Researchers at the National Institute of Standards and Technology (NIST) have demonstrated that ordinary blue light can be used to significantly improve the ability to see objects engulfed by large, non-smoky natural gas fires--like those used in laboratory fire studies and fire-resistance standards testing.
As described in a new paper in the journal Fire Technology, the NIST blue-light imaging method can be a useful tool for obtaining visual data from large test fires where high temperatures could disable or destroy conventional electrical and mechanical sensors.
Graphic illustrating the NIST narrow-spectrum illumination method for imaging through fire. Blue LED light is directed through a gas fire, reflects off the target object behind the flames and is captured by a camera after passing through an optical filter. This reduces the observed intensity of the flame by 10,000-fold and yields highly detailed images.
Credit: Graphic created by N. Hanacek/NIST based on a concept by M. Hoehler/NIST
The method provides detailed information to researchers using optical analysis such as digital image correlation (DIC), a technique that compares successive images of an object as it deforms under the influence of applied forces such as strain or heat. By precisely measuring the movement of individual pixels from one image to the next, scientists gain valuable insight about how the material responds over time, including behaviors such as strain, displacement, deformation and even the microscopic beginnings of failure.
However, using DIC to study how fire affects structural materials presents a special challenge: How does one get images with the level of clarity needed for research when bright, rapidly moving flames are between the sample and the camera?
"Fire makes imaging in the visible spectrum difficult in three ways, with the signal being totally blocked by soot and smoke, obscured by the intensity of the light emitted by the flames, and distorted by the thermal gradients in the hot air that bend, or refract, light," said Matt Hoehler, a research structural engineer at NIST's National Fire Research Laboratory (NFRL) and one of the authors of the new paper. "Because we often use low-soot, non-smoky gas fires in our tests, we only had to overcome the problems of brightness and distortion."
To do that, Hoehler and colleague Chris Smith, a research engineer formerly with NIST and now at Berkshire Hathaway Specialty Insurance, borrowed a trick from the glass and steel industry where manufacturers monitor the physical characteristics of materials during production while they are still hot and glowing.
"Glass and steel manufacturers often use blue-light lasers to contend with the red light given off by glowing hot materials that can, in essence, blind their sensors," Hoehler said. "We figured if it works with heated materials, it could work with flaming ones as well."
Hoehler and Smith used commercially available and inexpensive blue light-emitting diode (LED) lights with a narrow-spectrum wavelength around 450 nanometers for their experiment.
Initially, the researchers placed a target object behind the gas-fueled test fire and illuminated it in three ways: by white light alone, by blue light directed through the flames and by blue light with an optical filter placed in front of the camera. The third option proved best, reducing the observed intensity of the flame by 10,000-fold and yielding highly detailed images.
However, just seeing the target wasn't enough to make the blue-light method work for DIC analysis, Hoehler said. The researchers also had to reduce the image distortion caused by the refraction of light by the flame--a problem akin to the "broken pencil" illusion seen when a pencil is placed in a glass of water.
"Luckily, the behaviors we want DIC to reveal, such as strain and deformation in a heated steel beam, are slow processes relative to the flame-induced distortion, so we just need to acquire a lot of images, collect large amounts of data and mathematically average the measurements to improve their accuracy," Hoehler explained.
To validate the effectiveness of their imagining method, Hoehler and Smith, along with Canadian collaborators John Gales and Seth Gatien, applied it to two large-scale tests. The first examined how fire bends steel beams and the other looked at what happens when partial combustion occurs, progressively charring a wooden panel. For both, the imaging was greatly improved.
"In fact, in the case of material charring, we feel that blue-light imaging may one day help improve standard test methods," Hoehler said. "Using blue light and optical filtering, we can actually see charring that is normally hidden behind the flames in a standard test. The clearer view combined with digital imaging improves the accuracy of measurements of the char location in time and space."
Hoehler also has been involved in the development of a second method for imaging objects through fire with colleagues at NIST's Boulder, Colorado, laboratories. In an upcoming NIST paper in the journal Optica, the researchers demonstrate a laser detection and ranging (LADAR) system for measuring volume change and movement of 3D objects melting in flames, even though moderate amounts of soot and smoke.
Paper: C.M. Smith and M. Hoehler. Imaging Through Fire Using Narrow-Spectrum Illumination. Fire Technology. Posted online July 23, 2018. DOI: https:/
Michael E. Newman | EurekAlert!
Tangled magnetic fields power cosmic particle accelerators
14.12.2018 | DOE/SLAC National Accelerator Laboratory
In search of missing worlds, Hubble finds a fast evaporating exoplanet
14.12.2018 | NASA/Goddard Space Flight Center
The more objects we make "smart," from watches to entire buildings, the greater the need for these devices to store and retrieve massive amounts of data quickly without consuming too much power.
Millions of new memory cells could be part of a computer chip and provide that speed and energy savings, thanks to the discovery of a previously unobserved...
What if, instead of turning up the thermostat, you could warm up with high-tech, flexible patches sewn into your clothes - while significantly reducing your...
A widely used diabetes medication combined with an antihypertensive drug specifically inhibits tumor growth – this was discovered by researchers from the University of Basel’s Biozentrum two years ago. In a follow-up study, recently published in “Cell Reports”, the scientists report that this drug cocktail induces cancer cell death by switching off their energy supply.
The widely used anti-diabetes drug metformin not only reduces blood sugar but also has an anti-cancer effect. However, the metformin dose commonly used in the...
A research team from the University of Zurich has developed a new drone that can retract its propeller arms in flight and make itself small to fit through narrow gaps and holes. This is particularly useful when searching for victims of natural disasters.
Inspecting a damaged building after an earthquake or during a fire is exactly the kind of job that human rescuers would like drones to do for them. A flying...
Over the last decade, there has been much excitement about the discovery, recognised by the Nobel Prize in Physics only two years ago, that there are two types...
12.12.2018 | Event News
10.12.2018 | Event News
06.12.2018 | Event News
14.12.2018 | Power and Electrical Engineering
14.12.2018 | Physics and Astronomy
14.12.2018 | Physics and Astronomy