Not being aware of what's in front of you or to your side is perhaps the root cause of most worker versus vehicle accidents on construction sites. Part of the problem can be addressed with technology. There are many luminescent and retroreflective safety clothes and products on the market today to help people and vehicles stand out more noticeably on jobsites. But the physiology of how you see and perceive plays a key role.
How the eye works
What you see in sharp focus, as well as the perception of color, is processed by a small area at the back of the eye called the fovea. This is where most of the cone receptors are located—sensors of color and fine detail. The large area around the fovea is where peripheral information is gathered by rod sensors, which specialize in luminance differences, general shapes, and movement (the fovea also recognizes these details). This is referred to as peripheral vision.
Cones function best when lighting is bright, while rods capture detail when lighting conditions are poor.
The fovea only processes about 2 degrees of our visual field. You can visualize this by holding your thumb up at arm's length; the invisible area behind your thumb nail being what the fovea perceives. Also every eye has a blind spot where the optic nerve leaves the back of the eye. You compensate for this by moving your eyes quickly over a scene so that your brain can build an image. Human eyes see much more under well-lit conditions and much less under dim lighting.
Because of this physiology, you are sometimes prevented from having an accurate view of reality.
Imagine that you are driving down a road or highway either during the day or at night, and you are looking at the scenery: a billboard or some movement more than 15 degrees away from the road's shoulder. At that moment, your foveal vision (color and detail) of the roadway disappears, as well as any construction workers or flag persons now in your path, who believe you see them.
The color of safety
Brian Linzie is a senior vision scientist at 3M in St. Paul, Minn., who studies how the brain works and how people think and see. He says the fovea processes color information. The color of safety garments and devices is perceived under lighted conditions. “The two most popular colors for this use are fluorescent red-orange and yellow-green, because fluorescent surfaces appear lighter or more luminescent to us and these colors also contrast well with other colors. The natural world doesn't have fluorescent colors and our attention focuses on color that stands out.”
But if all the safety colors on a construction site were the same color, none of them would appear to stand out. “If luminescent red-orange is the color used to identify safety hazards on a construction site, then yellow-green might be a better safety color to identify construction personnel—you focus attention on what stands out,” he adds.
Linzie says research efforts are attempting to answer whether there is one color that stands out more than all the others. So far the best advice is to use colors for safety purposes that contrast with any given background. For that reason fluorescent yellow-green often tends to pop out more in rural settings, while fluorescent red-orange can contrast more in brighter urban areas.
Night protective clothing
Just as your eyes are drawn to colors that appear more intense in the light, they are attracted to intense light under nighttime conditions. Reflectors accomplish this goal by returning much more of the light from a car's headlights to drivers than the surrounding surfaces. This makes these areas appear brighter and thus helps make pedestrians more noticeable.
As mentioned earlier, your peripheral vision is good at seeing movement and focusing on luminance differences that separate objects from their background. Linzie says there are two types of reflectors: beaded and prismatic. Beaded reflectors consist of very small glass beads that are silvered on the back side and oriented in the same direction to create a bright mirror. The beads are embedded in a plastic film to hold them in position. Companies such as 3M have been able to create bright reflectors that can be viewed from wide angles to the source of light.
Class 2 ANSI/ISEA 107 garments feature both horizontal and vertical bands of reflectors that easily can be seen when vehicle headlights shine on them. But Class 3 garments can perform even better because they combine reflectivity and emphasize pedestrian motion by placing reflectors on wrists and ankles—strong light in motion catches the eye the best.
If you are on the side of a roadway, it's natural to believe drivers will see you in their headlights, but this may or may not be the case. At night, wear reflectors on your wrists and ankles to reflect your movement. Don't rely on a white T-shirt to reflect more than a darker piece of clothing—in studies, 3M has proven that nonreflective fabrics offer little luminance at night, no matter the color. In the daylight, wear colors that contrast with the environment. However, your best defense is to believe you aren't seen and act accordingly.
Tips on How to Train Your Brain
Safety can be increased by using luminous colors, but most of all it depends on your state of mind. Here are some suggestions on keeping your brain active.
- When you drive, constantly scan between the shoulders of the road. Don't maintain focus on one point.
- During daylight hours, focus your attention far enough in the distance so you have time to react. At 60 mph, this distance would be about 1000 feet.
- Don't overdrive your headlights at night; slow down.
- Think about looking for objects, such as people or deer. You will detect them faster if they appear.
- Watch for movement.