US 3523893 A
Description (OCR text may contain errors)
United States Patent 3,523,893 FIRE EXTINGUISHING POWDER COMPOSITION Zbigniew J. Lobos, East Brunswick, N .J., assignor to Stop-Fire, Inc., Monmouth Junction, NJ. No Drawing. Filed Mar. 22, 1967, Ser. No. 625,034 Int. Cl. A62d 1/00 US. Cl. 252-5 4 Claims ABSTRACT OF THE DISCLOSURE A dry composition of ammonium phosphate-base fire extinguishing powder with finely divided boron oxide in admixture therewith and the process of making the same.
The present invention relates to ammonium phosphatebase fire extinguishing powders, more particularly, to the drying of such powders chemically when the ingredients are being mixed together.
Ammonium phosphate-base fire extinguishing powders are generally referred to as A, B, C since these powders are useful in combating all types of fires which are known as class A, B, and class C fires. However, these ammonium phosphate-base fire extinguishing powders, like many other substances, have the harmful property of picking up moisture from the atmosphere up to the point of saturation at given relative humidity and temperature. It has been found that in one generally used type of such a fire extinguishing powder the moisture content of the powder rapidly increases above 60 percent of the relative humidity of the atmosphere and reaches 4.0 percent at 90 percent of the relative humidity. Carefully controlled tests have produced the following results with respect to the moisture content in the powder at different relative humidities of the atmosphere:
Relative humidity of the air, Moisture contents in the percent: powder, percent 0.022
The particular fire extinguishing powder used in the above tests has the following composition:
Parts by weight,
percent Monoammonium phosphate 91.85 Tricalcium phosphate precipitated 5.00 Silica (300 mesh particles) 0.45
It is pointed out that because during production the powder is in contact with the surrounding atmosphere for a relatively short period of time, the actual values for the moisture in the production powder are not quite as high as the point of saturation ascertained in the laboratory for different relative humidities. At relative humidities of about -90 percent, it was noted that in several production runs the moisture contents were only up to about 0.3 percent.
The presence of moisture in dry chemical fire eX- tinguishing powders is extremely troublesome for a number of reasons. The moisture is mainly responsible for caking of the powder thus adversely affecting the free-flowing of the powder and the rate of dispersion on a fire. Thus, the extinguishing eifect of such a fire extinguishing powder is significantly lower. Moisture also lowers the bulk Amino-acetic acid (glycine) (200 mesh particles) Silicone 'ice density of the powder and, as a result, a greater volume of powder is required for the fire extinguisher. For example, an A, B, C powder with 0.01 percent of th moisture has 10 percent less volume than the same weight of the powder with 0.23 percent of moisture.
Any suitable silicon may be used, such as dimethyldiethoxysilane, partially hydrolyzed methylhydrogen polysiloxanes, or organopolysiloxanes.
A major disadvantage of moisture in fire extinguishing powders is that moisture lowers the electrical resistance of the powder, thus making the powder useless for extinguishing electrical fires. The following data, which was found experimentally, will illustrate the affect of moisture on electrical resistance of the powder:
Electrical resistance Moisture percentage: in megohms 0.020 10,000,000 0.048 950,000 0.083 300,000 0.105 23,000 0.140 9,500
There are two sources of the moisture content in A, B, C powders. One source is the moisture already present in the ammonium phosphate and in the other ingredients, but mostly in the tricalcium phosphate. Secondly, moisture is picked up from the humid atmosphere during the production of the powder. During the production operation the greatest quantity of moisture is picked up from the atmosphere during the sifting operation and during the vacuum air conveying of the powder. It will at once be apparent that in both of these operations the powder is in short but direct contact with the huge volume of the moist atmosphere. Further, the finer the powder the larger will be the surface area exposed to the atmosphere and, accordingly, the greater will be the absorption of the moisture from the atmosphere.
In order to produce an A, B, C fire extinguishing powder of good quality it is of prime importance to remove the moisture from the powder. Up to the present time, there were two possible approaches of removing the moisture from the powder. These approaches may be summarized as follows:
(1) Dehumidifying the atmosphere in the powder production department to lower the relative humidity of the atmosphere to about 40 percent; and
(2) Drying the mixed powders.
The first approach is not satisfactory because of the ingredients themselves are partly responsible for the moisture content of the powder. Thus, controlling the atmosphere alone would only partially remove moisture from the powder.
The drying of the fire extinguishing powder is preferably accomplished by passing the powder through a heated oven or by heating the powder in a jacketed mixer and then removing the moist air by means of a vacuum pump.
It is clearly apparent that the foregoing methods of drying require expensive installations of equipments, require additional space in the production department, increase the time of a production run and hence decrease the total production of powder, and the costs of production are substantially increased while only a small quantity of moisture is actually removed from the powder. The quantity of moisture actually removed may represerit only a small fraction of 1 percent.
It is therefore a principal object of the present invention to provide a novel and improved composition of dry ammonium phosphate-base fire extinguishing powder.
It is another object of the present invention to provide an extremely inexpensive, simple but very convenient chemical process for drying ammonium phosphate-base fire extinguishing powders without requiring any additional installations.
It is a further object of the present invention to provide a novel and improved chemical fire extinguishing powder having an ammonium phosphate base and wherein the moisture is removed chemically.
In one aspect of the present invention the foregoing objects are achieved and the above-mentioned disadvantages are eliminated by a dry ammonium phosphate-base fire extinguishing powder composition according to the present invention. According to the present invention, the ingredients of an ammonium phosphate-base fire extinguishing powder are mixed together. Boron oxide as a drying agent is then mixed to the batch of powder as the last or next to the last ingredient. In some instances the boron oxide may be mixed with the ingredients of the powder after a liquid silicone as a polymerization agent has been added. The time of the moisture removal from the fire extinguishing powder depends upon the fineness and quantity of the boron oxide added. The greater the quantity and the finer the boron oxide the shorter will be the time of dehydration. The entire process is performed at room temperature.
Other objects and advantages of the present invention will be apparent to those skilled in the art from the following description.
According to the present invention boron oxide (B is used as the drying agent for an A, B, C powder. The boron oxide reacts with water with formation of boric acid in accordance with the following formula:
The boron oxide is added as the last ingredient to every batch of the ammonium phosphate base A, B, C fire extinguishing powder. The quantity of the boron oxide which is added to a particular batch will depend upon the quantity of the moisture in that batch of powder. The moisture in the powder, in turn, will largely depend upon the humidity of the atmosphere. In general, 0.2 percent parts by weight of boron oxide will be added during a dry day and up to 0.6 percent parts by weight will be added in the days with a high relative humidity. The time for the removal of the moisture from the batch of powder will depend upon the fineness and quantity of the boron oxide added.
In order to enable the polymerization to proceed of the liquid silicone used as an ingredient for the A, B, C powder some water content is necessary. Therefore, a small quantity of moisture must remain within the powder or the time of the polymerization of the silicone must be shorter than the time for the removal of the moisture. The quantity of moisture may be regulated by controlling the quantity of the boron oxide added. The time of the moisture removal can be regulated by con trolling both the quantity and finess of the boron oxide powder. It should be borne in mind that the time for polymerization of the silicone is considerably shorter than the time required to remove the moisture from the powder.
Typical mixtures wherein moisture is removed from ammonium phosphate-base fire extinguishing powders according to the present invention are given in the following examples, the parts being by weight:
EXAMPLE I 91.85 percent of monoammonium phosphate, 5.00 percent of tricalcium phosphate precipitated, 0.45 percent of silica and 2.00 percent of amino-acetic acid are mixed together at room temperature in a glass jar. The total quantity of the powder is 200 grams. The mixture contains 0.234 percent of moisture. After mixing of the foregoing ingredients, 0.6 percent of boron oxide 120 mesh screened was mixed with the mixture. Then, 0.5 percent of a silicone (dimethyldiethoxysilane) was added to the mixture. After 24 hours the sample was examined with a moisture analyzer and the moisture content was discovered to be 0.068 percent. After one week the moisture content was noted to be 0.016 percent.
EXAMPLE II A similar sample of fire extinguishing powder as set forth in Example I and having a moisture content 0.234 percent was mixed with 1.0 percent of boron oxide and then 0.5 percent of the silicone was added. After 24 hours the moisture content was 0.033 percent and after one Week the moisture content was noted to be 0.010
EXAMPLE III 700 lbs. of the fire extinguishing powder according to Example I and containing 0.100 percent moisture was mixed with 3 lbs. of boron oxide and then 0.5 percent of the silicone added and the entire contents mixed. After 24 hours the moisture contents dropped to 0.016 percent and after a week the moisture content was found to be only 0.002 percent. It is pointed out that in this example, 2 lbs. of the boron oxide would be sufiicient to achieve virtually the same result.
In Example III, the ingredients including the boron oxide were mixed in a liquid-solid V-blender.
As pointed out above, the boron oxide reacts with the water to change into boric acid which is a mild antiseptic.
In all three examples, boron oxide of 120 mesh was used. However, since boron oxide of mesh is commerically available it is preferred to use boron oxide of this fineness. 100 mesh boron oxide reacts rather slowly With the fire extinguishing powder and accordingly it is possible to add more than the calculated quantity of every batch of the powder. The excess boron oxide will protect the fire extinguishing powder against moisture for a period of several days in the event the container of the powder is accidentally opened and relative humidity of the surrounding atmosphere is high.
Dow Corning liquid silicone 1107 is used in the fire extinguishing powders of the above three examples. This silicone is methyl and hydrogen polysiloxane which in the presence of the moisture and a suitable catalyst generates hydrogen gas and polymerizes into long-chained solid polymer which forms an anti-caking and water repelling coat around each particle of the powder. The catalysts which may be used for the polymerization of the silicone are those shown in U.S. Pat. 3,179,589 issued Apr. 20, 1965.
Other typical compositions of ammonium phosphatebase fire extinguishing powders to which boron oxide may be added in accordance with the present invention are as follows:
Boron oxide may be added to all fire extinguishing powders to remove the moisture therefrom except those which contain carbonates or bicarbonates of ammonium or alkali metals. Thus, boron oxide may also be used with fire extinguishing powders for light metal fires which contain mostly sodium chloride or graphite as the main ingredients. At the present time only ammonium phosphates are used as the main ingredients of all A, B, C fire extinguishing powders.
Thus it can be seen that the present invention discloses an extremely simple chemical process for removing moisture from ammonium phosphate-base fire extinguishing powders. The moisture is removed by the simple step of mixing boron oxide powder into a mixture of the ingredients of the fire extinguishing powder. The presence of the boron oxide in the fire extinguishing powder causes a reaction with the Water to form boric acid which in itself is an eflective fire extinguishing agent. The composition of this invention is a dry fire extinguishing powder which will remain dry for a period of time even after its container is opened to the atmosphere.
What is claimed is:
1. A dry fire extinguishing powder consisting essentially of 59-93% monoammonium phosphate, 0.2-1% boron oxide, and the remainder a member selected from the group consisting of silica, mica, barium sulfate, mag- UNITED STATES PATENTS 2,550,113 4/1951 Flowers 252-68 XR 3,048,470 8/1962 Mannhein et a1. 252385 XR 3,172,852 3/1965 Lobos 2525 3,214,372 10/ 1965 Lobos 2525 MAYER WEINBLATT, Primary Examiner U.S. Cl. X.R.