Burning issues: load cells and bush fires
The Australian bush fires have dominated the news this month, and despite some very welcome rain and cooler temperatures in the last few days, the emergency is far from over. Our article this month investigates how load cells are helping scientists research the effect and possible solutions for wild fires.
A wind tunnel for studying wildfires
Wildfires are, buy their very nature, unpredictable and affected by natural factors such as wind, vegetation type, the land topography and more. A team in Canberra built a dedicated fire-proof wind tunnel to allow them to safely study of fuel combustion during a bushfire by reproducing a range of conditions. Load cells were, quite literally, taking centre stage in this project.
“A floating 1m2 platform (2m long × 0.5m wide) in the floor of the second half of the working section is intended to enable the measurement of fuel mass loss during combustion experiments … The platform sits on top of three load cells within a sealed chamber underneath the floor of the working section to ensure that air movement does not influence movement of the platform. Such a device will, in conjunction with gas phase emission monitoring equipment in the exit section, allow the correlation of emission factors with fuel consumption rates and fire behaviour.”
California landscape planting
California is no stranger to the dangers of wild fires: over 2.5 million people and 1 million buildings at at risk of destruction in the event of a wildfire. One way to mitigate the risk is through the selection of landscape vegetation for the edges of inhabited areas, to impact on the spread of urban–wildland interface (UWI) fires as a team of researchers explained in their paper:
“One of the major concerns in the vulnerability of structures is ornamental vegetation in the ‘home zone’,within about 2 m of the structure. This vegetation can act as a ‘ladder fuel’ similar to the behavior seen in wildfires.”
The team measured the heat release rate (HRR) of plants in a kiln in a natural upright position, to see which were the most resilient. The system used was an Intermediate Scale Biomass Calorimeter, which uses various sensors including platform load cells. As the team reported: “Multiple regression showed the overwhelming importance of foliage and moisture content to peak HRR.”
Bush fires and rocks
Long after the fire has passed and the vegetation has started to regrow, bush fires leave a lasting legacy. Bush fires can quickly heat up rocks to 500 degrees C within a matter of minutes, causing thermal shock that literally splits the rock apart. These fractures can affect the line of the natural planes of weakness, so the rock may fail in unexpected ways, especially when then weathered by wind or rain. In a thesis for the University of Twente, a student used load cells to measure how a slope of weathered mine waste (rock) might fail according to the grain size. The student cerated a set-up “in which granular material can be sheared dynamically” using a load cell to measure the force exerted on a container.
How many trees?
What has distinguished Australia’s current fires from past years is that it’s not just the scrubby bush that is burning, it’s the forests too. Commercially managed forests are monitored and measured for tree numbers, size and growth, a process known as “mensuration”. The challenge is to estimate the volume (mass) of carbon contained within the forest. Modern tree harvesters use load cells and data loggers to measure a given section of forest, and the figures extrapolated to cover the entire area. We assume that this level of data would give firefighters a better idea of how much potential fuel was locked up in a given area of forest, and potentially react accordingly.
Tree surgery with load cells
Equally, load cells can help with tree felling in normal circumstances. The issue for tree surgeons is that they won’t know the shock load and weight of a given branch before they cut it. Hence they also won’t know the forces their rigging equipment will be put through either. According to an article in Weighing Review, a new Impact Block enables instructors to demonstrate real time shock load data to students. It can also be used to:
“Delve deeper into dynamic load situations by researching where forces on the anchor point are at their greatest, while investigating what is happening to the rigging before and after that moment … Unless we understand the forces, we can’t understand the safety factors.”
Help with fire relief in Australia
If you’d like to support the fire relief effort in Australia, these reputable and long-established organisations are accepting donations:
