Paging all chemistry experts: how can I tell if it's N2 or Air?

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I have this line in the lab which was N2. They did some work and re-labeled it with "Oil Free Compressed Dry Air", but they didn't remove the Nitrogen label. Whan I asked WTF is this, they removed the CDA label and told me it's N2. I don't trust them and I want to check, without climbing in the ceiling to check where the line is really connected. Even then I can't be 100% sure.

if this were another place I would burn a candle and see if it burns, it should NOT if this is indeed N2. I cannot burn a candle here, I would set up fire alarms. I could force one of my less friendly co-workers breathe this stuff and see if they pass out. But I am looking into some non arson, non violent methods.

any ideas?

Thanks