A common question during Hazardous Area Classification studies is whether a relief valve requires zoning under DSEAR and Hazardous Area Classification. Relief valves are designed to operate only during emergency overpressure events, but they still need to be assessed as potential sources of release.
The short answer is yes. Relief valves must be considered when carrying out DSEAR relief valve zoning assessments, and calculations are often required to determine the extent of any hazardous area.
Zoning for Relief Valve Leakage
Even when a relief valve is not lifting, there is potential for minor leakage through the valve internals. This is typically assessed as either:
- Primary source of release, meaning it may occur in normal operation but only for short periods
- Secondary source of release, meaning it is not expected during normal operation
The classification depends on how likely leakage is under normal operating conditions. In both cases, the release rate is generally small, and the hazardous zone extent is calculated around the discharge point.
Flanged connections into the relief valve must also be assessed. These joints are in continuous contact with live process fluid and may represent an additional potential release source as part of the HAC study.
Relief Valve Zoning for Relief Events
The second scenario to consider in relief valve zoning is the relief event itself. When the valve activates, the release rate is significantly larger than minor leakage, but the event is much less frequent.
This is typically classified as a secondary source of release due to its infrequency (not in normal operation). A separate dispersion calculation is carried out to determine the hazardous area zone around the discharge location.
Depending on discharge height, ventilation, fluid properties, and release rate, the resulting zone could vary considerably in extent and shape.
Why Proper Assessment Matters
Failing to assess relief valves correctly can lead to either under classification, which creates safety and compliance risk, or over classification, which increases capital expenditure through unnecessary ATEX rated equipment.
A structured relief valve hazardous area classification zoning assessment ensures proportionate classification, supporting compliance while avoiding excessive conservatism.
If you are reviewing your Hazardous Area Classification or DSEAR compliance, our team can provide clear, calculation based assessments tailored to your site.