FOAMING COMPOSITION FOR REDUCING PRESSURE ASSOCIATED WITH THE SHOCK WAVE GENERATED BY BURSTINGS

D e s c r i p t i o n

The present invention relates to a foaming composition capable o-f reducing or weakening pressure associated with the shock, wave generated by burstings. In greater detail, it relates to a foaming composition possibly containing a clay, for the purpose of further increasing the draining time of the foam and prolonging the average lifetime of the same.

It is known that a foam can be defined as a physical system essentially consisting in the dispersion of a gas in a solution formed with a foaming liquid and water.

In principle, the parameters characterising a foam are a) the chemical composition used in preparing it, b) the expansion ratio (RE), that is the value of the ratio between the produced foam volume and the volume of the liquid solution employed for producing said foam, and c) the draining, that is the value of the time necessary to enable the foam to separate 25 to 507. of the solution used for preparing it.

The chemical composition somewhat affects the expansion ratio, foam draining and resistance to chemical attacks by external agents. The value of the expansion ratio characterizes the foam smoothness and plasticity and the value of the draining time assesses the greater or lower foam resistance to spontaneous collapsing and thermal shocks.

It is also known that a sudden variation in the thermodynami parameters (pressure, temperature, specific volume, gas velocity) taking place at the inside of an explosive during the explosion of a charge,

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- *? - 198 PCI7IT93/00066

generates a shock wave at the explosive—surrounding medium interface, which shock wave propagates spherically in the considered medium (air or foam in the case herein taken into account) at a decreasing supersonic speed until a given distance from the charge is reached and then at the speed of sound.

Since the bursting phenomenon does no longer supply energy for supporting the shock wave, as the shock wave gradually moves away from its source (bursting point ⁾ there is a decrease in the maximum pressure characterizing it, whereas there is an increase in the pressure decay time. If we fix a spatial plane impinged on by the shock wave, pressure after a sudden growth w ll decrease in time according to an exponential law.

In conclusion, pressure variation associated with shock wave can be represented in time and space with curves of the type shown in the graph of fig. 1.

Therefore, taking into account time, pressure varies according to the law:

9 r - i mix ^e -

wherein ϋ ^" (referred to as constant time ⁾ represents the time during which pressure has reached 377. ⁽ 1/e ⁾ of its maximum value relative to the maximum pressure. The area subtended by the curve, computed for a lapse of time of about 6.7 v7 , represents the wave impulse:

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I = PdWt

If the shocl- wave encounters an obstacle on its way, in close proximity to said obstacle there will be the sum of the effects duie both to the incident wave and the waves reflected by the obstacle itself, so that the maximum pressure at said area is expected to reach higher values than those associated with waves that can freely propagate in the medium. It is well apparent that these effects will be the greatest for incidences perpendicular to the obstacle and zero when the incidences are parallel thereto.

In recent times foams have been deeply examined for evaluating their capability of reducing pressure associated with the shocl- wave generated by a bursting. This capability would be connected with the ohysical transformations accompanying the destruction of the foam surrounding the explosive. In particular, part of the energy from the shocl wave would be consumed in the form of worl- for converting the foam into small water droplets and a subsequent part of energy would be employed for carrying out evaporation of said droolεts. It has been estimated that particular foam types may in all tar e up more than 907. of the pressure generated by a bursting.

From US-A~3,97ϋ,580 a fluid for extinguishing flames has been I- nown which comprises an aqueous gel containing a polyacryla ide combination as the gelling agent, in particular a mi ture containing 0.5 parts of pol yacrvlamide and 7. 7 parts of bentonite per loo parts bv weight ot water. The resulting final product is applied to an area attacl ed by flames to give a cold damp covering inhibiting further fire propagation.

I n PE-0S-: 1 o , 0 a h l an t ^ t i ng comp os i t i on i n e i C\'-m

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of a gel is described, which contains bentonite or montmori 1 lonite as the gelling agent.

From EP-421,166 a method of decontaminating containers for inflammables comprising the steps of generating fire-preventing foam, filling the container to be decontaminated with said foam, cutting said container and knocking down said foam for subsequent disDosal is disclosed, in which method all !- nown foams available on the market can be used.

Finally, from IT-A-22120A/B9 a foaming composition is I- nown which is adapted for use in extinguishing flames or chocking fumes from acid and/or toxic and/or inflammable vapors, and more particularly for inactivating vessels containing liquid, solid or muddy materials generating acid, toxic and/or inflammable gases, which composition comprises urea, ethylene glycol , an ethoxylated alcohol sulfate, carboxymethylcel1ulose sodium salt, a fat alcohol and optionally a fluoπnated surface-active agent and bio- polymers.

Therefore in all literature cited above no mention is made to any foam capable of wealenmg the shocl- waves generated in case of burstings.

Accordingly, it has been an object of the present invention to find a foaming composition adapted to supply a foam capable of reducing or greatly wealening pressure associated with the shocl- wave generated by burstings. In particular, the applicant intended to find new foam o-f the above described type, possibly affording an increased draining time (as defined above) , a longer average lifetime and greater elasticity, thereby being safe and resistant in time, that is adapted to be safe) v applied to explosives that for . ffε s_>π\' ^|L \' re.rPi canπci be exploded r OΠC .

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This may be for example the case of a charge that on exploding could cause damage to the surrounding environment and that on the other hand cannot be removed or destroyed without danger.

It has now been found that the intended purpose could be successfully achieved by a foaming composition as hereinafter defined.

0 In one aspect, the present invention therefore provides a foaming composition adapted to supply a foam capable of reducing or greatly weal-en πg pressure associated with the sho l wave generated by a bursting, which composition is characterized in that it comprises: 5 carboxymethyl cellulose (solution) , glycols and glycol ethers, an ethoxylatεd alcohol sulfate, a fat alcohol and water, in association with a clay preferably selected from the group consisting of attapulgite, bentonite, montmori 11onite and sepiolite or vermiculite. 0

In a second aspect, the invention provides a foaming composition comprising: _< urea, NaCMC (carboxymethvl cellulose sodium salt) , monoethy] ene glycol, an ethσxylated alcohol sulfate, a tat alcohol and water . _ __>

For production of the foam proper, the above described composition suitably blended with water, is mixed with air or an inert gas, nitrogen for example, as far as 10- 1 of foam per litre of the employed solution ara θ obtained. Due to its particular composition, this foam has a very long draining time, that is high stability in time. When applied to an explosive, the foam tends to form an absorbing shield that wi 11 restrain n re iuce the shocl wave αenerated by the explosive burst. 5

It has been surprisingly found that even with a small addition of clε^y, which is capable of forming gel with allv 3 H α 3 n α s a □.lire":

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derivatives for example, foams having draining times 50"/. longer than 24 hours can be achieved.

In a first preferred embodiment of the present invention, the foaming composition comprises 107. by weight of a 27. carboxymethy] cellulose solution, B-107. by weight of a foaming agent, and a water balance.

In this preferred embodiment, the foaming agent comprises 10 to 227., preferably 13 to 207. by weight of a sulfated ethoxylated alcohol; 5 to 207., preferably 8 to 167. by weight of glycols and glycol ethers; 1 to ZV. , preferably 1 to 27. by weight of a fat alcohol , and a water balance.

In a second preferred embodiment of the invention, the foaming agent comprises: 2 to 107. by weight of urea; 3 to 157. by weight of ethylene glycol; 10 to 207., preferably 13 to 157. by weight of a sulfated ethoxylated alcohol; 0.2 to 157., preferably 0.5 to 77. by weight of carbαxymethyl cellulose sodium salt; 0.1 to 0.57., preferably 0.1 to 0.37. by weight of a fat alcohol , 5 to 87. by weight of clay and a water balance.

At all events, carboxymethyl cellulose will have a substitution degree of 0.4-1 and a maximum viscosity (in a 27. water solution) of 4000 cp.

In order to evaluate the efficiency of the foams being the object of the present invention, bursting tests have been made, the methodol l gi es and results of which are set forth hereinafter.

For safety reasons, the tests have been carried out in a 1 m ^" - ⁵ metal anI- consisting of A ron side walls provided with reinforcing belts resting on a bottom formed with an iron plate.

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An iron cylinder provided with a central ho e has been laid on the tanl- bottom and on said cylinder the "target" has been arranged, which target consists of a sheet copper square piece above which, at a predetermined distance, a trinitrotoluene (T.N.T.) charge primed with an electric initator is maintained. The foam to be examined is then put into the tank as far as an 80 cm level is reached, so that the charge-target assembly is completely immersed.

Then the explosion of the charge is caused, the copper square piece is recovered and the occurred deformation or complete separation of the central area is ev luated.

By measuring the volume of the occurred flaring and based on the mechanical features of resistance to deformation of the material , it has been possible to compute the deformation-producing pressure. Thus, through the use of the empirical formulae by Henrych

(J. Henrych "The Dynamics of Explosion and its Use",

Elsevier Scientific Publishing Company, 1979) , the value of the overpressure in air (kg/crrP) associated with the shocl wave of a charge of W (. g) weight located at a distance P (m) from the target has been calculated:

Dp =

Dp =

Dp - — + -i- —-

R _ R-- R- for 1_R_1 wherein R ⁽ correct distance) =

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(m/lg ^{1 3} )

³ J W In this manner t is possible to compute which pressures would have generated explosions in the air of T.N.T. charges weighing 0.025, 0.050 and 0.140 Ig, respectively.

By comparing the theoretical pressures with the achieved ones it has been found that the decrease in the explosion pressure occurred in the foam ranges between 90 and 987..

In confirmation of the results achieved through measuring of the deformations in the sheet copper, an experiment has been carried out n which the shod wave pressures have been recorded by means of piezoelectric pressure transducers.

^" I hrough use of the above described devices, tests of burst in water, air and foam of varying densities have been made with compressed T.N.T. charges of increasing weight. Thus the following has been ascertained: a) all experiments carried out in the presence of foams have produced a noise and a "blow" effect in the surrounding atmosphere much lower than those resulting from similar tests carried out in the air; and b) of the different types of tested foams, the foam having the greatest water contents (expansion ratio between l and 20) is characterized by the greatest: absorption power ranging between 90 and 987..

Based on the achieved results, attemps have been made to interrelate the pressure decreaFe obtained with a given type of foam with the thi πess of the o^m itsel .

In Table 1 neJow. the achieved results are shown and in

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part cular:

- next to the distance R in cm, also data relating to the common logarithm of the correct distance R are reproduced wherein W is the weight in grams of the charge, and

- next to the maximum pressure recorded for each test in kg/cm ³ , the value of the commom logarithm of this parameter is reproduced too. 0

In this manner a straight course between 1 og ^* R and log Pmax can be highlighted (see diagram of fig. 2 .) and, by the least squares method the following relation can be drawn:

15 log p = 1.08649505 - 0.22799544 log Pmax.

Thanks to this equation, by fixing a given max-imum- pressure value, Pmax. , the related correct distance ^" p can be drawn and, by fixing a given charge weight W, the 0 thickness of a foam R = R ³ -JW capable of knocking out pressure to said value can be drawn. Thus, for example, it is possible to establish that for a charge weighing 1 kg, a foam thickness of about 1 is necessary for knocking out a pressure up to a value of 5 kg/cm".

: <

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TABLE 1

Charge Di stance Maximum Pressure

Weight R = cm R=cm.g" lg R Pmax=kg/cm ^:2 lg Pma;-

0.876 3.21 0.506

20 6.84 0.835 7.06 0.849 17 5.81 0.764 27.7 1.442

15 38.4

5.13 0.710 Pmax : 56.05 1.749 73.7

50 13.57 1.132 1.00 0

50 45 12.21 1.087 1.02 0.009 37 10.04 1.002 5.94 0.774

100 50 10.77 1.032 1.13 0.053 70 15.08 1.178 0.81 - 0.091

150 50 9.41 0.974 2. oo .3 1

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EXAMPLE - Foam preparation

1)

A composition to be applied in the form. of a foa is prepared which contains the following ingredients: urea.

NaCMC monoethylene glycol sulfated ⁽ Cισ-Cι^) ethoxylated alcohol 1 fat alcohol water q.s. to 1007.

2)

A second composition is prepared which contains the following ingredients: glycol, glycol ether 8-16 wt7. (C-2-Ci-v) fat alcohol 1-2 wt7. ethoxylated alcohol sulfate 13-207. wt7. water q.s. to 1007.

107. of composition 2) is admixed with: beπtonite 5 wt7.

27. NaCMC solution 10 w X water q.s. to 1007.

4)

87. of composition 2) is admixed with: a.ttapulgite 8 wt7.

27. CMC solution 10 wt . water q.s. to 1007.

5) Composition 1 ⁾ is used as such (without clay) in a 67. water solution, and the produced foam has a draining time ranging between 1 and 4 hours depending on the achieved expansion ratio.

A] 1 the above mentioned compositions ar~> capable of forming with air or an inert gas an extremely active foam for reducing or widely weakening pressure associated with the shock wave generated by a bursting.

πbviour-l v any er n si-i1]ε-c! in >^> art c ul r>.~\

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changes or modifications to the invention, playing for example on the polymer, the protein or the different components of the foaming composition. As in particular it would be long and tiresome to list all fat alcohols, or glycols or other surface-active agents, any variation falling within the scope of the present invention is to be considered as quite obvious and foreseeable.

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