Great job renosteinke, Crouse Hinds used to provide a lot if useful info on explosion proof installations...I once got a free video to present to the other electricians in the plant that showed what can happen if the installation is done right and what it looks like when it's not done right.
The basic idea is, what we loosely refer to as an “Explosion Proof” installation does not prevent or contain an explosion at all, rather it is an installation that is designed to contain the flame front and cool the escaping gasses to a point where they will be rendered harmless to the outside environment.
One thing that should be made very clear to anyone installing or maintaining a hazardous location is that ANY mated surface should be clean and free from excessive lubricant. Machines surfaces, including threads should be smooth and free from gouges, or pits caused by age or mistreatment. If your die isn’t sharp the threads may be incomplete (ripped) and provide a path for the flame front. If you dissemble fittings and connections and those threads or mated surfaces are old and rusty they may not provide an adequate seal if you reassemble them using the old parts without dressing the threads and or installing new machined surfaces.
On starters and other enclosures, the mating surfaces of the door and other sealing surfaces are machined to a tolerance of several ten thousands and if the enclosure is not treated properly those surfaces will not perform as designed in the event of an explosion.
Also the improper installation of seals and drains (EYD, EYS) can lead to a failure of the equipment to contain flame front of the explosion. If a seal is not properly poured an enclosure on the other end of the conduit in a non hazardous location can be blown off the wall if an explosion occurs in the Haz Loc.
As an example imaging a conduit leaving a Haz Loc and going to the raceway in an MCC, if hot gasses explode into the MCC other, possible critical, equipment could be shut down because the insulation on wires in the raceway are heated above the rated temp of the insulating material which resulted in those wires shorting and the circuit tripping of line or failing to start when needed.
As with any electrical installation, lives can hang in the balance, all the necessary precautions should be taken to insure that the equipment is installed and will operate properly.
