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 helps eliminate the buildup of static electricity by allowing it to safely dissipate into the ground.
Both the National Fire Protection Association (NFPA) and the Occupational Safety and Health Administration (OSHA) have bonding and grounding requirements.
NFPA addresses the need for bonding and grounding in NFPA 30, the Flammable and Combustible Liquids Code. In the 2021 edition of NFPA 30, 126.96.36.199 states that dispensing of Class I liquids from a container by means of air is only permitted under the following conditions:
- The pressure must be generated by means of a listed hand-operated device,
- Must not exceed six pounds per square inch (psi) gauge pressure,
- A pressure relief must be provided, and
- The device must be bonded and grounded or not be capable of generating a static charge under any operating condition.
Where the use, handling, and storage of flammable or combustible liquids is only a limited activity (incidental operation), per 188.8.131.52, means must be provided to minimize generation of static electricity that meet the requirements of 6.5.4. All equipment (tanks, machinery, piping, etc.) must be designed an operated to prevent electrostatic ignition. All metallic equipment where the potential for an ignitable mixture to be present must be bonded and grounded.
OSHA’s requirements for bonding and grounding in general industry are referenced in the Flammable Liquids Standard, 29 Code of Federal Regulation (CFR) 1910.106(e)(6)(ii). The regulation states, “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 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 all containers of Category 1, 2 or 3 liquids (liquids with a flashpoint 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 flashpoint, causing an explosion.
Common examples of Category 1 liquids include acetaldehyde and ethyl ether. Examples of Category 2 liquids are acetone, benzene, and toluene. Styrene and turpentine (mineral spirits) are examples of Category 3 liquids. The flashpoint for a chemical can be found in section nine of the safety data sheet (SDS).
The diagram below is an example of a complete bonding and grounding system. The bonding wire is shown connecting the lid of the receiving container to 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 wires 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 or 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.