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Safety Tools – Atex Tools

Category:

Description

EX designation

ATEX (Atmosphere -Explosive)

94//EC Directive

Harmonises legal provisions of member states for devices and protection systems for designated use in potentially explosive areas. New: ATEX 95 (Old: ATEX 100a)

1999/92/CE Directive

Minimum requirements for improving the health and safety protection of the worker at risk from explosive atmospheres. New:ATEX 137 (Old: ATEX 118a)

Designation examples:

  • Use in gaseous atmospheres: II G EEx ia IIC T4
  • Use in dusty atmospheres: II 2 D T90ºC IP64
  • Use for minig applications: I M2 EEx ia I

Device group:

I
mining
II
all other explosive areas
Category:
1 Zones 0/20
2 Zones 1/21
3
Zones 2/22
M1
Mining (In case of firedamp, continuation of operation is possible)
M2
Mining (Must be switched off in case of firedamp)
Atmosfera:
G
Gas
D
Dust
Types of ignition protection:
o
oil immersion
p
pressurisation
q
powder filling
d
pressure-proof housing
e
increased safety
ia
intrinsic safety (required for Zone 0*) *depends on device category
ib
intrinsic safety (adequate for Zone 1 (+2))
m
encapsulation
s
special protection
n
normal operation under normal conditions (for Zone 2 only)
nA
non-sparking
nC
protected contacts
nR
carcasa resistente al vapor
nL
limited energy
nP
simplified
Temperature classes:
T1
450°C
T2
300°C
T3
200°C
T4
135°C
T5
100°C
T6
85°C
Explosion group:
I
Methane (mining)
IIA
Propane
IIB
Ethylene
IIC
most dangerous group (e.g. hydrogen)
Max. surface temperature:
a) Limit temperature 1=213 of min. ignition temperature of dust present
b) Limit temperature 2=min. glow temperature of dust present minus 75k (applies for layer hicknesses of up to 5mm)
The smaller value for the limit temperature must be aboye the indicated max. surface temperature of the device.
IP Code:
Figure 1 Contact and foreign body protection:
5
Protection against dust deposits
6
Protection against dust penetration
Figure 2 Water protection:
0
(no protection)
1
vertically falling drip water
2
drip water on operating device inclined to 15° 3=spray water
3
spray water
4
spray water
5
jet water
6
strong jet water
7
temporary immersion
8
continuous immersion
Explosion Protection

The important principles for integrated safety explosion protection are as follows:

  1. Measures are taken to avoid hazardous atmospheres whenever possible.
  2. Measures are taken which prevent the ignition of hazardous atmospheres.
  3. Measures are taken which limit the explosive effect to a safe degree.

This differs from:

Primary explosive protection:
These are precautions taken to prevent or restrict the formation of hazardous explosive atmospheres.

Secondary explosive protection:
This covers the second group of measures, which are intended to prevent the ignition of an atmosphere that is capable of exploding.

Definition in accordance with 1999/92/EC Directive (ATEX 137) Reference values (not standardised)
Zone
A device from the following device category must be used (see 1999/92/EC-ATEX 137 Directive)
e
Area in which a potentially explosive atmosphere as a mixture of air and flammable gases, vapours or mists is present either frequently or over a prolonged period. P>1000 h/a
0
1
G
Area in which under normal operation a potentially explosive atmosphere as a mixture of air and flammable gases, vapours or mists can occasionally form 10…1000 h/a
1
2 (1G also possible)
G
Area in which under normal operation a potentially explosive atmosphere as a mixture
of air and flammable gases, vapours or mists is not normally present but may occur for just a short period.
<10 h/a
2
3 (1G, 2G also possible)
G
Area in which a potentially explosive atmosphere in the form of a cloud of flammable airborne dust is present either constantly, over prolonged periods or frequently. >1000 h/a
20
1
D
Area in which under normal operation a potentially explosive atmosphere in the form of a cloud of flammable air-borne dust can occasionally form. 10…1000 h/a
21
2 (1D also possible)
D
Area in which under normal operation a potentially explosive atmosphere in the form of a cloud of flammable air-borne dust is not normally present although may occur for just a short period. <10 h/a
22
3 (1D, 2D also possible)
D

Division into Temperature Classes

The temperature class indication can be guaranteed only if the ambient temperature specified for the operating device is respected (seeTechnical Data or Rating Plate). Strict compliance is a mandatory requirement.

Once the maximum surface temperature of any apparatus reaches the ignition temperature of the surrounding hazardous atmosphere an explosion can occur.

Because of this, all equipment classified to Group II is divided into temperature classes. To allow for the possibility of potential hazardous atmospheres, the lowest ignition temperature must always be higher than the maximum surface temperature.

Temperature classes of flammable gases and vapours and permitted surface temperatures of the operating device in accordance with DIN EN 50014
Temperature class T1
T2
T3
T4
T5
T6
Ignition temperature in ºC >450
>300
>200
>135
>100
>85
Maximum temperature in Cº 450
300
200
135
100
85
Examples Propane / Methane / Ammoniac
Ethylene / Alcohols / Acetylene
Petrol / Solvents
Ethylether / Acetaldehyde
Carbon-disulphide
Below Explosive Level
Explosive Area
Above Explosive Level
Mixture to thin
Mixture too rich
No combustion
Partial combustion
No explosion
No explosion
100% <<<<<<<<<<<< Concentration of air<<<<<<<<<<<<<< 0%
0% >>>>>>>>>> Concentration of substance>>>>>>>>>> 100%

Explosions are dependent on many parameters.

Only for atmospherical conditions and pure substances sufficient comparative values and data are shown. An explosion can only occur where a flammable substance in the form of gases, vapours, smoke and dust exists along with sufficient oxygen to support -combustion and there is a source of ignition.

E.g.:

Hydrogen: 4,0 to 77,0 % in air
Propane: 1,7 to 10,6 % in air
Ammonia: 15,4 to 33,6 % in air
Methane: 4,4 to 16,5 % in air

Fundamentals of dust explosion protection
Fundamental principles:

The manufacturer of operating devices for areas rendered potentially explosive through dust must indicate the maximum surface temperature of all devices that dust can penetrate (usually expressed in °C – indication of the temperature class should be avoided here).This temperature is part of the dust Ex-designation.

Designation examples:

II 2 D T90°C IP64

(If the ignition protection type is based on the housing, the housing protection rating should also be stated as an IP Cede). or il 2 D Ex iaD 21 T96°C

Dust explosion protection – temperature:

Combustion and explosion parameters for dusts depend on the their condition. Parameters that affect combustion and explosion behaviour include particle size, particle shape, water content, purity and where applicable the content of the flammable solvents. The particle size distribution and the mean value (value for average particle size) should also be known.

In accordance with 1999/921/G Directive (ATEX 137, replacing:ATEX 118a), the system operator employer is obliged to make a hazard assessment and must therefore be aware of the minimum glow temperature of the dust.

There are simple calculations to determine the two ” temperatures ” and they are carried out thus:

  1. Limit temperature 1 = 213 of minimum ignition temperature
  2. Limit temperature 2 = minimum ignition temperature* mines 75°K

These two limit temperatures must now be examined to confirm which guarantees the greater safety..

Example 1:
Minimum ignition temperature = +330°C, minimum glow temperature = +300°C:

  1. Limit temperature 1 = 213 x +330°C = +220°C
  2. Limft temperature 2 = +300°C – 75°K = +225°C

Greater safety: Limit temperature (1) = +220°C Here a device with a max. surface temperature in the event of failure <= +220°C must be used. As stated, the device designation includes a corresponding value.

Example 2:

Minimum ignition temperature = +186°C, minimum glow temperature = +180°C:

  1. Limit temperature 1=213 x +186°C = +124°C
  2. Limit temperature 2=+180°C- 75°K = +105°C

Greater safety: Limit temperature (2) = +105°C.
Here a device with a max. surface temperature in the event of failure <= +105°C must be used.

The value for the glow temperature applies with a dust layer thickness of 5mm.The temperature safety distance must be increased for larger layer thicknesses.

Special case – Category 3 devices:

In contrast to Category 1 and 2 devices, potential hazards in the event of failure (e.g. short circuiting, connection break etc.) do not have to be considered for Category 3 devices (for use only in Zones 2 respectively 22).The device is evaluated only in respect of hazards during normal operation, it is relatively unlikely that the device should fail at the same time as a shortterm explosive atmosphere is present No EC Type Approval Test Certificate is therefore required for Category 3 operating devices. The manufacturer may confirm that the operating device complies with the relevant standard. Nonetheless, Category 3 devices are still tested by a certified centre and. EGAMASTER, S.A is then awarded a declaration of conformity. (- Of course, Category 2 operating devices also offer significantly greater safety in Zones 2 respectively 22.)

Dust explosions – albeit of a predominantly minor nature – occur relatively frequently.

A leaflet issued by the Government Safety Organisation of the Federal Republic of Germany states:

“According to documentation published by property insurers, it can be assurned that an average of one dust explosion per day occurs in the Federal Republic of Germany; around one in four of these explosions are caused by foodstuff or animal feed dusts.”

Dust explosions are a world-wide problem. Between 1980 and 1990 in the USA, for example, some 200 serious foodstuff or animal feed related dust explosions were recorded, causing 54 deaths, 256 injuries and property damage amounting to 165 million US dollars.