Facility safety: Warning signals

October 2, 2007
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Warehouses and loading bays are busy places, with forklift drivers and trucks constantly coming and going. Within the worksite, people move amongst the fray, going from one building to another. To help increase safety, warning light systems can be used to prevent vehicle collisions and vehicle-pedestrian accidents at industrial sites. The variety and functionality of these systems has expanded in recent years.

Flush lights — In-pavement lights completely flush to surrounding ground are a relatively new development. These lights emit exceptionally bright light very close to the ground, so they are visible from driving height at a great distance.

Forklifts or equipment can drive over fully flush lights without a disruptive bump. They are useful in industrial settings where forklifts interact with other traffic or pedestrians. And they are not prone to abuse by snowplows, so they are valuable for outdoor use in snowy climates.

Warehouse forklifts — As many as 25 percent of forklift truck accidents are caused not by the driver but by controllable environmental factors.1 One way to improve the safety environment is to make sure forklift drivers receive ample warning of potential conflicts.

When a forklift is fully loaded, the drivers’ forward vision is blocked, so forklifts typically travel in reverse. Drivers must crane around to look behind the vehicle as it travels, resulting in a limited field of vision. Forklift drivers are required to honk when approaching intersections. However, the safety value of honking relies on other drivers (or pedestrians) to listen and behave defensively.

An in-ground warning light system can provide a driver with across-the-path notification of other approaching drivers, giving them time to slow, or stop, their forklift before entering the intersection. A “stop bar” of lights unmistakably indicates that it is unsafe to cross an intersection or pass through a doorway.

Trucking bays — Often, forklifts, pedestrians and cars use the area where trucks approach loading bays for inter-building traffic. Flashing activated beacons in conjunction with signs can provide general warnings about the area — for example, “Slow when flashing; trucks may pull out.”

However, in-pavement lights provide a more explicit demarcation of a dangerous area. For example, when trucks are pulling out, a cross street can be “blocked” with a line of red warning lights. Similarly, a line of lights across an entrance/exit to a warehouse can be activated when dangers are present on the other side.

Pedestrian crossings — Pedestrian walkways alongside busy traffic zones can be laterally demarcated with a line of in-pavement lights that become activated when walkways are in use. Similarly, pedestrian crosswalks between buildings within a facility can be treated with traffic-facing, in-pavement lights that are either pushbutton or detector activated. Flashing lights provide an unambiguous warning that pedestrians are present.

Flash patterns — The MUTCD (Manual on Uniform Traffic Control Devices) provides the Federal Highway Administration’s guidelines for in-pavement lights. Guidelines address device height (a maximum of .75 inches), layout in the roadway for crosswalks (a minimum of one per lane), and flash patterns.

In section 4L.02 of the MUTCD 2003 edition, guidelines specify that lights should flash between 50 and 60 times per minute, or approximately once per second. According to the MUTCD guideline, flash patterns should not be between 5 and 30 flashes per second, as flash patterns in this frequency range can cause seizures.

Activation mechanisms — Simple and durable, pushbuttons work well when a walking employee is seeking to activate warning lights. Automatic detectors are commonly used when vehicles such as trucks or forklifts must activate systems. In warehouse aisles — with constrained traffic flows and nearby mounting structures — microwave detectors are common. For roadway applications, wired loop detectors work well. Finally, when the goal is to detect a person or vehicle entering or exiting a region or building, infrared break-beam activation can prove effective and reliable.

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