Burning Profile of Cigarettes - Article Example

Question One: The ability of cigarettes to ignited different materials in different situations? How cigarettes burn? Cigarettes are made of tobacco, combustible paper, and filter on the other end. Its burning its burning behaviour depends on the type and brand. Scientifically, the burning profile of cigarettes includes smouldering for about 30 to 40 minutes before the affected material burst into flame. Smouldering can occur at very low oxygen concentrations and progress at very slow rate. Heat from the glowing combustion zone (the burning end of the cigarette) can be from 600 to 700 degrees centigrade at its char the tobacco and releasing distillation and pyrolysis products. At the cigarette burns, the tobacco adjacent to the glowing front becomes almost pure carbon. The amount of air flow can significantly increase smouldering rate by up to ten times resulting to flame. However, fires that originate from smouldering require specific conditions to develop. For instance, smouldering from the burning end of cigarettes requires a pile of materials that are not only susceptible (piles sawdust, corrugated cardboard, celiulosic fabrics such as cotton or rayon, baled cotton, and other) but in firm contact. For example, cigarettes landing on a typical carpet with only generate a small burn around the burning tip of the cigarette. Similarly, fire is unlikely when a cigarette lands on a sheet of paper because it will only result to slight localized charring. In waste bin, regardless of the amount of torn and crumpled paper, a burning cigarette can only produce minor smouldering fire that can last for several minutes. However, smouldering may be longer for materials such as absorbent tissue. In bed, smouldering fire caused by a cigarette seldom occur in sheets only because the ignition source of bed sheets is a flame and the combustion type is flaming combustion. Similarly, quilts and pillows made of polyester cannot be ignited by cigarettes neither place under nor on the quilt under a polyester-cotton sheeting material. However, double sheet and bed scrambled up will ignite as the cotton, the most commonly used cover fabric material resistance to cigarette is poor. Smouldering spread quickly in cotton filling while less dense foam has less resistance to cigarette. However, cigarette resistance is high when the fabric is tensioned very tight because it decreased the connection area between the fabric and the filling. In sofa and other furniture, cigarettes can smoulder at 700 degrees centigrade in about 30 to 60 minutes resulting t In petrol and contrary to common belief, glowing cigarettes cannot normally ignite this flammable liquid because petrol has 5.9% value at the upper flammability limit suggesting high oxygen requirement for ignition. The amount of oxygen in the glowing or burning tip of the cigarette is not enough to ignite petrol. Question Two: What is spontaneous combustion? It is a combustion process where a chemical reaction (exothermic) takes place internally of the materials producing heat under different circumstances. Auto ignition without flame occurs when heat from such materials reached a certain temperature enough to ignite the material or nearby combustibles. These materials include hay and straw, oily rags, dust accumulations, and others. Oxidation is an exothermic reaction and since the rate of a chemical reaction (combustible materials and oxygen) increases for each 10 degrees centigrade, it will generate heat at a rate faster than natural ventilation can disperse. However, when oxidation takes place on the surface of a solid or liquid then the heat that is generated will be lost to the environment by convection. In contrast, if the material has a large surface area to volume ratio then heat production is greater while heat loss is reduced (thermal runaway) due to the insulating effect of its bulk. Consequently, provided that oxygen is sufficient, internal temperature of the material will rise until there is no longer a balance between heat production and heat loss and the material ignites. Self-heating is common in solid fuels and although some materials are capable of self-heating they do not necessarily ignite as there should be thermal runaway before self-ignition can occur or when heat generated is greater than the of amount of heat loss (heat loss coefficient). It usually occur at the centre of the fuel package. Ignition resulting from self-heating often requires the following to occur: a. Surface area of the combustible material generates heat more than it can disperse. b. Lower ambient temperature c. Materials must be porous and permeable and capable of oxidizing and producing a char without melting d. Sufficient oxygen to support combustion e. Size and shape of the fuel package (round and square will sustain self-heating than large flat surfaces). f. Fuels with smaller surface are more likely to self-heat. Question Three: Locating the seat of the fire a. Recognise the need to use the scientific method There is a need to recognise the need to find the cause of the fire and identify objectives of the fire investigation such as the origin of the fire, materials that ignited and start the fire, how they come together and why, and so on. b. Define the problem There is also a need to define the problem because fire incidents are different and there may be some difficulties in locating the seat of the fire when there was a flashover. Investigator should determine the safety concerns to be addressed and the resources to complete the task. c. Collect data After the problem is defined, the data to be collected should be clear. Depends on the required data, it may necessary to interview witnesses to get an idea where the fire actually started, find and collect evidence of the ignition source, fire behaviour and dynamics, and the amount of fuel load. The data collection should be systematic, documented, and concern about preservation of evidence for future testing or legal presentation. Find physical evidence, fire patterns, fuel load, ventilation, building construction, and other facts. Collect debris samples for lab test and document witness statements. d. Analyse data Data collected should be analysed utilizing scientific method. Factual information from blood samples, finger prints, and others should be extracted systematically. e. Develop hypothesis The investigator should develop an informed hypothesis based on the evidenced gathered and result of data analysis then proceed with hypothesis testing. f. Test hypothesis Testing hypothesis is generally confirming the current hypothesis with existing scientific knowledge and drawing conclusions that can withstand legal and scientific scrutiny. g. Select final hypothesis Final tested hypothesis should be selected and reported in written or oral forms. Question Four: There is some technique to find the origin of the fire. Time and Temperature Techniques In relation to finding the seat of the fire, finding the origin of the fire can be done by time/temperature depended techniques. In other words, this can be achieved by the finding the area with the greatest damage or where the fire burn the longest. However, this technique does not always work because assumption that area where the fire burns the longest is the origin of the fire can be invalidated by the fact that fires in some areas were extinguished last. Moreover, it is not always true that an area with greater damage is the origin of the fire because extent of damage is determined by the amount items or materials susceptible to burning. For example, a fire can start in the bathroom (where little damage can be done) and spread in the living room where large amount of combustibles are available. Ventilation can also affect the extent of damage as fires in compartment are dependent on oxygen passing through the vents. For example, a fire occurring in a well-ventilated may be more intense and has greater damage than those fires occurring in areas with limited ventilations. More importantly, characteristic of the fuel package can greatly impact the extent of damage and duration of the fire and therefore areas with greater damage is not necessarily the origin of the fire. In effectively determining the origin of fire, it may be necessary for investigators to instead look the depth of char, spalling of plaster, damage of floor concrete, distortion in steel beam, and other temperature indicators. This is because temperatures inside the compartment can yield a number of interesting facts about the previous fire. For example, the variations in the depth of char show the direction of fire travel and therefore can be used to trace back the area of fire origin. Other temperature indicators that might be helpful are the patterns left on the furnishings. For example, a chair with more damage on one side indicates the side where the fire travelled. Similarly, melted metals indicate a certain temperature that an area reached during the fire. Geometrical Techniques Flaming fires often burn upwards and outwards at a much greater rate than they burn down and therefore it is helpful to look at the lowest area of burning with the structure. However, this may be complicated by structural collapse and others and therefore not applicable in all situations. Fire patterns on walls and floors can be of great value (provided there was no flashover) to determine the origin of the fire. For example, a V pattern on the wall indicates that fire spread up and out from something at the base of the V. At any time in the investigation, the investigator locating the origin of fire may call other specialist such as forensic scientist to assist in the investigation. These include engineers, chemist, electricians, mechanics, and the like who have the expertise to determine the cause and origin of fire. Once the area of origin is established through fire patterns and other geometrical technique, fire investigator can now excavate and remove the superficial layer of debris that has accumulated as the fire progressed. Excavation may yield valuable information about the disposition of objects and items of furniture or materials in the compartment before the fire occurs. Finally, the investigator may create a fault-tree diagram where logical sequence and position, the conditions and chains of events that are necessary for a give fire to occur. Human Indicators Technique Information from eyewitness can be of great help in investigation as they can tell the area where fire was seen first. Similarly, if there were victims, the position bodies can tell where the fire was coming from. The observation of fire fighters are also essential and can help in determining the characteristic of the fire, its direction, and severity. There may be some instance, that some witness tell about some strange activities or people behaviour in the area where the fire occurs or investigator noticed some strange behaviour when he is interviewing a witness or occupants of the building. Similarly, photo and videos related to fire can help the investigator develop his hypothesis about the actual fire. Interactive Indicators Indication of forcible entry, presence of incendiary device and accelerants can lead investigator to examine the possibility of arson. Similarly, investigator can also look for the arson if there was disturbance in the area before the fire. Question Five: Arson Arson is in general deliberate fire-setting that can be either wilful or milieus. Reasons for Committing Arson People usually commit arson for profit. For example, a business near bankruptcy, unable to complete business contract and others that wants to get large amount of insurance money. Arson can occur due to vandalism or to cause damage for its own sake. Vandalism often occurs in schools, abandoned structures, vegetation, and trash containers. The fire setter is often living near the area of fire-setting. Arson can be political as a result of extremism. For instance, setting fire on institutions and business that were ecologically damaging, business with labour disputes, and groups wanting create chaos in order to advance their cause. Arson can also result from excitement of the arsonist who in a way is looking for thrills, attention, or recognition. It can also arise from the need to obtain recognition for discovering or extinguishing the fire that he himself set. Arson to conceal a crime such as business owner destroying records showing embezzlement of cash, supplies, supplies, inventory, and others. Burglars setting fire to high fingerprints or conceal the fact that theft occurred. Signs of Arsons Accidental fires never start in different places at the same time and therefore if there are multiple origin of fire then the possibility of arson are high. Arsonist intentionally set multiple ignition points to maximise fire growth, cause confusion, and trap building occupants by blocking access to all exits. Similarly, if the fire started in the most improbable place then it is likely deliberate. There will be some smell of flammable liquids such as kerosene as well as accelerants or agents used to initiate a fire and increase the rate of fire growth. Finally, investigators suspecting arson may notice some unexpected fire behaviour such as unusual fire growth and spread and other factors that indicate intentional fire such as disable fire sprinkler, alarm, and others. What and how to collect? Advantage and disadvantage Primarily, the investigator must consider looking at the video or photo of the fire if available as these has the advantage of telling what actually happen in the fire incident. However, these can be of no use when they are too bright or too dark, quality is poor, and filled with background noises. Investigator can also take note of important details in the fire scene as such information is vital to the investigation but the fire scene is usually wet with water from fire fighting still dripping from upper part of the structure. Similarly, it may be difficult to write in a newly burned building (smell, charred materials, collapsed structure, and others) thus notes may end up unreadable. Laptops can resolve this writing difficulty but electronic equipment is also vulnerable to water and heat. It may be more effective to take photos or video (just ensure quality), measurement, gather samples for lab test, and other convenient means to avoid difficulties in fire ground data collection. Question Six: What is dust explosion? Primary explosion Primary dust explosion often occurs in an enclosure (usually light gauge metal) where dust is airborne and in an atmosphere containing sufficient oxygen for combustion with right ignition source. The burning dust particles, flames, and hot gases generate pressures strong enough to rupture the enclosure and expand resulting to a dust cloud that can be ignited by the original source of ignition or by the combustion products of the primary explosion. Secondary explosion Secondary explosion is the result of the primary explosion or the expansion effect mentioned above. Secondary explosion can be catastrophic as the pressure waves being transmitted throughout the plant building can result to structural collapse. Moreover, flames from dust explosion can reach longer distance resulting to fires outside the vicinity of the primary explosion. Question 7: Overcurrent protection devices: Fuses and Circuit Breaker Fuses are usually designed to protect a device and the function with two current rating. One rating is the current value at which they will disconnect from the supply while the other is the current value at which they can operate safety without damaging the equipment they are connected. However, it will take several minutes for the link to melt if the over current is less than 1000 amperes thus it is important to select the correct the overcurrent device. For instance, if the circuit of equipment is protected by 15 ampere fuse and there is 16 amperes flowing in the circuit, the link will not melt quickly to disconnect the circuit from the supply. For this reason, the operator of that equipment may be already shocked before the circuit breaks. Residual current breaker Residual current breaker responds more quickly than a fuse or circuit breaker when a fault in the circuit occurs. This is because it can detect very small (as little as 30mA) changes in the current in the live and neutral wires and breaks the circuit immediately. Moreover, if the current escape down the earth wire, current in the live wire will be different from the current in the neutral wire and therefore trips and switching everything before anybody gets hurt. Read More