Electrical Classification
Safety and area classification
Safety principles
Installations in which flammable materials are handled or stored should be designed, operated and maintained so that any releases of flammable material, and consequently the extent of hazardous areas, are kept to a minimum, whether in normal operation or otherwise, with regard to frequency, duration and quantity.
In the case of maintenance activities other than those of normal operation, the extent of the zone may be affected, but it is expected that this would be dealt with by a permit-to-work system. In emergency situations, reliance should be placed on the isolation of unsuitable electrical equipment, shut-down of the process, isolation of process vessels, containment of spillages and, if possible, the provision of additional emergency ventilation.
In a situation in which there may be an explosive gas atmosphere, the following steps should be taken:
a) eliminate the likelihood of an explosive gas atmosphere occurring around the source of ignition, or
b) eliminate the source of ignition.
Where this is not possible, protective measures, process equipment, systems and procedures should be selected and prepared so the likelihood of the coincidence of a) and b) is so small as to be acceptable.
Such measures may be used individually if they are recognized as being highly reliable or in combination to achieve an equivalent level of safety.
Area classification objectives
Area classification is a method of analyzing and classifying the environment where explosive gas atmospheres may occur so as to facilitate the proper selection and installation of apparatus to be used safely in that environment, taking into account gas groups and temperature classes.
In most practical situations where flammable materials are used, it is difficult to ensure that an explosive gas atmosphere will never occur. It may also be difficult to ensure that apparatus will never give rise to a source of ignition. Therefore, in situations where an explosive gas atmosphere has a high likelihood of occurring, reliance is placed on using apparatus which has a low likelihood of creating a source of ignition.
Conversely, where the likelihood of an explosive gas atmosphere occurring is reduced, apparatus constructed to a less rigorous standard may be used. In both situations, the area classification should be carried out by those who have knowledge of the properties of flammable materials, the process and the equipment, in consultation, as appropriate, with safety, electrical and other engineering personnel. Electrisk has the experience necessary to adequately and accurately electrically classify your areas.
Dust can be explosive too…
The nature of a dust explosion. A dust explosion is the rapid burning of a cloud of dispersed dust accompanied by the release of thermal energy in a pressure wave. The flame can travel rapidly through the dust cloud, igniting other adjacent combustibles.
An initial explosion often dislodges settled dust from building structures and machinery. This dislodged settled dust may be ignited by glowing residue from the initial explosion, and a secondary explosion may follow. The quantity of dust thus redispersed may cause more extensive injury and property damage than the initial dust cloud. Good housekeeping in an area made hazardous (classified) by dust is vitally important, and will keep accumulations on structures and machinery to a minimum.
Even a puff of air in the presence of an ignition source or a small flame can initiate a dust explosion. While dust accumulated as a layer will not explode ordinarily, it may melt, char, or burn. This burning can generate heat and air turbulence that may disperse further amounts of dust, which may then explode. Therefore; atmospheres that have the potential to become explosive must be electrically classified as hazardous as well—an expertise readily available from Electrisk.