known in
the
field and preferably compliant with the regulatory provisions for explosion
risk protection
(ATEX fans). In particular, these fans 15 generally comprise a peripheral gap
of 2 to 3 mm
to avoid static electricity phenomena. Electric tracing may be provided to
avoid frost in that
peripheral gap. Furthermore, reinforcements of the side wall 3 supporting said
fans 15 can be
provided to take the normal vibratory modes of said fans 15 into account.
The choice of the number, power and flow rate of the fans 15, as well as their
implantation on the side wall 3, are made so as to obtain the aforementioned
stratification as
well as convection of the air in the entire inner space 5 with a slow speed,
as a fonction of all
of the parameters involved, and in particular: the dimensions and the clutter
of the room, the
geometry of the stratification area inside the room (layers 10, 11, 12), and
the nature of the
potential contaminants (and in particular their greater or lesser density).
Furthermore, in order to avoid the appearance of lateral preferential
convection
phenomena at the walls 2a and 2b, the central part of the side wall 3, bearing
the air
extracting means 1, is "loaded" with fans 15 so that the air extraction
capacity is greater in
the central part 13 of said side wall 3 than in the end portions 14a, 14b.
Figure 3 provides an example of the implantation of the fans 15 on the side
wall 3.
The air intakes are implanted on the side walls 2a, 2b, 4 separate from the
side wall 3
provided with the air extracting means 1 so as to allow a supply of air
adapted to the desired
convection in the inner space 5. The air intakes can be distributed on all of
the side walls 2a,
2b, 4 separate from the side wall 3, provided with air extracting means 1.
Portions 16a, 16b on the side walls 2a and 2b are provided without air intakes
close
to the wall 3, so as to avoid risks of contaminants returning from the outside
into the room.
Furthermore, the density of air intakes on the side walls 2a, 2b, 4 is
generally greater close to
the lower 7 and upper 6 walls than in a central portion of the side walls 2a,
2b, 4, i.e. the air
intakes will be located in the upper and lower portions of the side walls 2a,
2b and 4.
The air intakes can be traditional air intakes and for example comprise a set
of
inclined strips positioned in openings formed in the wall, adapted to reduce
the air entry
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speed in case of outside wind. They can also comprise heating means to prevent
snow or ice
deposits, and comprise a protective cover.
However, according to one preferred embodiment, the air intakes are as
described
below.
Air intake according to the invention
In reference to figure 4, an air intake according to the invention on a wall
20 (of a
room or any other type of closed chamber) comprises three main parts, which
are, in the
direction of the airflow:
- an air entry conduit 21;
- an enclosure 22; and
- a grid 23 equipped with profiled fins.
The air entry conduit 21 is preferably positioned parallel to the wall 20. It
comprises
a beveled open end intended for the air entry, and another end that
communicates with the
enclosure 22. Preferably, the air entry conduit 21 is oriented so that the
open end is oriented
downwardly. In this way, any accumulation of snow or water in the air entry
conduit 21 is
avoided.
Preferably, the air entry conduit 21 is provided with baffles 24, which are
intended
on the one hand to create pressure losses so as to break the dynamics of the
outside wind,
and on the other hand to stop the snow carried into the airflow 28.
Preferably, there are no
more than four baffles 24. Typically, the baffles 24 are plates fastened, for
example by
welding, to the inner wall of the air entry conduit 21, inclined (i.e. forming
an angle smaller
than 90 with said inner wall) and oriented toward the open end of the air
entry conduit 21.
For example, the baffles 24 can form an angle of about 60 with the inner wall
of the conduit
and the baffle 24 closest to the open end of the conduit can form an angle of
about 45 with
the inner wall thereof.
The baffles 24 (or a portion thereof) can be provided with a heating means 26
(for
example electric resistances) making it possible to melt the snow accumulating
on said
baffles 24 (the water resulting from the melting snow being driven outside the
air entry
conduit 21 by gravity).
Preferably, the baffles 24 have a différent roughness on the surface oriented
toward
the enclosure (called upper surface) and on the surface oriented toward the
open end of the
conduit 21 (called lower surface). The lower surface is advantageously rougher
than the
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upper surface (i.e. the asperities on the lower surface have a larger average
height than the
asperities on the upper surface), which makes it possible to effectively stop
the snowflakes
present in the air from entering the conduit 21. For example, the baffles 24
can be made from
316L stainless steel having an absolute roughness of 1 to 1.5 .tm (passivated
descaled sheet
5 metal) or approximately 8 m (industrial weld sheet metal), and scratches
can be added on
the lower surface.
It is advantageous to provide drains 25 on one or more baffles 24, and
especially on
the baffle 24 closest to the open end of the air entry conduit 21, so as on
the one hand to
make it possible to discharge the water resulting from melting snow in the air
intake, and on
10 the other hand to minimize the turbulence phenomena under the baffle 24
closest to the open
end of the air entry conduit 21.
The width of the air entry conduit 21 must be large enough to avoid the
effects of a
local increase in the air speed in the conduit 21. In fact, at the
perpendicular of each baffle
passage, the snow accumulation that is deposited on said baffles will reduce
the section
thereof, and therefore increase the air passage speeds.
Between the air entry conduit 21 and the enclosure 22, a protective grid 27 is
provided to stop the snowflakes carried in the flow of air. For example, the
protective grid
27 can be a 316L stainless steel plate perforated at 80% ("honeycomb" plate).
Between the air entry conduit 21 and the enclosure 22 (or plenum), a
protective grid
27 is provided to stop any snowflakes carried in the airflow. For example, the
protective grid
27 may be a 316L stainless steel plate perforated at 80% of the "honeycomb"
type.
The enclosure 22 (or plenum) has a larger section than that of the air entry
conduit 21
along a plane perpendicular to the wall 20, and for example along the
horizontal plane
(which in the illustrated embodiment is the plane perpendicular to the average
airflow
direction in the air entry conduit 21). This enclosure 22 makes it possible to
reduce the speed
of the air before arrivai on the profiled grid 23, and therefore to break the
dynamics due to
the outside wind, thereby avoiding the freezing phenomena on the grid 23.
Preferably, the
dimensions of the enclosure 22 are chosen so that the speed of the air is
reduced to a value
below or equal to 0.5 m/s in the enclosure 22. Preferably, the enclosure 22
has an inclined
upper wall so as to avoid an accumulation of snow thereon.
The air injection grid 23 is positioned in an opening formed in the wall 20
and allows
the air to pass through the wall 20. Preferably, the air injection grid 23
comprises a
convergent shape, so as to increase the speed of the air when it passes
through the wall 20.
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Thus, the section of the air injection grid 23 that is available for the
passage of air on the
enclosure 22 side (i.e. the side outside the room) is larger than the section
of the air injection
grid 23 that is available for the passage of air on the side opposite the
enclosure 22 (i.e. the
side inside the room).
The air injection grid 23 can be provided with a heating means so as to still
further
decrease the risks of freezing. This heating means can be electric resistances
positioned in
cavities placed on the path of the air and posing an obstacle thereto.
The air injection grid 23 can be a commercially available grid distributed by
Halton,
as for example described in document SE 500838.
EXAMPLE
The following example illustrates the invention without limiting it.
Modeling was done on a natural gas liquefaction module 50 m long, 36 m wide
and
16 m high. The outside temperature is hypothetically -33 C and the outside
wind has a speed
of 17 m/s. Fans in extraction mode are implanted on one of the walls
perpendicular to the
length direction of the module. Air intakes are positioned on the other walls.
The inner space of the module is modeled in three zones: a (lower) zone 10
that is
2.80 meters high, heavily cluttered, capable of containing heavy contaminants;
an
(intermediate) zone 11 that is 4.25 m high, moderately cluttered, capable of
containing
middle-density contaminants; and an (upper) zone 12 that is 7.15 m high,
capable of
containing light contaminants.
Modeling makes it possible to define an implantation of fans on the wall as
well as
secondary ventilation in zone 10 (vertical ventilation) and in zone 12
(horizontal ventilation)
as shown in figure 2 so as to correct the dead spaces. The assembly makes it
possible to
obtain a laminar state airflow with a low speed in the entire module.
The characteristics used for the main ventilation (extraction ventilation) are
summarized in table 1 below:
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Table 1 - characteristics of the main ventilation (air extraction)
Zone 10 Zone 11 Zone 12
Airflow rate (without 69,120 m /h 103,680 m 3/h 172,800 m -/h
secondary
ventilation)
Airflow rate (with 45,723 m /h 98,042 m '/h 202,008 m -/h
secondary
ventilation)
Average air speed 0.126 m/s 0.176 m/s 0.218 m/s
(with secondary
ventilation)
Number of fans 6 6 8
installed
Number of fans 5 5 7
running
Airflow rate per fan 9,145 m '/h 19,609 m -/h 28,858 m '/h
Manometric height 650 Pa 650 Pa 650 Pa
Diameter of the fan 450 mm, 630 mm, 900 mm,
6 blades, 26 3 blades, 15 4 blades, 23
Power 3.4 kW 6.0 kW 8.5 kW
Motor 4.0 kW 7.5 kW 11 kW
Revolutions per 2,900 2,900 1,450
minute
Fan + motor mass 26 kg + 70 kg 53 kg + 106 kg 160 kg + 172 kg
All of the fans are of the helical Solyvent-Ventec Axipal BZI type. Standard
EN
14986 is applicable (zone 1, T3). The flow rate (5%) and pressure (10%)
reductions, due to
the presence of increased peripheral gap, were taken into account to calculate
the power.
The characteristics used for the secondary ventilation are summarized in table
2
below:
Table 2 - characteristics of the secondary ventilation
Zone 10 Zone 12
Number of fans 6 6
installed
Number of fans 5 5
running
Airflow rate per fan 28,858 m '/h 9,145 m /h
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Manometric height 810 Pa 90 Pa
(400 Pa d namic) (40 Pa dynamic)
Diameter of the fan 630 mm, 630 mm,
4 blades, 33 3 blades, 24
Power 8 kW 0.32 kW
Motor 11 kW 1.0 kW
Revolutions per 3,000 950
minute
Fan + motor mass 60 kg + 172 kg 58 kg + 38 kg
All of the fans are of the helical Solyvent-Ventec Axipal BZI type with an
elongated
shroud. Standard EN 14986 is applicable (zone 1, T3). The fans are of the "jet
fan" type.
Explosion simulations were done on the module of this example. Out of 64
simulations performed, the dilution of the gaseous contaminants obtained owing
to the
invention caused the likelihood of explosion to drop by a factor of 10
relative to a
"traditional" fan of reference.
