Forensic Chemistry: Detection of Odorless Accelerants at a Fire Scene - Assignment Example

Forensic chemistry Question 1: detection of odorless accelerants at a fire scene No. This is not the case as there are various methods of forensic analysis of fire debris that do not necessarily depend on smell. Preparation of the samples used to experiment the used accelerants range from solvent extraction, distillation of steam to solid phase micro extraction. All these methods are mainly coupled with gas chromatography. In view of these, the forensic analyst aims at getting the patterns realized rather than the specific compounds that were used. From this argument, it is clear that the odor of the accelerants makes little sense in gathering the forensic evidence as such will be gathered from the used patterns more easily. Question 2: Features of a deliberate fire incident and the difference between the deliberate incident and an accidental fire scene There are various features or indicators of deliberate fire or arson. The most common is the presence of fuel as arsonists will always need an accelerant to speed up the burning process. Some other indicators can arise from the status of the doors and the windows. It is common to find them propped open as a way of ventilating the house to speed up the burning process. In the case that the windows and the doors are found blocked, there is a likelihood that the persons involved attempted to conceal the fire before it could be realized. If the happens are in a business location, missing stock in the business may indicate arson. This is raised from the fact that there would still be stock in the building if the fire was accidental. In case that the fires are in a business or a home, the owner can be liable of an insurance fraud in he happens to have had debts. Above all the discussed features of likely fire indicators, accelerants are the most likely indicators. In the case of arson fires and the when the fires are caused by an accelerant such as gasoline, the poured of accelerant, depending on its depth insulates the substrate. This limits the temperature increase in the substrate. Owing to the fact that the accelerant cannot burn beyond its boiling point, it scorches at a certain point. Question 3: Fundamental behaviors of physically unrestrained fires Physically unrestrained fire occurs when there is free reaction of the radicals. In such a case, the generic steps that are followed by the fire are as follows: - Initiation: this is the formation of the radicals in the following manner; CO + O2 -> CO2 + .O Propagation occurs when reactions by the radicals against each other result to production of more radicals; .O + H2O -> .OH + .OH, CO + .OH -> CO2 + .H Termination occurs when two free radicals combine to form neutral species; .H + .OH -> H2O Question 4: Volume = 2 X 2.5 X 3m = 15m2 Using the ideal gas equations, one can get the mole equations PV = nRT Where P = 1atm, V = 15m3 = 15, 000 liters, N = number of moles, R = (0.082atm*L)/mole*K T = (20 + 273) *K From the above values, we substitute to get n, N=PV/RT PV= 1 atm * 15, 000L RT = ((0.082atm*L)/mole*K)*( (20 + 273) *K) = 0.082atm L/mole N = 15, 000 atm L/ 0.082atm*L/mole 182926.83 moles 1mole = 44 grams The amount of propane = 8048780.48 grams Rate of discharge = 100grams per hour Time taken = amount / rate = 80487.8 hrs b) If the atmosphere is 0.89, the time taken will be less. The more the pressure, the more the propane will tend to be concealed to the container and thus take more time to spread. c) I relation to the figure in the textbook, it is necessary that one takes into consideration the shape of the room, the source of the gas and the location of the source. These three will tend to have an impact on the spreading of the gas. Question 5: The power of an explosive is given by the explosive index of that material. This is given by the following formula: QVexplosive/QCpicric acid *100 From this formula, it is evident that the material with the highest QVexplosive in figure will have a higher power index and thus will more likely be the most powerful. Therefore, the most powerful material is C2H5OH(l) -277.7 Question 6: Dry Ice Bomb It is possible to make a bomb out of dry ice alone. This is made possible by using the procedure outlined hereby; get some dry ice and break it down into pieces that can fit in a bottle neck. Put the pieces in a plastic bottle and pour some water to cover the ice fully. Close the bottle tightly and put it at a distance. It explodes after some time with a loud sound. The bomb explodes in 10 to 30 seconds. Question 7: propellants The speed of a bullet is given by: - V = sqrt (2mpQn/mb); Where, mp is the mass of the propellant in grams Qn is the heat evolved per gram of a propellant, mb is the mass of the bullet in grams heat of combustion of nitroglycerin is 364KJ/mol Assuming 65% heat transfer, the total heat transferred is 65% of 364 = 236.6KJ/mol; 1 gram of nitroglycerin = 0.0044 moles Heat evolved will be 236.6/0.0044 = 53772.72KJ, V= (53772.72 *1000*0.75)/2.15 V = 4331.04m/s Question 8: silencers Silencers are also called suppressors or moderators as they are basically used to reduce the level of noise being discharged from a firearm. The moderator consists of some coupled baffles attached to a tubular chamber and fixed at the end of a barrel of a fire arm. A fire arm’s noise is made up of two basic components. The primary noise is from the immediate and fats expansion of the propellant gas as it leaves the muzzle of the gun. The second noise comes from the crack of the bullet that happens at a supersonic speed. In real sense the supersonic bullet cannot be controlled. The silencer acts to control the noise level from the bullet by controlling the expansion rate of the propelling gases. Effective silencing requires that the ammunition travels at a lesser speed when compared to sound. This makes the noise level controlled to an extent that one will not take it to be a gun. A gun that has been fitted with a silencer cannot therefore be used to conceal evidence. This is from the fact that the action of suppressing the sound does not have an effect on the discharged gas as it only controls the rate of expansion. The matter that would be collected for evidence analysis is still maintained in the firing of the weapon. References Suzanne, Bell (2006). Forensic Chemistry Pearson/Prentice-Hall. Read More