What is Static Electricity?
stat·ic e·lec·tric·i·ty (noun) a stationary electric charge, typically produced by friction, that causes sparks.
The Basics:
-The world is made of atoms
-Atoms have electrons protons and neutrons
-Protons and neutrons are held tightly to the nucleus of the atom.
-Electrons are loosely connected to atoms and can easily move to other atoms
-It is simply the contact between two different materials. Electrons move around to equalize and bring everything to the same charge.
-Rubbing or friction increases the contact area between the materials and facilitates a faster transfer of these particles – a static electric discharge (spark) can occur.
Conductivity
Electrical conductivity is the measure of a material’s ability to allow the transport of an electric charge.
Many metals have HIGH conductivity
Many Insulators like glass or plastic have LOW conductivity
Alcohol has
LOW conductivity
Whenever materials with LOW conductivity are moved, there is a potential for static electricity buildup!
How is static electricity generated / built up?
1.Flow of a liquid through a pipe.
2.Flow of grain through a pipe.
3.When liquids are transferred into non-conductive containers.
4.When liquids are transferred into conductive containers.
Why does this matter?
Ethanol Vapor Is Flammable!!
Electrostatic discharges can create an ignition source for flammable alcohol vapors in or near storage tanks and piping.
How is static electricity regulated?
There are standards for dealing with static electricity & flammable liquids. The International building and fire codes refer to NFPA (National Fire Protection Association) and OSHA requirements:
NFPA 77 helps users control the hazards associated with the generation, accumulations, and discharge of static electricity by providing a basic understanding of the nature of static electricity, guidelines for identifying and assessing the hazards, techniques for controlling them by process modification and bonding and grounding, and guidelines for controlling static electricity in selected industrial applications.
OSHA Regulation 29 CFR 1910.106 (e)(6)(ii)
Grounding. Category 1 or 2 flammable liquids, or Category 3 flammable liquids with a flashpoint below 100 °F (37.8 °C), shall not be dispensed into containers unless the nozzle and container are electrically interconnected. Where the metallic floorplate on which the container stands while filling is electrically connected to the fill stem or where the fill stem is bonded to the container during filling operations by means of a bond wire, the provisions of this section shall be deemed to have been complied with.
How to mitigate static electricity risks
Grounding
Grounding is the process of removing the excess charge on an object by means of the transfer of electrons between it and another object of substantial size.
When a charged object is grounded, the excess charge is balanced by the transfer of electrons between the charged object and a ground.
Grounding is Achieved via one of the following methods:
Connect to Building Steel
Connect to Water Pipe
Connect to Underground Steel Rod (Ufer Rod)
Bonding
The practice of intentionally electrically connecting all exposed conductive items not designed to carry electricity in a room or building as protection from electric shock.
When is grounding/bonding needed?
WHENEVER flammable liquid is being moved!!!
-Conductive containers & piping (such as steel) will be able to be grounded.
-Non-conductive hoses can be grounded by having a metal trace wire throughout.
Conductive (Often Metal) Piping, must be grounded:
NFPA77 10.1.1
All parts of continuous all metal piping systems should have a resistance to ground that does not exceed 10 ohms.
Non-conductive piping shouldn’t be used to transport flammable liquids, because
Non-conductive pipes can generate static electricity at the same rate as conductive pipe, but the rate of dissipation is much slower, and charges have no where to go, resulting in a spark.
The code is rather vague on this:
NFPA77 10.3.1
Where nonconductive hose or tubing must be used because of process conditions, the hazards of static electric charge generation should be thoroughly investigated.
IF RUBBER OR SIMILAR NON-CONDUCTIVE HOSES ARE DESIRED, USE ONE WITH A CONDUCTIVE TRACE WIRE IN IT.
Other Safety Practices
Limit Splashing:
When non conducting fluids (or solids) free fall through air they pick up a significant static charge.
When there is spraying or splashing static electricity can build up.
This can be a source of sparks
NFPA77 11.1.1.1
Metal portable tanks should be bottom filled, if possible.
Slower Speeds:
Faster flow= higher current
Filter Considerations:
If a FILTER is used in the hose, it should be moved upstream, because this increases static charge due to increase in the contact area
NFPA77 10.5.1.2
Common industry practice is to provide 3o seconds of residence time in the pipe or conductive host down-stream of the microfilter
By:
Matthew Taylor-Rennert
Colleen Moore
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