[0001] The present invention relates to a fire-fighting system.
[0002] In recent times, the use of nitrogen as an inerting gas to provide effective fire
prevention, within environments to be protected, is becoming widespread.
[0003] As is known, by lowering the level of the oxygen, in an environment, below a minimum
initiation level, it is in fact possible to prevent and completely eliminate the risk
that a combustion process might occur.
[0004] In practice, it is possible to create environments that are characterized by a low
content of internal oxygen and in which it is not possible to establish or maintain
any combustion process.
[0005] There is already abundant technical documentation produced by various research laboratories
which, by virtue of initiation tests performed according to standards, have verified
and certified in an extremely precise manner the initiation threshold of combustion
processes for a very large number of commonly used materials.
[0006] It has been found that the minimum residual oxygen threshold required for the initiation
of combustion processes for most materials is well above the minimum survival threshold
for man.
[0007] This observation has allowed to design environments that are perfectly compatible
with human presence and at the same time are perfectly safe with respect to the risk
of fire.
[0008] The advantages of this prevention method, which eliminates completely the risk of
damage due to fire, are evident; however, its practical application has revealed some
limitations and drawbacks.
[0009] Currently, regardless of the size of the enclosed space to be protected, the detection
of the residual oxygen values inside the enclosed space is performed by means of sensors
which draw the air to be analyzed simultaneously from multiple intakes. The air is
mixed unintentionally within the sampling duct and is analyzed.
[0010] The residual oxygen value obtained from the analysis is then compared with an objective
value, and if the objective value is lower than the found value the mechanism for
introducing nitrogen into the environment is activated.
[0011] The arrangement of the sensors, in the applications known so far, does not allow
to check specifically any inflows of air from outside.
[0012] In practice, only in the most refined solutions sensors are used which, as explained
above, collect and mix in the collection duct the samples of multiple sampling points.
[0013] Moreover, the sensors and/or points for sampling from the environment to be protected
are distributed on the walls in a more or less constant manner.
[0014] In conventional systems, the introduction of nitrogen into the environment occurs
always at a delivery point, regardless of the size of the environment to be protected,
assuming that the nitrogen introduced in the enclosed space, due to the known physical
property of gases, tends to mix with the gas that is present within the environment
to be protected and tends to create a mix that has a more or less constant residual
oxygen content.
[0015] However, in practice this does not occur due to at least three factors.
[0016] The first factor relates to the fact that the mixing of the nitrogen introduced at
the delivery point with the remainder of the atmosphere inside the environment occurs
in a non-negligible finite time, which is directly proportional to the size of the
environment. Because of this, at each instant within environments of medium or large
size there are residual oxygen concentrations that can even be significantly different
from each other.
[0017] The second factor relates to the fact that oxygen is heavier than nitrogen and therefore
tends to stratify with respect to nitrogen. This phenomenon therefore increases in
practice the effects of the first factor, facilitating the creation of regions with
different oxygen concentrations within a same enclosed space.
[0018] The third factor consists in that no environment is perfectly hermetic and nitrogen
escapes from the environment to be protected, not only through the necessary and provided
openings, for example doors, which every environment necessarily has, but also through
cracks, sockets, electrical ducts, gaps and in general through countless other openings
which are not intended, not desired and/or not considered both during design and during
the practical execution of the environments to be protected.
[0019] This third factor, like the two preceding ones, facilitates the creation of regions
having a different residual oxygen gradient.
[0020] DE19934118 discloses a system and apparatus for extinguishing tunnel fires, wherein the tunnel
is split into different areas and has separators which in turn have concentration
areas forming an inert area. A container holds the inert gas and is situated in the
walls of the tunnel, in whose walls inlet openings or other flow apparatus are situated.
Separators are formed via mechanical devices.
[0021] The aim of the present invention is to provide a fire-fighting system based on the
introduction of inert gas such as nitrogen which overcomes the drawbacks of the cited
prior art.
[0022] Within the scope of this aim, an object of the invention is to provide a fire-fighting
system which is capable of optimizing the introduction of nitrogen and/or of any inerting
gas for the purpose of active fire prevention, within an environment, so as to direct
the nitrogen directly where a gap might occur which might allow an outward gas leak.
[0023] Another object of the invention is to provide a fire-fighting system that allows
to minimize the introduction of nitrogen or other inert gas that is required to maintain
a certain residual oxygen content within an environment and therefore to reduce energy
consumption considerably, with respect to the conventional systems known so far and
applied to environments of substantial size.
[0024] A further object of the present invention is to provide a fire-fighting system that
ensures a constancy and uniformity of the residual oxygen value in the entire volume
of the environment to be protected, without the need to install fans or other ventilation
equipment, contrary to conventional systems wherein an auxiliary ventilation is required
in order to ensure this uniformity.
[0025] A further object of the present invention is to provide a system which, by virtue
of its particular constructive characteristics, is capable of giving the greatest
assurances of reliability and safety in use.
[0026] A further object of the present invention is to provide a system that can be provided
easily by using commonly commercially available elements and materials and is also
competitive from an economic standpoint.
[0027] This aim and these and other objects which will become better apparent hereinafter
are achieved by a fire-fighting system, comprising a network distributing inert gas
into a closed environment through injection points; a plurality of sampling points
that take samples of atmosphere in said closed environment in order to measure the
quantity of oxygen that is present; an inert gas generator connected to said injection
points; an oxygen analyzer connected to said sampling points; said inert gas generator
being controlled by said oxygen analyzer so as to send inert gas to the injection
points when the oxygen content measured by said sampling points exceeds a preset value;
said system being
characterized in that it comprises a virtual grid which divides said environment into a plurality of regions
having variable dimensions: smaller regions at openings of said environment toward
the outside, and larger regions where there are no openings; each region comprises
at least one injection point and at least one sampling point; said sampling point
of each region being distant from the respective injection point.
[0028] Further characteristics and advantages will become better apparent from the description
of preferred but not exclusive embodiments of the invention, illustrated by way of
non-limiting example in the accompanying drawings, wherein:
Figure 1 is a top view of a closed environment divided by means of a grid, according
to the present invention;
Figure 2 is a top view, similar to the preceding one, of the complete fire-fighting
system according to the present invention.
[0029] With reference to the cited figures, the fire-fighting system according to the invention
is applicable advantageously to a closed environment, generally designated by the
reference numeral 1, which is constituted for example by a large environment, on the
order of 10,000 m
3 to 500,000 m
3.
[0030] The environment 1 is divided by means of a virtual grid, shown schematically by dashed
lines 2 in the figures, which has a variable spacing, i.e., defining regions having
different dimensions.
[0031] The grid 2 is used to sensibly arrange the sampling points 4 in order to perform
ambient air analyses.
[0032] In particular, the grid has a tighter spacing, i.e., smaller regions, where openings
3 of the environment to be protected are defined, and has a wider spacing, i.e., larger
regions, where no openings are provided in the environment.
[0033] The sampling points 4 are arranged at different heights, within each region identified
by the grid 2, and are connected to a control unit with an analyzer 12 by means of
sampling ducts 13.
[0034] By positioning the sampling points 4 in this manner, the following advantages are
achieved.
[0035] The sampling points 4 allow to highlight very precisely, throughout the life of the
fire-fighting system, the critical points of the environment 1 to be protected. Accordingly,
it is very easy to verify locally, within a large environment, the regions where it
is desirable to intervene in order to restore locally the desired level of isolation
in the environment 1.
[0036] The grid 2 also allows to arrange an inert gas distribution network that intervenes
locally, where the increase in the oxygen level has occurred. Local intervention on
the gas leak allows to reduce the quantity of inert gas, that is introduced in the
environment 1, to the minimum quantity required in order to restore the local balance
at the desired values of residual oxygen.
[0037] The intervention inertia of the preservation system is very small. The fire prevention
system in fact does not wait for the oxygen that has entered the environment to propagate
and dilute most of the protective atmosphere that is present within the environment,
but acts immediately exactly at the point where the problem is occurring, consequently
containing the impact of the problem to the region where it has been detected.
[0038] By means of the statistical analysis of the residual oxygen values detected in the
sampling points, it is possible to recognize, prevent and correct trends of the prevention
system that might lead, in the best case, to energy waste due to excessive injection
of inerting gas within the system with respect to what is actually required in order
to keep the system under control and might cause, in the worst case, the environment
to leave the safety zone.
[0039] The system according to the invention also comprises a network for the distribution
of the protective gas which allows to uniformly distribute the gas within the environment
volume.
[0040] In particular, the inerting gas is distributed by means of a distribution network
which comprises T members 5 which are mutually connected and are fed by a central
nitrogen generation unit 9 which is connected to the T members by means of feed pipes
11.
[0041] Each T member has injection points 6 which are controlled by automatic valves 7,
driven by the analysis and monitoring software of the prevention system.
[0042] A characteristic of this distribution system is that the gas injection points 6 are
distributed on a matrix, like the residual environment oxygen sampling points 4, but
are offset with respect to the sampling points, in order to prevent a short-circuiting
between the analysis of the residual oxygen and the introduction of inert gas/nitrogen,
which would hide the actual severity and diffusion of an isolation problem of the
environment to be protected.
[0043] The benefits of this system for the distribution of inerting gas in an environment
are several.
[0044] The distribution system according to the present invention optimizes the quantity
of inert gas that is introduced in the environment, which is conveyed only where it
is actually necessary, therefore reducing its consumption.
[0045] The system therefore reduces the energy consumption required to keep the environment
1 safe.
[0046] The system also allows a reduction of the gradients of the different values of residual
oxygen within the environment and a greater uniformity of the residual oxygen value,
to be maintained within the environment, ensuring that regions with oxygen values
out of control and/or out of the safe zone are not present within the environment.
[0047] Preferably, an inert gas lighter than air is used, for example nitrogen, and the
distribution system is provided at zero height; i.e., at the level of the floor of
the environment to be protected.
[0048] This improves the mixing of the inert gas with the oxygen that is present within
the enclosed space to be protected, which stratifies if it is heavier than the introduced
inert gas.
[0049] In this manner, once again the possibility of having regions with different oxygen
values is reduced, with the consequent benefits listed above.
[0050] A further characteristic of the present invention is that part of the mixture, that
is present within the environment 1, is drawn directly from the partitioning regions
dedicated to the operating intakes 3 and is then reused, mixed with the external air,
in the nitrogen generators in order to improve their efficiency.
[0051] In practice, the environment 1 has mainly two types of openings: safety doors-openings
3, which are intended indeed for the safe evacuation of people in case of emergency,
and "work door" openings, designated by the reference numeral 33, which are intended
for normal access to the structure and through which people and goods normally pass
(Figure 1).
[0052] In these environments the differentiation is not only theoretical, but has an important
practical consequence.
[0053] While it is assumed that safety doors 3 must be used only rarely in case of a real
emergency, and therefore in case of opening it is not necessary to control/minimize
the inflow of oxygen from outside, in the case of work openings 33 it is in fact assumed
that they are operated even several times per day. Hence the need to partition the
normal axis regions by using a double door which defines an antechamber 8.
[0054] The double door system reduces the inflow of oxygen into the environment to be protected.
[0055] By sampling gas from the partitioned region 8, a slight negative pressure is created
in the region which attracts air both from the outside and from the inside of the
environment to be protected.
[0056] By suitably designing the natural openings of the partitioned region it is possible
to create dynamically, during the ordinary operation of the system, a partitioned
region that has a clearly defined residual oxygen content, the value of which can
be designed so as to be as close as one wishes to the content that is present outside
the environment to be protected, approximately 20.9%, or to the value that is present
within the environment 1 to be protected, for example 15%.
[0057] This refinement improves the efficiency of nitrogen generators by approximately 30%.
In practice, the nitrogen generators generate an oxygen-poor gas mix, which therefore
is nitrogen-rich, starting from a gas mix that already initially has a lower oxygen
level than the ambient atmosphere.
[0058] Another advantage of this system is the improvement of the efficiency of the partitioned
region, as a barrier to the inflow of oxygen into the environment to be protected,
during the normal operation and life of the system.
[0059] Both of these benefits cooperate to improve the efficiency of the system and to reduce
significantly its energy demand.
[0060] In practice it has been found that the invention achieves the intended aim and objects,
a firefighting system having been provided which is absolutely effective and capable
of reducing energy consumption.
[0061] The installation of the system according to the present invention is also substantially
more economic than the installation of a traditional water-based system (sprinklers).