The most common generators of static electricity are processes involving flammable liquids. Static electricity is generated by liquids flowing through pipes, and in mixing, pouring, pumping, filtering, or agitating liquids. The rate of generation is influenced by the conductive of the liquids, the amount of turbulence in the liquid, the interfacial surface area between the liquids and other surfaces, liquid velocity, and the presence of impurities.
Some specific locations where static electricity is generated include:
- Piping Systems – In piping systems the generation rate and the subsequent accumulation of static charge are a function of the flow rate, liquid velocity, pipe diameter, and pipe length.
- Filling Operations – The turbulence experienced in filling operations, caused by large flow rates, splashing or free-falling liquids, greatly increases the charge accumulation above the level generated in piping systems.
- Filtration – Filters, because of their large surface area, can generate as much as 200 times the electrostatic charge generated in the same piping system without filtration.
- Dispersing Operations – Of all operations, dispersing operations can be particularly hazardous in view of the extremely high rate of charge generation when particulates are present. With poorly-conductive liquids the charge accumulation can cause hazardous sparking in the vapor space, such as to an exposed agitator blade in a mixer or to a conductive fill pipe. High charge generation rates can also occur when liquids are mixed, thinned, tinted or agitated.