Technical Update - Understanding Dilution in Purge & Pressurization Systems

What is dilution as defined in IEC60079-2?

As defined in IEC60079-2, dilution is the continuous supply of a protective gas, after purging, at a rate that ensures any flammable substance inside a pressurized enclosure remains outside explosive limits at potential ignition sources. In simple terms, dilution ensures that even if a flammable gas, vapor, or liquid escapes inside the enclosure, it is quickly reduced to a safe concentration.

Where or when would the dilution method be useful?

Dilution is particularly valuable in pressurized enclosures that may contain an internal source of release, such as:

• Process gases

• Vapors

• Liquids that could leak or escape inside the enclosure

Once purging is complete, the dilution phase begins. A continuous flow of protective gas enters and exits the enclosure, maintaining concentrations below the Lower Explosive Limit (LEL), or in the case of inert gas, above the Upper Explosive Limit (UEL). This prevents the formation of an explosive atmosphere and ensures ongoing safe operation.

Which applications are likely to contain an internal source of release?

• Gas analysers

• Other enclosures where flammable substances may be released internally

Expo Technologies’ solution: SmartPurge II
For customers who require purge and pressurization with dilution, Expo offers the SmartPurge II, a fully certified Type X purge and pressurization system for Zone 1/21 and Class I, Zone 1/21 hazardous areas.

SmartPurge II supports three operating modes:

• Leakage Compensation (LC)

• Dilution mode – using an intrinsically safe solenoid-operated air supply valve

• Continuous Flow (CF)

In dilution mode, after purging, SmartPurge II delivers a controlled flow rate of protective gas to dilute any flammable substances inside the enclosure to below hazardous limits, fully in line with IEC60079-2 standards.