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Bonding and Grounding
The process of bonding and grounding can be defined as providing an electrically conductive pathway between a dispensing container, a receiving container and an earth ground.
This pathway eliminates the buildup of static electricity and allows it to safely dissipate into the ground. The Code of Federal Regulations, 29 CFR 1910.106(e)(6)(ii) states, "Category 1 or 2 flammable liquids, or Category 3 flammable liquids with a flashpoint below 100°F (37.8°C), shall not be run/dispensed into containers unless the nozzle and container are electrically interconnected. The National Fire Protection Association (NFPA), NFPA Code 30, 2008 edition, Chapter 18, Section 22.214.171.124 states that all liquids above their flash point must have static control that complies with Chapter 6 Section 6.5.4. Where the metallic floorplate on which the container stands while filling is electrically connected to the 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." This means that all containers of Category 1, 2 or 3 liquids (liquids with a flash point lower than 100°F) need to be bonded and grounded during dispensing. This includes non-metallic containers, even though the construction material may not be recognized as conductive (for example, polyethylene). If the containers are not properly bonded and grounded, the resulting static spark could be capable of raising the vapor temperature above the flash point, causing an explosion.
Some common examples of Category I liquids include alcohol, toluene, acetone and benzene. The flash point can be found on the material safety data sheet (MSDS) that accompanies the chemical from the manufacturer or distributor.
The diagram below is an example of a complete bonding and grounding system. The bonding wire is shown connecting the lids of the receiving container and the dispensing container. The grounding wire is shown connecting the dispensing container to the common ground within the facility. The common ground is in turn connected to an earth ground. (Any ground source that is adequate for power circuits or lightning protection is sufficient for protection against static electricity.) This system provides an electrically conductive pathway for static electricity to follow and safely dissipate into the ground.
For bonding and grounding to be effective, a metal-to-metal connection must be maintained between the bonding and grounding cables and the containers. To accomplish this, all paint, dirt, rust, etc. must be removed from the area of connection. These connections can be of two basic types: permanent and temporary. Permanent connections can be made by using solid or braided wires, and must incorporate either screw-type clamps, welding or other similar means. Temporary connections should use only braided wires in conjunction with spring clamps, magnetic clamps or other similar methods of maintaining metal-to-metal contact.
The difference between solid and braided wire is as follows: Solid wire is a single, complete strand of wire that is not known for its durability. For this reason, solid wires should only be used for permanent connections, or those that will not be handled often. Braided wires consist of several strands of wire wrapped together to provide greater strength and flexibility. With these characteristics, braided wires are recommended for use with temporary connections. Additionally, the National Fire Protection Association, in NFPA 77, states that either insulated or uninsulated cables can be used. Insulated cables are those with a protective rubber coating that completely encompasses the wire. Uninsulated cables, which have no coating, allow for quick, easy inspection. Insulated cables should frequently be checked for continuity. The minimum size (gauge) of the cables is determined by strength and durability rather than current-carrying capabilities.
Commonly Asked Questions
|Q.||Where do I bond and ground a polyethylene safety can?|
|A.||Most manufacturers of polyethylene safety cans will include a grounding lug for the connection of bonding and grounding cables.|
|Q.||Do safety cabinets have to come with a grounding lug?|
|A.||Safety cabinets are not required by federal regulations to have a grounding point; however, in order for that cabinet to receive Factory Mutual (FM) approval, it needs to be equipped with one.|
|Q.||Is it acceptable to hold the nozzle of the dispensing container in contact with the opening of the receiving container rather than attaching a bonding wire?|
|A.||No, this is not an acceptable practice because it is difficult to maintain an electrical bond between these two items. Bonding wires should be used.|
National Fire Protection Association, NFPA 77, Recommended Practice of Static Electricity
Uniform Fire Code, UFC Div. VIII Sec. 79.803
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The information contained in this publication is intended for general information purposes only. This publication is not a substitute for review of the applicable government regulations and standards, and should not be construed as legal advice or opinion. Readers with specific questions should refer to the cited regulation or consult with an attorney.