The Shocking Hazard of Static Electricity
Crane Army Ammunition Activity
Children of all ages enjoy playing with static electricity. It can be used to deliver a surprise shock to a friend, make long hair stand on its end or help a balloon stick to a pet’s fur. While these are fun and harmless uses of static electricity, it can have shocking impacts in the industrial environment. If left unmitigated, static electricity hazards can cause ignition of flammable gasses and vapors or set off electrically initiated munitions unintentionally.
Static electricity is created when there is an imbalance of electrical charges on the surface of an object. The electrons in the atoms are rearranged, resulting in some atoms being positively charged and others negatively. It is most often created when two surfaces come into contact and then separate. The charging rate increases when the speed at which the objects come into contact and separate is increased. The faster your feet move along the rug, the more static you have. Where can this be seen in the industrial environment? Last I checked, shag rugs are not standard in manufacturing. However, static can be produced whenever one material moves across another. This can be commonly seen in material chutes, conveyor belts, a liquid flowing through pipes, paint-spraying operations and drive belts.
There are several methods to mitigate the static electricity hazard. Recall the hierarchy of hazard controls: elimination, substitution, engineering, administrative and personal protective equipment. If possible, remove or substitute the source of the static generation. For example, if you have material being moved using a short conveyor belt, it may be safer and just as economical to move it by cart. In many cases, it is not possible to eliminate or substitute. Another method is substituting nonconductive materials for conductive ones. Analysis must be done to determine if this would help or hinder static mitigation.
Most of the hazard mitigation will be in engineering controls and administrative procedures. The easiest and most effective safety measures are grounding and bonding. Grounding involves connecting the materials involved to a ground to dissipate all electricity, returning the material to neutral. Bonding is connecting two conductive materials together to eliminate the electric potential. For example, if you are pouring material out of a scoop to a bowl, there may be a potential between the scoop and the bowl due to the flowing material. By bonding the bowl and scoop together, they remain at the same potential and will not spark, as the static will travel and be balanced through the conductive connector.
The operator can also be bonded to the equipment to avoid an arc from the person to the equipment. More expensive and involved engineering controls might include air ionizers and close control of humidity to eliminate static in the air. Lastly, PPE can be utilized as the last line of defense. PPE might include conductive clothing and shoes or insulated materials and clothing. Again, close analysis needs to be completed to ensure the proper PPE is chosen. We want protection rather than a hazard.
Why is static electricity important? One would think a small shock doesn’t hurt. It may seem that way, but under the right conditions, a small shock could be explosive. In July 2007, a steel tank was being filled with naphtha, used in painting, near Wichita, Kansas. Naphtha is a Class 1B flammable and known for a low electrical conductivity. Even though the tanker trailer, pump, piping and storage tank were all bonded and grounded, enough static electricity built up in the fluid that it caused a spark in the float. The static built up as a result of the pumping process repeatedly starting and stopping and air in the piping. This caused an explosion, launching the 15,000-gallon tank 130 feet and resulting in property damage to the company and nearby businesses and residences. Bonding and grounding were not enough to stop this incident.
Three months later at a Des Moines, Iowa, facility owned by the same company, a portable tank of ethyl acetate caught fire, spraying the liquid around the room and on the operator. The operator’s clothes ignited, but he was able to remove the clothing and avoid serious injury. The area where the fire started also did not have sprinklers or a fire wall, allowing the blaze to spread to the flammable storage warehouse. A large portion of the facility was destroyed. The nozzle and hose were not bonded or grounded. Those are big consequences from a small static spark. More information on these incidents can be found on the Chemical Safety Board’s website at https://www.csb.gov/.
Another aspect to consider is how other PPE could introduce static hazards. We do not want to greatly increase risk in one area by reducing it in another. An example of this is face masks. With the risks of the pandemic, workplaces everywhere are trying to protect their employees from exposure. Many use disposable cloth procedure masks. These are cheap and easily donned. However, when analyzed using a static meter, the masks held up to 7,000 volts of static electricity, more than enough to set off common flammable materials, let alone many sensitive explosives.
Overall, static electricity may seem minor, but left unmitigated, a small spark could cause ignition of flammable gases, vapors and explosives. Utilize smart and proper hazard controls to take the spark away from the workplace and bring the spark back to the work.