What counts as 'equivalent to natural ventilation'? 2

[xJAyx]

I am designing an enclosure for some process instrumentation using Hydrogen as one of my process gases.
NFA497 rule 5.4.1 states that I can be considered an unclassified area if my gases are contained within a suitable well maintained piping system in an area with adequate vetilation.
NFPA 497 Rule 5/4/2 states that adequate ventilation can be an enclosed or partly enclosed space with ventilation equivalent to natural ventilation with safegaurds against failure.

But I can not find where 'equivalent to natural ventilation' is defined. Can anyone point me in the right direction or share their experiences?

 

[stookeyfpe]

I dislike the term "adequate ventilation." It offers nothing to address the performance of the ventilation system.

For small enclosures, I recall that API RP 500 has some guidance on the area of ventilation openings to maintain a small enclosure as an unclassified area. Essentially, the design requires a fairly large opening at the bottom of the enclosure and on the opposite wall an equal size opening at the top of the wall.

 

[JLSeagull]

Review the requirements for adequate ventilation such as Section 17.11 of NFPA 30-2008, Flammable and Combustible Liquids Code.

If applicable to the refining or petrochemical industry, review Section 4.6 of API RP 500, Recommended Practice for Classification of Locations for Electrical Installations at Petroleum Facilities Classified as Class I, Division 1 and Division 2. Each standard provides guidelines regarding adequate ventilation.

 

[xJAyx]

Is there a site where I can read the API documents for free (similar to the NFPA site)? I am not in the petroleum industry, but I think that this would be an appropriate (ie safe) guideline for my application.