Why arson evidence is packaged in metal cans
Forensic investigation into fires is conducted right after the fire brigade has extinguished the fire and the scene has been declared safe for entry. Fires can fall under various categories natural, undetermined, deliberate, or accidental. Deliberate fires, are also referred to as arson and are of the greatest significance to the investigator (Saferstein, 2010). The FBI (Federal Bureau of investigation) has defined arson as, “Any willful or malicious burning to attempt to burn, with or without intent to defraud, a dwelling house, public building, motor vehicle or aircraft, personal property of another, etc” (Reid, 2011). The first stage of an investigation involves finding the cause of the fire and its origin. During the collection of evidence from an arson scene, the evidence is packaged in airtight metal cans (Reid, 2011).
One of the reasons for this is that some of the evidence collected may still be hot. If they are placed in other containers such as plastic or envelope, they might burn the containers and render crucial evidence irrelevant. The melting point of metal cans is high and, therefore, there will ensure there is no spillage if the forensic investigator collects a sample of flammable liquid from the scene. Metal cans are also important in the collection of arson evidence because they do not contaminate the evidence collected. The airtight lid on the metal container will help in preventing further oxidation of the sample as this can destroy evidence (Saferstein, 2010).
The differences between high and low explosives
There are two types of explosives: the high explosives and the low explosive. The high explosives are also referred to as detonating while the low explosives are also known as burning mixtures. The main difference that exists between detonation and burning is that in burning the mixture will burn at a very fast rate and will need to be ignited to produce an explosion. On the other hand, detonation occurs instantly and does not need to be lit to produce an explosion. Chemically, the difference between the two is the proximity of oxidizing and reducing compounds. Detonating mixtures require little external energy to break them apart and cause an explosion. Unlike the burning mixture, they contain molecular bonds that require little energy to break. This is a result of having the oxygen very close to the reducing agent in the detonating mixture and therefore can easily be used. In the low explosives, the bonds are very strong and require a lot of energy to break them. This makes them require external sources of energy to produce an explosion (Siege & Houck, 2010).
High explosives do not need to be confined so that they can explode as is the case with low explosives. High explosives require just a small force to explode that is offered by a detonator or a blasting cap. Low explodes require a lot of force to explode, which is provided by the fire where it is ignited. Both explosives have also different explosion velocities. The high explosives are known to have shattering power, while the low explosives are known for their heaving power (Siege & Houck, 2010).
The high explosives undergo a chemical reaction through the explosive material at very fast speeds, which are higher than that of sound through the same substance. The speed in the low explosives is generally lower than that of sound through the same substance (Siege & Houck, 2010).
References
Reid, S. T. (2011). Criminal Justice Essentials. Chichester, West Sussex ; Malden, MA : Wiley-Blackwell.
Saferstein, R. (2010). Criminalistics: An Introduction to Forensic Science. Upper Saddle River, NJ : Prentice Hall.
Siege, J. A. & Houck, M. M. (2010). Fundamentals of Forensic Science. Burlington, MA : Academic Press.