FIA7

FIR 4305, Fire Investigation and Analysis 1

Course Learning Outcomes for Unit VII Upon completion of this unit, students should be able to:

8. Analyze explosions and explosive combustion. 8.1 Explain key safety considerations when investigating clandestine drug lab or explosive fires.

Course/Unit Learning Outcomes

Learning Activity

8.1 Unit Lesson Chapter 3 Unit VII PowerPoint Presentation

Reading Assignment Chapter 3: Chemical Fires and Explosions

Unit Lesson Experienced firefighters and risk managers know that low-frequency/high-risk incidents present many difficulties for responders as the stakes are high, and we often lack experience in dealing with these types of situations, which can lead to unsatisfactory outcomes. This unit will cover the topics of explosions, chemical fires, and hazardous materials, which certainly meet the definition of high-risk and low-risk occurrences. We will not only look at the distinct nature and at features of these fires, but we will also focus on the increased safety measures that these situations require of the fire investigator. Investigating Explosions Safety is paramount when investigating a scene that could involve any type of explosive. The fire investigator must first verify that there are no secondary devices. The scene should be rendered safe by those with explosive ordinance training, such as by Explosive Ordinance Disposal (EOD) personnel or teams. The National Fire Protection Association (NFPA, 2017) recommends using specialists whenever explosives may be involved. Once the scene has been cleared for secondary devices, the investigator must determine if any structures involved in the incident are safe to enter and inspect. Here again, outside expertise may be required before proceeding with the investigation. The support of experts in building construction and/or structural engineering may be needed before entering a structure. An explosion is described as the sudden conversion of mechanical or chemical energy into kinetic energy. In an explosion, gases are produced and released under pressure (NFPA, 2017). Some explosions can be accidental, occurring as the result of mechanical defects or natural gas leaks. Some can be set to appear accidental, and some may be intentional as in a terrorist activity. In the intentional explosion incidents, special care must be given to ensure that there are no secondary devices aimed at first responders. In all three of the aforementioned scenarios, the safety issues regarding explosions remain the same. Please see Table 3-1 on page 187 in the textbook to review common types of explosives.

UNIT VII STUDY GUIDE

The Investigation of Explosions and Explosive Combustion

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The objective in an explosive scene examination is largely the same as in a fire scene, which is to determine the spot that the explosion originated from and then the cause. This is often further complicated by the size of the blast area, which often covers large areas, and fragments being thrown anywhere from several feet to miles away from the seat of the blast. The following video shows the violence that a natural gas explosion can muster. In Sun Prairie, Wisconsin, a 4-inch natural gas line was hit by contractors doing work in their downtown area. The resulting explosion, which was captured on a dashboard cam, resulted in 25 buildings being damaged, but more importantly, 13 injuries and a firefighter being killed in the line of duty. First responders had evacuated approximately 250 people from the area before the explosion. Please click the link below to view the video. Madison.com. (2018, December 20). Sun Prairie gas line explosion [Video]. YouTube.

https://www.youtube.com/watch?v=5Efo_Bsgs1I There are two characteristics of explosive damage: low-order damage and high-order damage. With low-order damage, which is created by a slower pressure rate, you will notice damage such as bulged out walls, roofs partially lifted, dislodged windows with the glass still intact, and large pieces of debris or fragments. With high- order damage, which is created by a rapid rise in pressure, the investigator will observe such damage as shattered wall and roof members, shattered debris, or fragments that are pulverized and thrown great distances. The smaller the pieces and the further they are thrown, the higher the energy of the explosion, combustion, deflagration, or detonation. There are seated and non-seated explosions. The difference between the two is very distinct. In a seated explosion, there is a crater or area in which the greatest damage can be found. These types of explosions are typically generated by boilers, explosives, or a boiling liquid expanding vapor explosion (BLEVE). In contrast, non-seated explosions occur when fuels are diffused or dispersed across a large area. Such explosions can reach subsonic velocities. This type of explosion was illustrated in the Sun Prairie, Wisconsin, video above. Vapors of such ignitable liquids or fuel gases are the most commonly encountered explosion. However, non- seated explosions can also be triggered by a workplace hazard as simple as dust. Many types of dust from organic materials such as flour, sugar, or wood, are just as flammable as inorganic dust sources such as paint, plastics, and pharmaceuticals. Click the link below to access a short video that explains this common workplace explosion hazard. Aurora Pictures. (2013, March 13). Combustible dust [Video]. YouTube.

https://www.youtube.com/watch?v=_bp9hGxPRlc

Click here to access a transcript for the video. Processing the Scene A preliminary search of the scene will often reveal the direction of the spread of blast fragments or the blast pattern and the seat of the explosion. The use of aerial drones to survey and document the scene from above are of particular use in explosive scene investigations. If you do not have access to a drone, the use of an aerial apparatus and news or law enforcement helicopters to photograph and record the scene would provide a much better overall view than ground photography can capture. As mentioned earlier, safety is paramount in these types of incidents, and a rule of thumb for a preliminary perimeter is 1.5 times the distance from the seat of the explosion to the furthest fragment. This may be adjusted as more information becomes available, but it is a good rule of thumb. The perimeter should be marked with scene tape, ropes, or barricades—just as in a structure fire. Technology is rapidly evolving in the investigative field, and we now have access to better tools to assist us in documenting these types of scenes. Total Station survey systems and 3D laser imaging instruments are now replacing tape measures and are more accurate and can pinpoint the position of evidence using GPS. Another aid to the investigator in these situations are the following mnemonics: the Four Rs and the Four Cs. The Four Rs are recognition, recovery, reassembly, and reconstruction. The Four Cs are container, concealment, content, and connections (Icove & Haynes, 2018). These are simple memory aids to help the investigator. The Four Rs are a way of keeping a scene search in logical order. The Four Cs remind the investigator what to examine and look for (i.e., what type of container, how or where it was concealed, what

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the contents were, what explosive materials were used, and by what method or connections [including any sequence of events] that could have caused the explosion). Dealing with Chemical Fires and Hazardous Materials The textbook suggests that, for numerous fires, hazardous material either starts the fire or, at some point, becomes involved in a fire. Of the two, it is more likely that hazardous material was involved in the ignition of the fire, causing it to burn more intensely due to hazardous material being involved. Fires involving a hazardous material can also increase the fire spread rate and make the suppression efforts even more dangerous. Hazardous gases, liquids, and solids are commonly found within any structure. Natural gas and liquid propane are among the most common gases found in residential structures. Many residences heat or cook using one of the aforementioned gases. Consider the vapor density of these gases when investigating a fire where they are possibly involved. For instance, two of the most common gases encountered are natural gas and propane. Natural gas is lighter than air, and propane is heavier than air. What does this mean for the fire investigator? When examining a scene where either of these gases could have been involved, consider possible ignition locations either near the floor level or slightly higher. For example, an ignition source for propane would more than likely be at or near floor level since propane, being heavier than air, will sink toward the floor. Fire investigators will come across even more hazardous liquids than gases during an investigation. Flammable liquids can become more volatile and explosive when exposed to the high temperatures of a structure fire. Because flammable or combustible liquids, such as cleaning solvents, mineral spirits, or similar liquids, are so common in both residential and commercial buildings, extra attention should be paid to verify that these, in fact, belonged in the building at the time of the fire; if not, then an intentional act may have occurred. Due to the ease at which drug manufacturing supplies can be obtained, more and more explosions and fires are occurring at surreptitious methamphetamine labs. These drug manufacturing sites can be set up anywhere—from a bathroom of an occupied residence, to the back of a station wagon, or in an abandoned structure. These types of explosions and fires require extra vigilance, and you should always beware of their indications when investigating a fire. Some hazardous materials used in manufacturing these illegal drugs could include ammonium nitrate, lye (drain cleaner), lithium (lithium batteries), anhydrous ammonia (liquid fertilizer), ethyl ether, or white gas. Not only are these materials fire hazards, but they also may prove dangerous, even after being involved in a fire. Use extreme caution when in these environments. Some jurisdictions have designated units or teams that specifically deal with these clandestine labs; they can assist in identifying them and will handle dismantling and disposing of the remaining hazardous chemicals.

References Icove, D. J., & Haynes, G. A (2018). Kirk's fire investigation (8th ed.). Pearson. National Fire Protection Association. (2017). NFPA 921: Guide for fire and explosion investigations.