In the following video, a hydrocarbon gas release occurred in a Refinery on July 2009 in Texas:


In my experience, I have often discussed with people having a strange idea: for them in order to avoid a gas explosion in their plant the Hazardous area classification is enough (and you can understand that they apply the classification just because it is a law requirement or it is indicated in their company standard).

So sometime you can see in some plants where in hazardous area there are equipment suitable and certified for Hazardous (that’s good!) but just at half a meter outside the classified area a standard equipment (not suitable for hazardous area – and that’s not good!!).
They trust in the Hazardous area classification and in particular that the flammable gas cannot betray their trust: but sometime the flammable gases are not polite.

What they don’t know is that the purpose of hazardous area classification is to minimize the probability of ignition of small leaks: It is not concerned with massive releases, which are generally defined as “catastrophic release” or "Major Accident".

For instance in the "IEC 60079 Part 10-1: Classification of areas – Explosive gas atmospheres"  it is indicated:

“IEC 60079 …is intended to be applied where there may be an ignition hazard due to the presence of flammable gas or vapour, mixed with air under normal atmospheric conditions, but it does not apply to …catastrophic failures which are beyond the concept of abnormality dealt with in this standard”.

And they specify in a note what they mean:  “Catastrophic failure in this context is applied, for example, to the rupture of a process vessel or pipeline and events that are not predictable”.

Another important standard for Hazardous area classification is the API RP 505, where we can find that:

“the following items are beyond the scope of this document: …Catastrophes such as well blowouts or process vessel ruptures. Such extreme events are not predictable and require emergency measures at the time of occurrence.”

What could be the right solution for these events?

The best solution generally is not a single one but the right combination different measures, especially for some kind of industries with an high risk of Major Hazard Events.

Generally I have seen a combination of the following actions:

• Equipment suitable for Zone 2 Hazardous area in process areas also outside the classified area and especially for emergency devices (emergency lighting, navigation aids, etc.);

• installation of gas detectors with a logic that in case of confirmed gas can activate the shutdown of all potential sources of hazard and ignition and in particular the de-enegization of all the equipment not-suitable for hazardous area.