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Hazardous Area Classification (HAC) for Pressure Relief Valve

Hazardous Area Classification (HAC) for Pressure Relief Valve

Hazardous Area Classification (HAC) for Pressure Relief Valve

Hi all,

Should pressure relief valve be considered as primary or secondary grade of release in IEC 60079-10-1? Section B.2.3(d) and B.2.4(d) said that relief valves can be primary or secondary depending on whether they are expected to lift during normal operation or not. My understanding is that relief valve is not expected to lift during normal operation, thus it should be secondary grade of release. We see many time that the relief valve usually have both Zone 1 and Zone 2.

According to IP-15 section, pressure relief valve is considered as secondary grade of release. To cover any fugitive emissions that may occur, a Zone 1 of nominal 1 m radius should be placed around the end of any discharge point. Where a process relief valve lifts at its design intent the extent of the resultant Zone 2 should be determined.

In summary, my conclusion is that, for relief valve, there will always be Zone 1 to cover the fugitive emission (1m or 1.5m) and Zone 2 to be determined by individual standards. Is this statement true?

RE: Hazardous Area Classification (HAC) for Pressure Relief Valve

Grades of release as defined in API RP 505 is:
Continuous : 1000 or more hours/year
Primary: 10 hours/year to 1000 hours/year
Secondary: less than 10 hours/year

In your case it appears to be an engineering judgement between Primary & Secondary.
This relates directly to Zone 1 or 2.
Even if you were to err towards the safer side and classify the area as Zone 1, would it have any effect since chances are very low you have any electrical equipment in the vicinity?
API RP 505 Fig 18 shows a 3m (10 ft) bubble of Zone 2 in adequately ventilated area.
The text reads: The criteria affecting the extent of the classification of the areas around relief valve vents in nonenclosed
areas are too diverse to specify distances. Individual engineering judgment is required for specific
cases, but in no case should the classification be less than that shown by Figure 18.

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