Electrician

[Pushpin]

Can anyone explain to me what Table 515.3 means when it refers to tanks and dike walls. I thought anything within the dike up to the dike wall was Class 1 Div 1. We are storing gas, methanol. diesel ect.:-?

 

[rbalex]

... I thought anything within the dike up to the dike wall was Class 1 Div 1...

It is common misconception. This generally comes from drawing the reasonable, but unnecessary, conclusion that below grade locations are usually Division 1. Actually, if there were relatively good ventilation, even below grade locations would not truly need to be Division 1; however most below grade locations have no ventilation at all.

Dike areas are usually different. Air flow is usually unrestricted so unless there is a great impediment to it, such as the ?? dike height is greater than the distance from the tank to the dike for more than 50 percent of the tank circumference,? a Division 2 classification is sufficient. See NFPA 497, Figure 5.9.4(a) or APR RP500, Figure 6, Section 8.2.1.1 as typical examples

Table 515.3 is extracted from Table 8.2.2 of NFPA 30 which is the governing Standard for the bulk storage of flammable and combustible liquids.