Being seen on the scene: The science behind turnout trim
|Editor's note: During a recent media event at 3M's headquarters in Minnesota, FireRescue1's Cristi Laquer was given a first-hand look at the technology that goes into making high-visibility trim.|
By Cristi Laquer
Photo Cristi Laquer
A display of high-visibility garments at 3M in St. Paul, Minn., shows part of the range of safety clothing the company helps produce.
State and federal standards, including NFPA 1971, the Standard on Protective Ensembles for Structural Fire Fighting and Proximity Fire Fighting, require firefighters to wear high-visibility materials as part of their personal protective equipment. To meet the standard, turnout gear manufacturers equip all their gear with thoroughly-tested visibility trim.
"Obviously, firefighters work in a hostile environment," said Pat Freeman, technical services director for Globe. "If you have a firefighter working late at night or lost in a smoke-filled room, visibility is key."
Many manufacturers' high-visibility trim comes from 3M, the Minnesota-based company perhaps best known for making everyday office supplies. But 3M has been employing its materials and light expertise to help improve firefighter visibility for more than 25 years.
The principles behind 3M's work on reflective PPE materials are rooted in basic human physiology.
In essence, an object or person can be completely visible, but if they are not conspicuous — if they don't "pop out" at a viewer — they are unlikely to be noticed.
"We're very bad at seeing objects we're not already aware of," Linzie said. Linzie was among the team of 3M vision experts at a recent media event held at the company's headquarters in St. Paul, Minn.
Tim Gardener, regulatory affairs manager for 3M's occupational health and safety division, explained how motion, contrast in luminance (the amount of light an object gives off) and contrast in color as compared to a background are all factors in conspicuity. "Increasing those factors increases conspicuity, which is a major factor in struck-by accidents," he said.
3M's testing facilities are equipped with sensors that can record the absolute amount of light an object gives off. But Joe Otte, marketing manager for 3M's visibility and insulation solutions division, stressed that testing how people see things is of the utmost importance. "Human factors research gives us an in depth understanding of how our customers actually use our products," Gardener said.
An example is 3M's Night Track testing facility, which is as close as it gets to trying out products at a real emergency scene.
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Participants in the test are driven toward the scene. When they first spot a person, they are told to press a button. This human research gives scientists a quantitative measurement of the distance at which various materials are likely to be spotted.
"Search tasks, where people are asked to find an object or person as quickly as possible in an unfamiliar visual field, are the main method of measuring conspicuity," said Gardener.
Night and day firefighter visibility
High-visibility trim manufacturers such as 3M have two very different technologies to account for the contrasting conditions firefighters face during night and day. "Retro-reflective" technologies can be found pretty much everywhere — from the surfaces of street signs and traffic cones to bicycle reflectors and high-visibility garments.
"Retro-reflective surfaces are covered with tiny prisms so that, when they're struck by a bright light, they reflect back more concentrated light than normal surfaces," Otte said. This makes them appear much brighter than surrounding objects, making them very conspicuous at night.
The 3M Scotchlite retro-reflective trim used on turnout gear is covered with tiny glass beads. Since the beads are round, they are very effective at reflecting light back no matter the angle at which it strikes.
This Scotchlite material is sold to manufacturers for use as trim, and it can also be cut into letters or logos to make individual firefighters identifiable in dark or smoky conditions.
Meanwhile, during the day…
Photo Cristi Laquer
3M Visibility and Insulation Solutions team members stand on the Night Track at dusk to demonstrate the contrast between two colors of fluoresceent material, a white t-shirt and a gray sweatshirt in low light.
"Retro-reflectors work best under nighttime light conditions, so fluorescence is needed for daytime visibility," Gardener said.
Fluorescent materials need daylight to function because they absorb ultra-violet rays, which humans can't see, and re-emit them as visible light, making them look much brighter than surrounding objects.
Fluorescent materials are made in three standard colors: red, yellow and green. 3M's human testing has shown that fluorescent red is better for peripheral visibility, while objects in fluorescent yellow stand out more when they're straight ahead. This is because humans have different kinds of receptors in different parts of our eyes, and they are sensitive to different colors.
Following a pattern
While trim can vary, it's always in approximately the same pattern, since NFPA 1971 dictates both the amount and location of high-visibility trim on garments, according to Freeman. The trim pattern, consisting of rings around the waist, ankles, arms and wrists, makes it easy to instantly identify a firefighter from a distance. And there is a scientific rationale behind this configuration.
"Studies show that the best way to identify the human body is to outline the human body," Freeman said.
Seeing something is actually a two-step process — picking out the object, and then identifying what it is, according to Gardener.
"The pattern of striping on firefighter gear is designed to make the person wearing it easy to identify," he said. "Just by highlighting a few points on the body, we can easily identify whether something is a human or an animal.
"Once a driver has identified that there's a human there, then they can effectively avoid hitting that person."