WO1993009848A1

WO1993009848A1 - Method for extinguishing fire with a breathable gas and water spray mixture

Info

Publication number: WO1993009848A1
Application number: PCT/DK1992/000334
Authority: WO
Inventors: Torbjørn Gerner LAURSEN
Original assignee: Laursen Torbjoern Gerner
Priority date: 1991-11-12
Filing date: 1992-11-12
Publication date: 1993-05-27
Also published as: DK185691D0; AU2942992A

Abstract

A method to extinguish or control fire, in which human life is not endangered, and with a fast extinguishing action, in a typical form comprising an amount of gas for oxygen dilution stored in the cylinder (1) and an amount of water stored in a cylinder (2) supplied as water fog or water spray. In case of fire or the likeliness of fire to break out, the valves (4) are actuated, whereby gas floods through piping (6) and nozzle (8), and the water floods through piping (5) and nozzle (7), and both water and gas is discharged into the enclosure (3). By the method it is possible to extinguish fires with an amount of gas and water that by themselves separately are not providing extinguishment. An Oxygen dilution lowering the concentration of Oxygen in the enclosure from 21 % to 17 % combined with a supply of water fog or water spray of 500 g/m3 extinguishes the majority of normally used combustibles.

Description

METHOD FOR EXTINGUISHING FIRE WITH A BREATHABLE GAS AND WATER SPRAY MIXTURE

The invention relates to a fire extinguishing method and system, that within -an enclosed room of a defined volume in particular or an area, is extinguishing fire in gases or liquids, is extinguishing primarily the gas-phase fire of combustible solids and to some extend the deep seated fire of combustible solids, in a way that will not be harmful to human beings, and will not have environmental ill-effects.

A fire extinguishing method or a fire extinguishing agent will usually work by one of the following principles:

1) Dilute the Oxygen concentration in the surrounding air to well below

2) Lower the temperature of the combustion zone to a level at which the chemical reactions of the combustion process will stop. 3) Separate Oxygen and combustible material.

4) Chemical interference in the combustion proces, by using a substance which in the molecule contains atoms of the Halogen-group. (These substances are identified by the term "Halon").

With reference to 1):

The most commonly used method is to use CO: (Carbon Dioxide). CO: is an efficient fire extinguishant, but due to the strong respiratory stimulation, extinguishing concentrations are deadly to human beings even at short term exposure. And as CO: is a much heavier gas than atmospheric air, the rise is not limited to the protected enclosure, but areas situatated below the protected enclosure, and other enclosures connected to the protected enclosure through ventilation shafts, cable tunnels and similar, may also be unsafe.

The high relative gravity of CO: may also have a negative effect on the extinguishing efficiency if the enclosure is not airtight, and especially by leaks in the lower section of the enclosure the extinguishing effect may not be maintained for more than a few minutes.

N: (Nitrogen) is also known as an effective oxygen diluting gas. But the use of N: is not safe to human beings, because of the reduced amount of oxygen

SUBSTΓTUTE SHEET during fire extingusihing. The human body do not have any reliable or significant symptoms for a too low oxygen concentration, and even a life threatening reduction of the Oxygen concentration may not be noticed.

US patent no.4,807,706 describes a method whereby the Human safety is improved by using a small amount of CO2 in order to stimulate the breathing of human beings during exposure to atmospheres with low oxygen concentrations. The disadvantage of this method is that certain combustion processes produce a lot of smoke and toxic fumes, and in such case the fact that a person is breathing faster may result in a slightly increased effect of the said toxic fumes. Another disadvantage of the method is that the storage of the involved gases is very bulky, involves large capital investments, or may be technically complicated.

With reference to 2):

The most commonly used substance to extinguish fires by reducing temperature is water, which by the high heat capacity, and especially the heat of evapourization, is very efficient. Water may however be damaging to the equipment it protects, and certain types of fire and certain 3-dimensional applications can not be extinguished easily or safely by water.

With reference to 3):

Foam (foam produced by air, water and a foam compound) and powder (dry chemical fire extinguishing powder also have an additional anticatalytic effect) effectively separates Oxygen and combustible, thereby preventing fire to continue. The fire extinguishants may themselves be damaging to the materials they protect, and especially for the primary goal of this invention, enclosures with a defined volume, they are usually not to be preferred.

With reference to 4):

Halons are very efficient fire extinguishants, but it has been discovered that they are very harmful to the environment, by their Ozone depleting effect. This knowledge has led to a international agreement to ban Halon and stop '<»

production and usage. New chemicals are being developed with molecules basically formed by Carbon, Fluorine and Hydrogen, which have somewhat the same fire extinguishing effect as Halon, but are expected to be less harmful to the stratospheric Ozone layer, but at the same time they can be 5 expected to have a high GWP (Global Warming Potential) and by use as fire extinguishants, high temperatures will make them decompose into other substances which may be toxic and highly corrosive.

The aim of the invention is to provide a fire extinguishing method and system 10 which is capable of extinguishing a great variety of combustible materials and a great variety of applications in which:

The personnel safety standard is very high

There is no environmental ill effects.

The fire extinguishing method does not lead to substantial 15 material damages.

Capital investment and storage volume requirement is reduced compared to that of inert gas storage such as Argon or

Nitrogen.

20 As already mentioned, it is known to extinguish fire by reducing the Oxygen concentrattion well below 15%, and in order to do so it is required to have available a gaseous, oxygen diluting, fire extinguishant (for example Nitrogen or Carbon Dioxide) in an amount as a free volume equivalent to at least 40% of the enclosure volume. It should be noted that the actual amount of gas

25 available shall alway be in excess of the 40%, because the gas can not be discharged into an enclosure without loss of the extinguishing gas. Particularly in case of combustibles which require a lower Oxygen concentration to be extinguished, and subsequently a high extinguishing gas concentration, the utilization of the extinguishing gas is considerably less than

30 that obtained when lower extinguishing gas concentrations can be used.

Another method which have alreday been mentioned is the use of water, which in one typical installation, known as water sprinklers, is designed to supply 5mm-30mm water, per square meter, per minute. In this application 35 type it is evident that the water itself may be damaging to materials stored in the enclosure. A well known method to increase the extingushing efficiency of water is to apply in the form of very small water droplets with an average droplet size of 0.1 mm or even much less. This method is known as water spray or water fog, and can be acheived by special nozzles and/or high pressure and/or different kind of atomizing processes, but even though there is an apparant increase in extinguishing efficiency, this efficiency may only be present during discharge of the water, which is a considerable disadvantage. It is known that the use of water spray or water fog is considerably reducing the consumption of water and thereby some of the damaging effect of the water.

According to the present invention, there is provided a method for use in fire control, fire extinguishing or fire prevention, in which the oxygen concentration is reduced in an enclosure of a specified volume, and at the same time an amount of water in the form of water drops, water spray or water fog is being supplied .

In a typical form of the invention the fire extinguishing system consists of a supply of a non-combustible and non-toxic gas which is also not taking part in the combustion process, preferably an inert gas or Nitrogen, and a supply of water . The amount of gas is 20% of the enclosure volume, and the amount of water is 500 g per m3. The water is supplied through a water spray or water fog nozzle of known construction, in such a way that the water spray flow and the gas flow are physically crossing each other, or touching each other during discharge, in order to physically mix the gas and the water spray. By doing this it is ensured to have a good distribution of gas and water spray throughout the enclosure, and altogether the combination of the gas extinguishing by oxygen dilution and the cooling extinguishing action of water, is reducing considerably the amount of each part being used, compared to using them separately. A typical form of the invention is illustrated in fig. 1.

As an example of the extinguishing effect of the invention, the extinguishing of Heptane indicates the achievement of the invention. To extinguish Heptane by using an Oxygen diluting gas, it is required to have efficiently available an amount of gas equal to or exceeding 40% (as a gas design concentration (m3 gas per m3 of enclosure) this equals 47%), or to have available an amount of water, supplied in a certain droplet size, of some 3050 g/m3. the same extinguishing effect can be achieved by the invention by using 20% gas (22% as the design concentration), and 800 g water per m3, which is considerably less than half of each of the 2 fire extinguishants used separately.

In order to achieve this significant efficiency increase, the water can be supplied by using any known method to produce water fog or water spray, and any particular water droplet size of this water fog, water spray or water ^"mist, shows considerably increased efficiency in testing. The extinguishing gas can also be supplied by any known method and the amount of extinguishing gas as a percentage of the enclosure volume can be selected as any concentration in the range 10% to 50%. More than 50% can also be used, but in this case special conciderations may be necessary in order to maintain a high personnel safety level. The most significant efficiency increase is within the limits of 12% to 28% Inertgas, and an amount of water, supplied as water spray or water fog, of

1700 g/m3 to 200 g/m3. The correlation between amount of water in the form of water droplets of a certain size, and the extinguishing concentration of Nitrogen, is indicated, for Heptane, Ethanol and dry birch wood, in the graph of fig. 2. In the diagram the area above the lines indicate extinguishing concentrations

In a form of the invention, in which a slight additional increase in efficiency can be noticed, a part of, or all of the extinguishing gas used is Carbon Dioxide, and this Carbon Dioxide is used as a propellant of the water. The amount used should never exceed the human short term exposure tolerance, which is approximately 0.5% to 8%. A noticeable increase in efficiency is observed when the pressure of water and Carbon Dioxide after absorption is above 6 Bar at 15 °C.

An alternative use of the invention is to use it in a form where the Oxygen diluting extinguishant or the chemical extinguishant in itself is designed for an extinguishing concentration, but with an additional supply of water in the form of water spray or water fog. By applying the water spray in the early phase of the gas discharge a considerable shorter extinguishing time is noticed, a speed up of the extinguishing process which can only be achieved by the known methods when the flow rates or the amounts of extinguishant are greatly increased.

I fig. 1 a form of the invention is illustrated in which the extinguishing gas is stored under pressure in one or more containers (1) and water is stored under pressure in one or more containers (2). In case of fire in the enclosure (3),detected by man or by fire detectors of known construction, the cylinder valves (4) of known construction are actuated simultaneaously or at certain time intervals, so that the water floods through the piping (5), and the extinguishing gas floods through the piping (6). The water spray or water fog is created by the use of a nozzle (7) of known construction, and the extinguishing gas is finally apllied by the nozzle (8) of a known construction. In fig. 3 a form of the invention is shown in which the nozzles (7) and (8) are combined in one nozzle, in which the extinguishing gas and the water is effectively mixed. The water floods through the atomizer nozzle (9), and the gas is led through the nozzle cap (10) at the pipe fitting (11), in such a way that the water spray or water fog (12) is forming a homogenous mixture of extinguishing gas and water, which is efficiently mixed into the complete atmosphere of the enclosure.

The construction of components such as pressure cylinders, valves, actuation devices, distribution systems, piping, nozzles and fire detectors is known in a great variety and is not withnin the aims or the claims of the invention.

Claims

1. A method of fire control and fire extinguishing, in a defined enclosure volume or in a less specified area, while maintaining mammalian life, in particular human life, characterised in that, in the enclosure an extinguishing mixture of gas and water spray or water fog, that includes an Oxygen diluting or in other way extinguishing gas, that will lower the Oxygen concentration of the enclosure atmosphere, or interact chemically in the combustion process, and simultaneaously or with a delay, supply and amount of water spray or water fog which will absorb some of the energy developed by the combustion proces or the igniting source.

2. The process of claim 1, characterised in that the supply of extinguishing gas in itself does not provide fire extinguishing or fire control, and that the supplied amount of water fog or water spray in itself does not provide fire extinguishing, but that the particular combination is fire extinguishing or is providing fire control, in a way that the Oxygen concentration is not reduced below human tolerance, and that the amount of water is considerably limited hence reducing the possible damaging effects of water.

3. The process of claim 1, characterised in that the supply of extinguishing gas in itself is fire extinguishing, and that the supply of water in the form o water spray or water fog, is reducing the extinguishing time.

4. The process of claim 1, characterised in that the water is pressurized by Carbon Dioxide, that when it evapourizes during discharge and fire extinguishing is helping to split the small water drops into even smaller particles, and thereby also releasing an additional amount of gas which will contribute to a slightly increased extinguishing efficiency.

5. The process of claim 1, characterised in that the Oxygen concentration in the enclosure in which fire extinguishing takes place, is reduces to between 8% and 19%, and that the water supplied as water spray or water fog is supplied as an amount of between 50 g/m3 and 2000 g/m3.

6. The process of claim 1, characterised in that the Oxygen concentration in the enclosure in which fire extinguishing takes place, is reduced to between 15% and 17%, and that the water supplied as water spray or water fog is supplied as an amount between 500 g/m3 and 900 g/m3.

1. The process of claim 1, characterised in that the water fog or water spray is applied directly into the discharging extinguishing gas, that gas being an oxygen diluting gas.

8. The process of claim 1, characterised in that the water fog or water spray is applied directly into the discharging extinguishing gas, that gas being a chemically working extinguishing gas.

9. The process of claim 1, characterised in that the water fog or water spray is applied through the whole gas flooding time, a part of the gas flooding time.

10. The process of claim 1, characterised in that the water fog or water spray is applied thorughout the enclosure, or in parts of the enclosure, during the gas flooding time and after, or after the full discharge of the extinguishing gas.