What is an ATEX zone?

An ATEX zone is a space of a machine/plant or working area where there is a potential explosive atmosphere. The ATEX directive 2014/34/EU evaluates these zones as follows:

ATEX Zone 20: high probability of explosive atmosphere (over 1000 h/year)
ATEX Zone 21: average possibility of explosive atmosphere (between 10 and 1000 h/year)
ATEX Zone 22: low possibility of explosive atmosphere (under 10 h/year)

In particular, TAMA AERNOVA is capable to manufacture products suitable for installation in ATEX zones 22 and products that process directly dusts which can generate a potential explosive atmosphere.

Which are the most important characteristics to consider in dusts evaluation?

Each evaluation of the dust explosive risk has to base on the nature of the processed dust. This is because every dust has different innate characteristics that give them the explosiveness, regardless how they are processed. Among these characteristics, particles dimension is the one that affect the most this phenomenon and the reactivity of the sample. It is impossible to distinguish definitely explosive dusts and not explosive dusts according to them particles size. However, it is believed that particles with diameter greater than 500 μm have a low explosion tendency: this value is often assumed as limit beyond which a dust can’t explode. A decrease of the particles diameter entails an increase of the reactivity, a growth of the maximum pressure Pmax (Bar) and the growth of the pressure maximum speed Kst (Bar* m/s).

In particular, the Kst parameter is very important because it represents a constant that allows to categorise the explosion force in four risk classes:

Range Class Explosiveness
Kst = 0 St0 Weak explosion
0 < Kst < 200 St1 Moderate explosion
200 < Kst < 300 St2 Impetuous explosion
Kst > 300 St3 Dangerous explosion

It is good to remember that the Kst constant value depend on the following factors:

Dust type
Source type
Dust particles size
Dust concentration/amount
Moisture

For the calculation of the risk it is fundamental to also consider the minimum ignition energy (MIE) of the dust cloud; in particular:

MIE < 100 mJ indicates an ignition potential from an operator's electrostatic discharge;
MIE < 25 mJ indicates a potential trigger from an electrostatic discharge caused by dust bulking.

Our certification:

II 3 D Ex h IIIC T200°C Dc -10°C‹T‹40°C

II - Group = it identifies the group of the machine and it is divided into: I mine; II other groups, not mine (directive 2014/34/EC).
3 D - Category = the number identifies the installation area (1= 20 zone, 2= 21 zone, 3= 22 zone), the letter identifies the type of pollutant: D=Dust, G=Gas (Directive 2014/34/EC).
Ex H - Type of protection. The product is manufacture so that it can’t transform in the ignition cause during the normal operation (UNI EN 80079 -37).
III C - It depends on the dust type processed: C= Conductive dust, B= non-conductive dust, A= flammable fibre. The roman numeral stands for: II= concerning Gas, III concerning dusts.
T200° - The higher value reachable by each component of the machinery.
DC - Equipment protection level EPL (Dc = 22 zone)
-10°C < T < 40°C - Environmental temperature range by which the filter can be installed.

How do we equip our ATEX products?

When it is impossible to exclude an explosion, in addition to protect the filter with venting systems, it is necessary to avoid the explosion spread. It must be prevented that the explosion turns back, in the opposite direction, to the distance that connects the filter to the factory, risking that the venting involves the workers. In order to do this, it is necessary to use compartmental components such as non-return valve and rotary valve. Only in this way it is sure that the explosion venting will happen in an exact and marked zone, without obstacles or employees, in complete safety and under control.

Warning: the compartmentalization is a basic element of the ATEX directive. A plant without compartmental components can’t be considered suitable.

The missed compartmentalization of the system may result in secondary explosions that, in most cases, are the most dangerous both for people and for the machineries since they happen in non-delimited places.

1. Explosionproof panels
The explosionproof panels are installed in a specific part, usually between the hopper and the filter body/unit or in some cases on the top. These panels preserve the pressure increase generated by the explosion within the structural limits of the filter. In case of explosion, the panels open to vent part of it (fume and flame) to a marked and signalled safety zone.


2. Compartmental rotary valve
The ATEX rotary valve represents a compartmental component of the plant, because it prevents that the explosion spreads in the dusts discharge area, protecting the integrity of the nearby machineries or directly connected to the filtration system and the personal safety.


3. Compartmental non-return valve
Like the rotary valve, the ATEX non-return valve has the task to compart the explosion, avoiding its spreading before the filtering system, protecting the integrity of the nearby machineries or directly connected to the filtration system and the personal safety.


OTHER COMPONENTS
Fan
The ATEX fan must have a certification suitable for the installation zone. The certification guarantees that the component does not represent an ignition cause for the explosion.