The transfer of flammable/combustible corrosive liquids is a common function in the pharmaceutical and fine chemical industry. Transfers of liquid are typically conducted from a fifty-five gallon drum to a reaction vessel using a portable pumping system. This transfer process generates the potential for static discharge which may serve as an ignition source for flammable liquids. This paper discusses a case study at a pharmaceutical manufacturing plant (International Specialty Products in Columbus, Ohio,) and will review:
the hazards posed by static electricity discharge when transferring flammable liquid,
a unique request by our production department for one style of a portable drum pump for all flammable/combustible liquid pumping activities, and
the solution with a discussion of the layers of protection for the pumping task.
The premises with regard to the occurrence of electrostatic discharges involving our liquid transfers are:
In order for a potentially electrostatic discharge to occur, there must be a mechanism by which an object's surface becomes electrostatically charged, and accumulation of that charge and subsequent discharge
The primary route of charge generation will be through contact electrification where two materials are brought into contact and then separated (in our case the fluid and the pump.) The level of charge generation is dependent on the speed of the fluid, force of liquid contact, and characteristics of the coating surface
The metal parts of the pumps can be charged through induction. The action of the pump inside the housing can accumulate charges on the metal portions of our pump
Our pump system can also be charged if a charged non-conductive liquid flows through it. This charge occurs on the surface of the pump.
The generation of electrostatic charges is not itself of safety concern. The concern is if static charge accumulates and then an electrostatic discharge occurs generating an ignition source. These discharges can provide energies which are above the minimum ignition energies of many of the flammable and combustible liquids used at our facility. In a pump system, there are two main potential locations where a charge may accumulate:
The metal parts of our pump will accumulate electrostatic charge if they are not grounded.
The internal surfaces of the pump can become charged through contact with the fluid being pumped.
Figure 1. Typical application of portable drum pump for transfer of flammable liquids. (available in full paper)
Our Production Department sought to have one type of pump for all liquid additions to our reactor systems. An existing two-pump system was the traditional method to safely transfer flammable non-conductive liquids. A metal pump was used for non-conductive flammable liquids and a polypropylene pump was used for corrosive liquids. During Hazard and Operability (HAZOP) studies, a scenario involving human error for selection of improper pump (polypropylene pump) was chosen to transfer a non-conductive flammable liquid.