Basic information on the EX explosion atmospheres

What is an explosion hazard zone?

EXPLOSION HAZARD ZONE – a space in which a mixture of flammable substances with air or other oxidizing gases may occur, with a concentration between the lower and upper explosive limits.

Properties of a Flammable Substance-Air Mixture

Flammable Properties:

- Lower Explosive Limit (LEL) is the lowest fuel concentration in a flammable mixture below which ignition of the mixture by an initiating factor and further spontaneous flame propagation under specific test conditions are not possible.

- Upper Explosive Limit (UEL) is the highest fuel concentration in a flammable mixture above which ignition of the mixture by an initiating factor and further spontaneous flame propagation under specific test conditions are not possible.

- Autoignition Temperature

Flammable properties

Autoignition temperature is the lowest temperature at which a flammable substance ignites upon contact with a hot surface or as a result of thermal radiation from that surface (without the participation of an external flame or spark).

Gases and liquid vapors with an auto-ignition temperature below 85 oC are considered auto-igniting at room temperature.

TEMPERATURE TABLE

IGNITION ENERGY

An explosion requires ignition. For ignition to be possible, the so-called IGNITION ENERGY.
Minimum ignition energy, Emin is the lowest energy of a capacitor in an electrical circuit, the discharge of which causes ignition of the mixture and propagation of a flame under specific test conditions.
The minimum ignition energy value is a parameter that allows for the assessment of the explosion hazard posed by energy sources existing in the area under consideration.

IGNITION SOURCES

THE MAIN IGNITION SOURCES MAY BE:

• Mechanically generated sparks
• Electrical sparks
• Electrostatic sparks
• Hot surfaces

MINIMUM IGNITION ENERGIES OF GAS-AIR MIXTURES

DIVISION OF EQUIPMENT

Group I: methane in underground mine workings
Group II: gas, mists, vapors

IIA – propane group (260 µJ)
(122 gases and vapors, e.g.: Acetone, methyl and ethyl alcohol, acetone)
IIB – ethylene group (95 µJ)
(27 gases and vapors, e.g., ethylene, hydrogen sulfide)
IIC – hydrogen group (18 µJ)
(4 gases: acetylene, hydrogen, hydrazine, carbon disulfide)

Group III: dust and other
IIIA – explosive flocs
IIIB – non-conductive dust
IIIC – conductive dust

EX CLASSIFICATION

Zone G - Gases, mists, vapors
Zone D - dust
Zone 0 - an explosive atmosphere occurs continuously and persists for a long time
Zone 1 - an explosive atmosphere occurs sporadically
Zone 2 - an explosive atmosphere does not occur during normal operation, and if it does occur, it persists for a short time.

EQUIPMENT SAFETY CATEGORIES ACCORDING TO DIRECTIVE 94/9/EC

EQUIPMENT CATEGORY 1 - these devices provide a very high level of safety and allow for continuous operation where explosive atmospheres are constantly present => Zone "0"
DEVICE CATEGORY 2 - these devices provide a high level of protection => Zone "1"
DEVICE CATEGORY 3 - these devices provide a normal level of protection => Zone "2"

DEVICE MARKING

CE 0344 Ex II 2 G Ex e ia IIC T6
CE – quality declaration
0344 – identification number of the certification body
II – explosion group
2 – device category -> Zone 1, 21
G – gas hazard / D – dust hazard
Ex e ia – explosion protection type
IIC - explosion subgroup
T6 - temperature class – 85C

Classification of protection types:
d – flameproof construction according to IEC 60079-1, Polish standard PN-EN-50018:2000
ib – intrinsically safe construction according to IEC 60079-111, Polish standard PN-EN-50020:2000
e – reinforced construction according to IEC 60079-7, Polish standard PN-EN-50019:2000
q – with powder/sand shielding according to IEC 60079-5, Polish standard PN/E-08113 standard
n – devices intended for zone 2
k – waterproof
ia – intrinsically safe
p – with overpressure gas shield according to IEC 60079-2, Polish standard PN/E-08112
o – with oil shield according to IEC 60079-6, Polish standard PN/E-08114
m – hermetic enclosure
s – special version

PRODUCT OVERVIEW

Control stations:

- polyester, stainless steel
- zones 1, 21

Junction and branch boxes:

- aluminum, Polyester, stainless steel
- zones 1, 21