The supply of fresh air and the discharge of the exhausted air are of significant importance for workers’ health and it is a part of the safety work environment conditions. That is also very important in some specific industries where volatile are flammable gases, dust or harmful substances are emitted in the air.
Examples of such industries are:
– Woodworking factories
– Laboratories
– Chemical industry
– Painting chambers
– Car industry and car services
– Car parks
– Silos for grain storage
– Chemical and paints storages
– Fireworks manufacture and storage
– Military industry
– Petroleum refining facilities
– Flammable and combustible liquids storage.
In this case the ventilation is very important and one way to ensure the security and safety of the installation is using explosion proof fans.
The level of explosion proof is determined by Directive 94/9/EC on equipment and protective systems intended for use in potentially explosive atmospheres (ATEX).
Once the fan is selected correctly according to the needed air flow and pressure, the next step is to choose the right protection class of the fan’s motor. The symbols after the sigh for explosion environment give information about the application, zones, temperatures and the type of environment, where the electric appliance could work.
According to Directive 94/9/EC equipment operating in hazardous area is divided into two main groups. The first group “I” are units that use to work in mines. The second “II” are the units used in any other possible explosive environments.
Equipment category is defined by the type of environment in which it will work.
Zones 0, 1, 2 refer to gas and 20, 21, 22 to dust. The zones themselves define the level of explosion risk – 0 refers to a place where an explosive atmosphere is constantly present. Zone 1 determines an environment in which an explosive atmosphere is likely to occur in normal operation occasionally. Zone 2 corresponds to places in which an explosive atmosphere is not likely to occur in normal operation, but if it does only occurs for short periods.
The third component of the European mark is the type of protection. The following types are specified:
EExia/ib – Intrinsic safety
EExe – Increased safety
EExd – Flameproof
EExp – Pressurization
EExq – Powder filling
EExm – Encapsulation
EExo – Oil immersion
EExn – Type „n”
Depending on whether it is danger of explosion due to gas or dust the following sub-groups are defined according to the type of gas or dust.
The last characteristic is the temperature. This is the highest acceptable surface temperature on motor surface. It must be beyond the ignition temperature of the atmosphere (gas, dust).
The classes are as followes:
It is important to say that certain chemicals may have characteristics that required safeguards beyond those required for any of the certified atmospheric groups. Chemicals with low ignition temperature are a very typical example.
Atmospheres containing specific metal dust also have safeguards beyond those specified in the directive. For example zirconium, thorium and uranium dust have an extremely low ignition temperature and minimal ignition energy, lower than any classified in group I or II material.
In some specific cases it is required not only an explosion proof fan motor bur also a spark proof construction of the fan. This means all major components are made from materials that will not produce sparks as a result of struck (or other kind of direct impact on the impeller/blade during work).
Do not forget that the use of an explosion proof motor alone or aluminium blade/impeller does not make the fan “explosion proof”. Only approved and certified according to the European standards products could guarantee and minimize the risk of explosion in applicable hazardous atmosphere.