Quantitative classification of equipment protection level in concept of zone classification with downtime of protective measures

Handling flammable materials has a risk that can create explosive atmosphere. Such locations are classified as hazardous area, depending on the frequency and volume of explosive atmospheres. General electrical equipment is prohibited in the hazardous area and explosion protected equipment is used. These are the spatial isolation of ignition sources within the fire triangle, but even time isolation can prevent explosion hazards as well. It is proposed a method to classify zones from the calculation of downtime of protective measures based on failure rates and repair times of protective measures related to ventilation in explosive gas atmospheres with the Functional Safety under the time isolation concept. On the other hand, according to International Electrotechnical Commission (IEC) System for Certification to Standards Relating to Equipment for Use in Explosive Atmospheres, explosion protected equipment was also classified as an Equipment Protection Level, "EPL". The EPL should be selected according to the risk of the hazardous area. However, in IEC60079–14:2013, users can choose any EPL according to their risk assessment. In this paper, we clarify the quantitative risk difference of EPLs with expansion the idea of classifying hazardous area from the downtime of protective measures and introduce a means to quantitatively classify the EPL of equipment in an explosive gas atmosphere.