ZONES Revisited

The term “ZONE” & its concept is a coordinated way to classify Hazardous Areas

Before we embark on our journey into the ZONES , let us update our information about the following terms :-

Inflammable & flammable

Flammable and inflammable do not mean the same thing. If something is flammable it means it can be set fire to, such as a piece of wood. However, inflammable means that a substance is capable of bursting into flames without the need for any ignition. …The opposite of both words is non-flammable.

To avoid the confusion of the prefix “in” (as in inflammable) which appears to be the OPPOSITE of flammable, the preferred term is “FLAMMABLE”

Explosive Atmosphere

It is a mixture with Air, under atmospheric conditions, of Flammable substances, in the form of gas, vapour, dust, powder, fibres or flyings, which, after ignition permits self-sustaining flame propagation.

Explosive Gas Atmosphere have gas or vapours as the Flammable substance

Explosive Dust Atmosphere have dust, powder

Hazardous Area

An Area in which Explosive Gas Atmosphere is or may be expected to be present, in quantities such as to require special precautions for the construction, installation & use of the equipment.

The definition of Hazardous Area dose not quantify the following 2 parameters: –

1. The Frequency of the occurrence…. (How Many Times)
2. The Duration of each occurrence …. (For How Long)

The vagueness in the definition is given clarity by the concept of ZONES.

….. So let us see & visit the ZONES.

First an official definition.

Hazardous Area classification based upon the frequency of the occurrence and duration of an Explosive Atmosphere.

So.. Zone is an industrial area or a portion  of an industrial area (within an industrial facility) where by virtue of the industrial process & the involved materials,   there are chances of explosions .

We will use the following guidelines for our journey.

“AREA-WISE , DURATION & MAGNITUDE of EXPLOSION “

Let us proceed

The first stop is the INDUSTRIAL LEVEL

The process area governed by Industrial Standards of IEC , ISO and other respective authorities and Industrial Safety protocols .

This is a SAFE or a NON-HAZARDOUS AREA .

All industrial process being carried out here does not involve the Flammable materials . This part or level of the industrial facility is SAFE as far as explosion by virtue of flammable material is concerned .

Therefore no need to mark this level .

We will not find any Zones at this level.

Proceeding further inside

Beyond or besides  the Industrial Area there is a area marked as Hazardous Area .

Rating : Zone 2

That area in which an  Explosive Gas Atmosphere , consisting of a mixture with air of Flammable substance in the form of gas, vapor or mist is not likely to occur in normal operation but, if it does occur , will persist for a short period only.

(I am following the preferred symbols as suggested in IEC 60079-10-1-2015….but in 3D)

As we move deeper into the process area beyond Zone 2 , we will find that the Hazardous Atmosphere is more persistent and its duration is more than that of Zone 2.

The Rating of the area has to be changed to ZONE 1 (Stronger & DANGEROUS than Zone 2).

Official definition : That area in which an  Explosive Gas Atmosphere , consisting of a mixture with air of Flammable substance in the form of gas, vapor or mist is likely to occur in normal operation . The occurrence is periodic or occasional.

Further deeper into the process area beyond Zone 1 , we will find that the Hazardous Atmosphere is more persistent and its duration is more than that of Zone 1.

The Rating of the area has to be changed to ZONE 0 (Stronger & DANGEROUS than Zone 1).

ZONE 0

Official definition : That area in which an  Explosive Gas Atmosphere , consisting of a mixture with air of Flammable substance in the form of gas, vapor or mist is present all the time  . The occurrence may or may not depend on the on-going industrial process .

An ideal format