Hazardous Locations Classifications

For an area to be classified as hazardous, the following three requirements for a Fire Triangle must be present simultaneously:
      Flammable gas, dust, or fiber
      Ignition source
      Air/oxygen.
Hazardous locations are broken into Divisions, Zones, Classes and Groups. These enable the manufacturer to specify exactly the type of hazardous location for which the product has been certified. The first classification describes the presence of flammable material in a hazardous location, either continuously, intermittently, or abnormally. The apparatus grouping states what type of flammable material is present: either gas, dust, or fiber. The temperature codes indicate the maximum temperature the device''s external enclosure can reach. This is summarized in Table 1.

Table 1:       Hazardous Locations Classifications

Protective Concepts

For a product to be approved for a hazardous location, it must be designed so that an explosion of the flammable or combustible material surrounding the device does not occur. There are different methods of protection to achieve this. Viatran uses the three most accepted methods in the pressure transmitter market: Intrinsic Safety, Explosion Proof (Flame Proof), and Suitable for Use in Hazardous Locations.

Intrinsic Safety
An Intrinsically Safe piece of equipment is an electrical device that is incapable of causing an ignition of the prescribed flammable gas, vapor, or dust, regardless of any spark or thermal effect that may occur in normal use, or under any conditions of fault likely to occur in practice. This means that the device design is limited in such areas as PC Board layout, surface temperature, protection of electrical components, and power supply to the device. The devices are certified with either specific Intrinsic Safety Barriers (Loop certification) or general Intrinsic Safety Barrier parameters (Entity certification). These barriers are used outside the hazardous location and limit the amount of current, voltage, capacitance, and inductance entering the certified device. Often considered the safest and most technically elegant approach, there are many benefits of an Intrinsically Safe device to the customer. Expensive and cumbersome explosion-proof enclosures and conduit connections are not needed, electric shock is minimized, and controls can be maintained without shutting down the process.

Explosion Proof / Flame Proof
An Explosion Proof (or Flame Proof, as classified in IEC and Cenelec standards) device is an electrical device designed with an enclosure capable of withstanding, without damage, an explosion within it of a specific gas, fiber, or dust. In turn, it prevents ignition of these same materials surrounding the enclosure by a spark or flame from the explosion within. Factory Mutual formerly limited its Explosion Proof standard by requiring that the explosive external material be able to enter the device to cause an explosion. This excluded hermetically sealed devices from approval consideration. FM has recently modified their definition to include these devices. This certification usually requires that devices be designed with sturdy and durable enclosures with conduit connections. The primary benefits of this type of protection are that the device is not limited by low available power nor does it restrict PC Board layout. Viatran has also designed some of the smallest Explosion Proof devices in the industry.

Suitable for Use in Hazardous Locations
Factory Mutual developed this unique approval as a way for products to receive hazardous location approvals that cannot conform to existing protection concepts. There is no documented standard and the definition of this certification is unique to each product. In Viatran''s case, this protection concept was utilized for our hermetically sealed products that did not meet FM''s former Explosion Proof definition. Products that receive this approval are certified to the same Divisions as a comparable Explosion Proof or Intrinsically Safe device.