Standby Generator Rooms with Diesel Day Tanks 1

[cmerch]

I am currently designing a standby generator room with a 300 gallon day tank. From an IBC standpoint my room will classified as a H-2 Occupancy. What type of NEC Hazardous Space Classification would this room have. Based on the 2011 NEC 500.5(B)(2)(1) it appears that now if combustible liquid-produced vapor are present due to accidently rupture the space needs to be rated Class I, Div. 2. The combustible liquid language was not present in previous version of the NEC. Is anyone aware of anything I can do to avoid rating the space.

 

[stookeyfpe]

Which edition of the IBC? If you are under the 2009 or 2012 IBC, you do not need to classify the room as a Group H occupancy based on the volume of fuel. See IBC Table 307.1(1) foot note i. If you chose this option the tank installation will be required to comply with the requirements in 2009 IFC Section 603.3.2.

You can avoid area classification if your tank is properly engineered. 2009 IFC Section 603.3.2 requires the tank fill connection to be located on the exterior of the building. The tank's normal and emergency vent are also required to be terminated outdoors. If your tank is specified with integral secondary containment, a rupture of the primary tank would prevent the escape of vapors. Such an abnormal operation is contained within the unit equipment or vented outside the building. I would not apply area classification in such a case.

 

[cmerch]

Stookeyfpe, I appreciate the information. I am under IBC 2009. I will look into the IFC requirements. I'm still not certain with regards to the electrical classification of the space. The vaguiness of NEC Section 500 is difficult to manage. While I agree with your statements about the double wall tanks, we also have a fuel delivery system within the room. The part of the section (2011 NEC 500.5(B)(2)(1)) that really trips me up is "...normally be confined wihtin closed containers or closed systems from which they can escape only in case of accidently rupture or brakdown of such contain or systems..." would you suggest double wall piping on the fuel system would eliminate need for the rating.

 

[stookeyfpe]

Pipe with secondary containment is one option but it can be expensive and a pain in the posterior. As an AHJ I would accept flanged connection with welded fittings.

 

[SprinklerDesigner2]

I will answer this when I get home but for now I am out of the office.