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Definition of Explosion Proof
Explosion Formation
Explosion takes place in the conditions of the following factors

There are three factors will make it possible for a real explosion, even through we can take some measures to avoid the formation of explosive atmospheres, the leaked combustible substance still present probably, so Combustible substances, such as gas, vapor, mist and dust may exist, besides, we are impossible to avoid Air (oxygen) in any environment, so what we can only do to avoid explosion is only to control Ignition source.

Since there inherently exists electrical power for all electrical products used in oil and gas projects. The electrical circuit may probably produce high temperature, electrical sparks and even visible fire in case of short circuit, over-current and any other failure of the whole circuit, in that case, the electrical circuit will become Ignition source to make it possible for a real explosion.

Thus, we must use explosion proof products to avoid the formation for the Ignition Source to ensure the safety.

Explosion Protection

In order to avoid explosions and consequential dangers, the operator must incorporate effective explosion proof protection precautions.
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Avoid the formation of explosive atmospheres
Avoid the ignition of hazardous explosive atmospheres
Confining explosion impact to a negligible extent

Principle of Explosion Proof

All explosion-proof electrical products mainly have three measure to stop electrical circuit to be an ignition source outside the enclosure below:

01
Isolate the electrical circuit between inside the enclosure and outside the enclosure to avoid the explosion escape from the inside to the outside of the enclosure even through electrical circuit can become an ignition source inside the enclosure.

What is Ex d
Ex d is called flame proof type which means electrical circuit probably produce electrical spark or high temperature, at the same time, combustible substances, such as gas, vapor, mist and dust will enter into the electrical circuits enclosure, thus we can not avoid forming the ignition source inside the enclosure, then it means we can not avoid explosion inside the enclosure, but we can put all electrical circuit in a specialized designed metal enclosure, normally aluminum alloy, when electrical circuit inside the enclosure become the ignition source, the internal space inside the enclosure will form an explosion, after explosion occurs inside the enclosure, we have designed an special flameproof path for all heat and impact to escape from inside the enclosure to outside the enclosure, when the heat and impact escape to the outside enclosure:

No. 1: The heat energy could be reduced to a negligible energy automatically to avoid this heat to be the ignition source outside the enclosure, then no explosion will form outside the enclosure to protect the life and building safety.

No. 2: The impact could be reduced to a negligible energy automatically to damage the life and building safety outside the enclosure.

02
Limit the energy of electrical circuit to avoid the electrical circuit to be an ignition source, such as control the temperature, limit the sparks, eliminate the fire.

What is Ex e
Ex e type is called increased safety type which means all circuits are safe normally but we make some measures to increase the safety level to ensure no arcs sparks or hot surfaces.
In some cases, when the electrical circuits operate normally, that electrical circuit inside will not produce any electrical sparks and dangerous high temperature, but we will take some other measures to make sure the higher safety such as using high quality electrical insulating material to limit the temperature rise, extend the electrical clearance and creepage distance to increase safety for the electrical circuit.
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What is Ex i
Ex i type is called intrinsic safety type which means are circuits are safe normally but we change the circuit layout to limit the electrical current to limit the sparks energy and surface temperature. Ex I type normally could be used in Extra-low Voltage(ELV), Extra-low Current such as remoter, instrument, telecommunications， alarm related products.

03
Isolate the electrical circuit between inside the enclosure and outside the enclosure to avoid the electrical circuit to be an ignition source inside the enclosure.

What is Ex o
Ex o type is called oil immersion type which means the electrical circuit probably is unsafe but we use special explosion-proof oil to immerse the electrical circuits to isolate the electrical circuits from combustible substances outside the enclosure.

What is Ex m
Ex m type is called encapsulation type which means electrical circuit probably is unsafe but we use special explosion-proof glue to seal the electrical circuits to isolate the electrical circuits from combustible substances outside the enclosure.

What is Ex q
Ex q type is called powder filling type which means electrical circuit probably is unsafe but we use special explosion-proof powder to seal the electrical circuits to isolate the electrical circuits from combustible substances outside the enclosure.

What is Ex p
Ex p type is called pressurization type which means the electrical circuit probably is unsafe but we aerate inactive gas, such as Nitrogen: N2 into the inside enclosure(the electrical circuit is inside the enclosure) to make sure the air pressure inside the enclosure is higher than the standard atmospheric pressure outside the enclosure, as a result, the combustible gas or dust can not enter into internal space inside the enclosure to isolate the electrical circuits from combustible substances.

What is Ex n
Ex n type is called restrict breathing" type which means electrical circuits are safe normally but we melt, extrude, and glue the complete enclosure to restrict breath inside the enclosure to isolate the electrical circuit inside the enclosure to prevent combustible gas outside the enclosure entering into internal space inside the enclosure. This is the lowest level explosion-proof measure to make sure safety because combustible substances probably enter into the internal space of the enclosure in case, soEx ncould be used inZone 2/Class I Division 2''.

Classifications of Explosion Proof
Classifications for Group/Class, Zones/Divisions
Hazardous locations are classified into different Group/Class, Zones/Divisions depending on the composition and presence frequency of flammable substances.

Classifications for Flammable Substances
Flammable substances are classified into different groups depending on how easy the exact flammable substances could be ignited.

Classifications for Temperature

Explosive temperature is the highest temperature of a surface of an explosion-proof electrical products when this explosion-proof electrical products work normally. As we know, explosion-proof electrical products is still an electrical products which will produce heat when normal operated, but if the temperature of surface of explosion-proof electrical products is higher than spontaneous ignition temperature of the outside combustible gas or dust, this electrical products will ignite the combustible gas or dust outside the enclosure directly, in a word, explosion-proof electrical products have become an ignition source itself even electrical circuits inside the enclosure are explosion-proof type. So the temperature group may be classified into different groups.

Note: When we intended to install an explosion-proof electrical products in an gas or dust atmosphere where the spontaneous ignition temperature is 100℃(T5), so we could exactly install explosion-proof electrical products whose temperature group is 85℃(T6) but we could not install explosion-proof electrical products whose temperature group is 135℃(T4).

In a word, as for temperature group of explosion-proof electrical products, the lower, the better! because lower temperature group could be used for wider scope of combustible gas or dust.

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