WO2003097171A1

WO2003097171A1 - Extinguishing system, extinguisher and method for extinguishing fires

Info

Publication number: WO2003097171A1
Application number: PCT/FI2003/000372
Authority: WO
Inventors: Jari Kukkonen; Timo Nissinen; Jouko Arvola; Pentti Hukkanen; Aro Fahlenius
Original assignee: Kemira Oyj
Priority date: 2002-05-15
Filing date: 2003-05-14
Publication date: 2003-11-27
Also published as: AU2003231335A1; FI113013B; FI20020913A0; FI20020913A; EP1503828A1

Abstract

The invention relates to an extinguishing system and to an extinguisher comprising an extinguishing liquid that is an aqueous solution of potassium formiate, the extinguishing system or extinguisher producing a droplet size in the range from 10 to 2000 µm.

Description

Extinguishing system, extinguisher and method for extinguishing fires

The invention relates to an extinguishing system and a fire extinguisher comprising an extinguishing liquid, and to a method for extinguishing a fire. The expression "extinguisher" in this disclosure stands for an extinguishing system comprising an extinguishing liquid or an extinguishing device containing an extinguishing liquid.

For many reasons, water is the most commonly used extinguishing liquid. The quenching effect of water is based on its capacity of cooling, of limiting oxygen supply to a fire and of insulating or diluting a burning substance.

The amount of water required for quenching depends on the generation of heat in the fire and the means, amount and form of water supply. The droplet size has a great impact in this conjunction. The smaller the water droplets, the faster the rate of heat absorption into the water from flames and combustion gases. However, in the practice, the droplet size should be large enough to avoid flames attaining the droplets from being entrained from the object on fire by air currents and the buoyancy force of the fire pillar.

With water used for fire extinction, the chief drawbacks are its tendency to freeze in cold spaces, water serves as a substrate for bacterial, algae and other organic growth, and above all the poor capacity of water to quench burning liquids, such as petrol or napalm, and burning cooking oils, such as rapeseed oil and lard.

In order to enhance the quenching effect of water or its other properties, humidifiers, flow-promoting agents, anti-freezing agents, anti-bacterial and anti- algae agents, i.e. bioxides and both foaming agents and film-forming agents are frequently added to water.

The addition of humidifiers to water facilitates the extinction of objects that are difficult to quench, such as cotton bales and plastic products. Humidifiers result in improved penetrating and spreading capacity of water due to reduced surface tension of water.

Flow-promoting agents are added in order to decrease pressure loss in the fire hose and to facilitate pumping of quenching water. Biocides serve to prevent the growth of microbes that are harmful to humans, such as legionella bacteria, in the quenching water, or they serve to prevent clogging of different extinguishing nozzles, sprinklers or even pipe works by bacterial or algae growth. Bacterial activity may even result in breakage of metal constructions due to corrosion.

Liquid extinguishers and extinguishing systems operating with quenching water are suitable for use only at normal temperatures. For this reason, anti-freezing agents are added to the quenching water in order to prevent the quenching water from freezing. In pipe works passing through cold spaces the extinguishing liquid can be replaced during guard periods also with compressed air or any other compressed gas, or the entire pipe work may even be equipped with heat jacketing. Heat jacketings serve to maintain the temperature of quenching water above the freezing point.

Hence there are means and chemicals allowing improved extinguishing properties of water and expanded fields and objects of use for quenching water.

Besides extra cost, the problem of nearly all conventional foaming agents and film- forming agents is that they are more or less harmful both to the environment and to humans. In addition, foaming agents and film-forming agents are frequently corrosive with regard to metals. Furthermore, in case the surface of the foam or the surface film breaks for one reason or the other, such as strong evaporation of petrol combustion gases, the fire may be reignited. Consequently, foaming agents and film-forming agents do not always ensure reliable fire extinction, especially when the object to be extinguished is complex and tricky in construction.

In the extinction of food oil fires, it is essential that the extinguishing agent form solid residues on the cooking premises. For this reason, foaming agents and film- forming agents as well as conventional powder extinguishers are not applicable for the extinction of food oil fires. The cost of cleaning and indemnity for water damage will be far to high for these particular extinguishing agents to become widely popular among consumers.

Anti-freezing agents are either strongly corrosive, such as calcium chloride and sodium chloride, or they increase the fire load, such as ethene glycol, propylene glycol and glycerol. Chloride-based salts may also form at high temperatures chlorine compounds that are toxic for humans. Ethene glycol, propylene glycol and glycerol, again, increase the environmental impact due to their high oxygen consumption, and in cold spaces, they increase the viscosity of quenching water, thus preventing the formation of small water droplets that are essential for quenching, so that the quenching effect decreases. On top of that, ethene glycol, for instance, is a very toxic substance.

There are commercially available liquid extinguishers based on citrate and acetate for the quenching of food oil fires. However, these liquid extinguishers are not applicable for quenching burning liquids, such as oil and petrol. As stated initially, the amount and quenching effect of water, i.e. extinguishing liquid, required for quenching depends on the heat generation of the fire and on the means, amount and form of quenching water supply, i.e. on the extinguisher and the extinguisher system. In addition, organic salts of a high molecular weight such as citrate have also a relatively high viscosity at low temperatures, whereby the adequately small droplet size that is essential for quenching cannot be achieved.

It is also known that calcium acetate or lactate pressurised with carbon dioxide can be used in the quenching of a JP-8 burning liquid instead of the environmentally hazardous Halon 1301 (CF₃Br) [Anthony E. Finnerty et al. "Water-Based Halon Replacement Sprays", USA Army Research Laboratory, Report Number ARL- TR.1138, July 1996].

It is also known that solid sodium, potassium and ammonium salts, such as sodium bicarbonate, potassium bicarbonate, sodium chloride, ammonium hydrogen phosphate or potassium formiate, potassium acetate, potassium citrate and potassium lactate, are usable in solid form in the quenching of burning liquids [GB- B 1 596 045]. Nevertheless, solid extinguishing agents are inapt for the quenching of burning liquids when aqueous solutions are formed therefrom. The water contained in a liquid extinguishing agent goes first down under the burning liquid or food oil, then gets over-heated and eventually explodes as steam with an expansion coefficient of the order of 2000:1. Consequently, the formed explosion fireball may be spread for instance all over the kitchen. The commercial citrate and acetate based liquid extinguishers mentioned above are indeed suitable for food oil fire prevention, but they are by no means suitable for quenching burning liquids. The very low combustion temperature of burning liquids impedes the use of these commercial citrate and acetate based liquid extinguishers. The relatively large droplet size produced by these extinguishers is not sufficient to drop the temperature of the burning liquid below the combustion temperature.

Consequently, there is not one single extinguisher that would be simple, non- polluting, environmentally friendly, harmless to humans, non-freezing and non- corrosive to metals, and which would also be capable of putting out A fires, such as wood and fibrous material, B fires, such as burning liquids, e.g. oil and petrol, C fires, such as gases, D fires, i.e. "metal fires" (aluminium and magnesium), E fires, i.e. electric fires and K/F fires, such as food oils.

The purpose of this invention is thus to provide an extinguisher (i.e. an extinguishing device or extinguishing system including an extinguishing liquid) that could be used for applications not possible with the existing systems. Another object of the invention is to provide an extinguisher allowing minimising of the problems mentioned above, both in terms of extinction techniques and of environmental aspects.

In accordance with the invention, there has thus been provided an extinction system or an extinguisher containing an extinguishing liquid that is an aqueous solution of potassium formiate, the extinction system or extinguisher producing a droplet size in the range from 10 to 2000 μm, preferably in the range from 100 to 1000 μm.

In accordance with the invention, there has also been provided a method for putting out a fire by means of an extinction system or an extinguisher including an extinguishing liquid, the extinguishing liquid, which is an aqueous solution containing potassium formiate, being sprayed on the object on fire in the form of an atomised spray having a droplet size in the range from 10 to 2000 μm, preferably

100 to 1000 μm.

Said extinguishing liquid preferably contains 40 to 75% by weight of potassium formiate.

The extinguishing system or extinguisher of the invention is preferably maintained under a pressure of 0.2 to 10 MPa, especially preferably under a pressure of 0.5 to 3 MPa, the extinguishing liquid being sprayed as an atomised spray having a droplet size in the range from 10 to 2000 μm, preferably 100 to 1000 μm. Said extinguishing liquid may also contain additives, such as an anti-corrosive agent and/or an agent preventing reignition. Typical anti-corrosive agents include sodium methasilicate, which prevents the corrosion of aluminium preferably in an amount of appr. 0.1 to 1% by weight, and triazo compounds, such as benzotriazole, which prevent the corrosion of cupper and brass, preferably in an amount of appr. 0.001 to 0.1% by weight. An agent preventing reignition may consist e.g. of monoammonium phosphate, ammonia and/or urea, in an amount of 1 to 10% by weight.

The extinguisher and method in accordance with the invention can be used for the extinction of A, B, C, D, E and/or K/F fires.

The extinction system of the invention may consist of an extinction system known per se, which may be of stationary type and may release the extinguishing liquid through nozzles, sprinklers or similar as an atomised spray, and accordingly, the extinguisher of the invention may be of mobile type, which releases the extinguishing liquid as an atomised spray.

The use of the aqueous solution based on potassium formiate together with the extinguisher or extinction system that produces droplets of a size of approx. 10 to 2000 μm, preferably approx. 100 to 1000 μm, enabled surprisingly to put out technically extremely demanding B fires (petrol and napalm), in addition to A fires (wood). These extinguishers were not capable of quenching B fires using merely water.

The extinguisher of the invention (extinction system/extinguisher - extinguishing liquid) allows the quenching of food oil fires as well, because the droplet size achieved with the extinguisher of the invention is smaller and thus the quenching power many fold higher compared to the conventional liquid extinguishers based on citrate and acetate.

It is very plausible that the extinguisher of the invention (extinction system/extinguisher - extinguishing liquid) enables the quenching of metal fires (D fires) as well, for which e.g. calcium chloride salts are currently used, which form a fire-insulating salt layer on the metal surface. Potassium formiate probably acts in the same way, especially if potassium formiate contains e.g. methasilicate that forms an insulating combustion slug.

The small droplet size of quenching water prevents gas fires (C fires) as such, and in electric fires (E fires), it forms an important electric insulation between the object on fire and the extinguisher. Electric current must be interrupted between the burning object and the extinguisher. Formiate and/or silicate salts which are formed on the burning surface serve also to insulate the object on fire from the extinguisher. In electric fires, the burning material otherwise pertains to class A or D, and thus it can be quenched merely by the extinguishing liquid used in accordance with the invention.

The invention utilises the previously known benefits of an aqueous solution of potassium formiate, i.e. low corrosive action, low freezing temperature, safety of use, biodegradability and biostatics.

The invention is described in further detail below by means of examples.

Examples

A plurality of quenching tests was carried out determining the efficiency of an aqueous solution of potassium formiate as the extinguishing liquid in B class fires. As the test extinguishing liquid, the product Meltium (Kemira Chemicals Oy) was used, which is an aqueous solution based on potassium formiate, having the following composition and properties:

Active ingredient: potassium formiate 50% by weight

Freezing point: - 58°C pH: 9-11

Density: 1.34 kg/dm³

Viscosity: 2.5-10^"3 Pa-s (2.5 cP)

Surface tension: appr. 20% lower than that of water

Biodegradability: 28 d (more than 90% degraded)

LD₅₀ value: 5,500 mg/kg In certain tests the extinguishing liquid Meltium SPE was used, which corresponds to the product Meltium, but contains urea as an additive, so that Meltium SPE contains 5% by weight of urea.

Residual fuel (a mixture of petrol and fuel oil) and napalm was used as the B fire load. Witco Stereate powder was used as napalm powder. The napalm had been prepared in aircraft petrol. As wood, the tests used shed-dried firewood (length about 30 cm, diameter about 5 to 10 cm).

The objects of extinction were:

- halves of 200 1 barrels split longitudinally, containing about 20 1 of fire load (napalm of liquid fuel)

- car tyres put on fire with napalm and

- a napalm pool of about 2 m

The tests used the following extinguishers:

- Softex 6E manual extinguisher

- Firexpress micro droplet foam extinguisher - Ifex micro droplet impulse extinguisher ("backpack model", 13 1).

Test l

Extinguisher: Softex 6 E manual extinguisher Extinguishing agent: Meltium SPE

Burning substance: mixture of petrol and fuel oil

Extinction: The extinguisher was emptied in 30 s. Fire-retardant effect, the fire was not quenched.

Test 2

Extinguisher: Firexpress Extinguishing agent: Meltium SPE Burning substance: mixture of petrol and fuel oil Extinction: quenching time 4 s. Reignition occurred. Test 3

Extinguisher: Ifex Extinguishing agent: Meltium SPE Burning substance: mixture of petrol and fuel oil

Extinction: One shot 1.5 s. Two shots 5 s at a distance of 2.5 m. Two shots 7 s. at a distance of 5 m.

Test 4

Extinguisher: Firexpress Extinguishing agent: Meltium SPE Burning substance: Napalm Extinction: 6 s.

Test 5

Extinguisher: Firexpress Extinguishing agent: Meltium Burning substance: mixture of petrol and fuel oil Extinction: 4 s. and 2 s.

Test 6

Extinguisher: Firexpress

Extinguishing agent: Meltium Burning substance: Napalm Extinction: 2 s. and 3 s.

Test 7

Extinguisher: Firexpress Extinguishing agent: Meltium

Burning substance: mixture of petrol and fuel oil + wood Extinction: 3 s. Test 8

Extinguisher: Firexpress Extinguishing agent: Meltium Burning substance: Napalm + wood Extinction: 1 s. Test 9

Extinguisher: Firexpress Extinguishing agent: Meltium Burning substance: Oily wood Extinction: 1 s.

Test 10

Extinguisher: Firexpress

Extinguishing agent: Meltium

Burning substance: 6 pieces of car tyres + 3 1 of napalm

Extinction: 3 s. (reignition at the end of 10 s, with extinction in 4 s.)

Test 11

Extinguisher: Ifex Extinguishing agent: Meltium Burning substance: 6 pieces of partly charred tyres + 3 1 of napalm Extinction: 1 s. (one shot)

Test 12

Extinguisher: Firexpress

Extinguishing agent: Meltium

Burning substance: Napalm pool of about 2 m²

Extinction: 28 s. and 13 s.

Test 13

Extinguisher: Ifex Extinguishing agent: Meltium Burning substance: Napalm pool of about 2 m

Extinction: 7 s. At the second attempt, the fire was not put out (running out of extinguishing agent).

Test 14

Extinguisher: Softex 6E manual extinguisher Extinguishing agent: Softex film foam Burning substance: Napalm pool of about 2 m Extinction: 12 s.

The tests confirmed that the achieved droplet size has a significant impact on the effect of the extinguishing liquids used especially in B class fires. The manual extinguisher Softex 6 E filled with Meltium SPE did not put out the fire, but had a slightly fire-retardant effect (test 1). The Softex extinguisher is intended for use with a film foam extinguishing agent and its nozzle does not form micro droplets.

By contrast, extinguishers producing micro droplets, such as Firexpress and Ifex, were efficient extinguishers with both the extinguishing liquids. Due to the specific weight of these extinguishing liquids, the recoil of Ifex (1 1/shot) was markedly stronger than with quenching by water.

Extinction tests were also conducted with a Firexpres extinguisher using merely water as the extinguishing agent. These tests indicated that a Firexpress extinguisher is unable of putting out an oil fire.

Car tyres ignited with napalm normally required water in amount of about 7 to 8 1 in quenching by means of Ifex. With Meltium, the tyres were extinguished with one single shot, i.e. 1 litre.

Firexpress was somewhat more pleasant in use than Ifex, because it produces micro droplets continuously as long as there is still extinguishing liquid in the container.

It was also found that, using Meltium, wood that has been extinguished in liquid fuel is not readily reignited when removed from the liquid fuel. In conclusion, we note that the tests indicate the droplet size of Meltium to have a notable impact on the extinguishing effect in B class fires. The micro droplet technique achieves good extinction results without film-forming agents. The specific weight of Meltium, which is higher than that of water, and its surface tension, which is 20% lower than that of water, enhances its introduction and absorption into the object on fire. Absorption into the object has a promoting effect in A class fires, especially forest fires and land fires. In addition, Meltium maintains the humidity of the application object over a longer period than water. Consequently, Meltium can be used in forest and land fires to limit fire propagation by distributing it from an aircraft over the area through which the fire risks to spread.

Claims

1. An extinguishing system or an extinguisher, which comprises an extinguishing liquid and produces a droplet size in the range from 10 to 2000 μm, preferably in the range from 100 to 1000 μm, characterised in that it contains an aqueous solution of potassium formiate as the extinguishing liquid.

2. An extinguishing system or an extinguisher as defined in claim 1, characterised in that the extinguishing liquid contains 40 to 75% by weight of potassium formiate.

3. An extinguishing system or an extinguisher as defined in claim 1 or 2, characterised in that it is maintained under a pressure of 0.2 to 10 MPa, preferably 0.5 to 3 MPa, and in that extinguishing liquid is sprayed as an atomised spray having a droplet size in the range from 10 to 2000 μm.

4. An extinguishing system or an extinguisher as defined in any of the preceding claims, characterised in that the extinguishing liquid additionally contains an anti- corrosive agent.

5. An extinguishing system or an extinguisher as defined in claim 4, characterised in that the extinguishing liquid contains 0.1 to 1% by weight of sodium methasilicate in order to prevent the corrosion of aluminium and/or 0.001 to 0.1% by weight of a triazole compound, such as benzotriazole, to prevent the corrosion of cupper and brass.

6. A method for quenching a fire by means of an extinguishing system or an extinguisher comprising an extinguishing liquid, characterised in that the extinguishing liquid, which is an aqueous solution containing potassium formiate, is sprayed on the object on fire as an atomised spray having a droplet size in the range from 10 to 2000 μm, preferably in the range from 100 to 1000 μm.

7. A method as defined in claim 6, characterised in that the extinguishing liquid contains 40 to 75% by weight of potassium formiate.

8. A method as defined in claim 6 or 7, characterised in that the extinguishing system or the extinguisher is maintained under a pressure of 0.2 to 10 MPa, preferably 0.5 to 3 MPa.

9. A method as defined in any of claims 6 to 8, characterised in that the extinguishing liquid further contains an anti-corrosive agent.

10. An extinguishing system or an extinguisher as defined in claim 9, characterised in that the extinguishing liquid contains 0.1 to 1% by weight of sodium methasilicate in order to prevent the corrosion of aluminium and/or 0.001 to 0.1% by weight of a triazole compound, such as benzotriazole, to prevent the corrosion of cupper and brass.

11. A method as defined in any of claims 6 to 10, characterised in that the fire is a fire classified as A, B, C, D, E and/or K/F class fire.