Hazardous Area Classification for Outdoor Flanges/Valves 2

[Skaffer]

Hi,

Just a quick question, going through API 505, and oil and gas handbook for hazardous area classification, I find it odd and overkill that they require 3m around outdoor flanges and valves regardless of pressure, some of these are just 2 or 4 inch well below 100 psig, while indoor can be derated with enough ACPH how can outdoor be just as bad with a technically unlimited amount of ventilation? Any help or tips or even material to look at would be great but these zones seem much too general and conservative for even zone 2 (natural gas).

Thank you.

 

[DonUK]

I suppose they have to allow for there being no wind.

 

[moltenmetal]

This is a judgment call. There are plenty of natural gas joints in the delivery piping to users' facilities, feeding natural gas appliances, and those joints don't make all the surrounding electrics instantly Div 2. That it's nat gas and not denser than air, makes things even less hazardous- unless it's inside an enclosure which can concentrate any leakage and help you get above the LEL.