It is interesting to note that static discharge from a human being may reach 60 mJ or more. A safety precaution with humans involved is to consider the human body capable of igniting a flammable environment with an MIE equal to 100 mJ or lower. A spark that is perceivable to the touch has around 20 mJ.

The energy levels produced in a given environment is a function of the process of charge separation, accumulation, and discharge. This combination gives the risk associated with static charges on flammable and combustible liquids. Good conductors are the best electrostatic generators, but this property allows them to discharge charges quickly. However, the Low conductivity liquids cannot discharge swiftly and they accumulate electrostatic charges, making them ‘static accumulators’. For this reason, the low conductivity products are the most dangerous. For example, ungrounded conductive objects such as truck tankers which are on rubber tires receiving charged liquids such as petroleum and liquids of highly refined products are typically static accumulators.

With increase in static accumulation, static potential increases, giving rise to an electric field. As electric field intensity reaches above 3kV/mm, which is the dielectric strength of air, sparks may occur leading to explosion.

In addition to the above, the presence of oxygen in the flammable environment also aids the explosion process. For this reason, use of inert gases such as Nitrogen is preferred.

Given the complex nature of circumstances that may potentially contribute to unsafe environments, ESD Control Systems could help advise based on detailed assessments the best course of action and path to eliminating static electricity hazards.