You could try to satisfy your immediate needs by cutting a discreet bit off and putting a match to it. (I've done that many times and, whilst I've had a certificate in one hand saying that the material is adequately treated to be fire retardant, from the other hand I've had to drop the merrily flaming material into a bin.)
However, if it didn't burn, it would only tell you that the bit you cut off wont burn when tested now. Another part, that you haven't cut off, might burn readily and it tells you nothing about how it will perform in a month's time. Also, being art, it might not be possible to chop a bit off.
If the people that treated it 5 years ago can be traced then I'd have a word with them. I wouldn't ask for any guarantees or anything, just ask for an opinion on the likely performance today.
You haven't told us if there is other fire loading in the atrium, the size and of the hangings, how close they are to other fire loadings, if they're within the reach of the public, if there is smoke control in the atrium, if anyone's means of escape might be affected if these art works catch fire, etc. I've dealt with a lot of hangings of one type or another in shopping malls. If they are completely out of reach of people and are away from other items that might burn and electrical equipment I don't generally worry about fire retardancy. How would they ever catch fire?
If your hangings have a real risk of catching fire, for whatever reason, then you might want to examine what the full consequences of them catching fire might be. If they pose a real threat to anyone then they must, of course, be shown to be suitably fire retardant, but if they would burn away without spreading fire and without posing a threat to anyone then perhaps you can be more lenient on requiring fire retardancy.
Stu
