Bonding and Grounding
When Transferring Flammable Liquids
Written by Steve Hudgik
NPFA 30 is the "Flammable and Combustible Liquids" code. NFPA 30-2012 section 18.5.2.2 states that a: "means shall be provided to minimize generation of static electricity. Such means shall meet the requirements of 6.5.4."
NFPA 30-2012 section 6.5.4 states: "All equipment such as tanks, machinery, and piping shall be designed and operated to prevent electrostatic ignitions. All metallic equipment such as tanks, machinery, and piping where the potential exists for an ignitable mixture to be present shall be bonded and grounded."
OSHA also requires bonding and grounding when transferring flammable liquids. OSHA 1910.106(e)(6)(ii) states:
"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."
OSHA 1910.106(f)(3)(iv) covers static protection and requires "Bonding facilities for protection against static sparks during the loading of tank vehicles through open domes. The OSHA standard goes on to state:
"Protection shall consist of a metallic bond wire permanently electrically connected to the fill stem or to some part of the rack structure in electrical contact with the fill stem. The free end of such wire shall be provided with a clamp or equivalent device for convenient attachment to some metallic part in electrical contact with the cargo tank of the tank vehicle. - OSHA 1910.106(f)(3)(iv)(b)"
What both NFPA and OSHA are saying is that the electrical potential of the container being filled, and the supply source, must be the same. This applies without regard to the size of of the container or source. If the source is a 55 gallon drum and the container is a gas tank on a generator, they both need to bonded and grounded. If the source is a railroad car and the container is a large storage tank, they both need to be bonded and grounded.
What Is Electrical Bonding?
Electrical bonding establishes electrical continuity and conductivity among all metal parts in an area. Electrical bonding means that all exposed metallic non-current carrying parts are electrically connected. This prevents an difference in electrical potential from developing among various parts, even if the connection to ground be lost.
What Is Electrical Grounding?
To ground something means to connect it to "earth," or to a conductor that serves as "earth," using a permanent low-resistance electrical conductor. The grounding conductor provides a path for static electricity to go to the ground instead of creating a spark.
Bonding and grounding must include both the container from which the liquid is coming and the one into which it is going. The containers must be electrically joined to ensure there is no difference in potential. This is most commonly done using a bond wire that is permanently attached to one container and which clamps to the other container.
OSHA states that containers must be electrically interconnected (bonded and grounded) when transferring category 1 or category 2 flammable fluids. How are these defined?
What Is A Flammable Liquid?
Flammable liquid means any liquid having a flashpoint at or below 199.4° F (93° C). Flammable liquids are divided into four categories as follows:
Category 1: shall include liquids having flashpoints below 73.4° F (23° C) and having a boiling point at or below 95° F (35° C).
Category 2: shall include liquids having flashpoints below 73.4 °F (23° C) and having a boiling point above 95° F (35° C).
Category 3: shall include liquids having flashpoints at or above 73.4° F (23° C) and at or below 140° F (60° C). When a Category 3 liquid with a flashpoint at or above 100° F (37.8° C) is heated for use to within 30 °F (16.7° C) of its flashpoint, it shall be handled in accordance with the requirements for a Category 3 liquid with a flashpoint below 100° F (37.8° C).
Category 4: shall include liquids having flashpoints above 140 °F (60° C) and at or below 199.4° F (93° C). When a Category 4 flammable liquid is heated for use to within 30° F (16.7° C) of its flashpoint, it shall be handled in accordance with the requirements for a Category 3 liquid with a flashpoint at or above 100 °F (37.8° C).
When a combustible liquid is heated to within 30° F (16.7° C) of its flash point, it shall be handled in accordance with the requirements for the next lower class of liquids.
It does not take much of a spark to ignite a fire or explosion when there are flammable fumes. Bonding and grounding is a required safety measure when transferring category 1 or 2 flammable liquids from one container to another.
Safety Signs and Labels
Safety signs and labels are an important component of your flammable liquid safety program. Areas in which flammable liquids are transfer from one container to another should be identified by signs and include separate no smoking warning signs. The procedure for transferring the flammable liquid should be clearly posted. The flammable liquid should be identified by labels that also identify all of the associated hazards as well as any required PPE.
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