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Friday
Aug032012

Bonding, Grounding & Static Electricity

The function of bonding and grounding during transportation incidents is of vital concern to hazardous materials responders especially when flammables are involved. Many such responses are during the phase of leaking or pre-ignition. If this occurs, the obvious objective is to keep the event in this phase. Once ignition occurs, the haz-mat phase of the incident becomes on hold until the Fire Department accomplishes extinguishment. To prevent ignition during transfer operations from the damaged railcar or highway tanker to a like, undamaged container requires the principles and tactics of bonding and grounding. During transfer static electricity from flow operations increase in unequal amounts on both the damaged car and the un-damaged car. This build-up generates into a coronal point that can jump a gap in the form of an exterior spark. This energy becomes large enough to ignite close by flammables. This ignition can result in firefighter deaths and further destruction to the scene.

Transfer of the electrons, or units of electricity occurs through conduction {objects that touch} or induction {objects that do not touch}. Static electricity is generated through movement from one container to another. By the haz-mat responder providing a method of grounding & bonding, he can remove three {3} of the four {4} conditions for ignition. 1] A means to generate a spark. Continual flow of product will increase static energy over time. Removing this accumulation lessens the ability to generate this spark. 2] Enough static charge to bridge this “gap”. By grounding all transfer appliances and containers; this reduces the total amount available to bridge any “gap” thus eliminating charge to create a spark. 3] A Spark with enough ignition energy. Grounding and bonding reduces ignition energy and can keep it below “its peak” spark levels. 4] Flammable atmospheres.

In some cases the interior of a tank can be inerted or “blanketed” by injecting an inert gas into and between the surface of the flammable product and interior ceiling of the tank. This will replace any flammable friendly atmospheres with ones that prevent ignition. In most cases this will be an operating condition that cannot be entirely eliminated. Hence the importances of reducing these rouge charges and preventing their build-up.

Bonding is the process of electrical connection between two objects to create a system of equilibrium. This is accomplished by direct contact between the two objects via an appropriate sized electrical conductor or “cable”. Grounding is the process of connecting these objects to an electrical “pathway” dispersed into the earth. This can be done by connection directly into the earth via a grounding “rod” or surface “plate” on top of the earth surface that may not be bridged, such as concrete. It is also appropriate to connect these objects to large metal structures or building grounding “bus work” specifically made for grounding electrical operations.

The ultimate issue with industrial and hazardous materials responders is one of “How” to accomplish these goals. There are any number of official sources regulating the format for bonding and grounding. The NEC {National Electrical Code} has one, The NFPA {National Fire Protection Association} has one, and the list goes on. Railroads, DOT over the road tankers, Bulk fixed sites, and I am sure many others all have a “system”. The problem for the hazardous materials team is which one do we use? One for the bulk sites may not be acceptable to the railcar guys. Therefore, your team will have to choose which one best suits your safety needs on an emergency incident. Terminology is important when discussing these issues between response organizations. Included are some common terms that will aid discussions when you meet with varying groups.

Amperes-The amount of current through a point in one second {6.24X10 electrons/second=1 ampere

Bonding- The connection of two or more objects by a conductive material, usually metallic cables called, conductors

Breakdown Voltage- The point at which an insulator will begin to conduct electricity, usually in the form of a “spark”

Capacitance- The surface storage area of a material in numbers of electrons

Conductor- Any material that allows free flowing electrons to pass along its surface with little resistance

Charge- The number of electrons on a body at a given time {6.24X10 electrons=1 coulomb}

Charge Relaxation- The amount of time that is needed to dissipate a charge through a liquid to ground

Current- The mathematical measurement of Amperes or electron flow

Electricity- The flow of electrons

Grounding- The connection of charged objects to the earth that allows proper dissipation of electron charge

Incendive- A spark that contains enough energy to ignite a vaporous mixture is said to have “incendivity”

Ignitable Mixture- A vaporous mixture which will flash-over and burn continuously

Insulator- Any material that resists or contains the flow of electricity from passing over or through it

Joule’- The amount of energy that is contained in one 4.5 sledge hammer traveling at one meter/sec striking your face or jaw. Static sparks are measured in “milli-joules”

Labeled- Any equipment having a tag verifying safety and soundness that is acceptable to the AHJ {Authority having Jurisdiction}

Listed- A published list of the above, acceptable to the AHJ

Ohms- The amount of resistance to the flow of current

Potential- Stored energy that is able to do work, in hydraulics potential is equivalent to pressure, usually measured in volts while “ground” is considered complete zero. The difference between a charge and ground is referred to as “potential difference”

Resistance- Measured in Ohms, and is the difficulty that a current encounters in passing, or flowing through a circuit or electrical conductor

Semi-Conductive Hose- Any hose that has high enough resistance to limit the flow of stray electrical current to safe levels, yet not so high as to prevent charge relaxation of static electrical charges to ground

Should- Indicates a recommendation that is advised but not required by law according to code statutes

Static Electricity- An electrical charge that manifests an electrical field component but not a magnetic field component

Static Spark- A impulsive charge across the “gap” of two points not connected

Static Transfer- The inductive or conductive balancing of charges seeking equalization throughout a circuit system

Volts- The pressure that forces the flow of electrons from one point to another

 Additionally, your organization will have to be adaptive towards other entities working within your incident parameters. If one such opposition occurs, your Chief or team leader will have to determine if “their” system is safe for your team members to work around. These differences are small in most cases, but I have seen many incidents delayed for hours due to unsure decisions over the “system” or procedure being different and causing great concern for the well-being of responders. Whatever system you choose should be transferred to entities operating in your response domain well before an incident happens. Be sure that these differences can be noted and worked out before responding to an emergency involving these facilities. All coordinators from the team leader to the CEO should work together to be “on the same page” as to which technique will be used on scene. Waiting until the incident occurs could cost lives and delay tactical operations.

                                          Haz Mat Mike

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