Prevening Electrostatic Discharge in ATEX Environments
EDITOR ’ S CHOICE CARBON LOADING POLYPROPYLENE
AXAIR FANS
Prevening Electrostatic Discharge in ATEX Environments
To avoid electrostatic discharge , plastics used in explosive fume extraction systems that move air , or are situated in an area where potentially hazardous fume are present , must be electrically conductive or static dissipative . The most effective way of dissipating electrostatic discharge is to add conductive carbon black to the polymer matrix .
For the context of this article , we ’ ll consider how polypropylene corrosion resistant fans which are the preferred construction material used to handle toxic and hazardous fumes in fume extraction systems , are modified to enhance the ATEX suitability for zone 2 potentially explosive environments . These ATEX certified polypropylene fans are manufactured from polymers that have special branched carbons with a structure that can transport the flow of electrons and dissipate electrostatic charge .
In potentially explosive environments , if the conditions call for it , such as the build-up of IIC hydrogen gas in large quantities , the presence of static discharge can be enough to ignite and cause an explosion . The concept of ensuring a product is ATEX certified ensures that the fan component in our case , is not itself , a risk or an ignition source . ATEX fans reduce the risks of creating sparks from friction , static electricity or from arcs in motor malfunctions for example . In ATEX product labelling , Ex h markings signify that the nonelectrical fan component ( excluding the motor ) has been constructed sufficiently to be used as intended in an explosive environment . In short , precautions during the manufacturing process have reduced this risk .
By nature , without additives or fillers , commercial plastics are electrical insulators . Charges deposited on the polymer surface are living therefore a long time , and the longer the lifetime , the more likely the possibility of an electrostatic discharge event such as static discharge . The rate of charge dissipation is known as the charge decay time , this considers the electric resistivity which tells us how strongly a material opposes the flow of electric current , and the dielectric permittivity , which characterises the ability of the material of storing an electrical charge when subjected to an applied voltage .
For static dissipation , we must reduce the decay time of the charge , by enhancing conductivity and reducing permittivity . The loading of polymers with conducting additives reduces the resistivity of polymers .
Due to the presence of static charges , polymers must be turned into materials capable of draining these charges and protect the devices from static discharges . Therefore be able to conduct electricity to some extent . Commercial polymers are natural electrical insulators , so they need to be engineered to become antistatic dissipative or conductive . This is realised either through chemical treatment or through the addition of conductive agents during the processing .
One of those fillers is known as carbon black , a relatively inexpensive and processible filler material , formed by burning hydrocarbons in a limited oxygen environment . These are used extensively in packaging but also used , as shown in our ATEX corrosion resistant range , for CB filled high density and low-density polypropylene .
Simply put , carbon loading is a process in which carbon black particles or fibres are incorporated into the polypropylene during manufacturing . This addition of carbon enhances the conductivity allowing it to dissipate accumulated static charge more effectively , minimising the risk of ESD . Where airflow passes through fan blades , friction can generate static charges on the fan surfaces , and in environments with combustible materials , static charges can ignite or trigger an explosion
So , in a nutshell , that ’ s how we ensure that our ATEX polypropylene fans are manufactured in line with the ATEX directive , making them suitable for their intended use .
For further information , please visit www . axair-fans . co , uk
10 PECM Issue 67