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Jun 2022

Laser scanning to pinpoint the seat of a fire

Source: Asia Insurance Review | Jun 2022

Andy ChooThis article shares my experience in using laser scanning technology for traffic crash reconstructions and how it can be applied across a broader range of investigations. It was the knowledge gained from the crash reconstruction industry that led to the ‘ah-ha’ moment, in retrospect. In essence, had I used a 3D laser scanner at the outset for one of the fires that I had investigated, I would likely have been able to find the seat of fire or area of fire origin with a great level of certainty, says EFI Global Asia’s Mr Andy Choo.
 
 
While with the Singapore Civil Defence Force, I witnessed the adoption of ‘new’ technologies for fire-scene documentation. This included advancement from the analogue (film) camera to the digital camera including the use of a particular panoramic rotating-line digital camera called the Panoscan. Significant fires would be ‘Panoscanned’ as our fire investigation team wanted to ensure the full documentation of burn patterns, effects and the aftermath of the fire at the determined area of fire origin, as well as the unaffected spaces.
 
The post-stitched image from the Panoscan was like a virtual reality movie, allowing for a spatial appreciation of the scene, and enabling the investigation team to corroborate statements given by witnesses of the fire.
 
The fire
One of the memorable fires that I investigated was a fatal fire that resulted in the loss of two lives while another family member suffered a broken limb due to him jumping from the second floor to escape from his burning room. The two-storey semi-detached house was badly burnt, and it took the responders about two hours to extinguish the fire. The extent of damage was so severe that the typical reading of burn patterns and effects was impossible. It was an all-hands-on-deck case as I requested assistance from my fellow team leaders from other shifts. Despite the collective investigative experience of these team leads totalling about 60 years, none could agree on where the fire could have started.
 
It was only after canvassing the neighbourhood for witness interviews and footage recordings that we found a security closed-circuit television from a nearby unit that had captured the fire from the peripheral corner of its screen. The small image captured showed that the fire started on the ground floor within the general area of living room.
 
The ‘ah-ha’ moment
Fast forward some years later, it was upon joining the Health Sciences Authority’s traffic crash reconstruction team as a senior forensic scientist that I realised the usefulness of laser scanner for both documentation and investigative purposes. One of our capabilities was the ‘placement’ of an object that was photographed or filmed into a scanned virtual world (point cloud - a set of data points in space) to a good degree of accuracy. This special application methodology is called ‘camera matching’.
 
Upon scanning a crash site, the raw data would be processed with additional workflow using proprietary software, thus allowing us to place and match any captured images to the point cloud and work backwards to determine the position of the camera. Once the camera has been properly positioned in the point cloud, we are able to match any object in the photograph to the real world. More specifically, we are able to pinpoint the location of an object at a crash site. This allows us to determine the respective position of a person, motorcycle, or other vehicle involved in a crash at the time when the image or video was captured.
 
In retrospect, had we adopted and used the laser scanner and applied the methodology of camera matching, I would have been able to determine where the fire likely originated; this would have allowed my investigation team to narrow the focus to specific entities that might have been the possible source(s)of the ignition.
 
Laser scanning and other documentation tools
Laser scanning is a technology that employs lasers to measure an object’s geometry to craft a digital 3D model via imaging software. This technology, originally developed for the space and defence applications in the 1960s, was subsequently applied to historical preservation projects, architectural and civil surveying, mining and archaeological projects and the public safety industry.
 
3D laser scanning
 
It can capture 3D data of objects, regardless of their surface features or size. Given that the objects are scanned with lasers, they do not need to be physically touched to take precise records of the existing dimensions.
 
Other commonly used types of scene documentation tools include photography or videography via digital camera; sketches; rulers, measuring tapes; compasses; inclinometers; levellers; survey equipment; and photogrammetry.
 
Captured photo to match 3D world
 
Why laser scanning and not measuring tape
The selection of scene documentation tools depends on the requirements of the organisations and report outcomes. Investigators consider such factors as accuracy and precision requirements and the contributing weightage to the outcome findings in choosing which tool to use. The key is finding the right balance between the requirements and the cost of implementation.
 
For example, in a traffic crash reconstruction, it is necessary to document an undamaged vehicle that may have stalled or parked some distance away from the offending vehicle. It is likely that a digital camera and non-calibrated measuring tape would suffice because it would not have an impact on the findings for the calculation of the speed of the offending vehicle.
 
On the other hand, the earlier fatal-fire scene would be the appropriate case for use of a laser scanner. In this case, the investigative team would want to accurately match the fire plume to a specific location in the living room.
 
The above explanation could be seen by certain laser scanning and metrology experts as being too simplistic and my justification is that this is not a technical paper. Suffice to say that the accuracy, precision and point cloud quality of a laser scanner depend on additional factors and are also based on the scanning technologies used.
 
A 3D point cloud of the Colosseum
 
Conclusion
There is always a need to be on the lookout for cross application of technologies that are being used by specific areas of expertise and industry. The problem is that very often, we are often too busy to look beyond our own area of expertise or into other industries. The above shared experiences are humbling, and I believe that we should all be opened to learning, no matter how experienced and well trained we believed we might be. Afterall, the Chinese proverb still holds true xué rán hòu zhi bù zú or “xué rán hòu zhi bù zú”; loosely translated to ‘you’ll know what you lack after learning’. A 
 
Mr Andy Choo is director of EFI Global Asia.
 

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