Case study: explosion protection at a petrochemical plant

A petrochemical plant combining solvent storage with powdered-solids handling was reviewing its explosion protection document. The assessment showed that existing venting did not cover every item of equipment and that no isolation device separated units connected by ducting. This is the technical approach taken and the reasoning behind each decision.

The starting point

The installation carried two distinct risks under the same ATEX umbrella: explosive vapour atmospheres in the solvent tank farm and combustible dust atmospheres in the pneumatic conveying line and bag filters. Tank vents discharged to atmosphere without a certified flame arrester, several units on the solids line had no sized vent area, and none of the ducts linking filter, cyclone and silo had explosion isolation.

What the regulations require

The framework is twofold: Directive 2014/34/EU (ATEX 114) governs equipment intended for explosive atmospheres, while 1999/92/EC (ATEX 153) requires the operator to classify zones and maintain an explosion protection document. In practice that translates into three technical decisions: prevent the explosive atmosphere from forming where possible, remove ignition sources, and — where neither is enough — limit the effects of the explosion through venting, suppression and isolation.

The solution implemented

• Explosion vent panels sized to EN 14491, using Kst and Pmax values measured in the laboratory with the plant's actual dust rather than table values.
• A flap-type explosion isolation valve in the suction duct, compliant with EN 16447, to stop the flame front and pressure wave propagating to the adjacent unit.
• Flame arresters certified to EN ISO 16852 on the solvent tank vents, selected by the explosion group of the vapour and by the deflagration or detonation type foreseen.
• Pressure-vacuum valves sized to API 2000 on the atmospheric tanks, replacing open vents.
• Spark detection with automatic extinguishing on the pneumatic conveying line, as a barrier ahead of the explosion itself.

Why isolation was the key element

The most common error in installations like this is protecting each unit separately and forgetting the ducts between them. An explosion starting in a filter accelerates as it travels along the duct and reaches the adjacent silo at far higher pressure and speed than the original event: the receiving vessel, sized for a normal deflagration, fails. Venting alone does not prevent this; only an isolation device — flap, fast-acting valve or chemical barrier — cuts the propagation.

What transfers to other plants

• Characterise the dust in the laboratory before sizing: real Kst and Pmax completely change the vent area required.
• Treat every interconnecting duct as a protection point, not as pipework.
• Check the flame arrester's chemical compatibility and service temperature, not only its explosion group.
• Close the documentation loop: protection is only valid once it is reflected in the explosion protection document and in the maintenance plan.

Tecnovent designs and supplies complete explosion protection systems: venting, isolation, suppression, flame arresters and tank protection. If you are reviewing your plant's explosion protection document, describe the installation and we will propose the scope.