Static charge is a small variable which affects the quality of the product indirectly, so we should understand how it can be avoided. Static charges can also have a major impact on human safety and is a health hazard.
Static charges is a major cause of fire and explosions in many industries handling flammable liquid and many incidents have been reported around the world in pharmaceuticals also due to static charges.
What is Static Electricity :
Static electricity is an imbalance of electric charges within or on the surface of a material. The charge remains until it is able to move away by means of an electric current or electrical discharge. Static electricity is named in contrast with current electricity, which flows through wires or other conductors and transmits energy.
A static electric charge is created whenever two surfaces contact and separate, and at least one of the surfaces has a high resistance to electrical current (an electrical insulator). The effects of static electricity can be demonstrated by the spark as the excess charge is neutralised when brought close to an electrical conductor (e.g. a path to ground), or a region with an excess charge of the opposite polarity (positive or negative). The familiar phenomenon of a static shock, more specifically, an electrostatic discharge–is caused by the neutralisation of charge.
Static electricity is generated when two or more objects rub with each other charge does not generates due to friction it rather generates due to increase in surface area when we rub two things.
Generation of Static Charges in Pharmaceuticals:
Pharma manufacturing have come across many operations in line with the above categories wherein it is prone to generate static electricity for e.g.
- Solvent dispensing
- Fluidised bed drier
- Powder transmission
Electric charges can build up on an object or liquid when certain liquids (e.g., petroleum solvents, fuels) move in contact with other materials. This charge can occur when liquids are poured, pumped, filtered, agitated, stirred or flow through pipes. This buildup of electrical charge is called static electricity. Even when liquids are transported or handled in non-conductive containers, something rubbing the outside surface of the container may cause a static charge to build up in the liquid. The amount of charge that develops depends, in part, on how much liquid is involved and how fast is it flowing or is being agitated or stirred.
Transferring a liquid from one metal container to another may result in static electrical sparks. To prevent the generation of static electricity and prevent sparks from causing a fire, it is important to bond metal dispensing and receiving containers together before pouring. Bonding is done by making an electrical connection from one metal container to the other which ensures that there will be no difference in electrical potential between the two containers and, therefore, no sparks will be formed.
In pharmaceuticals because in pharmaceuticals we deal with Volatile and Flammable substances like Iso propyl alcohol , Methylene chloride which tends to burn even at single spark and could create accident in industry as well as a risk to persons working in area.
The chances of static build-up may lead spark explosions, fires, property damage and injury to workers. Occupational Safety and Health Administration (OSHA) has regulation for these liquid dispensing systems to ensure the processes being safe enough for men at work and the environment.
Vibro sifter (during the sifting of materials):
Vibro sifter consists of specially designed motor mounted vertically at the center of the base plate of the screen. The screen is in between feeding hopper and bowl. The material is fed on to the centre of top screen. The undersize material passes rapidly through the screen during its travel to the periphery. The oversize material gets continuously discharged through a tangential outlet.
Due to the vibration the friction between the screen and the product material static current is being generated in the body of the sifter. Unless the product is flammable in nature then it will not lead to an explosion but it has a great impact on the operator around it, once the operator gets in contact with any conductive part of the sifter he/ she gets the electric shock. To avoid such situation it has to be properly grounded and on real time it should be monitored and controlled before starting the operation. The static current grounding device should be integrated for monitoring and control of the process.
It can be eliminated by providing earthing to the sifter or static electricity clamp can be used.
Fluidised bed Drier :
Drying is a process of removal of liquid from solid products with the help of heat. Various process of drying is being implemented. Drying is a function of contact area, between the drying media and the product.
In fluid bed drying, heat is supplied by the fluidisation gas, in some cases the heat also being supplied by heating plates or tubes which are immersed in the fluidised layer.
These fluid beds are designed to dry powder particles where the residual moisture content is higher than what is wanted in the final powder. Hot drying air is distributed through specially designed perforated plates on which the powder particles/ agglomerates are resting.
Static charge will generate due to rubbing of materials and if binding of IPA or MDC.
Static charge generated due to the powder or granules which gets fluidised inside the dryer unit should be degenerated with proper grounding system otherwise it will may cause damage to the material or may affect the personnel working in the area.
Powder transmissions are being done by any of the following methods like conveyors, gravitational flow or flow through a pipeline with dry air. In case of gravitational flow and pneumatic conveying the friction caused between the powder and wall generates the static electricity at both ends i.e. at pipeline and the product. So the pipeline and the collecting bin should be properly grounded so that the static current generated is dissipated properly. Same grounding system (used in case of Vibro sifter) can be deployed to control the static charge generated in the system.
Static charge generation is a common remarkable occurrence for any flowing or vibrating mechanism. Where there is friction between two independent surfaces there is static charge generated and generation of static charge can’t be fully eliminated but can be controlled.
Below are the precautions which can be taken to prevent and control the generation of Static charge in pharmaceuticals.
- Earthing or Static Charges Clamp to be provided to all manufacturing equipment’s to avoid static charges and persons working in manufacturing area should wear cotton clothes.
- The conductance of equipment wheels and footwear should be increased to prevent the development of static charges.
- We can increase the conductance of the nonconductor materials by using conductor film.
- We know that maximum Indian pharmaceuticals are not taking safety precautions to avoid static charges in the equipment’s but prevention is better than cure so everybody should take care of it to avoid any damage to the Product as well as personnel.
- Earthing should be checked and verified before starting of operation of the particular equipment’s and if necessary it shall be included as a checkpoint in Line clearance checklist of all equipment’s.