Group I
Devices are separated into different temperature classes (T1 through T6) with respect to EN 50014. The maximum temperature of the exposed surface of an electrical apparatus must always be lower than the ignition temperature of the gas or vapor mixture where it is used. The table shows that only in a few cases a temperature class higher than T4 (e.g. carbon disulfide - T6) is necessary. A more accurate explosion group, respective to temperature class, increases safety only if the presence of ambient gases can not be fully ruled out.
Ignition protection includes constructive measures on devices which ensure that an ignition source and a dangerous quantity of an explosive mixture do not occur at the same time in the same place. If not otherwise expressed, this ignition protection is valid for zone 1.
|
Type
|
Ignition
Protection
|
Basic Principle, Applications |
|
D
|
Flameproof
enclosure
|
The
parts that can cause an explosive atmosphere are in an enclosure
that can withstand the pressure developed during an internal explosion
and which prevents transmission of the explosion to the explosive
atmosphere surrounding the enclosure. Applications: switchgear, control and indicating equipment, motors and other spark-producing parts, gas warning instruments |
|
E
|
Increased
safety
|
Measures
are applied so as to prevent the possibility of excessive temperatures
and of the occurrence of arcs or sparks in the interior and on the
external parts of the electrical apparatus which does not product
them in normal service. Applications: terminal and connection boxes |
|
I
|
Intrinsic
safety
|
A
type of protection in which the electrical apparatus contains intrinsically
safe circuits, which are incapable of causing an explosion. A circuit
or part of a circuit is intrinsically safe when no spark or any
thermal effect in this circuit, produced in the test conditions
prescribed in the standard (which include normal operation and specific
fault conditions) is capable of causing ignition. Applications: measurement and control equipment, e.g. GfG´s EC 25 transmitter |
|
M
|
Molding
|
The
parts which can ignite an explosive atmosphere are enclosed in a resin
sufficiently resistant to environmental influences in such a way that
this explosive atmosphere cannot be ignited by sparking or heating
which may occur within the encapsulation. |
|
P
|
Pressurized
apparatus
|
A
protective gas (inert air or another suitable gas) prevents the
surrounding atmosphere from entering the enclosure of the electrical
apparatus by maintaining a higher pressure than that of the surrounding
atmosphere. The pressure is maintained either with or without a
continuous flow of the protective gas. Applications: motors and light fitting |
|
O
|
Oil
immersion
|
The
electrical apparatus or parts of the electrical apparatus are immersed
in oil so that an explosive atmosphere, which can be above the oil
or outside of the enclosure, cannot be ignited. Applications: transformer |
Monitors are usually divided into three groups:
- LEL:
Monitoring combustible or explosive gases
For measuring dangerous concentrations of combustible gas and vapor mixtures. The measuring range is usually 0 to 100% of the LEL (Lower Explosion Limit). The TLV (Threshold Limit Value) default is set at 10% and alarms sound before any potentially explosive conditions can occur.
- OX:
Monitoring oxygen deficiency or enrichment
Before entering an area such as a manhole or drain, the presence of an adequate concentration of oxygen in the air (20.9%) is critical. The OX monitor sounds an alarm if there is not enough or if there is too much oxygen in the atmosphere.
- TOX:
Monitoring toxic gases
Monitors for toxic gases detect low concentrations (ppm) of poisonous gases or vapors. The user is warned before a harmful concentration is reached (i.e. carbon monoxide detectors sound an alarm at 35 ppm). Modern instrumentation can also calculate the average exposure limit over different periods of time (STEL, TWA).
Category "ia"
An ignition may not be caused during:
An ignition may not be caused during:
