If you ever shuffled across a carpeted floor in your socks and then felt a little “zap” when you touched a metal doorknob, you’ve experienced the shocking effect of static buildup. Now imagine a static charge that builds up to as much as 50,000 V, and you start to appreciate the hazards that many forklift operators face every day!
How static builds up
Static electricity is generated when two dissimilar materials are rubbed together. Friction tends to displace electrons from one material to the other, creating an electrical imbalance, or static charge. Insulating materials, such as rubber, are the most prone to accumulating static until it makes contact with a more conductive material. The conductor allows the static to discharge, releasing the displaced electrons and restoring balance in the material. The release might appear as that tingle in your fingertips when you open the door, or as a massive bolt of lightning generated by turbulence in the atmosphere or, a static charge building-up in a forklift that can create major safety hazards for Material Handling operations.
The problem with non-marking tires
Forklifts using black tires generate static but they’re continuously releasing their potential charge because of the carbon black used to give the rubber compound its black color. Carbon black is conductive, so it grounds the tires and gives them built-in anti-static properties.
Some applications, however, require non-marking tires: Forklifts that operate indoors, on warehouse floors with light-coloured coating and surface finish or in food processing plants, for instance, are often fitted with non-marking tires.
The rubber compounds used in non-marking tires generally contain silica in place of carbon black. Where carbon black is conductive, silica is an insulator. As a result, static generated in the tires is stored rather than dissipated. The static continues to build up in the machine until it contacts another conductive material to release the charge. Unfortunately, the human body is an excellent conductor and an easy path for the electrical charge to take. Metal facility components can also provide an outlet for the static spark, including electronic controls and elevators. In either case, the results can be dangerous and costly.
A hazard to people and materials
During a full shift of high speed travel and heavy loads maneuvering, forklifts can store up static charges to dangerous levels. The static charges on a forklift can be strong enough to severely injure a human being. This is why you will often see operators take pains when they dismount to ensure that they break off contact with their truck before they set foot on the floor, sometimes leaping from their seat to avoid a severe static shock. The potential for a slip & fall accident, or for disabling shock causes operator stress, ultimately leads to lack of productivity, another problem that the overall static build-up issue can cause.
Over and above the risks for injuries, facilities handling volatile fumes and chemicals have to be cautious with the forklifts. Propane-powered trucks are vulnerable to gas leaks from their own fuel tanks, as well as gas in the vicinity of a filling station. Paper and textile mills are also subject to the fire hazards of sparking the fine dust that these materials produce. In facilities that handle electronic components, static charges can wipe out circuits, data chips and firmware. Control boards and sensors that are built into the forklift itself, as well as control devices and alarms installed in the facility can even experience a major power outage.
The challenge of static buildup
For many years, the problem of static buildup has simply been part of the business. Non-marking tires have a role in plant hygiene and product quality; their tendency to create static is just part of the price you pay for those benefits. Some methods of mitigating the problem have been implemented, and we’ll present them in a future article
Like most safety issues, the solution to hazards of static electricity must be addressed at multiple levels. The real opportunity for safety is in the hands of tire manufacturers like us to respond with new tires and compounds to overcome the unique challenges of non-marking tire design. Extensive research and testing has led us to significant progress in the development of long-wearing, non-marking tires that have anti‑static properties similar to conventional black tires. We will be exploring the different solutions, and their impact on forklift fleet management, in Part 2.