Do you remember the cell phone gas fire scares of the early 2000’s? Because of a couple of erroneously spread Internet rumors, people all across the world became convinced that use of their cell phones while at the gas pump could lead to explosions, injuries, even death!
Despite the fact that the rumors were all proven to be false, several gas station chains, including the one whose safety report was misquoted to create the rumors, posted stickers warning against cell phone use. One Chicago suburb even passed a law banning the use of cell phones at gas stations.
If you look closely, those stickers are still on a majority of gas pumps, at least in the US and Canada. But while there has never been a case where cell phones caused gas fires, the same is NOT true for static electricity.
We’ve talked a lot in the past about the danger even a small electroStatic discharge (ESD) can pose to sensitive electronics. But in a combustible atmosphere, that tiny spark can cause a lot more damage than the cost of replacing a damaged circuit board.
Static is Everywhere
Walking across a room, rustling your clothing, even just the act of raising your arm to scratch your nose can generate a sufficient static buildup to create a subsequent ESD if not dissipated. Under normal conditions, you won’t even notice the buildup until you feel the shock of the discharge being released.
When you’re not working with sensitive electronics, you probably don’t even consider this to be a problem, certainly not in your home or driving in your car. But like all charges, if it’s not given a route to ground, the charge continues to build, increasing the voltage. And if you happen to be in an area with flammable liquids, vapors and even dust, that static charge can cause explosive consequences.
The first step to avoid incidents in any environment conducive to these volatile exposures is to eliminate as many potential ignition sources as possible. But there are often unconsidered, hidden dangers, especially in an industrial setting that can act as accidental ignition switches.
Isolated Conductors = Hidden Dangers
Isolated conductors are conductive objects – metal flanges, fittings or valves in pipework systems, portable drums – which are either inherently or accidentally insulated from being grounded. Because of this, any static charge they generate becomes a potential ignition point.
The best way to avoid this problem is by utilizing bonding and grounding. Bonding is the process of joining two or more objects or containers with electrically conductive wires to neutralize the potential charge between them. Grounding is a more specific form of bonding where an object or container is connected to the ground.
There are a variety of ways to effectively employ bonding and grounding. While OSHA does not give clear directives on how to ground, they do specify when and where grounding as well as bonding procedures should exist.
The most obvious example to point to is the common ground, seen in every building – a metal rod is attached to the outside of a building and literally grounded a few inches into the soil. While this method works great for homes, the size of large industrial expanses, such as warehouses or factory floors, means other methods may be more suitable.
For manufacturing or large storage areas, there are a few options. They all involve grounding clamps connected to grounding cables.
If the area has access to the building’s main cold water pipe, a very common semi-permanent solution is to use a bronze pipe clamp as an alternative to the direct building ground. C-Grounding clamps are another popular semi-permanent solution. Of course, always check the reliability of the ground conductivity in these instances.
If you’re like many industrial complexes, though, the isolated conductors are often temporary items, like drums, containers and vessels that come and go as needed. For these instances, you can get a variety of steel- or aluminum-constructed clamps that attach to the container, connecting it through a stainless steel cable to a grounding point, making the drum or vessel safe.
Depending on the environment, you can also effectively ground using the drop valve of a mixing tank or connecting your ground cable to a previously grounded surface – a table or workstation that is already connected to the grounding apparatus.
Whatever method you choose, bonding and grounding are essential for the safety of everyone working in an industrial environment, whether they’re piecing together circuit boards, helicopters… or gas pumps.
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