Handling Static Charge in Pharmaceutical Manufacturing

Static charge is the electric current developed by the rubbing of moving parts of equipment or contact and separation of material particles. It is generated in different pharmaceutical manufacturing equipment during processing. Sometimes it is generated by the continuous flow of the powder on the equipment surface.

Moving metal parts may also generate the static charge if there is a film of the oil between the shaft and the bearing that breaks its circuit from the earth. Insulation on some parts of the machines can also help to hold the static charge in the equipment.

Numerous types of equipment are there in pharmaceuticals those can cause the charging of the powders as blenders, FBD, vibro sifters, rapid mixer granulators, colloidal mills, mixers, packing machines, coaters and hose pipes. But vibro sifters and fluid bed dryers are common.

One of the static charge examples have seen is an incident when I was working in a pharmaceutical manufacturing unit; a powder was burned in sifter during the sifting due to the static charge when the worker sifting the material was wearing the plastic gloves and pressing the material on the sieve. It should be prevented from building up to a hazardous level where it may harm the product as well as the human.

The material having volatile solvents can get flamed by a spark due to static charge. It may cause damage to the material or may affect the personnel working in the area. Static charge in equipment those have pressure during operation as FBD may dangerous for the operators too.

I have also seen a blast in fluid bed dryer during the drying of the material due to static charge that was having the isopropyl alcohol and it was sufficiently strong to harm the operator working in the area.

Static charge can also affect the product quality. It can have an adverse effect on powder blend uniformity. Particles having same charge (negative or positive) may come together and can have a negative impact on blend uniformity. Negatively charged API particles may accumulate near the wall of FBD or finger bag and can affect the content uniformity of the final product.

Following methods can be used to prevent and control the damage from the static charge in pharmaceutical industries.

1. Earthling of the equipment is primary measure to prevent the static charge by moving it to the earth. All equipment in the manufacturing area must be earthed properly and personnel working in the area should wear cotton clothing.

2. The conductance of the equipment wheels, floor and footwear should be increased to prevent the development the static charge.

3. Increase the conductance of the of non-conductor materials by using conductor films etc.

4. Increase the conductance of the atmosphere by humidification of the area or ionizing the air. Relative humidity more than 65% makes a very thin layer on the equipment surface that can prevent the accumulation of the static charge on the equipment surface.

The earthing connections of the equipment should be checked and tested periodically especially after the equipment maintenance. Bonding of the different parts of the equipment with conductor wire can also help to neutralize the static charge and we must find the ways to prevent static electricity in all equipment and instruments.