When you vent down equipment either during process preps at the end of pressure cycles or on a re-start after shutdowns do you vent the "NITROGEN" into the open plant areas. IE FOR OUTSIDE BUILDINGS.

Take the case, Column has just been pressure tested to 6 barg nitrogen we now pressure cycle 3 times to 6 barg to remove all the oxygen ready for start up.  In my place we have always vented the N2 locally as fast as praticaly as it does contain chemicals.  Now I've always been told (when i was a younger engineer) that the dispersion is so effective that it dilute the nitogen to prevent a hazard - BUT HOW DO I KNOW THIS. 

I was asked the same question by an engineer whom I mentor and I could not provide an adequate answer - so hense the question.  So(filter),

Does anyone test the air whist doing this ? use Air monitors, limits plant access while venting, uses dedicated vent stacks etc. 
Are you aware of issues while venting this way?, is there a safety concern

I am well aware of the concerns to high N2 Concentrations from Confinded space entries and opening large manways but this seems a grey area to me where we dont have policys on whats acceptable so i'm looking for general advice on what else other companys do.

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My understanding of the severity of nitrogen exposure is a little different than yours.  Obviously oxygen deficiency is a real problem.  In a lot of oxygen deficient atmospheres simply evacuating to a normal atmosphere can save a casualty.  With nitrogen, if you get enough to collapse, their is a very good chance that you will die.  One of the very real problems is that it is very difficult to resucitate a casualty with first aid after being exposed to nitrogen...it is very difficult to purge or displace the nitrogen from the lungs and the body can't do it itself once brought into a normal atmosphere.

I know my comment has very little to do with the original post but I thought I would point out the severity of exposure to a supposedly benign gas.  I worked in a plant where I could be inches away from 150,000 amps of dc current, exposed to acid fumes, caustic, hexavalent chromium, etc. and the only real thing that scared me was exposure to nitrogen.

It obviously depends on what line size you are venting through. In my experience with reactor (un)loading, when a reactor is swept with N2 through a 1" connection, the N2 from the top manhole is diluted very easily such that at a few ft from the manhole the O2 percentage measured is 20.
Yes, you will want to vent to a safe location if possible and you will want to limit access around the vent outlet to prevent people from being blown into their faces.

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