In the Lab with Origin and Cause: Destructive Examinations
September 19, 2022
In May 2016, we set up a fire during a conference in Kingston, Ontario. The aim of this was to demonstrate our non-destructive and destructive testing processes during fire investigations. Here, we are taking you through our investigative process, with images from the scene and the different examination stages.
The fire incident
Figure 1: Live footage of the kitchen showing onset of the fire. Footage source: The International Association of Arson Investigators, Ontario chapter.
The area of origin in the kitchen was a heating element on the electric range. Figure 1 shows a flame starting to appear inside the pot. The vapours from the oil were heated sufficiently enough to cause ignition of these vapours.
There was visible smoke damage at the top layer of the kitchen area. The flames are not initially very big. But as the fire progresses, the smoke starts to layer down and lower into the room. If the smoke starts to migrate from the kitchen to another part of the house, people sitting in that area should start to detect the odour of smoke.
The flames intensified as the oil heated up, and the smoke damage became even more severe as the fire progressed.
Figure 2: Progression of the fire.
The flames were impinging on the underside of the kitchen cabinet directly above the electric range.
Figure 3: The flame, right before the fire was put out.
At this point (figure 3), some of the oil has probably progressed to the top of the electric range. There is more smoke damage layering up into the ceiling of the room. However, it took a few minutes for the oil and the vapours from the oil to ignite to a stage where the intensity of the flames encompassed the entire area above the electric range.
Within seconds, the entire area above the electric range was engulfed in flames, which started to link up to the ceiling space.
Conducting the examination
We first took a photograph that shows an overall view of the kitchen area where the electric range was located.
Figure 4: The overall view of the scene.
Figure 4 shows all the items that potentially contributed to the fire in the original locations – the stove still in the corner and the pot on the rear left surface top heating element. There are very clear burn patterns on the sidewall, the wall behind the electric range, and the kitchen ceiling space.
Figure 5: A front view of the electric range.
Figure 5 shows that some of the damage in the kitchen area includes the surface of the painted ceiling. There is a V pattern extending above the electric range, which shows where the fire damage is located.
Figure 6: The damage sustained by the ceiling.
The kitchen cabinets directly above the electric range were also affected by scorching and fire damage.
Figure 7: A close-up of the top cabinets.
We typically take a photograph with the cabinet doors open to show that there was no fire inside the kitchen cabinet. Here, we took another up-close photograph of the surface top of the electric range with the pot still in place.
Figure 8: The range, with the pot on top.
There were some discoloured patterns on the surface top. The yellowish stain shows the remains of the oil that spilled over. There were two other appliances in the kitchen. We took another photograph showing these appliances. These items need to be eliminated as potential ignition sources during the investigation.
Figure 9: An overall view of the control area for the electric range.
You’ll notice some burn patterns on the range; there’s more damage on the left-hand side of the electric range than on the right side.
Figure 10: Close-up photographs showing the controls melting (left) and completely intact and unaffected by heat damage (right).
Why investigate a cooking fire?
There are several reasons for investigating cooking fires. First, you need to make sure that the cooking fire wasn’t a result of a manufacturing defect of the appliance that was the subject of the fire. Additionally, an investigation is required to determine liability in apartment fires involving a tenant and a landlord.
Another reason for investigating these fires is corroborating witness statements. It’s very important to obtain witness statements that tell us about their observations during the incident.
Suggestions of a malfunction of the equipment.
If someone mentions that the equipment hasn’t been functioning correctly, it’s very important to bring the equipment back into the lab. This ensures that it can be examined to corroborate whether that is correct.
- Technical verification of a suspected cause for a failure
A failure might have happened to cause a fire. One of the most important things is to try and determine what that failure is and why it occurred.
- Improper installation of a device
We often come across equipment installed improperly, and bringing the equipment into the lab may corroborate that fact.
- Improper use of equipment
- Process of elimination
When looking at equipment involved in a fire, it may need to be eliminated as a cause. For example, although the range appeared to be the obvious cause of the fire, it is crucial to eliminate other nearby appliances as potential ignition sources.
Steps of lab investigations
We conduct our live examination in two ways – destructive and non-destructive examinations.
The reason for a non-destructive examination is to avoid the spoliation of evidence. We need to preserve the evidence so that all interested parties have the opportunity to examine the evidence. Furthermore, a non-disruptive examination provides credibility.
This process involves four steps. Namely:
- Visual inspection
- X-ray technology
Non-destructive testing: Example
In the case of our conference illustration, non-destructive testing of the electric range was conducted. Our forensic team looked at the surface top elements, documented them, and pulled them out of the sockets.
Figure 11: Removal of the elements.
Our investigators looked at the ends of the surface top elements and documented the positions of the Zinc pins for the stove controls. The zinc pins go into the infinite control or the stove control itself, which is how you operate the stove.
Once all the front components are documented, the investigator can examine the rear of the stove. If the stove is in decent condition, we document the removal of the stove control panel and the main panel.
After looking for obvious electrical failures, we capture an X-ray image of the stove. After removing the covers, we can also document the terminal block responsible for distributing power throughout the electric range. We also document the broil elements wiring and the wiring servicing each stove control.
Depending on the stove’s condition, we may have to shoot an x-ray to determine the positions of the controls and/or look at the cam position. After the visual inspection of the units, we then contact the client to report our findings. Our report involves a list of parties or people they may want to notify to pursue possible subrogation. A destructive examination is conducted at a later date when all the parties have been notified.
X-ray imaging of the components
This is the second step of the visual examination. Due to the fragility of some of the exhibits, we sometimes bring them in, and we have to remove the x-ray tube and x-ray the exhibit in situ. We do this by pointing the tube at the component we wish to examine – in this case, the stove controls.
Figure 12: The x-ray setup for the range controls.
Here, we affixed the imaging plate to the rear of the stove. Once all the necessary elements are in place, we safely clear the area and generate x-ray images. Once that x-ray is developed and reacts with the film, we take that film, put it inside our scanner, and process the image. We also use this technology within the x-ray booth. The booth is set up to carry smaller appliances, such as coffee makers, toasters, duplex receptacles, and power strips.
Examination of the coffeemaker revealed that it did not sustain any electrical failures. This fact was affirmed by evidence of fire exposure damage to one side of the appliance. However, we conducted an additional x-ray examination to confirm that no internal electrical failures could have occurred.
Figure 13: X-ray images of the side (left) and top (right) profiles.
The x-ray images of the stove controls confirmed that the stove was off. Upon reaching this conclusion, we contacted our client to notify them of our results.
Figure 14: An x-ray image of a power strip.
We can also use x-ray technology to identify electrical failure in components such as power strips and receptacles.
The fourth step of non-destructive testing is noticed. At this point, we have completed the unit’s visual examination, conducted the X-rays, and identified the potentially interested parties. We then contact our client, and it is the onus of our client to contact the interested parties so that we can arrange a destructive examination.
At this stage of the investigation, all interested parties are present and participating in the destructive examination. They are taking their photographs and notes so they can conclude regarding this appliance’s involvement in the cause of the fire.
We start by examining the surface top elements. We also look at the switches to determine whether they have been turned on or off. After that, we take off the back panels to examine the electric range’s electrical and internal control components.
We examine the switching mechanisms on the more damaged side of the electric range and take photographs as we go along.
Figure 15: Initial stages of destructive testing.
We also take photographs of the undamaged or less damaged side for comparative purposes. Typically, we go from the area with the least damage and move toward the most damaged area. Here, we took off the control knobs, identified the position of the stem for the controls, and compared them to the more damaged ones.
Removal of the control knobs allowed us to identify the rotational position of both switching mechanisms. By comparing the controls, we observed that the upper control was in a different rotational position than the three others. We then took photographs to document that condition.
Figure 16: A close-up of the damaged control knob.
We also want to ensure that the electrical wiring and controls in the back of the range are in good condition. If they are in poor condition, we need to examine them for evidence of failure or malfunction.
Figure 17: Removal of the back panel during destructive testing.
During destructive testing, we also look for evidence of fire damage to the controls or internal wiring to the electric range. The bottom portion of the electrical panel of the range shows the connections to the different heating elements. It shows some controls and the terminal block where the power cord attaches to the electric range.
Figure 18: The terminal blocks.
One of the things we first do is examine the power cord to identify evidence of failure or malfunction that may have contributed to the cause of the fire. In this case, there was no damage to the insulation material or the actual male plug for the electric range. There was virtually no damage to the internal wiring.
A certain position of the selector switches can be seen from the rear of the appliance. This position identifies the rotational position of the stem for the selector switch, which then controls the on/off condition of the heating elements.
Figure 19: The two switching mechanisms on the left side of the electric range.
Examining the switching mechanisms enabled us to corroborate the x-ray results, which indicated that the top selector switch was in an “on” position. After examining this, looking at the damage that’s not very apparent in the control area or in the wiring, examining the heating elements at the stovetop, and noticing the rotational position of the controls, it is easy to conclude that there is no evidence of failure or malfunction of the electric range.
We concluded that one of the surface top heating elements of the electric range had been left on and that this fire was a result of unattended cooking. The heating element was left unattended with a pot of oil on top, resulting in the oil being heated up to its ignition temperature, eventually igniting and causing this fire. The fire then damaged the electric range on the surface top, more so on the left side because that’s where the pot was located.