Static Electricity and Flammable Liquid Safety

By Renee Witherspoon, MS, CSP, CIH, CHMM, South Plains Chapter President

Bonding to a plastic bucket?

We are familiar with static electricity when we walk across a floor and then touch a door knob and watch as a spark jumps from our hand to the knob, or when we take clothes out of the dryer and they are stuck together.  We can deal with a little static cling, but that static spark in the presence of flammable vapors, gases or dusts can produce a fire or explosion.

Bonding Wire and the Plastic Pail

While on a recent tour of a manufacturing facility, I noticed a storage area for flammable and combustible liquids.  Although the general housekeeping was excellent, there was a 55-gallon steel drum of Stoddard solvent (flash point 102-110°F) with a bonding wire attached to the rim of a 5-gallon plastic pail (see photo).  Since non-conductive liquids such as Stoddard Solvent produce static as they flow through pipes or hoses, static electricity could build-up. If the plastic pail is used for transferring flammable or combustible liquids, there could be the potential of a fire.  Because the grounding wire was attached to a non-conductive plastic pail, I realized that grounding and bonding as it pertains to flammable liquid safety would be a great safety training topic for these employees.

Bonding and Grounding for Flammable Liquids

According to the definition, a bonding system connects various pieces of conductive equipment together to keep them at the same potential energy.  Bonding assures electrical continuity and its capacity to conduct safely any current likely to be imposed (NEC 250).  The best method to bond containers is to securely attach a special metal bonding strap or wire to both containers making sure that there is a metal to metal contact (see diagram).

Grounding is a special form of bonding in which conductive equipment is connected to an earthing electrode or to the building grounding system in order to limit voltage imposed by lighting, line surges or unintentional contact with high-voltage lines (NEC 250).  A resistance of 1 megaohm or less is generally considered adequate.  Examples of good grounds include cold water pipes that are upstream from the meter and driven grounding rods similar to those used to ground electrical systems. Both grounding and bonding connections must be bare metal to bare metal, paint and rust must be removed to maintain a good connection.

Only non-conductive liquids will accumulate a charge by flow. Examples of non-conductive liquids include solvents and fuels produced from petroleum including xylene, toluene, gasoline and mineral spirits.  These liquids tend to hold on to their charge when they flow through hoses because they cannot conduct electricity well enough to discharge when in contact with a conducing material, like a metal pipe or container that is grounded.

Diagram: Bonding and Grounding

Use a Safety Can

When dispensing flammable or combustible liquids care must always be taken to dissipate static electricity and minimize the potential for fire.  Although a 5-gallon pail may be convenient and cheap, the open surface of the liquid could collect enough flammable vapors to be within the flammable range of the chemical.  A static spark has enough energy that a fire or explosion could result.  Using a safety can is a great way to minimize the potential for a fire.

A safety can is defined as: “an approved container, of not more than 5 gallons capacity, having a spring-closing lid and spout cover and so designed that it will safely relieve internal pressure when subjected to fire exposure.” (OSHA 29 CFR 1910.106(a)(29))

Safety cans comes in two types: Type I is the basic safety can that has one opening for pouring and filling; the Type II safety can has separate openings for filling and dispensing.  Type II safety cans will typically have a nozzle extension that to allow filling the container from the bottom which is recommended to minimize splashing.

GHS Updates Definition of Flammable Liquid

If you are familiar the flammable and combustible liquid classes as Class I, Class II and Class IIIA and IIIB, it is time to forget about that, and get to know the new classification system for the Globally Harmonized System (GHS).  The OSHA standard on Flammable and Combustible Liquids 29 CFR 1910.106 has been updated to reflect recent GHS updates.  Flammable and combustible liquids are still divided into different groups depending on their flash point and boiling point, but now any liquid having a flashpoint at or below 199.4 °F (93 °C) is considered a flammable liquid, and divided into four GHS categories, see Table 1.  According to this new classification system, Category 1, 2, or 3 flammable liquids with flashpoints below 100 °F (37.8 °C), cannot be dispensed into containers unless the nozzle and container are electrically interconnected.

Flammable Liquid Storage and Preparedness

When flammable and combustible liquids are stored, one of the approved methods of storage is inside a flammable liquid storage cabinet.  Use of a cabinet will protect the flammable liquid against a flash fire and contain any spilled material that could further spread a fire.  These cabinets are also designed to protect the internal contents from a fire outside the cabinet.  Although the maximum quantity of flammable liquids that can be stored inside a single cabinet is no more than 60 gallons of a Category 1 flammable liquid (Class 1A flammable liquid) (NFPA 30), a good rule of thumb is to not store more than what you can use within a reasonable timeframe.  Before storing any flammable or combustible liquids it is important to verify that the chemicals being storage are compatible.

Since a fire is a primary concern when handling flammable and combustible liquids, the best advice is to be prepared.  Personnel need to be trained to handle emergencies and Class B fire extinguishers need to be readily available to keep a small fire from becoming a big fire.

Conclusion

Accumulation of the static charge can be controlled, but you have to know what to look for.  Make sure that all of your equipment is sufficiently conductive and properly grounded to minimize the possibility of fire.  Although a 5-gallon plastic pail may be convenient for transferring flammable liquids, think “safety first”, use a safety can and be prepared to respond to an emergency situation.

There are many State and local codes concerning bonding and grounding to find out more about the requirements in your particular area, contact your local fire marshal.

References:

  • Flammable and Combustible Liquids, 29 CFR 1910.106. www.osha.gov
  • How Do I Work Safely with Flammable and Combustible Liquids (Static Electricity), Canadian Centre for Occupational Health and Safety. www.ccohs.ca
  • Grounding and Bonding, National Electrical Code (NEC) Article 250, National Fire Protection Association, 2014 www.nfpa.org