Working Safely in Potentially Explosive Areas
Companies operating in such widely differing sectors as the chemical and pharmaceutical industry, the gas supply sector and the varnishing industry use combustible materials that can potentially explode. These ‘explosive protection zones’, or ‘Ex-zones’, are classified into various areas and zones depending on the nature of the flammable material (gas and vapour, or dust) and also on the probability of the presence of an explosive atmosphere i.e frequency and length of time that the hazard exists.
Combustible gases and vapours are classiﬁed into three explosion groups (IIA, IIB and IIC) according to the minimum amount of energy required to ignite them. The most easily ignitable group is class IIC.
The ATEX Directive was introduced in July 2006 to ensure that people working in potentially explosive atmospheres are properly protected.
Electrostatic charge and discharge
These days, anyone working in a potentially explosive area must follow strict safety rules and use proper ATEX-compatible protective equipment. It doesn’t matter whether you are working with combustible gases or easily ignitable dust. In addition to naked flames, incandescent materials and sparks, electrostatic discharge is an ignition hazard that causes serious accidents time and time again.
An electrostatic charge occurs if a material has built up too many electrons (negative charge) or not enough electrons (positive charge). In commercial and industrial situations, this can happen whenever non-conducting isolating or poorly conducting materials are used in processes involving friction or separation. Examples include: removing paper, textile, rubber or plastic tracks from rollers or cylinders, passing powdery material through pipes, transferring liquids between containers, stirring and decanting liquids, and walking on an insulating surface.
When/if an electrostatic charge is built up and is not dissipated slowly to earth, then a spark can be generated as the charge is rapidly grounded, for example upon approaching or coming into contact suddenly with an earthed conductor. If the energy of the spark is sufficiently high, it has the potential to ignite the explosive atmosphere. This means that in the event of discharge in a potentially explosive environment, an ignitable spark can be created and cause a major disaster.
Tyvek® and Tychem® antistatic garments and Ex-zones
The DuPont solution is simple. The surface of antistatic garments made of Tyvek® or Tychem® is coated with an antistatic chemical that attracts moisture from the air, producing a thin, conductive salt layer on the surface of the clothing. The surface coating creates a homogeneous conduction effect, i.e. any locally generated charge – caused by friction, for example – can be discharged earth if the resistance to earth is continous and sufficiently low.
With dedication and ingenuity, DuPont engineered Tyvek® and Tychem® protective apparel that can meet the antistatic requirements of the ATEX Directive, as well as the requirements of the EN 1149-5 surface resistance performance standard. For heat, flame and chemical protection in Ex-zones a limited flame-spread (meeting EN ISO 14116 index 1) and dissipative protective coverall, worn above index 2 or 3 heat-flame garments is recommended.
Use of Tyvek® and Tychem® protective clothing in Ex-zones
According to tests conducted by the Swiss Safety Institute in Basel, Tyvek® and Tychem® protective clothing are suitable in numerous volatile situations.