Ceiling tile condition

Wondering if there are any ideas on how to determine the condition of old ceiling tiles. The tiles in question appear to be bowing in some areas--Is there a way to assess the liklihood that they will loosen and come crashing down?
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Suspended ceiling tile - 2'x4' stuff? Hopefully the only thing they're supporting is their own weight, which they should easily be able to do unless they've sagged so much from weight above, water, or become fragile with age. The sag would have to be most extreme for the edges to slip out of the track. Generally, if you don't touch them, they stay where they are.
R
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I have no experience with this, but I just installed some. You can get them with the same pattern in different thicknesses. In the store the 1/2" thick tiles (non-"fire-rated", ~$40/case?) would bow when you picked them up with two hands right out of the box. The exact same 2'x4' tile size and pattern, but "fire-rated", and 5/8" ($60/case) was much better. I don't know if it was just the thickness that made them "fire-rated". I'm not sure of the prices, or if they are available in cheaper non-"fire-rated" in 5/8" thickness too. I'm talking about Armstrong tiles at HD, and the random-textured pattern which can be cut in any direction from looking at it. However I have no idea if the 5/8" fire-rated ones will sag eventually over time.
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2x4 ceiling tile bow due to humidity. The center can and will bow down an inch or more. Commercial installers demand that the HVAC equipment be running and will be left on before they will install tile. The bowing is very real. I have not seen any fall out of the grid short of a roof leak with saturated tile.
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