Foam Blanket Research Articles

Tuning thermal stability of fluorine-free foam by nano-MDH inorganic flame retardant

Foams enhanced by nanoparticles (NPs) have become an important way to develop new type of fluorine-free firefighting foams. This study focuses on thermal stability of foams generated by the mixed dispersion of CoatOsil-77 silicone and BS-12 hydrocarbon surfactants as foaming agent and nano-magnesium hydroxide (nano-MDH) as foam stabilizer. The interaction between nano-MDHs and surfactants were studied. Thermal stability of nano-MDH enhanced foam was explored by investigating drainage and volume attenuation of foam and heat transfer in vertical foam blanket. Stabilization mechanism of nano-MDH enhanced foam under heat was clarified. Results show that nano-MDHs have a weak interaction with the BS-12 molecules and almost has no interaction with the CoatOsil-77 molecules. Initial foam height of mixed dispersion increases at the presence of nano-MDHs, but further increase in the concentration of nano-MDH decreases its foaming ability. At room temperature, foam drainage and coarsening are accelerated by low concentration nano-MDH (1 wt%) and delayed by high concentration nano-MDH (>1 wt%). Meanwhile, foam was strengthened by rising nano-MDH content after exceeding 1 wt%. Drainage and volume attenuation of foam and heat transfer in vertical foam blanket were significantly delayed and the corresponding thermal stability was strengthened by nano-MDHs. This study can offer a possibility for tuning thermal stability of fluorine-free foams based on nano-MDHs.

Improvement of the phenolic composition and the antioxidant capacity of red guava (Psidium guajava) and watermelon (Citrullus lanatus) powders by means of foam blanket drying

Red guava and watermelon have good sensory and nutritional attributes. However, they are highly perishable. Aiming to improve this condition, drying is presented as a technique that promotes the reduction of water content, extending the useful life of products. The elaboration of guava and watermelon powders by drying in a foam blanket with optimization of the proportion of the foaming agent (powdered albumin) and agitation time (10′) were studied, and the influence of the drying method on the physicochemical quality, phenolic composition and antioxidant capacity of the material. Density, stability and% expansion was evaluated and the optimal condition for foam formation was: 5 and 15% (w/w) of additive for guava and watermelon, respectively. The foam was dried at 68 °C. The physicochemical properties of the powders showed that the technique is a viable alternative in obtaining a by-product that is easy to reconstitute. All powders showed an increase in phenolic content that potentially contributed to a greater antioxidant capacity after the drying process in all tests performed. This result reveals the drying potential for the production of fruit powders, adding value to these raw materials, promoting the potential for application in the manufacture of good quality by-products.

Fluorosurfactant retention in the foam blanket during gravitational drainage of an aqueous film-forming foam

A model aqueous film-forming foam (AFFF) comprising a fluorocarbon surfactant (6:2 FTSaB), hydrocarbon surfactant, solvent, and water was deployed on a heptane fire with the gravimetrically-drained foam solution collected at regular time intervals and analysed for surfactant concentration.Foam drainage behaviour within the model foam system was non-linear for both control (no fire exposure) and fire-exposed tests, as would be expected. However, the concentration of fluorosurfactant within the drainage solution was initially lower, increasing with time. This suggests that the fluorosurfactants are retained within the foam blanket for longer than other constituents of the model foam. This is proposed to result from the unequal probability of rupture in bubbles comprising the foam blanket: as the rate of foam collapse decreases with time, bubbles with lower stability burst until those with a higher persistence and higher surfactant content remain.

Experimental study of moist air flow in the gap between the aircraft\u2019s fuselage and its cabin wall

We carried out an experimental study on the moisture transfer and the heat transport in warm and humid air flows between the cabin lining and the fuselage skin. The measurements were performed in a rectangular gap channel, representing the space between fuselage and cabin wall. Long-term measurements were performed for three configurations: without insulation, with fibreglass blanket and with melamine resin foam blanket. To simulate realistic flight conditions in a laboratory setup, we applied a concept of scaling. This concept is intended to guarantee similitude between the real flight conditions and the laboratory experiment. The results reveal that without insulation, the moisture transfer rate is much higher compared to the configurations with insulation blankets. With insulation, most of the water evaporates during ground conditions and just a small amount is entrapped in the insulation. Without insulation, just a small part of the frozen water evaporates on the ground. When comparing the two insulation blankets, it is found that they both have a similar heat transmittance coefficient. However, the condensation rate of the water and the resulting accumulation of water are significant, higher for the fibreglass blanket.

The price of fire safety

Straight out of college, Ted Schaefer’s first assignment at 3M Canada was to provide technical support and formulate firefighting foams. It was 1980, and 3M was the dominant producer of fluorosurfactant-containing foams used to quell hydrocarbon fires after aircraft crash landings and to put out fires at oil refineries, chemical plants, and storage-tank facilities. From the 1970s through the 1990s, 3M’s Light Water fire suppressant—and other fluorosurfactant-based firefighting foams like it—were the “highest performing” foams available, recalls Schaefer, who earned a degree in chemistry from the University of Waterloo. The foams seemed to have few, if any, drawbacks. A concentrated formula, diluted with water, forms a heat-resistant foam blanket that rapidly cools and smothers most hydrocarbon-fueled fires. The fluorine content helps create a low-surface-tension film that rapidly spreads across the surface of a flammable liquid. A foam’s quick action in a fire can mean the difference between life and death.

Noise Control Capability of Structurally Integrated Resonator Arrays in a Foam-Treated Cylinder.

Corrugated-core sandwich structures with integrated acoustic resonator arrays have been of recent interest for launch vehicle noise control applications. Previous tests and analyses have demonstrated the ability of this concept to increase sound absorption and reduce sound transmission at low frequencies. However, commercial aircraft manufacturers often require fibrous or foam blanket treatments for broadband noise control and thermal insulation. Consequently, it is of interest to further explore the noise control benefit and trade-offs of structurally integrated resonators when combined with various degrees of blanket noise treatment in an aircraft-representative cylindrical fuselage system. In this study, numerical models were developed to predict the effect of broadband and multi-tone structurally integrated resonator arrays on the interior noise level of cylindrical vibroacoustic systems. Foam layers with a range of thicknesses were applied near the inside surface of the cylinder to represent different degrees of conventional blanket treatments. Excitations including point force as well as harmonic and random fluctuating pressure fields were considered. The results suggest that structurally integrated resonators can be tuned to address a variety of noise control requirements and effectively used in conjunction with foam blanket noise treatments, but their relative benefit is reduced when thicker foam treatments are used.

단백포소화약제의 유동성 변화에 따른 소화 특성

Foam extinguishing agent is widely used for extinguishing combustible liquid fires. Compared to other foam type extinguishing agents, protein foam has relatively low cost and low toxicity and produces stable foam blanket which is excellent in heat resistance and sealability, despite it has weak fluidity. Therefore the study investigated foaming characteristics followed by various factors affecting the fluidity of the protein foam extinguishing agent. The extinguishing characteristics differentiated by the changes in fluidity were also experimented. Foaming performance was compared by measuring the expansion ratio and the 25% drainage time. Moreover, the 25% drainage time and the extinguishing time was compared. The results showed that the 25% drainage time and the expansion ratio were increased as the pressure of nozzle and the concentration of hydrolyzed protein liquid enlarged. However the foaming and extinguishing performance were not improved when the condition exceeded certain level of pressure and concentration. The fastest fire extinguishing condition was the nozzle pressure 4bar with the 85wt.% of concentration of hydrolyzed protein liquid.

Evaluation of Surfactant Enhanced Water Mist Performance

Water-mist technology provides efficient fire suppression for compartments while minimizing water usage. Even with the many advantages of water mist systems, there is still room for improvement. Water mist systems have demonstrated effectiveness at suppressing flammable liquids (Class B) fires in compartments. However, an especially challenging fire suppression scenario for water mist systems is the small Class B fire. This scenario is often realized after a large fire has been reduced in size or ‘controlled’ by water mist. The small fire scenario is challenging because a small fire may not be able to generate enough vaporized water to displace sufficient oxygen for complete extinction. It should also be noted that even if the Class B fire is extinguished with a water mist system, re-ignition from the hot surrounding surfaces may occur at any time. In the present work, an additive is introduced into the water supply and its effect on the water mist suppression performance is studied. This ForafacTM additive is a specific formulation, which includes fluorinated surfactants for creating a robust fire suppression foam. The enhanced suppressant exiting the mist nozzle is dispersed in the form of small droplets (not as a continuous foam) similar to a pure water mist spray. However, these droplets create a foam blanket on the surface of the fire, which acts to isolate the fuel from the air. With this formulation, the efficiency of the water mist system is improved even on small fires and most importantly the re-ignition of class B fires is prevented.

Sealability Properties of Fluorine-Free Fire-Fighting Foams (FfreeF)

This contribution compares the sealability performance of recently developed three synthetic foam formulations (that do not contain fluorosurfactants or fluoropolymers) with that of an aqueous film forming foam (AFFF). We apply the sealability methodology outlined in the Australian Defence Force Specification, DEF(AUST)5706. This methodology specifies a 0.28 m2 small-scale indoor fire pan. The pan is first filled with 10 L of water and then 5 L of AVGAS (aviation gasoline, flash point of −50°C) or heptane (flash point of −4°C) is placed on top of the water. Foams were generated from a pressurised extinguisher with a foam nozzle as described in the standard’s specification, set to create foams with expansion of 4:1. The foam spread across the fuel until the entire fuel surface was covered with foam. At 5 min intervals, a lit taper was introduced into the space above the pan area by passing it twice around the surface of the foam in a circular motion at a height of approximately 15 mm from the surface of the foam. The results demonstrate differences in the sealability performance between AFFF and fluorine-free foams (FfreeF). Under laboratory conditions, with a foam blanket 1–2 cm deep, best-performing FfreeF formulation (RF6) provides about 30% of the durability of an AFFF for protection against evaporation of low-flashpoint flammable liquids. We also note in the results the significant differences among FfreeF with almost no sealability of AVGAS vapours offered by the two other formulations.

Mass transfer of volatile organic carbons through aqueous foams

A model is developed to study diffusive mass transfer of hydrocarbon vapor through a flexible foam blanket. The model accounts for the diffusion of hydrocarbon vapor through gas-phase and liquid lamellae, the combined gravity and capillary drainage from the plateau border, the thinning of foam lamellae caused by the forces of capillary suction, London–van der Waals attraction, and electrostatic double-layer repulsion, and foam collapse. Uniform bubble size is assumed, and hence, interbubble gas diffusion arising out of variation in bubble sizes alone is not incorporated into the model. A high-stability aqueous foam formulation that remains stable in the presence of oil (hexane) at foam–oil contact was developed using surfactants, stabilizers, and viscosifiers. Emission of hexane vapor through the foam was measured. The model predicts that the initially taller foam columns collapse faster. Their mass-transfer resistance is higher before the onset of collapse but not very different from that of the shorter foam columns at long times. If the solubility and diffusivity of the hexane gas in the foam liquid are unaffected, the foams with higher viscosities persist longer and provide greater diffusive mass-transfer resistance. Foam bubble size does not significantly impact the mass-transfer resistance of the foam column before the onset of foam collapse. However, the foams with smaller bubbles collapse earlier, and their ability to act as a mass-transfer barrier to the diffusing hydrocarbon vapor diminishes rapidly. The experimental results compared reasonably with the model for varying initial foam heights and bubble sizes.

Modelling Of Foam Spread On A Burning Liquid Fuel Surface

Theoretical models have been formulated describing the spread of foam on burning liquid fuel surfaces in pool-like configurations. The main driving force of the foam spread is due to differences in the hydrostatic pressure within the foam while the dominating resisting force is due to viscous friction between the foam blanket and the fuel beneath. Account is taken to the influence of ordinary drainage, radiation-induced drainage, and evaporation. A large number of experiments have been performed to generate input data and to generate data for verification of the theoretical models. A series of experiments with water as “fuel” in a 1⁄2-symmetric pool has been used to determine friction coefficients. These coefficients have then been scaled and used for other fuels to calculate the foam spread in a number of different scenarios, both with and without fire. There is in general a good agreement between the calculated and the experimental results.

FOAMSPEX: Large scale foam application-modelling of foam spread and extinguishment

Engineering models have been developed to predict foam spread and extinguishment under fire conditions on liquid fuels in a research project called FOAMSPEX. A large number of experiments have been performed to generate input data and to generate data for verification of the theoretical models. The experiments include laboratory measurements of foam properties, foam spread tests in various geometries, field trials of foam monitors, and full scale validating fire tests. This paper gives a brief description of the model. Emphasis is put on the part of the project related to the foam spread experiments and the final application of the model to large-scale tank fires. The main driving force of the foam spread is due to differences in the hydrostatic pressure within the foam while the dominating resisting force is due to viscous friction between the foam blanket and the fuel beneath for a pool fire. For foam spread in channels the friction between the foam and the sidewalls dominate. Account is taken to the influence of ordinary drainage, radiation-induced drainage, and evaporation. The foam spread experiments were conducted both in a channel and a pool configuration. Some experiments were designated to determine friction coefficients between the fuel and foam and between foam and sidewalls. These coefficients have then been scaled and used for other fuels to calculate the foam spread in a number of different scenarios, both with and without fire. Finally, the model has been used to indicate the foam spread in large-scale tank fire situations and the results have been compared with observations from some real scale tank fires. The results of the modelling support some of the existing recommendations according to NFPA 11 although it is clear that large diameter tanks will require higher application rates than presently stated. It is also found that the approximations introduced in the present models i.e. neglection of the consumption of foam due to the fire results in an underestimation of the time necessary to control the fire.

The determination of pressures and patterns for the male human buttocks and thigh in sitting utilizing conductive foam

Pressures and patterns for twelve male human buttocks and thighs in sitting in three different shaped seat pans were determined. Pressure was determined by multiple transducers situated geometrically on a conductive foam blanket which measured changes in resistance with an ohm meter as pressure was applied. The three chair seat pans consisted of a small round surgeons type stool, a standard biomechanic secretarial shaped chair, and a neutral posture chair which was a unique combination of a forward-sloping cultivator seat and an English saddle with wrap around leg trough support. Trunk-thigh posture angles of 90 and 127 deg for each chair were evaluated. The location of the maximum pressure points for all chair posture treatments had generally small tight patterns whose locations where consistent with the locations of the ischial tuberosities. The mean pressure was found to vary inversely with the total area. Thus, as the seat pan surface area decreased in total area in contact with the buttock-thigh, the larger the mean pressure became. Mean pressure values were also found to be in the same rank order and relative magnitude to subjective comfort for the buttock-thigh, conducted in related experiments on the chair-posture treatments. The neutral posture chair was found to reduce buttock-thigh maximum pressure from 118.94 mmHg (2.3 psi) to 62.06 mmHg (1.2 psi) and to reduce mean pressure by more than 50%.

Hangar fire protection with automatic AFFF systems

The control and extinguishment times of fuel fires using aqueous film-forming foams as the suppressant have been found to depend not only on application rate, but also on the type of discharging device. It is more effective to apply the suppressant directly to the burning fuel surface than to depend on flow of a foam blanket into the fire from the perimeter.