Civilization is said to have a great transformation after the invention of fire by mankind. Fire is a very good servant, but, a very bad master. As long as fire is under control, it serves a lot of useful purposes, but, once it goes out of control, it can create a lot of destruction. However, despite the presence of fire safety measures, the occurrence of accidents is oftentimes inevitable. It is this combination (of good servant and bad master), which is dangerous. Because of the useful purposes that it serves, people keep sources of fire in/around their houses/workplace. And, these sources could sometimes result in undesired fire. Had fire been something, which serves no useful purpose – the number of incidents of fire would have been very less – as people won’t keep sources of fire around them. The most common causes of fire other than natural lightening are manmade like: electrical, cooking and smoking. Fire mainly caused due to overloading short circuits etc., involving leakage of cooking gas, cooking oil etc., accompanied by a spark around the leakage and smoking in/around combustible materials.
The occurrence of fire-related accidents is oftentimes inevitable-in spite of all the safety precautions. Further, with the growing use of electricity based technological applications, carefree, competitive, jealous, and malicious behavior life style, crowded, haphazard and fire prone settlements lead to fire hazards in our surroundings, homes, factories, agriculture fields and forests which used to be considered as calamities earlier are becoming very common with time. Fire can destroy any thing which might have taken years to come up and most of the time, the life and property losses due to such large fire out breaks are enormous. The problem is not how to reduce the risk of fire (although that is a priority), but to educate people towards the safe use of technology, to be more concerned about our surroundings, to help each other and to decongest the poorly-built, densely inhabited and dangerous squatter areas. Unlike in rare cases when fires occurs naturally due to vegetation, geography and climatic conditions, fires hazards are usually man made, mostly accidental and sometimes due to our carelessness. Fires in offices, homes, agriculture field make huge loss of life and property. Forest fire not only kills the plants and vegetation that helps purify our air through photosynthesis but also produces a large amount of smoke which can directly affect our respiratory system. The smoke also contains a large amount of CO2, which is also the main component of green house gases which in turn is the cause of global warming. Many animals, birds, insects and mirco organisms along with plants and vegetation are killed and even if some survives, the habitat is greatly disturbed and it will be difficult to survive in the new totally different environment. The food chain that starts from plants to animals to higher cycle of food web can be destroyed. Forest fire also alter the soil texture and it encourages the more fire resistance species and with repeated fire it can change the natural habitat. Usually the fire occurs in dry season and with the onset of rainy season the fertile soils can be washed away. These are but some of the major effects of forest fire and there is a need to give bigger concern on this.
It seems ever since cavemen discovered fire we have been fighting to keep it under control and many technologies for fire control have been developed but with many limitations. Foremost technology to extinguish fires is the use of water but this method has lot of problems like non-availability of enough water, availability of water at a distance; break down of water supply system and manpower. Use of carbon dioxide, sand and other safe chemicals are also equally advocated and put to use for firefighting but all these technologies are not free from limitations. Different types of fire extinguishers based on the use of water, foam, CO2, CFCs and dry chemicals are commonly used for fire control. Fire extinguishers made compulsory in all offices, educational institutes, trains and all other places where ever there seems to be any remote possibility of fire out breaks. Knowing all the constituents of a fire and various kinds of fire-extinguishers, we have to fight a fire, depending on the circumstances, so have to decide as to what method/strategy of firefighting would like to be used. However, all these firefighting devices are not at all found to be fit and effective fire fighting devices because many a times they (fire extinguishers) are out dated without any materials left for use or people are not trained to handle them or due to their low capacity. Moreover, these fire fighting methods are prone to creating environmental pollution and are costly also. Large fires are sometimes controlled by back-firing. A back-fire is a second fire built and so directed as to run against the wind and toward the main fire. When the two fires meet, both will go out on account of lack of fuel. When properly used by experienced persons, back-fires are very effectual. In inexperienced hands they are dangerous, as the wind may change suddenly or they may be lighted too soon. In such cases they often become as great a menace as the main fire. Another practical system of fighting fires is to make fire lines around the burning area in order to isolate the fire area from its surroundings. In the centre of the lines a narrow trench is dug to mineral soil or the lines are plowed or burned over so that they are bare of fuel. Such lines also are of value around woods and grain fields to keep the fire out. They are commonly used along railroad tracks where locomotive sparks are a constant source of fire dangers.
Firefighting with sound waves
While the concept of using sound waves to extinguish flames is not new, previous attempts to realize the principle – including efforts by teams at West Georgia University and the US Defense Advanced Research Projects Agency (DARPA) – had not been successful. Recently, there is a new development towards the use of sonic fire extinguishers making use of sound waves (longitudinal waves) with compressions (high pressure) and rarefactions (low pressure) zones as effective, no-polluting and cost effective firefighting technology. This article presents the principle, working, latest developments and advantages of sonic fire extinguisher. The principle behind the extinguisher is simple: as they are mechanical pressure waves that cause vibrations in the medium in which they travel, sound waves have the potential to manipulate both burning material and the oxygen that surrounds it. If the sound could be used to separate the two, the fire would be starved of oxygen and, accordingly, would be snuffed out. The work could potentially be applied to swarm robotics where the device would be attached to a drone to be used in situations such as large forest fires or urban blazes, thereby improving safety for firefighters.
Seth Robertson and Viet Tran – both final-year undergraduates at George Mason University in Virginia, US -elected to explore the concept, developing a series of prototype sonic extinguishers for a research project. Since sound is made up of pressure waves, it can be used to disrupt the air surrounding a fire, essentially cutting off the supply of oxygen to the fuel. At the right frequency, the fire simply dies out, as researchers recently demonstrated with their sonic extinguisher. Apparently, bass frequencies (the basic frequency range of the bass: 40Hz-400Hz-4000Hz) work best. Tran and Robertson explored the impact of different frequencies of sound on small fires. They tried ultra-high frequencies, such as 20,000 or 30,000Hz (Hertz, or cycles per second), and could see the flames vibrating but not going out. They took it down low, and at the range of 30 to 60Hz, the fires began to extinguish. The goal was to create something portable and affordable like a fire extinguisher that would generate the sound wave at the correct frequency, which they were able to do with the help of an oscilloscope that measured the waves. They connected their frequency generator to a small amplifier and linked the amplifier to a small electric power source. These are hooked up to a collimator that they made out of a large cardboard tube with a hole at the end, which narrows the sound waves to a smaller area.
Whenever the acoustic field’s power is increased, so too, will the air velocity register a higher figure – which in turn thins the area of the flame where combustion occurs, where in scientific circles is called the “flame boundary.” The moment the flame boundary area is thinned, life gets much easier to extinguish the flame. Not only that, the acoustics have another job on hand which our eyes are not able to see – it disturbs the pool of fuel in order to create a higher level of fuel vaporization which will help widen the flame. This thins out the flame for it to be less concentrated, and subsequently, cool enough to extinguish. While ultra-high frequencies had little effect, the duo found that lower, bass frequencies – between 30 and 60 Hz – produced the desired extinguishing effect. At that rate, the waves move the air around them in such a way that they disrupt the rapid oxidation at the core of a fire. The process essentially separates the oxygen from the fuel source and quickly extinguishes the fire. The technology has been tested as effective on alcohol-based fires, and the team is working on figuring out ways to disrupt other fuel sources, like wood, oil, or fabric. Having acquired a preliminary patent application for the design, the researchers are now hoping to move onto further testing and refinements of their extinguisher, with the aim of taking steps towards a potential commercial application. Originally, Robertson and Tran envisaged their device as ideal for use on small fires in the home – for example mounted over a stove top – but are now investigating the possibility of applying the principle to broader applications. One possible use could be in space, where traditional extinguishing agents are hard to focus at a target fire. In space, extinguisher contents spread all over the place. But sound waves can be directed without gravity. Forest fires could one day be dealt with by drones that would direct loud noises at the trees below.
Success has been down to the determination and willingness to try many different approaches to harnessing sound waves that the current prototype has been the result of many trials and experiments. Consisting of an amplifier and cardboard collimator to focus the sound, the duo's final extinguisher prototype – which cost them only about $600 to develop – is a hand-held, 9 kg, mains-powered device with the capacity to quickly put out small, alcohol-fuelled fires. This new type of extinguisher uses sound waves to put out fires is chemical- and water-free and the invention offers a relatively non-destructive method of fire control. So far they have put out only fires started with rubbing alcohol – and to continue to refine their device. Although they originally conceived of the device as a way to put out kitchen fires and, perhaps, fires in spacecraft, a local fire department already has asked them to test their bass waves on a structure fire; they think the concept could replace the toxic chemicals involved in fire extinguishers.
Bottlenecks of technology
One of the problems with sound waves is that they do not cool the fuel so even if we get the fire out, it will rekindle if we don’t either take away the fuel or cool it. Further, a possible complication may lie in the heat inherent in larger blazes. As the sonic extinguisher contains no coolant, it may be unable to prevent larger fires from reigniting after the sound is turned off. The project also would have to address different types of fires - solid combustibles such as wood, paper or metals, or electrical equipment - and keep a fire from reigniting.