Some important points.
1)The fittings are different between oxy and nitrogen systems as stated several times already. SO TO ALL THOSE WHO KEEP SUGGESTING THIS, STOP IT. IT HAS BEEN MENTIONED HERE OVER AND OVER AND OVER.
2)Different coloured bottles... different shut off valve and regulator arrangements on the carts. If even basic training had been given, those involved should have known immediately that they were using the wrong cart.
3)Potentially fatal? Highly unlikely. An oxy system is never completely filled and therefore, there is no chance that the system would contain pure nitrogen or even a high percentage. If the system is showing empty, bottles are REPLACED with FULL bottles from stores. Those bottle would have been filled in the oxygen shop in component maintenance.
Normally, you would only have to add around 100-300PSI to the system. Off the top of my head, 1850PSI is the aprox. system pressure. 300PSI represents 16% of the total pressure.
The air we breathe is aprox. 78% nitrogen and 21% oxygen. In order for a potentially fatal level of nitrogen to be added, the aircrafts system pressure would have to have been considerably less than 380PSI!!!!!!!!!! If this were the case, It would indicate a major leak in the system and considerable troubleshooting would be carried out.
To say that this was a potentially fatal incident is just scare mongering. Far more potentially fatal would be filling a landing gear strut with oxygen due to the presence of oil and yes, this did happen im Melbourne once too.
Despite the scare mongering, those involved should be asked to sit down for tea and biscuits and to explain. I am guessing however, that the were probably not trained.