Hi Grizzly
Thanks for bringing this to our attention I must admit I had never considered it to be dangerous.
I have gone through the MSDS on nitrogen and there are many references to asphyxiation, under Hazard Alert - in high concentrations may cause asphyxiation, First Aid - Victim may not be aware of asphyxiation, Other Information - Asphyxiant in high concentrations, Do not breathe gas.
Just goes to show we need to read the MSDS's and supplier info very closely.
I don't think it matters whether it takes 5 secs or 5 mins it can be dangerous in confined spaces.
Paul