Reclassification by Ventilation

[cherry2000]

I believe this topic has been discussed in the forum previously..Can we reclassify an enclosed area with Ventilation? If we do not want to conduct fugitive emission studies, and we have three air changes (with detectors), is this good enough for a Zone 2 Classification as per API 505?

 

[mbt22]

I don't know about API505, but for IP15 that would be a definite no. Adequate ventilation, the rate needed to treat the enclosed area as if it was outside, is 12 air changes per hour. Dilution ventilation, typically reduces the zone 1 step, would be more like 40 changes per hour.

There are a whole series of requirements for the air changes to cover reliability (installed spares ready to go), what to do if ventilation is lost, how one could restart the ventilation and the like.

Matt

 

[cherry2000]

API has recommended dilution ventilatin is various sections, viz.6.6.2.4.5, 6.6.2.4.8,7.3 etc...also in the APpendix, the IEC method of Hypothetical volume has been explained.

 

[JLSeagull]

Review NFPA 496 2008. Other standards address adequate ventilation. Three air changes per what? I don't think that three air changes per hour work.

 

[cherry2000]

Well JLSegull..by definition, "adequate ventilation" is that which is sufficient to prevent accumulation of significant qts .....Now to prove this, we will have to carry out fugitive emmission calcs...if the volume of the enclosed space is large enough, and fugitive emission rate is small enough..even three air changes may siffice.

 

[JLSeagull]

Some standards have a clear definition of adequate ventilation. Three air changes per hour may not be adequate. In the event of gas detection additional ventilation should be activated. Sorry but I cannot name the standards right now. I have looked into this before. BTW you must address the rate such as three changes per minute, per hour, per day or per century. Three changes means nothing without the time period. And if you are so sure that three changes are adequate why ask the question?

 

[JLSeagull]

See NFPA 69 Explosion Prevention Systems Appendix D for ventilation calculations.

 

[rneill]

There may be local regulatory requirements that come into play as well. In Alberta, the local authority mandates a minimum of 6 air changes per hour for oil and gas facilities to be triggered by gas detection.

 

[JLSeagull]

Adequate ventilation differs for ammonia, paint booth, fugitive emissions, etc.

NFPA 30 Flammable and combustible liquids
A.3.3.57 Ventilation.
... sufficient to prevent accumulation of significant quantities of vapor-air mixtures in concentrations over one-fourth of the lower flammable limit (LFL).
Annex F has a calculation method and example.

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