Synergist - November 2010

The Static Electricity Hazards of Handling Flammable Liquids

BY MARK A. LUCAS

Around 1 p.m. on Oct. 29, 2007, a worker at the Barton Solvents warehouse in Des Moines, Iowa, was filling a 300-gallon steel tank with ethyl acetate (CAS 141-78-6), a flammable solvent. The worker secured the fill nozzle with a steel weight and was on his way to another part of the warehouse when a popping sound caused him to turn around. The tank was engulfed in flames, and the resulting fire set off a series of explosions that, according to reports, flung 55-gallon drums of chemicals hundreds of feet into the air. The main warehouse was destroyed; one employee was injured, and a firefighter suffered heat-related illness.1

A few weeks later, the U.S. Chemical Safety Board (CSB) determined that the Barton Solvents fire was likely the result of inadequate bonding and grounding. Static electricity accumulated on the surfaces of the steel weight and nozzle, igniting the ethyl acetate vapors and eventually setting off an explosion that could have resulted in significant loss of life.1

Since many electrostatic hazards involving flammable liquids do not ignite fires or cause explosions, the same conditions that ultimately destroyed the

Barton Solvents warehouse could exist in your facility. Knowledge of static electricity principles and control measures can help ensure that a similar event doesn’t occur at your work site.

Principles of Static Electricity

Static electricity—the buildup of electrical charges on the surface of objects— can occur whenever two different materials have been in contact and are separated (known as the triboelectric effect). Static charge will remain on the surface of objects until they are either bled off to ground or neutralized by a discharge. Most of us have experienced a static discharge when walking across carpet in the winter and touching a doorknob. However, many people are unaware that liquids and powders (dust) can also generate static electricity that, under certain conditions, can result in fires and explosions.

The following conditions are necessary for a static electric discharge:

1. an appropriate material for the static charge to accumulate (at least one of the surfaces must be an electrical insulator)

2. sufficient energy created

3. a means to discharge that energy
If an electrical charge is allowed to
accumulate due to insufficient ground-
ing, a static discharge may be generated
(i.e., neutralization of charge). Industrial
processes, such as moving metal pieces
on a conveyor belt or solvents (such as
hexane, toluene and varnish makers’ and
painters’ naphtha) flowing through pipes
into mixing vessels or spray painting,
can generate static charges.