GB2068725A - Fire-extinguishing powder composition - Google Patents

Abstract

A fire-extinguishing powder composition suitable for fire classes B and C, comprises from 30 to 40% by weight of the reaction product of potassium hydrogen carbonate and urea and 50 to 70% by weight of calcium carbonate, the components having an upper grain size of 100 <0>m, the grain size of at least 50% of the total mixture being <20 <0>m. A process for preparing the composition is disclosed as is a method of extinguishing fires.

Description

SPECIFICATION Fire-extinguishing powder mixture The invention is concerned with a fireextinguishing powder composition. More particularly the invention is concerned with a fireextinguishing powder composition suitable for file classes B and C. By fire-extinguishing powdersforfire classes B and C are meant those for extinguishing liquid and gas fires.

It is known that suitable materials for the preparation of efficient extinguishing powders for controlling liquid and gas fires include in particularthe hydrogen carbonates, sulphates and chlorides of sodium and potassium with appropriate processing.

It is also known from German OLS 2,206,019 that reaction products of potassium hydrogen carbonate and urea surpass in their extinguishing capacity the above-mentioned extinguishing raw materials known for a long time.

However, extinguishing powders based on the reaction product of potassium hydrogen carbonate and urea have the disadvantage that they have small bulk densities, which leads to the fact that the necessary quantity of extinguishing agent cannot be accommodated during the filling of extinguishingagent containers of specific volume size. However, specific filling quantities are stipulated for prescribed container sizes. This given ratio of container size and filling quantity is a test fundamental and consequently a basic prerequisite for the licencing of fire-extinguishing appliances and fire-extinguishing agents of this type.

There have been many attempts to overcome this disadvantage which is a consequence of the small bulk density. Consequently, it was proposed according to GB-PS 1,387,705 to use sand in order to increase the bulk density. The addition of fluorite has also been considered. Apart from the fact that sand possesses no extinguishing activity of any kind, extinguishing powders mixed with sand have a high abrasive effect and can cause damage during use especially to moving machine parts.

The problem of the invention is therefore to find a non-abrasive material which in combination with the reaction product of potassium hydrogen carbonate and urea increases its bulk density and is compatible therewith and which also does not influence disad vantageouslythe extinguishing activity of the reaction product of potassium hydrogen carbonate and urea.

We have now been able to devise a fireextinguishing powder of the above-mentioned type.

According to the invention, we provide a fireextinguishing powder composition comprising from 30 to 40% by weight of the reaction product of potassium hydrogen carbonate and urea and from 50 to 70% by weight of calcium carbonate, the components having an uppergrain sizeof 100,um,the grain size of at least 50% of the composition being less that 20,am.

Although according to German OLS 2,206,019 it is generally known for fire-extinguishing powders contain or be mixed with calcium carbonate, this is effected therein for other reasons and not on the scale specifically according to the invention, nor with the aim of improving the special fire-extinguishing powder of the above-mentioned type.

As has been shown, features material to the fireextinguishing powder according to the invention are, on the one hand, the grinding together of the components involved and, on the other hand, their special common grain size range. Too fine a powder leads upon application of the powder at the seat of a fire to large extinguishing ineffectiveness due to the given thermal upcurrent. On the other hand, too coarse a grain leads to segregration of the extinguishing powder and consequently to disadvantageous changes of its properties.

Surprisingly, it has been shown that an extinguishing powder of the type according to the invention has a more effective specific extinguishing capacity than an extinguishing powder based solely on the reaction product of potassium hydrogen carbonate and urea. This is surprising inasmuch as the active portion of the fire-extinguishing powder according to the invention in the total quantity is smaller.

This can be explained if the large specific surface of the calcium carbonate is taken into account in the special fineness. Presumably, due to adhesive forces very fine particles of the active reaction product are bound to fine parts of the calcium carbonate without agglomerating and can then become effective upon application to the fire as a result of the high addition of heat. A preferred composition of the mixture according to the invention consists of 30 to 40% of reaction product of potassium hydrogen carbonate and urea, 50 to 70% calcium carbonate with a 50% fraction of the total mixture below 20 ,um and 2 to 4% of a hydrophobic agent of known type. A suitable hydrophobic agent is siliconised silicon dioxide.

The extinguishing activity of the extinguishing powder according to the invention is thought to be achieved due to the fact that in the preparation of the extinguishing powder the grinding of the reaction product of potassium hydrogen carbonate and urea is effected together with the calcium carbonate, with simultaneous introduction of hydrophobic agent. In so doing, grain finenesses are obtained which are below 20 m for more than 50% of the composition with an upper grain limit of 100 ,am. The bulk density of this extinguishing powder according to the invention is generally 0.95 + 0.05 kg/dm3 and consequently meets the requirements in respect of the ratio of container volume and filling quantity.An extinguishing powder based solely on the reaction product of potassium hydrogen carbonate and urea has, in comparison, a bulk density only of 0.60 to 0.65 kg/dm3.

It is thus considered desirable to effect at least some adjustment in the grain size of the composition once the components have been intimately mixed. It is more convenient if all the adjustment is achieved in this manner.

Comparative Examples according to the following table gave the following results: Extinguishing powder A B Bulk density kg/dmi3 0.60 -0.65 O.95 + 0.05 Grain fineness below20,um 33% 55-60% below 40 tm 48% 75 - 85% below 100 m 90% 95100% Extinguishing capacity Test 7-- Object 1 Extinguishing time s 10.3 6.9 Consumption g 4.750 4.450 Specific extinguishing rate kg/m2 0.90 0.83 Reserve g 450 1.550 Extinguishing capacity Test 2 -- Object 2 Extinguishing time s 9;;6 9.5 Consumption kg 17.0 12.5 Specific extinguishing rate kg/m2 1.06 0.78 Reserve kg 23.0 37.5 Extinguishing powder A is a commercial extinguishing powder prepared from the reaction product of potassium hydrogen carbonate and urea with the addition of hydrophobic agents.

Extinguishing powder B is an extinguishing powder according to the invention, consisting of 38.2% by weight of the reaction product of potassium hydrogen carbonate and urea, 60.95% by weight of calcium carbonate and 0.85% by weight of siliconised silicon dioxide as hydrophobic agent.

The extinguishing capacity was determined as follows: Commercial fire-extinguishing appliances were filled in each case with the corresponding extinguishing powder A or B.

For test I 6-kg appliances were used.

Only 5.2 kg of extinguishing powder could be accommodated due to its small bulk density (not standard). There were used as fire objects for comparison test 1 flat sheet-metal tanks, four with a base area of 1 m x 1 m and two with a base area of 0.8 m x Q8 m, all having a depth of 0.1 m and containing Otto fuel (about 10 litres) resting on a water cushion.

There were used for comparison test 2 so-called P50 appliances in which only 40 kg of powder A, but 50 kg of powder B could be accommodated.

Likewise used as fire objects were flat sheet-metal tanks, but with a base area of 4 mx 4 m and the same depth, also filled with Otto fuel (in the same way with about 100 litres per tank). Extinguishing was effected with the above-mentioned appliances after a burning time of 30 seconds.

It can be seen immediately from the preceding comparative table that the extinguishing powder B according to the invention is superior in all points to the extinguishing powder A, in that not only is a higher bulk density obtainable, but also shorter extinguishing times are achieved with a reduced consumption of extinguishing powder and, moreover, the reserve of extinguishing agent remaining in the appliance is consequently larger.

Claims (12)

1. A fire-extinguishing powder composition comprising from 30 to 40% by weight of the reaction productof potassium hydrogen carbonate and urea and from 50 to 70% by weight of calcium carbonate, the components having an upper grain size of 100 the grain size of at least 50% of the composition being less that 20,am.

2. Acomposition as claimed in claim 1 which additionally contains from 2 to 4% of a hydrophobic agent

3. Acomposition as claimed in claim 1 or claim 2 having a bulk density of 0.95 + 0.05 Kg/dm3.

4. A composition as claimed in claim 1 substantially as hereinbefore described.

5. A composition as claimed in claim 1 substantially as hereinbefore described with reference to Example B.

6. A process for the preparation of a composition as claimed in claim 1 which comprises bringing into intimate contact in the appropriate proportions a reaction product of potassium hydrogen carbonate and urea, and calcium carbonate whereby a compos itionofclaim 1 is formed.

7. A process as claimed in claim 6 wherein at least some adjustment of the grain size of the composition is effected once intimate mixing of the components has been effected.

8. A process as claimed in claim 7 wherein all the adjustment of the grain size of the composition is effected once intamate mixing of the components has been effected.

9. A process as claimed in claim 7 or claim 8 wherein adjustment of the grain size occurs with simultaneous introduction of a hydrophobic agent.

10. A process as claimed in claim 6 substantially as hereinbefore described.

11. A method of extinguishing a fire which comprises applying to the seat of a fire an effective amount of a composition as claimed in any of claims 1 to 5.

12. A method of extinguishing a fire substantially as hereinbefore described with reference to Example B.