EP0703808B1

EP0703808B1 - Foaming composition for reducing the pressure associated with the shock wave generated by burstings

Info

Publication number: EP0703808B1
Application number: EP94918520A
Authority: EP
Inventors: Cesare Cusan; Gianfranco Ferroni
Original assignee: SAN MARTINO SpA
Current assignee: SAN MARTINO SpA
Priority date: 1993-06-11
Filing date: 1994-06-09
Publication date: 1997-09-10
Anticipated expiration: 2014-06-09
Also published as: ITMI931251A0; IT1264588B1; ATE157891T1; ITMI931251A1; EP0703808A1; DE69405566D1; WO1994028977A1

Abstract

A foaming composition is described which is capable of forming foams that are particularly appropriate for reducing or weakening the pressure associated with the shock wave generated by a burst, comprising particular surface-active agents and, in order to increase the duration and multiplicity of use thereof, either polymers, or proteins, or polymers and proteins.

Description

The present invention relates to a foaming composition capable of reducing or weakening the pressure associated with the shock wave generated by burstings. More particularly, it relates to a foaming composition which may contain either proteins or polymers, or proteins and polymers, for the purpose of further increasing the draining time of the foam and prolonging the average lifetime thereof.
It is known that a foam can be defined as a physical system essentially consisting in dispersing a gas in a solution formed by a foaming liquid and water.
The parameters characterizing a foam are in principle the following: a) the chemical composition used for preparing the foam, 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) draining, that is the time necessary to enable the foam to separate 25 to 50% of the solution used for preparing the same.
The chemical composition somewhat affects the expansion ratio, foam draining and resistance to chemical attacks by external agents. The expansion ratio value characterizes the foam smoothness and plasticity and the draining time value accesses the greater or lower foam resistance to spontaneous collapsing and thermal shocks.
It is also known that a sudden variation in the thermodynamic parameters (pressure, temperature, specific volume, gas velocity) occurring inside an explosive during the explosion of a charge, 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 consideration) 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. By spatially fixing a plane impinged on by the shock wave, pressure, after a sudden growth will decrease with the time according to an exponential law.
In the last years, foams have been deeply studied in order to evaluate their capability of reducing the pressure associated with the shock wave generated by a bursting. This capability would be likely to be connected with the physical transformations accompanying the distruction of the explosive-surrounding foam. In particular, part of the energy from the shock wave would be consumed in the form of work for converting the foam into small water droplets and a subsequent part of energy would be employed for carrying out evaporation of said droplets. It has been estimated that particular foam types can in all take up more than 90% of the pressure generated by a bursting.
From US-A-3,976,580 a fluid for estinguishing flames has been known which comprises an aqueous gel containing a polyacrylamide combination as the gelling agent, in particular a mixture containing 0.5 parts of polyacrylamide and 2.7 parts of bentonite per 100 parts by weight of water. The resulting final product is applied to an area attacked by flames to give a cold damp covering inhibiting further fire propagation.
DE-OS-2,310,078 discloses a blanketing composition in the form of a gel containing bentonite or montmorillonite as the gelling agent.
From EP-421,166 a method of decontaminating containers for inflammables is known, which comprises the steps of generating a fire-preventing foam, filling the container to be decontaminated with said foam, cutting said container and knocking down said foam for subsequent disposal, in which method all known foams available on the market can be used.
From IT-A-22120A/89 a foaming composition is known which is adapted for use in extinguishing flames or chocking fumes from acid and/or toxic and/or inflammable vapors, suitable in particular 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, carboxymethylcellulose sodium salt, a fat alcohol and optionally a fluorinated surface-active agent and bio-polymers.
From DE-A-1796269 a fire extinguishing concentrate consisting of foaming and stabilizing agents is known, comprising a mixture of a fat acid alkylolamide and a linear higher fat alcohol as stabilizer and an alkali-neutralized fat alcohol sulfate as foaming agent, wherein for improving viscosity and/or reducing the freezing point a glycol ether or a C1-C4-alcohol or a mixture thereof can be added.
Therefore in all the above cited literature no mention is made of any foam capable of weakening the shock waves generated in case of burstings.
In the Italian patent application IT-MI92A001563 in the name of the same Applicant it is disclosed a foaming composition capable of reducing the pressure associated with the shock wave generated by burstings, comprising carboxymethylcellulose, a clay and a foaming agent, wherein the clay may be bentonite, attapulgite, montmorillonite, sepiolite or vermiculite.
Although this foaming composition is capable of weakening or reducing the pressure associated with the shock wave in a satisfactory manner, there is still a requirement for further improvements, above all as regards the possibility of finding compositions adapted for use several times without being necessary to replace them or integrate them with fresh material.
Therefore the present invention aimed to find a new foaming composition adapted to supply a foam capable of reducing or greatly weakening the pressure associated with the shock wave generated by burstings and suitable to be used several times without needing to be changed or integrated. In particular, the applicant intended to find a new foam of the above described type, possibly affording an increased draining time (as above defined), a longer average lifetime and greater elasticity, thereby being safe and resistant in time, that is adapted to be applied safely to explosives that for several reasons cannot be exploded at once.
This can be for example the case of a charge that, on exploding, could cause damages to the surrounding environment and, on the other hand, cannot be removed or destroyed without danger.
It has now been found that the intended purpose can be achieved quite successfully by a foaming composition as defined here below.
The present invention therefore provides a foaming composition (a) adapted to supply a foam capable of reducing or greatly weakening the pressure associated with the shock wave generated by a bursting, said composition being characterized in that it comprises: glycols and glycol ethers, an ethoxylated alcohol sulfate, ethoxylated and non-ethoxylated fat alcohols, a coconut mono- or di-ethanolamide, isobutyl alcohol and water, in association with a polymer or polymers.
The term "polymer" or "polymers" means polysaccharides in general and in particular of the galactomannan type, such as guar flour and/or hydroxypropylated or ethoxylated caroba flour or caroba flour as such.
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, until 10-60 l of foam per litre of the employed solution are 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 will restrain and reduce the shock wave generated by the explosive burst.
It has been surprisingly found that even with a small addition of polymers having the capability of forming gel with water, foams having an expansion ratio included between 5 and 40 and preferably of 20, and 50% draining times varying from 13 to 24 hours, generally of 15 hours, are obtained. The addition of polymers proved to be particularly efficient, which polymers, in accordance with the formulation being the object of the invention, are suspended in a medium that does not solubilize them but, once dissolved in water, are capable of providing solutions having very high draining times.
The foaming composition of the invention comprises: 1 to 15% by weight of polymers, 3 to 15% by weight of glycols and glycol ethers, 40 to 60%, preferably 45 to 55% by weight of sulfated ethoxylated alcohols, 1 to 5%, preferably 1.5 to 2.3% by weight of C₁₂-C₁₄ fat alcohols, 10 to 25% by weight of isobutyl alcohol, 0.2 to 0.8% by weight of coconut mono- and di-ethanolamide and a water balance.
In order to evaluate the efficiency of the foams being the object of the present invention, bursting tests have been made the methodologies and results of which are set forth hereinafter.
For safety reasons, the tests have been carried out in a 1 m³ metal tank consisting of 4 iron side walls provided with reinforcing belts resting on a bottom formed with an iron plate.
An iron cylinder provided with a central hole has been laid on the tank bottom and on said cylinder the "target" has been arranged, which target consisted of a sheet copper square piece above which, at a predetermined distance, a trinitrotoluene (T.N.T.) charge primed with an electric initiator 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 evaluated.
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.
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 98%.
In confirmation of the results achieved through measuring of the deformations in the sheet copper, an experiment has been carried out in which the shock wave pressure has been recorded by means of piezoelectric pressure transducers.
Through the 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 10 and 20) is characterized by the greatest absorption power ranging between 90 and 98%.

EXAMPLE 1

In a reactor provided with stirrer, thermometer, feeders and a heating system, 6.51 kg of water, 14.11 kg of a sulfated C₁₂-C₁₄ ethoxylated (2 mol) alcool, 8.1 kg of a sulfated C₈-C₁₀ ethoxylated (1 mol) alcool, 8.76 kg of a sulfated C₉-C₁₁ ethoxylated (2 mol) alcool, 5.4 kg of isobutyl alcohol, 600 g of C₁₄ alcohol, 660 g of C₁₂ alcohol, 360 g of coconut di-ethanolamide, 150 g of an anti-fermenting agent are charged and the mixture is brought to pH 7 with 30 g of HCl. After heating to 50°C, 300 g of guar flour and 600 g of isobutyl alcohol are added. The mixture is held at 50°C for one hour and 6.6 kg of guar flour and 7.8 kg of isobutyl alcohol are added afterwards. After keeping the product at the above temperature for half an hour, it is finally discharged. Its viscosity measured at 20°C is 3000 cp, whereas in a 5% water solution it is 280 cp after 10 minutes and 440 cp after 30 minutes.
The above mentioned composition is capable of forming with air or an inert gas an extremely active foam for reducing or widely weakening the pressure associated with the shock wave generated by a bursting.
Obviously any person skilled in the art could make 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.

Claims

A foaming composition capable of forming with air or an inert gas, a foam to be employed for reducing or weakening the pressure associated with the shock wave generated by burstings as far as 98%, characterized in that it comprises:
- 1 to 15% by weight of polymers,

- 3 to 15% by weight of glycols or glycol ethers,

- 40 to 60% preferably 45 to 55% by weight of sulfated ethoxylated alcohols,

- 1 to 5%, preferably 1.5 to 2.3% by weight of C₁₂-C₁₄ fat alcohols,

- 10 to 20% by weight of isobutyl alcohol,

- 0.2 to 2% by weight of coconut mono- and di-ethanolamide and

- a water balance, wherein the polymers are selected from guar flour or hydroxypropylated or ethoxylated caroba and guar or caroba flour as such.
A method of reducing or weakening the pressure associated with the shock wave generated by a bursting, comprising covering of the explosive with a foam prepared from a composition according to claim 1, employed at a rate of 5 to 6% in water to give solutions having varying viscosities included between 200 and 800 cp, which is mixed with air or an inert gas, in particular nitrogen gas, until 10 to 60 l of foam per litre of the used solution are obtained, characterized in that the foaming composition is comprised of sulfated etoxylated alcohols, glycols or glycol ethers, C₁₂-C₁₄ fat alcohols, isobutyl alcohol, coconut mono- or di-ethanolamide, wherein, in order to increase the foam lifetime and ensure the repeated use thereof without being obliged to replace or integrate said foam, polymers are added.