arpadveress 
Breathing and draining devices shall incorporate permeable elements which can withstand the pressure created by an internal explosion in the enclosure to which they are fitted, and which
shall prevent the transmission of the explosion to the explosive atmosphere surrounding the enclosure.
They shall also withstand the dynamic effects of explosions within the flameproof enclosure without permanent distortion or damage which would impair their flame-arresting properties.
They are not intended to withstand continuous burning on their surfaces.
These requirements apply equally to devices for the transmission of sound but do not cover devices for
– relief of pressure in the event of internal explosion,
– use with pressure lines containing gas which is capable of forming an explosive mixture with air and is at a pressure in excess of 1,1 times atmospheric pressure.
Available on the market one shall find Ex e and Ex d type of devices. The way forward is simple – Ex e will fit into Ex e enclosures, and Ex d both to Ex e and Ex d enclosures.
Normally for flameproof enclosures these are ‘U’ type of Ex certified. U = accessory.
It means all Ex d installations we wish to add shall be (re-)certified with it sooner or later as per stage of development.
It is not a stopping plug, so reducers can be used.
As per we do Ex inspection it is an important milestone on the way of Ex compliance.
Keep up good work!
Arpad
